WO2020110091A2 - Actionneur en alliage à mémoire de forme - Google Patents

Actionneur en alliage à mémoire de forme Download PDF

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Publication number
WO2020110091A2
WO2020110091A2 PCT/IB2019/060339 IB2019060339W WO2020110091A2 WO 2020110091 A2 WO2020110091 A2 WO 2020110091A2 IB 2019060339 W IB2019060339 W IB 2019060339W WO 2020110091 A2 WO2020110091 A2 WO 2020110091A2
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WO
WIPO (PCT)
Prior art keywords
shuttle
sma
actuator
movement
pawl
Prior art date
Application number
PCT/IB2019/060339
Other languages
English (en)
Other versions
WO2020110091A3 (fr
Inventor
Anthony Hooley
Original Assignee
Anthony Hooley
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GBGB1819576.8A external-priority patent/GB201819576D0/en
Priority claimed from GBGB1819638.6A external-priority patent/GB201819638D0/en
Priority claimed from GBGB1903321.6A external-priority patent/GB201903321D0/en
Priority claimed from GBGB1907426.9A external-priority patent/GB201907426D0/en
Priority claimed from GBGB1907437.6A external-priority patent/GB201907437D0/en
Application filed by Anthony Hooley filed Critical Anthony Hooley
Priority to GB2107163.4A priority Critical patent/GB2593618A/en
Publication of WO2020110091A2 publication Critical patent/WO2020110091A2/fr
Publication of WO2020110091A3 publication Critical patent/WO2020110091A3/fr

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03G—SPRING, WEIGHT, INERTIA OR LIKE MOTORS; MECHANICAL-POWER PRODUCING DEVICES OR MECHANISMS, NOT OTHERWISE PROVIDED FOR OR USING ENERGY SOURCES NOT OTHERWISE PROVIDED FOR
    • F03G7/00—Mechanical-power-producing mechanisms, not otherwise provided for or using energy sources not otherwise provided for
    • F03G7/06—Mechanical-power-producing mechanisms, not otherwise provided for or using energy sources not otherwise provided for using expansion or contraction of bodies due to heating, cooling, moistening, drying or the like
    • F03G7/065—Mechanical-power-producing mechanisms, not otherwise provided for or using energy sources not otherwise provided for using expansion or contraction of bodies due to heating, cooling, moistening, drying or the like using a shape memory element

Definitions

  • the present invention relates to a shape memory alloy actuator.
  • the present invention also relates to a method of operating an SMA actuator.
  • a Shape Memory Alloy is an alloy that can be deformed when cold but which returns to its pre-deformed or 'remembered' shape when heated.
  • SMA material is NiTi (-50:50 alloy of Nickel and titanium). This material undergoes a phase change from Martensite to Austenite when heated through its transition region, and in so doing contracts by a substantial amount, typically between 2% and 8%.
  • the transition temperature is achieved by Joule heating of the SMA material, by the passage of electric current through it.
  • Actuators are components that are responsible for moving and controlling mechanisms or systems within an apparatus.
  • Shape Memory Alloys can be used to form actuators, temperature changes in the alloy allowing them to change shape to operate, which is usually achieved by passing an electric current through the material.
  • SMA actuators such as the straight-wire, bow string or“Vee”-type actuators, these usually being used as linear actuators
  • SMA wire which has been appropriately mechanically and thermally processed to produce a reliable and long lasting contraction during phase change.
  • Simple on/off control of the heating current to the SMA wire is used to control the actuator.
  • this type of control generally results in very low position precision, unless the position is defined by fixed mechanical end-stops.
  • SMA wire-actuators Another issue that can occur with SMA wire-actuators is overload, where the force applied to the SMA-wire due to abnormal conditions at the load (e.g. out of specification load conditions) is sufficiently large to damage or even break the SMA- wire.
  • some actuators e.g. simple single straight-wire actuators
  • end-stops that limit the stretching of the SMA-wire by load forces.
  • end-stops alone cannot prevent overload in the fully actuated position - that is, with the SMA mainly or wholly in the austenite phase - since it is possible for excessive force to be applied within the designed stroke range (i.e. within travel between the end-stops).
  • heating-drive e.g. electrical Joule-heating drive
  • SMA-wire when for example both wires in such an actuator are heated above the austenite-start temperature, and the total contraction in the load direction is greater than the designed stroke.
  • Miniature cameras have a requirement for a zoom-lens facility, especially in cameras inside cellphones.
  • OIS optical image stabilisation
  • AF auto-focus
  • an adjustable focal-length zoom facility e.g. 5:1 or 10:1 generally requires a much larger movement distance for one or more optical elements because large zoom implies long focal length, and it is desirable that the element(s) once moved, stay put indefinitely, until subsequently commanded to move elsewhere.
  • SMA shape-memory-alloy
  • Small electromagnetic motors could in principle be used to move optical elements for zoom function in miniature cameras, but they have not found favour, and cellphone electromagnetic zoom cameras do not exist in mass-production.
  • Such a filter will have an input port and an output port (generically l/O-ports), sometimes coincident resulting in a single-port filter, and sometimes forming diplexers or multiplexers by having a common input port and two or more output ports.
  • multiband filters are being developed employing multiple resonances per resonator, or multiple resonators per cavity.
  • Electromagnetically-coupled multi-cavity filters with a plurality of stages are also known in the art wherein a sequence of cavities are electromagnetically coupled one to the next (in sequence) with possibly additional couplings between non-sequential cavities, and wherein the electromagnetic properties of one or more of the cavities are individually tuned and sometimes dynamically tuneable (i.e.
  • Filter performance may be measured as some combination of factors including pass-band insertion-loss (ideally zero), stop-band rejection (ideally infinite), phase-linearity (usually ideally perfectly linear with signal frequency), ripple (ideally zero), group delay and power handling (PIM, breakdown due to discharge in air , multipaction breakdown).
  • PIM group delay and power handling
  • the filter is of bandpass or bandstop configuration it is characterised by a lower and upper cut-off frequency, the difference between which is called the bandwidth of the filter, and a“centre-frequency” between these two.
  • a tuneable bandpass or bandstop filter will in general have a tuneable centre frequency and sometimes also a tuneable bandwidth. This may in practice be implemented by separately tunable lower and upper cut-off frequencies.
  • Such an RF filter can also be designed to produce primarily a phase shift, and in this case the useful effect of the cavity is to produce a phase difference dphi between that of the input signal and the output signal where dphi may be a tuneable quantity: i.e. in this case it is primarily the magnitude of phase-shift that is tuneable, and not the frequency at which the phase-shift occurs.
  • dphi may be a tuneable quantity: i.e. in this case it is primarily the magnitude of phase-shift that is tuneable, and not the frequency at which the phase-shift occurs.
  • Such a device is called a phase-shifting filter or just phase-shifter and an ideal phase-shifter would produce no change in insertion loss throughout the passband, and no change in insertion loss over the full range of tuneable dphi.
  • both a phase-shift function and a frequency-filtering function may be combined and both may be tuneable or specifically optimised.
  • filter to encompass all of these types of device.
  • RF cavities comprising chambers with solid conductive walls entirely surrounding the cavity are known in the art, as are RF cavities comprising a pair of often but not necessarily parallel, conductive ground-planes, and in the latter case individual cavities between the ground- planes may be delineated either by: i) solid conductive walls; or ii) by one or a plurality of conductive vias appropriately spaced and connecting between the ground-planes; or iii) by a combination of i) and ii).
  • the input and output ports either: i) pierce the solid conductive cavity walls; or ii) are positioned between conductive vias connecting the ground-planes.
  • Physically adjacent cavities which are not necessarily sequentially adjacent cavities as far as the direct signal path through the filter is concerned, may be
  • Each such coupling may be comprised of: i) one or more holes or“irises” passing right through the solid conductive walls separating the physically adjacent cavities; or, ii) where the cavities are physically separated by one or more conductive vias connecting between the ground planes then by careful and appropriate positioning and spacing of the vias and again these couplings are said to be formed by irises - gaps between vias; or iii) by coupling wires protruding into both cavities to be capacitively coupled when the wires are electrically isolated, or inductively coupled when the wires are connected to the inside of the cavity; or iv) by conductive tracks placed on an insulating layer on the inside or outside wall of one or both ground-planes protruding into each of the cavities to be coupled capacitively or inductively. Combinations of these types of coupling within the same filter and even between the same cavities are possible.
  • the cavities may or may not contain one or more resonators.
  • a frequency- tuneable filter will have at least one cavity containing one or more resonators whereas a tuneable phase-shifter filter cavity may contain zero one or more resonators, and in the case where there is no resonator then instead a reflector is needed, and the phase-shifter may be realized with at least one side of the cavity being opened to a waveguide carrying the RF signal to be phase-shifted.
  • the resonators may be either conductive or dielectric or some combination of these.
  • Each of any conductive resonators within a cavity may be either connected to ground at one end only or connected to ground at each end or connected to ground in the middle or connected to ground at one or more half-wavelength intervals or not be connected to ground at all resulting in a floating conductive resonator.
  • the one or more cavities of a tunable phase- shifter filter may contain non-resonant components with one or more tuneable parameters the changing of which primarily effects the phase between input and output.
  • the parameter might be the position of the non-resonant component in the cavity.
  • the present invention may broadly be said to consist in
  • the invention may broadly be said to consist in a shape- memory alloy actuator, comprising:
  • stator body configured to receive the shuttle, the shuttle configured to move relative to the stator body
  • a movement and locking mechanism connecting between the stator body and shuttle, the movement and locking mechanism configured to engage with the shuttle to move the shuttle relative to the stator body;
  • the movement and locking mechanism comprising first and second movement portions configured to engage and disengage from the shuttle in use, the first movement portion biased away from engagement with the shuttle, the second movement portion biased into engagement with the shuttle, and an SMA element actuator configured so that actuation of the SMA element actuator causes the first movement portion to engage with the shuttle to move the shuttle a part- step in a first direction, the shuttle and second movement portion configured so that de-actuation of the SMA element actuator causes the shuttle to move the remainder of the step.
  • the shuttle comprises an elongate element configured to slide linearly in relation to the stator, with first and second long sides arranged in parallel with each other and the direction of travel, the first and second sides toothed, the first and second movement portions comprising first and second toothed pawls, the pawls and sides configured for mutual engagement.
  • the teeth of the first pawl are moved into engagement with the teeth on the first side of the shuttle by actuation of the SMA element actuator to move the shuttle a part-step, the first pawl and teeth on the second side configured so that once the part step has been completed, the first pawl teeth and teeth on the second side engage to cause the shuttle to move the remainder of the step.
  • the teeth of the pawls and the teeth on the first and second edges are configured with slopes of substantially 45 degrees each side.
  • the first movement portion comprises a leaf spring configured to bias the first movement portion away from engagement with the shuttle.
  • the second movement portion comprises a leaf spring configured to bias the second movement portion into engagement with the shuttle.
  • the leaf spring or springs comprise multiple leaves.
  • the shape-memory alloy actuator further comprises a second SMA element actuator, connected and configured so that when actuated, the second SMA element actuator moves the second movement portion out of engagement with the shuttle.
  • the shape-memory alloy actuator further comprises an overload spring configured to engage with the first SMA element actuator to at least partly absorb any overload force on the first SMA element actuator.
  • stator body and movement and locking mechanisms are formed as a unitary or one-piece element.
  • the shuttle comprises a toothed cog, the first and second movement portions comprising first and second toothed pawls, the pawls and cog configured for mutual engagement.
  • the teeth of the first pawl are moved into engagement with the teeth on the cog by actuation of the SMA element actuator to move the cog a part- rotation in a first direction, the first pawl and teeth on the cog configured so that once the part step has been completed, the first pawl teeth and cog teeth engage to cause the cog to move the remainder of the step.
  • the teeth of the pawls and the cog teeth are configured with slopes of substantially 45 degrees each side.
  • the first movement portion comprises a leaf spring configured to bias the first movement portion away from engagement with the cog.
  • the second movement portion comprises a leaf spring configured to bias the second movement portion into engagement with the cog.
  • the leaf spring or springs comprise multiple leaves.
  • the shape-memory alloy actuator further comprises a second SMA element actuator, connected and configured so that when actuated, the second SMA element actuator moves the second movement portion out of engagement with the cog.
  • the shape-memory alloy actuator further comprises a third pawl and third SMA element actuator, actuation of the third SMA element actuator causing the third pawl to engage with cog to move the cog a part-rotation in a second direction opposed to the first direction, the first pawl and teeth on the cog configured so that once the part step has been completed, the first pawl teeth and cog teeth engage to cause the cog to move the remainder of the step.
  • the invention may broadly be said to consist in a shape- memory alloy actuator, comprising: a stator body; a shuttle; the stator body and shuttle mutually configured for connection in use such that the shuttle can move in relation to the stator body; a movement and locking mechanism connecting between the stator body and shuttle, the shuttle and stator body mutually
  • the locking portion of the mechanism configured such that the locking portion of the mechanism can engage with the shuttle to hold the shuttle in position relative to the locking portion, and disengage to allow the shuttle to move relative to the stator body;
  • the locking portion of the movement and locking mechanism comprising an SMA element actuator, configured so that actuation of the SMA element actuator causes the locking portion to disengage, and de-actuation of the SMA element actuator causes the locking portion to re-engage.
  • the shuttle comprises a linear element, the movement and locking mechanism comprising a first stop-block, the first stop-block configured to engage with one long edge of the shuttle so that so that the shuttle is held in position relative to the first stop-block, actuation of the SMA element actuator causing the first stop-block to disengage from the long edge.
  • the shape-memory alloy actuator further comprises a second stop-block and second SMA element, the second stop-block configured to engage with the second long edge so that the shuttle is held in position relative to the second stop-block, the second SMA element configured so that activation of the second SMA element causes linear movement of the second stop block in a first direction parallel to the axis of the shuttle body.
  • the first and second long edges comprise ratchet teeth
  • the stop blocks comprising pawls configured to engage with the teeth on their associated long edge, the teeth of the first long edge and first stop block configured to prevent movement in a first direction when engaged, the teeth of the second long edge and second stop block configured to prevent movement in the second, opposite direction when engaged.
  • the shape-memory alloy actuator further comprises a first spring wire configured to bias the first pawl into engagement with the shuttle, and a second spring wire configured to bias the second pawl into engagement with the shuttle, the actuator further comprising a third SMA element configured so that activation of the third SMA element causes the second pawl to disengage.
  • the shape-memory alloy actuator further comprises a fourth SMA element, configured so that activation of the fourth SMA element causes linear movement of the first pawl in the second direction.
  • the pawls and shuttle are configured such that in use, activation of the SMA elements allows movement of the shuttle for one tooth length only.
  • each of the pawls comprises a pair of pawls, each pair comprising a stepper pawl and a passive pawl, on each side of the stator the stepper pawl trailing the passive pawl for linear movement of the shuttle caused by engagement of the stepper pawl on that side.
  • each of the pawls comprises a pair of pawls, each pair comprising a stepper pawl and a passive pawl, on each side of the stator the stepper pawl leading the passive pawl for linear movement of the shuttle caused by engagement of the stepper pawl on that side.
  • the pawl pairs are located in channels on the stator body, movement of the pawls in the direction of movement of the shuttle constrained by the edges of the channels, the pawls biased towards the edges of the channels and separated by a distance of substantially one tooth length.
  • the pawls comprise locking pawls, configured to lock into the engaged and disengaged positions.
  • the shape-memory alloy actuator further comprises locking SMA actuators configured to actively pull the pawls into an engaged state.
  • the shape-memory alloy actuator further comprises a further pair of stepper pawls arranged one on each side of the shuttle, the movement and locking mechanism configured to activate a further stepper pawl substantially halfway through the activation cycle of the primary stepper pawl on that side.
  • the shape-memory alloy actuator further comprises opposed- stepper SMA actuators connected to the stepper pawls and configured to pull the stepper pawls into engagement with the shuttle.
  • stator and shuttle are configured to have a zero-stroke starting position
  • the actuator further comprising a spring mechanism configured to reset the stator body and shuttle to the zero-stroke position
  • the shape-memory alloy actuator further comprises a pair of slew-back pawls, the spring mechanism connecting between at least one of the slew-back pawls and the stator so that movement of the shuttle relative to the stator activates the spring mechanism, the slew-back pawls and shuttle configured so that the slew-back pawls are carried with the shuttle in normal use,
  • the shape-memory alloy actuator further comprises wings extending from each side of the shuttle, and the stator further comprises a groove configured to receive the wings.
  • the wings are wedge-or triangular-shaped.
  • the slew-back pawls are configured to extend at least partly around the shuttle.
  • the shape-memory alloy actuator further comprises a reverse slew-back mechanism, comprising a reverse slew-back spring, and reverse slew- back pawls, the shuttle configured to extend through each side of the stator, the shuttle engaging with the reverse-slew back pawls at the opposed side of the stator from the slew-back pawls, the reverse slew-back spring configured to operate in the opposite direction to the spring mechanism.
  • a reverse slew-back mechanism comprising a reverse slew-back spring, and reverse slew- back pawls, the shuttle configured to extend through each side of the stator, the shuttle engaging with the reverse-slew back pawls at the opposed side of the stator from the slew-back pawls, the reverse slew-back spring configured to operate in the opposite direction to the spring mechanism.
  • the wire portions of the SMA element actuators are embedded in a heat-sink compound.
  • the movement and locking mechanism comprises a pair of pawls, the shuttle comprising a linear body with teeth on one long edge, the pawl teeth and the shuttle teeth symmetrical and configured to mesh with one another, each pawl independently engagable with the shuttle.
  • the teeth have a slope angle of substantially 83 degrees.
  • teeth on one or both of the shuttle and pawls are rounded.
  • one of the pawls comprises an active pawl, the movement and locking mechanism configured to allow the active pawl to move linearly along the same axis as the shuttle by between one and two tooth lengths, movement of the active pawl in the direction of travel of the shuttle limited by the configuration of the stator.
  • the shape memory alloy actuator further comprises SMA actuators configured to independently lift the pawls out of engagement with the shuttle, springs configured to bias the pawls into engagement with the shuttle, and linear SMA actuators configured to move the pawls in parallel with the shuttle.
  • the shape memory alloy actuator further comprises a cage, the pawls located within the cage, the cage and pawls configured to allow the pawls to slide freely substantially perpendicularly to the axis of the shuttle, the stator and cage configured so that the cage can move freely parallel to the axis of the shuttle but is prevented from moving perpendicularly to the axis of the shuttle, the linear SMA actuators connected to the cage.
  • the shape memory alloy actuator further comprises a balancing shuttle and balancing movement mechanism, the balancing movement mechanism configured so that movement of the first shuttle causes movement of the balancing shuttle in parallel but in the opposite direction to the movement of the first shuttle.
  • the movement mechanism comprises a swing arm pivoted at a point substantially midway between the shuttles and rotatably connected at each side to the shuttles.
  • the movement mechanism comprises pulleys and cables connected between the shuttles.
  • the movement mechanism comprises at least one cog, the shuttles aligned in parallel with the at least one cog between their inner edges, the inner edges comprising teeth configured to engage with the teeth of the cog, movement of one shuttle causing the at least one cog to rotate and move the other shuttle in the opposite direction.
  • the shuttle comprises a ratchet wheel and the movement mechanism comprises a verge.
  • the movement mechanism further comprises a spring connected to the verge to act to return the verge to an initial position once the SMA element actuator is disengaged.
  • the invention may broadly be said to consist in an SMA wire mechanical overload protection mechanism, comprising: a wire mount;
  • the mount and spring configured so that the spring can be located substantially within the mount with one end of the spring connected within the mount and the spring extending within the mount so that the free end is at or towards one end of the mount;
  • a wire terminal having a first end configured for connection to the spring free end, and a second end formed as a crimp end configured to receive the end of an SMA wire, the wire mount, terminal, and spring configured so that the terminal first end is in contact with and pulled onto mount by the spring, the spring exerting a pulling force so that the terminal first end remains in contact with the mount for any opposed pulling force exerted on the wire terminal that is under the level of the pulling force.
  • the spring comprises a serpentine tension spring.
  • the spring further comprises first and second pins that extend laterally from the body of the spring, the pins configured for insertion into a PCB, the pins and spring formed as a one-piece item from a conductive material, the first pin located at the mount connection end.
  • the SMA wire mechanical overload protection mechanism further comprises a PCB, the PCB having a hole configured to receive the first pin, and a slot configured to receive the second pin, the slot aligned with the axis of the spring and allowing movement of the pin within the slot as the spring stretches.
  • the invention may broadly be said to consist in a method of using a shape-memory alloy actuator as claimed in any one of claims 26 to 32, comprising the steps of:
  • the method of using a shape-memory alloy actuator comprises the further steps of:
  • the method uses a shape memory alloy actuator of the type that further comprises a spring mechanism configured to reset the stator body and shuttle to the zero-stroke position, the method comprising the further step of:
  • the method uses a shape memory alloy actuator of the type that further comprises a spring mechanism configured to reset the stator body and shuttle to the zero-stroke position, and a pair of slew-back pawls, the spring mechanism connecting between at least one of the slew-back pawls and the stator so that movement of the shuttle relative to the stator activates the spring mechanism, the slew-back pawls and shuttle configured so that the slew-back pawls are carried with the shuttle in normal use, the method comprising the further steps of:
  • the method uses a shape memory alloy actuator of the type that further comprises a second spring mechanism configured to reset the stator body and shuttle to a zero-stroke position, and a pair of slew-back pawls, the spring mechanism connecting between at least one of the slew-back pawls and the stator so that movement of the shuttle relative to the stator activates the spring mechanism, the slew-back pawls and shuttle configured so that the slew-back pawls are carried with the shuttle in normal use, the method comprising the further steps of:
  • the invention may broadly be said to consist in a miniature camera, comprising:
  • At least one optical element capable of movement substantially along the optical axis of the camera, the optical element mechanically directly or indirectly connected to a moving shuttle or output node that is connected to an SMA linear stepper actuator;
  • the body of the actuator fixed relative to the body of the camera, the direction of motion of the shuttle associated with the actuator substantially aligned with the optical axis of the camera, such that actuation of the actuator causes the at least one optical element to move along the optical axis of the camera;
  • the invention may broadly be said to consist in a miniature camera, comprising:
  • At least one optical element capable of movement substantially along the optical axis of the camera, the optical element mechanically directly or indirectly connected via a linkage to a moving shuttle or output node that is connected to an SMA linear stepper actuator; the linkage configured so that that movement of the actuator shuttle along the actuator movement axis causes movement of the at least one optical element along the camera axis via the linkage;
  • the invention may broadly be said to consist in a miniature camera, comprising: at least two optical elements or groups of elements configured for movement substantially along the optical axis of the camera;
  • At least two independently controlled SMA linear stepper actuator one for each optical element or group of elements
  • each optical element or group mechanically connected to the moving shuttle or output node of the associated independently controlled SMA linear stepper actuator; the body of each of the actuators fixed relative to the body of the camera, the directions of motion of the shuttles associated with the actuators substantially aligned with the optical axis of the camera, such that independent actuations of the actuators causes the optical element or groups thereof connected to each actuator to move independently along the optical axis of the camera;
  • the invention may broadly be said to consist in a miniature camera, comprising:
  • At least one optical element capable of movement substantially along the optical axis of the camera, the optical element mechanically directly or indirectly connected to a moving shuttle or output node that is connected to an SMA stepper actuator;
  • the body of the actuator fixed relative to the body of the camera, the direction of motion of the shuttle associated with the actuator substantially aligned with the optical axis of the camera, such that actuation of the actuator causes the at least one optical element to move along the optical axis of the camera;
  • the invention may broadly be said to consist in a miniature camera, comprising:
  • At least one optical element capable of movement substantially along the optical axis of the camera, the optical element mechanically directly or indirectly connected via a linkage to a moving shuttle or output node that is connected to an SMA stepper actuator; the linkage configured so that that movement of the actuator shuttle along the actuator movement axis causes movement of the at least one optical element along the camera axis via the linkage;
  • the invention may broadly be said to consist in a miniature camera, comprising:
  • At least two optical elements or groups of elements configured for movement substantially along the optical axis of the camera
  • At least two independently controlled SMA stepper actuators one for each optical element or group of elements;
  • each optical element or group mechanically connected to the moving shuttle or output node of the associated independently controlled SMA stepper actuator
  • each of the actuators fixed relative to the body of the camera, the directions of motion of the shuttles associated with the actuators substantially aligned with the optical axis of the camera, such that independent actuations of the actuators causes the optical element or groups thereof connected to each actuator to move independently along the optical axis of the camera;
  • the SMA stepper actuator is connected directly or indirectly to a leadscrew so as to rotate the leadscrew when the stepper actuator rotates, the leadscrew fitted with a nut that moves axially along the leadscrew when the leadscrew rotates,
  • the at least one optical element or group thereof connected directly or via a linkage to the nut.
  • the stepper actuator is connected to the leadscrew via gearing or belt.
  • the invention may broadly be said to consist in a phase or frequency tuneable device comprising:
  • At least one SMA actuator connected to the RF cavity, activation of the SMA actuator causing deformation and/or movement of the walls of the RF cavity;
  • phase or frequency tuneable device further comprises additional electromagnetic structures in the vicinity of, or inside, the RF cavity, activation of the SMA actuator further causing deformation and/or movement of the additional electromagnetic structures so as to affect the electric and/or magnetic components of one or several of the eigenmodes of electromagnetic field supported by the RF cavity.
  • the invention may broadly be said to consist in an RF tuneable filter device comprising a plurality of devices as in any of the preceding statements, each of the devices electromagnetically coupled to at least one other of the plurality of devices.
  • At least one of the electromagnetic couplings is in the form of an iris penetrating the solid walls or ground planes separating the devices
  • At least one of the electromagnetic couplings is in the form of an iris formed by a gap in a wall of conductive vias separating the Claim 1 devices.
  • At least one of the electromagnetic couplings between the devices is formed by non-grounded cross- coupling wires protruding into both of the cavities of the adjacent device or devices through an iris.
  • At least one of the electromagnetic couplings is formed by the provision of additional non-grounded conductive tracks formed on an insulating layer formed on the inside and/or outside of one or both of the ground planes sandwiching the cavities to be coupled, and wherein the conductive tracks are configured to protrude into both of the adjacent cavities of the devices.
  • the RF tuneable filter device further comprises a tuning device comprising SMA material in the shape of wires or ribbons or sheets applied in such a way as to achieve controllable deformation or controllable movement of a conductive or dielectric tuning element in the vicinity of the electromagnetic coupling, and wherein at least one of the electromagnetic couplings between the RF cavities of the devices is configured to be tuneable and is connected to the tuning device.
  • a tuning device comprising SMA material in the shape of wires or ribbons or sheets applied in such a way as to achieve controllable deformation or controllable movement of a conductive or dielectric tuning element in the vicinity of the electromagnetic coupling, and wherein at least one of the electromagnetic couplings between the RF cavities of the devices is configured to be tuneable and is connected to the tuning device.
  • the RF tuneable filter device further comprises one or more stages, the filter either being of the low-pass, band-pass, band-stop, high- pass or phase-shifting configuration comprising:
  • each cavity is electromagnetically coupled to at least one other cavity by an iris penetrating the solid walls or ground planes or by an iris formed by a gap in a wall of conductive vias between ground planes, and wherein one or more of the RF cavities has each one or more tuning elements penetrating into or wholly contained within the RF cavity and wherein each such tuning element is either wholly moveable or is deformable in such a way that the movement or deformation thereof changes the electromagnetic characteristics of the RF cavity so as to satisfy the tuneability requirement of the filter and wherein
  • the RF tuneable filter device further comprises at least one resonator wherein the or each of the resonators are made of one of: a conductive material; a low-loss dielectric material; a non-conductive material coated or plated with conductive material; a combination of the preceding elements.
  • the RF tuneable filter device further comprises at least one dielectric resonator formed from high permittivity low loss RF ceramic.
  • one or more of the resonators are in the form of one or more of: strips; T-shaped strips; rings; spirals or any other suitable shape that resonates at the required frequency.
  • the concurrent modes in the resonator are suppressed by shorting to ground the corresponding ends of the branches of the resonator structure.
  • the resonator comprises a dual-mode or triple-mode resonator with a minimum of two or three mutually orthogonal branches with a single common point.
  • the cavity is configured to support two or three orthogonal modes.
  • the tuneable RF filter comprises a plurality of RF cavities, external signal connections provided in the form of spaced input and output tapping points to a first or input cavity and a last or output cavity.
  • the tuneable RF filter comprises a single RF cavity, and wherein an external signal connection is provided in the form of an input/output tapping point to the cavity.
  • the tuneable RF filter comprises at least one resonator and at least two RF cavities wherein one or more of the resonators and zero, one or more of the inter-cavity couplings and zero, one or both of the input and output tapping points has each a tuning element penetrating into the resonator’s RF cavity or sited wholly within the cavity such that the movement or deformation thereof changes the capacitive loading or inductive loading or both of the associated resonator or coupling or tapping point, and wherein said movement or deformation of the tuning element is controllably caused by the controlled heating of one or more SMA-wires sited outside or partially or wholly within the RF cavity.
  • the tuneable RF filter further comprises at least one resonator, wherein one or more of the resonators is sited within an RF cavity and is caused controllably to change shape or mechanically deform by the controlled contraction of at least one controllably heated SMA-wire such that the movement or deformation thereof changes the self capacitance and/or inductance of the associated resonator in such a way as to controllably tune the resonator.
  • the tuneable RF filter further comprises at least one tuning element wherein each tuning element has the shape of a thin strip, or a rod, or a bar, or a tube, or more generally a long prismatic section with flat or curved surfaces.
  • the tuning elements are made of one or more of: conductive material; low-loss dielectric material; non- conductive material coated or plated with conductive material; a combination of these elements.
  • the dielectric tuning elements are formed from high permittivity low loss RF ceramic or a glass wafer.
  • one or more tuning elements that is tuning a resonator is aligned in the same direction of greatest extension as the resonator that they are tuning so that the gap between the tuning element and the resonator is also aligned with the resonator.
  • the tuneable RF filter comprises at least one resonator, the resonator or resonators having a longitudinal slot configured to receive a tuning element without this touching the resonator.
  • the tuneable RF filter comprises at least one conductive tuning element extending outside the RF cavity wall, wherein RF isolation for the portion of the tuning element protruding outside the cavity is provided by integrating an RF choke into the structure of the tuning element at least around the region where the tuning element exits the cavity and enters the cavity wall.
  • the choke comprises a capacitive load at the external end of the tuning element sufficiently large to be considered an RF short.
  • the choke comprises a series of one or more inductive sections each followed by a parallel capacitive section positioned down the length of the tuning element from the cavity to the external end of the element, the inductive sections being narrower than the capacitive sections.
  • the tuneable RF filter comprises a plurality of tuning elements wherein each of the tuning elements are each caused to move by one or more actuators, with one or more of the tuning elements sharing an actuator.
  • each actuator comprises an SMA-wire actuator and wherein the length of one or more sections of SMA wire are caused controllably to change by controllably changing the SMA wire temperatures.
  • the temperature of an SMA wire is changed by controlling the RMS electric current passing through the SMA wire, the filter further comprising a programmable device configured to control the current.
  • actuators are mechanically connected either directly or indirectly between the tuneable filter body and the moveable or deformable elements of the tuneable filter so causing the moveable filter elements to move relative to the filter body or to deform.
  • one or more of the actuators are mechanically connected only to the filter component that is designed to deform with no mechanical connection required between the actuator(s) and the RF filter body.
  • one or more of the actuators are mechanically connected only between two of the filter components that are required to move relative to each other.
  • the mechanical linkage of a tuneable element to its respective actuator is direct such that part of the tuneable element forms part of the actuator structure.
  • At least one tuning element is formed form a dielectric material and the associated actuator is not wholly separated from the inside of a respective cavity by the solid conductive wall of the cavity is RF electrically isolated by the suitably close positioning to the tuning element of one or more conductive vias connecting between the conductive walls of the cavity.
  • At least one tuning element is formed of a conductive material and wherein TEM mode propagation along the tuning element of RF energy from within the cavity to the outside of the cavity and towards its associated actuator is prevented by two or more buried vias located adjacent to and across the longitudinal line of the tuning pin and separated by substantially a half-wavelength corrected for the reactance introduced by the adjacent vias, for the propagation at this wavelength to be blocked and which capacitively loads the leaking TEM mode to stop the leakage.
  • the tuneable RF filter comprises multiple actuators controlling the movement of the totality of tuning elements wherein the synchronisation of the movements of all of the tuning elements is electrically controlled by the
  • control is by way of a pre-computed look-up table stored in the memory of a controller.
  • control is by way of an algorithm generating in real-time the actual required positions of all tuning elements to achieve the required state of the filter.
  • the tuneable RF filter comprises at least one moveable tuning element wherein each moveable tuning element is movably supported by a tuning support structure, the support structure partially or fully dielectric, and/or partially or fully conductive.
  • each SMA wire is enclosed within a dedicated void in one of the one or more Supports to ensure free movement of the SMA wire relative to the Support.
  • the tuneable RF filter comprises at least one moveable tuning element wherein each moveable tuning element is positioned slidably in a channel through the support, the channel configured to ensure free movement of the tuning element while maintaining a precise gap between and accurate distance from the tuning pin to the corresponding resonator, coupling or tapping point for all positions of the tuning element controlled by the associated Actuator.
  • each actuator is fully integrated into the filter.
  • the tuneable RF filter comprises at least one resonator, wherein the one or more resonators are movably mounted within a cavity and caused to so move by direct or indirect mechanical connection to one or more SMA-wires.
  • the tuneable RF filter comprises at least one resonator, wherein one or more resonators are configured so as to be deformable and are caused to so deform by direct or indirect mechanical connection to one or more SMA-wires.
  • one or more of the deformable resonators has the form of one of: a thin strip; a flat-section spiral; a flat-section helix; a shape which has at least one direction of low force deformation.
  • one or more of the deformable resonators is formed from elastic material such that it returns to its original shape after deformation and is capable of providing the necessary restoring force to stretch to its original cold length the SMA- wire that upon heating caused its deformation, once the SMA-wire has cooled again.
  • the shape of the deformable resonator is such as to effectively enclose the SMA wire in a Faraday cage and so isolate it from the RF energy in the surrounding RF cavity.
  • the SMA wire or wires provided to cause motion of the tuning element are attached to the low-impedance capacitive sections of the tuning element so as to maximally isolate them from any RF energy transmitted from within the cavity.
  • the tuneable RF filter comprises an SMA-wire positioned partly or wholly within an RF cavity wherein strong coupling of the SMA-wires to the RF field in the cavity is prevented by the use of ⁇ 100micron diameter straight SMA wire located entirely on or within the electric wall of the cavity.
  • the tuneable RF filter comprises an SMA-wire positioned partly or wholly within an RF cavity wherein strong coupling of the SMA-wires to the RF field in the cavity is prevented by positioning the line of the wire orthogonal to and symmetrical to the magnetic walls of the cavity and parallel to the electric walls of the cavity.
  • the tuneable RF filter comprises an SMA-wire positioned partly or wholly within an RF cavity wherein the SMA-wire or the SMA-wire together with its electrical connections are constrained to lie in a plane and that plane is positioned orthogonal to and symmetrical to the magnetic walls of the cavity and within the electric walls of the cavity
  • one or more resonant or reflective elements are positioned in a waveguide with conductive walls and wherein the one or more resonant or reflective elements are caused to move axially along the waveguide each by an actuator.
  • the waveguide conductive walls are formed from alternate metal and dielectric layers with adjacent metal layers joined together by rectangular arrays of conductive vias through the dielectric layers the rectangular arrays forming the walls of the waveguide whose axis is orthogonal to the metal and dielectric layers, and the waveguide cavity is formed by the removal of the dielectric and metal layers within and between the waveguide walls.
  • one or more resonant or reflective elements are constructed so as to reflect as perfectly as practically possible all of the RF energy incident at one end of the waveguide back to that same end of the waveguide with a phase directly proportional to the axial position of the moveable elements along the waveguide thus providing a single-port reflective tuneable phase- shifting filter.
  • two resonant or reflective elements are constructed so as to reflect as little as practically possible of the RF energy incident at one end of the waveguide back to that same end of the waveguide such that nearly all of the RF energy emerges from the other end of the waveguide with a phase directly proportional to the axial positions of the moveable elements along the waveguide and wherein a second Actuator is used to control the axial separation of the two resonant or reflective elements to optimise the input return loss with operating frequency thus providing a dual-port tuneable phase-shifting filter.
  • the tuneable RF filter comprises two separate sets of one or more resonant elements each set independently of the other moveable axially along the waveguide by independently controllable Actuators, wherein each set of resonant elements is responsive to only one of two different polarisations of waves incident on one end of the waveguide, for plane polarisation waves the different polarisations being orthogonal to each other, and for circular polarisation the different polarisations being of opposite sign.
  • This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.
  • FIG. 1 shows a side view of an embodiment of a latching bi-directional linear SMA stepper-actuator, or BSA, of the present invention, the BSA comprising a stator top half, a stator bottom half, and a shuttle, the stator bottom half rigidly attached to the stator top half, the shuttle sliding freely within and moving relative to the top and bottom stator halves and coupled in use to an external load.
  • BSA latching bi-directional linear SMA stepper-actuator
  • Figure 2 shows a side close-up view of a portion of the stepper mechanism of the BSA of figure 1 , showing detail of the shuttle which has ratchet teeth on each of it's two long edges, the ratchets facing in opposite directions so that those on the top edge allow ratchet sliding in the left-hand direction, and the ratchets on the bottom edge allowing ratchet sliding in the right-hand direction, SMA wires, springs and pawls for controlling movement of the shuttle within the stators also shown.
  • Figure 3 shows a perspective side view of a variation of the linear actuator of figures 1 and 2, this variation providing a fast-slew mechanism.
  • Figure 4 shows a close-up perspective view of the linear actuator of figure 3 at the point where the shuttle exits the structure formed by the upper and lower stators, showing detail of the connection between the stator top and bottom halves via a base component that rigidly connects the stator halves, and two pawls located against the right-hand edges of the stator halves that in the embodiment shown in this figure are held against and interlocking with the ratchet teeth on the shuttle by a heated and contracted SMA wire, but which are otherwise held apart and off the shuttle by a bent wire spring which applies a separating force to these two pawls.
  • Figure 5 shows a perspective end view of the linear actuator of figures 3 and 4, showing detail of the fast-slew mechanism, the mechanism having an SMA wire actuator that straddles a pair of pawls and which when actuated pulls these pawls towards each other and into teeth-meshing contact with the shuttle, and further showing detail of the chamfered entry points in the upper and lower stators which help to ensure clean re-entry of the pawls at the end of a fast reverse slew back of the shuttle, so that the pawls locate properly against their reference edges in the stators.
  • Figure 6 shows a view of the linear actuator of figures 3 to 5 part way through an indexed movement where the fast reverse slew back mechanism has been engaged, the pawls shown locked to the shuttle through the action of the actuated SMA wire actuator and carried along with the shuttle to the right, this movement stretching the long tension spring and priming it for action on the fast reverse slew-back at the end of the stepped/indexed stroke.
  • Figure 7 shows a variation of linear actuator that includes side wings on the shuttle, the wings sitting below the moveable pawls and supporting them against movement parallel to the ratchet teeth, the wings fitting into a V-groove in the base element that is formed by the stators.
  • Figure 8 shows detail of an alternative support arrangement for the moveable pawls, the pawls in this embodiment having wings which wrap around the top and bottom sides of the shuttle, the wings holding the pawls firmly in place to assist with eliminating movement when the pawls are pulled together and locked onto the ratchet teeth of the shuttle
  • Figure 9 shows a rear view of a variation of linear actuator provided with
  • the linear actuator having a first set of reverse-slew-back components as in the linear actuator of figure 1 , and a second set directed in the reverse sense relative to the ratchet teeth sets on the shuttle, the second set on the rear of the actuator and at the other end of the shuttle from the end used for the first set of such components.
  • Figure 10 shows a size comparison example of an actuator of an embodiment of the present invention configured with 100pm step-size and bidirectional travel of ⁇ 11mm (22mm total stroke), next to a US dime coin, both items shown to scale.
  • Figure 11 shows a close-up side perspective view of a stepper-pawl arrangement suitable for use in embodiments of the actuator of the present invention, with the stepper-pawl arrangement moved to the opposite side of its adjacent passive-pawl so that the SMA-wire actuator does not require routing through the passive-pawl, the pawls held in contact with the shuttle by compression springs, the pawls liftable together off the shuttle teeth by the action of an SMA-wire actuator.
  • Figure 12 shows a side view of an embodiment of linear stepper-actuator that uses a rack-and-pinion rack, the assembly comprising a grooved stator, a stepper-cage, a shuttle and two stepper-pawl stepper SMA-wire actuators.
  • Figure 13 shows a perspective close-up view of the linear-stepper embodiment of Figure 12 with the stepper-cage and shuttle removed to show detail of the two stepper-pawl stepper SMA-wire actuators, set into two grooves in the stator, and detail of a rod coupling the lift wire to the pawl.
  • Figure 14 shows a graph/chart of a performance example for a capacitor-driven SMA element using bursts for actuation, the element having a 25pm SMA wire with a roughly 130hm cold resistance surrounded by medium-thermal-conductivity
  • FIG. 15 shows a perspective view to one side and from above of a dual-cog arrangement suitable for use with any of the embodiments of figures 1 to 14 that can be used to balance the shuttle arrangement.
  • Figure 16 shows a side view of an embodiment of rotary inverse escapement suitable for use with the embodiments of linear actuator of the present invention, the escapement shown in two possible positions in the left- and right-hand views, the escapement comprising a verge that pivots about a pin fixed to a stator that rocks back and forth about an axis, so that teeth distal from the axis can interface with the teeth of a ratchet wheel, and SMA wires and their actuating mechanisms.
  • Figure 17 shows a perspective view from above and to one side of a first embodiment of SMA-wire mechanical overload prevention mechanism suitable for use with the actuators of the present invention, the mechanism having a wire mount mechanically coupled to one end of a pre-stressed tension spring via a first pin, the spring stretched so that the other end can be coupled to a second pin which rests in slots in the mount, a wire terminal with a crimp-end mechanically attached to the pin.
  • Figure 18 shows a perspective view from above and to one side of a second embodiment of SMA-wire mechanical overload prevention mechanism suitable for use with the actuators of the present invention, the spring in this embodiment having a terminal extended away from its crimp-section where the SMA-wire is attached via an extended section that is bent to form a serpentine tension spring, the extended section allowing for extension of the spring portion in the direction of the wire.
  • Figure 19 shows a perspective detail view of the spring of figure 18, the spring optimised for insertion directly into a printed circuit board (PCB) and having a single piece of flat metal formed into a crimp at one end, a pair of PCB insertion-pins and a serpentine tension spring, the tension spring section stretched in use into restraining mounts and held in place by the pins, the SMA-wire crimped into the crimp-end.
  • PCB printed circuit board
  • Figure 20 shows the spring of figure 19 inserted into a PCB, with a first pin inserted into a tight-fitting hole and soldered to a PCB track (not shown) to provide electrical connection, the other pin inserted into a slot which provides an end-stop for the pre stress tension in the spring.
  • Figure 21 shows an underside view of the PCB and spring of figure 20 and the tight fitting location of the first pin in the PCB, and a view of the slot giving clear space for the other pin to move freely under overload conditions, constrained only by the force of the spring.
  • Figure 22 shows a close-up perspective view of the SMA-wire mechanical overload prevention mechanism of figure 18 applied to a bowstring actuator, an SMA-wire crimped at both ends to mechanical and electrical connections engaging with a load- attach-pin at or near the wire’s centre, the load attach pin mechanically connected to the push-rod of the actuator via a connecting member and pin which in turn engage with the spring whose other end is mechanically connected to the push-rod.
  • Figure 23 shows a perspective schematic view of a double bowstring SMA-wire actuator with first and second SMA-wire mechanical overload prevention
  • Figure 24 shows a perspective schematic view of an alternative embodiment of actuator using a double bowstring SMA-wire, with first and second SMA-wire mechanical overload prevention mechanisms as shown in figure 17, one for each of the bowstrings to protect against overload, but sharing a common overload spring.
  • Figure 25 shows a perspective view of a fast cycle-time dual SMA actuator.
  • Figure 26 shows a perspective view from above and to one side of a double bowstring SMA-wire actuator fitted with a fast cycle-time dual SMA actuator as shown in figure 25.
  • Figure 27 shows a perspective view from above and to one side of an alternative form of double bowstring SMA-wire actuator fitted with a fast cycle-time dual SMA actuator as shown in figure 25, sharing a common overload spring.
  • Figure 28 shows the analytically modelled results for an embodiment of a simple straight-wire SMA actuator optimised for high-speed drive according to an embodiment of the present invention
  • the SMA actuator comprised of 17mm of 25micron diameter SMA wire, and pushing a load of mass of 225mg and a frictional force of 0.011 N
  • the vertical scale shows output stroke in mm (0.0 to ⁇ 0.7mm) while the horizontal scale is time from initiation of stroke, in milliseconds.
  • Figure 29 shows further analytically modelled results for an embodiment of a simple straight-wire SMA actuator optimised for high-speed drive according to an embodiment of the present invention
  • the SMA actuator comprised of 17mm of 25micron diameter SMA wire, and pushing a load of mass of 225mg and a frictional force of 0.011 N
  • the vertical scale shows wire heating current ( ⁇ 50mA to nearly 300mA) while the horizontal scale is time from initiation of stroke, in milliseconds.
  • Figure 30 shows further analytically modelled results for an embodiment of a simple straight-wire SMA actuator optimised for high-speed drive according to an embodiment of the present invention, the SMA actuator comprised of 17mm of 25micron diameter SMA wire, and pushing a load of mass of 225mg and a frictional force of 0.011 N, wire resistance [ohm] shown on the vertical scale against stroke [mm] on the horizontal scale is shown for maximum safe actuation speed.
  • Figure 31 shows the analytically modelled results for an embodiment of a single bowstring SMA-wire actuator optimised for high-speed drive as in one aspect of the present invention, comprised of 17mm of 25micron diameter SMA wire, with a crimp separation of 16mm, and pushing a load of mass of 225mg and a frictional force of 0.011 N, the vertical scale showing output stroke (or distance moved by the actuator load) in mm (0.0 to ⁇ 1.2mm) while the horizontal scale is time from initiation of stroke, in milliseconds.
  • Figure 32 shows the analytically modelled results for a single bowstring SMA-wire actuator having the same arrangement as described in figures 28 to 31 , showing drive current [mA] on the vertical scale against time [ms] on the horizontal scale is shown for maximum safe actuation speed.
  • Figure 33 shows the analytically modelled results for a single bowstring SMA-wire actuator having the same arrangement as described in figures 28 to 31 , the load acceleration [m/s/s] plotted against time [ms] to show how the available acceleration falls as stroke increases.
  • Figure 34 shows the analytically modelled results for a single bowstring SMA-wire actuator having the same arrangement as described in figures 28 to 31 , the drive voltage (for optimum safe high speed drive) plotted in volts against time in milliseconds.
  • Figure 35 shows an embodiment of a tuning element of the present invention relative to a resonator in a conventional solid-wall cavity.
  • Figure 36 shows an embodiment of a tuning element of the present invention relative to a resonator in a cavity constructed between a pair of ground planes.
  • Figure 37 shows an embodiment of two coupled and tuned resonators sandwiched between ground planes, with one plane removed for clarity.
  • Figure 38 shows an embodiment of the components needed for a complete tuneable two- resonator filter with I/O ports.
  • Figure 39 shows an embodiment of an alternative arrangement of the components of the tuneable filter of figure 38.
  • Figure 40 shows an embodiment of a 3D folded tuneable six resonator filter with three ground planes.
  • Figure 41 shows an embodiment of an integral tuner, Actuator and resonator.
  • Figure 42 shows an embodiment of an SMA tuneable-phase reflective waveguide phase-shifter filter.
  • Figure 43 shows an embodiment of a two-Actuator tuneable through-waveguide phase-shifter filter.
  • Figure 44 shows an embodiment of an alternative SMA integrated capacitive tuning element.
  • Figure 45 shows an embodiment of a twisting-mode SMA magnetic I/O coupling mode tuning element.
  • Figure 46 shows an embodiment of a bending mode SMA tuned resonator.
  • Figure 47 shows an embodiment of an alternative Faraday cage bending mode SMA tuned resonator.
  • Figure 48 shows an embodiment of a form of waveguide-phase-shifter with phase adjusted by an Actuator.
  • Figure 49 shows an embodiment of a modified form of waveguide phase-shifter capable of independently varying the phase of each of two orthogonal polarisations, and capable of modification to independently tune each of two opposite circular polarisations,
  • Figure 50 shows an embodiment of a phased-array antenna comprising an array of SMA-tuneable phase-shifters with an offset feed and a schematic beam produced by the array.
  • Figure 51 shows an outside view of an SMA linear stepper actuator
  • Figure 52 shows the as-manufactured (pre-assembly) components of the main functional layer of the actuator of Figure 51
  • Figure 53 shows the components of Figure 52 as assembled, and the two SMA actuator wires.
  • Figure 54 shows the functional components of an SMA rotary stepper actuator.
  • SMA Shape Memory Alloy
  • shape-memory-alloy material e.g. metals such as NiTi or Nitinol nickel-titanium plus additives
  • any and all polymer equivalent materials which have similar thermo-mechanical properties (a thermally induced phase-change accompanied by a significant change in length in at least one direction).
  • shape-memory-alloy material e.g. metals such as NiTi or Nitinol nickel-titanium plus additives
  • any and all polymer equivalent materials which have similar thermo-mechanical properties (a thermally induced phase-change accompanied by a significant change in length in at least one direction).
  • any reference to electrical Joule heating should be ignored for that particular material, and the defined temperature profiles for that material used instead.
  • the BSA 100 can be categorised generally as a load-shifting SMA actuator (LSSA).
  • the BSA 100 comprises three main components: a stator top half 1 , a stator bottom half 2, and a shuttle 3.
  • the top and bottom stator halves comprise a pair of bodies that are rigidly connected or attached to one another, with a central channel or aperture 101 between the two.
  • the shuttle 3 comprises an elongate member that is configured to locate into and move within and along the central channel 101 in use, the fit between the walls of the channel 101 and the shuttle 3 being snug or close, but allowing free movement of the shuttle 3.
  • the shuttle 3 slides freely within and moves relative to the top and bottom stator halves 1 , 2, and is coupled in use to an external load.
  • FIG. 2 A close-up view of a portion of the stepper mechanism is shown in Figure 2.
  • the shuttle 3 comprises ratchet teeth 102 on its two long edges, with the ratchets on opposite edges facing in opposite directions, the teeth 102a on the top edge shaped, positioned, and aligned to allowing ratchet sliding in the left-hand direction, and the teeth 102b on the bottom edge shaped, positioned, and aligned to allow ratchet sliding in the right-hand direction.
  • Upper and lower channels 103, 104 are formed in stators 1 and 2 respectively, aligned perpendicularly to the shuttle channel 101.
  • pawls 4, 5, 24, 26 are located in upper and lower channels 103, 104 that are formed within the upper and lower stator halves 1. 2 - upper pawls 4 and 5, and lower pawls 24, 26.
  • the pawls 4, 5, 24, 26 move within the upper and lower channels 103, 104 in parallel with the long axis of the channels, to engage with and disengage from the shuttle ratchet teeth 102a, 102b.
  • the top pawls 4, 5 block or prevent movement of the shuttle 3 to the right, and the bottom pawls 24, 26 prevent movement to the left when engaged with the teeth 102b.
  • the pawls can be lifted together off the shuttle teeth via activation of upper and lower SMA actuator wires 8 and 27 respectively.
  • the pawls are slidingly connected to the wires 8, 27 by rigid links - upper link 10 and lower link 25
  • Links 10 and 25 are configured to fit loosely into apertures formed through the pawls, so that when not actively lifted by the SMA wires, the pawls may themselves be freely lifted by motion of the shuttle teeth engaging on the pawl teeth in the appropriate unblocked direction.
  • the pawls may have multiple teeth arranged in a line so as to mesh with multiple successive teeth on the shuttle. This has the benefit of reducing wear on any individual pawl tooth, as well as reducing the interface forces between pawl and shuttle which in turn reduces the rate of wear, both for pawl and for shuttle.
  • the teeth of upper pawl 4 are held in contact with the shuttle teeth by a long bent- wire spring 9 anchored at the other end to base 1 , which exerts a force directed substantially towards the shuttle sufficient to retain pawl engagement under normal operating conditions, but small enough to be overcome by the lift-off force applied by SMA wire 8 when actuated.
  • the same spring wire 9, aligned generally in parallel with the channel 101 also holds pawl 4 in contact with the left-hand edge of the upper channel 103, which acts as a leftwards mechanical reference position for this pawl.
  • Pawl 4 is a passive-pawl that serves only to prevent reverse motion of the shuttle, when engaged with it.
  • a spring wire 6 holds the teeth of pawl 5 in contact with the shuttle teeth 102a.
  • Spring wire 6 is entirely above the stator and channels in the stator, except for the portion which enters pawl 5.
  • the left hand end of spring wire 6 is clamped to base 1 so as to apply a downward and a rightward force to pawl 5, locating it against the teeth 102a of the shuttle and against the right-hand reference wall of channel 103.
  • Pawl 5 is also attached to the end of SMA wire actuator 11 whose other end is connected within stator 1 in a cavity 12 formed in stator 1 and opening onto the upper side of the channel 101.
  • a mirror arrangement is present on the opposite side of the shuttle 3, with a lower channel 104 opposite and parallel to the channel 103, with pawls 24 and 26 corresponding to pawls 5 and 4 respectively, springs 28 and 105 corresponding to springs 6 and 9 respectively, SMA wire actuator 27 corresponding to SMA wire actuator 8, and SMA wire actuator 23 corresponding to SMA wire actuator 11 (with differences outlined below) connected within stator 2 in a cavity 50 formed in stator 2 and opening onto the lower side of the channel 101.
  • the teeth 102b on the lower side of the shuttle 3 are arranged in the opposite direction to teeth 102a on the upper side of the shuttle 3.
  • SMA wire 23 now has one end fixed in stator 2 at location 20, to the right of the lower channel 104, with the other end attached to a coupling link 21 located within cavity 50 which in turn rigidly couples to the first or left-hand end of push-rod 22 whose second end pushes to the right on pawl 24 (passing through a hole in pawl 26 en route), against the restoring force of bent-wire spring 28, which in this lower half of the actuator pulls pawl 24 to the left, and pushes it upwards so that its teeth mesh with those on the shuttle 3. Otherwise than reversing the direction of motion of the shuttle this lower half of the mechanism operates in the same way as that just described for the top half.
  • An alternative arrangement that avoids the use of push-rod 22 is to move the mechanism (the step-right mechanics described in the paragraph above) to the left away from the right-hand edge of base 2, so that there is space for the SMA actuator to be placed to the right of pawl 24 and to be mechanically attached thereto at one end of the SMA wire 23 and have the other end of the wire rooted in base 2 to the right of the right-hand edge of the channel 104. This would enable the SMA wire to pull pawl 24 to the right directly without the use of any link or push-rod.
  • the bent-wire springs are shown as a series of straight wire sections with right-angled joints for simplicity. However, in practice each spring would be made from a single piece of wire with smooth bends rather than the right- angled joints shown.
  • Alternative spring forms such as coil springs and flexures can equally well be used and the illustrations should not be taken as limiting in this respect.
  • flexure-type springs may be integrated with the base components 1 , 2 if these base components are made of suitable material (e.g. spring steel or stainless steel), by for example, etching or laser-cutting or ion- beam-cutting, or punching them out of the solid.
  • the pawls may then be also be integrated with the springs by a similar process in the same manufacturing step.
  • the SMA-wire actuators in the figures are in this embodiment electrically operated. However, for clarity, the electrical connections to the SMA wires are not shown in these figures. It is however convenient, where the body 1 ,2 material and/or the spring material is electrically conductive to use the body or the springs or both as at least one electrical connection to one or more of the SMA wires, and this is conveniently achieved by crimping those SMA wire ends to the body or spring to which they are required to be mechanically attached.
  • an electrical connection may be made via a wire-crimp soldered to a printed conductive (e.g. copper) track as per standard PCB technology.
  • a preferred solution when those components are not electrically conductive (and thus cannot themselves be used as an electrical return path) is to co-crimp such an SMA- wire Free-End with a flexible (and preferably insulated) conductive wire, preferably stranded copper wire, whose gauge and flexibility are consistent with the electric current to be supplied to the SMA-wire, and the forces the SMA-wire is capable of supporting in actuator mode.
  • a conductive track may be laid over the surface of the nonconductive component from the SMA wire-end to a remote electrical connection point, to avoid the use of separate wires.
  • the BSA stepping cycle for this embodiment is as outlined below, with individual times for each of the sequence events shown in [square brackets] at the end of each event.
  • t on is the time required to heat and actuate an SMA wire
  • t off is the time required for the SMA wire to cool and be ready for another actuation.
  • SMA wire actuator 27 is actuated to lift pawls 24, 26 in a pre-step-left
  • SMA wire actuator 1 1 is actuated to pull pawl 5 left. This pulls the shuttle 3 with it, and pawl 4 is prevented from moving left by the LH wall of cavity 103 and so is lifted up by shuttle 3’s ratchet teeth, while shuttle 3 is shifted more than one tooth left beneath it [t on ];
  • SMA wire actuator 11 is de-actuated to release pawl 5. This allows spring 6 to re-stretch SMA wire 1 1 and to push pawl 5 over the shuttle 3 ratchet teeth to its right end stop [t off ];
  • This step-left actuation cycle as described assumes that the actuator has to do work against the shuttle to move it to the left, e.g. if it is pulling against a spring, friction, or gravity.
  • the external load is pushing the shuttle to the left with sufficient force F r to overcome the braking effect of the ratchet pawls, then when both pawls 24, 26 are lifted off the shuttle by SMA wire actuator 27, the external load can move the shuttle 3 leftwards in an uncontrolled manner, if it pushes sufficiently hard, as the shuttle’s ratchet teeth 102a will simply slip underneath the engaged pawls 4, 5.
  • the value of F r can be adjusted by modifying the slope of the ratchet pawl teeth (as described below).
  • the BSA structure can be modified so that each pawl now has its own lifting SMA-wire, enabling all pawls to be independently engaged and disengaged.
  • the stepping cycle for this variation is as follows:
  • SMA-wire 11 (and similarly 22) are provided with force overload protection, as described in detail below.
  • Actuation of the shuttle 3 to the right is similar to the description above, but now using pawls 26 (passive-pawl), 24 (stepper-pawl), and SMA wire 23, and with the other two pawls 4, 5 lifted off the shuttle by means of SMA actuator wire 8.
  • each of the SMA-wires has to move its load by a small distance only ( ⁇ 2 tooth lengths or ⁇ 2 ratchet tooth heights) then the SMA-wires can be short and thus consume very little power.
  • the SMA-wires all operate directly in tension on their loads and so can apply their full tensile force capability (minus the opposing spring forces) to their loads.
  • the bidirectional stepping linear actuator is almost planar.
  • a typical ratchet tooth size may be as small as 100mpi long by 50 mhi high, in which case the SMA wires can be as small as ⁇ 2.5mm long, and 25 mhi in diameter, and consume only a few mJ of electrical energy to heat them to the Austenite state from ambient.
  • the electrical connections for applying heating current to the various SMA actuator wires are not shown (for clarity), and the ends of the SMA wires are electrically insulated from any metal parts (only) as required to avoid short circuits and to suitably isolate them (again, not shown for clarity).
  • a load-shifting SMA actuator designed to step in a particular direction operates completely autonomously, as for example in the embodiments of LSSAs described above.
  • the other LSSA is taken out of play by lifting all of its one or more pawls out of engagement with the shuttle, using SMA wire actuator(s).
  • SMA wire actuator(s) In many applications there will be a sustained period of stepping in one direction, followed by a possibly also sustained period of stepping in the other direction. In this scenario drive power used to continuously power the SMA wire pawl-lifts of the out of play LSSA is wasted.
  • latching pawl-lift mechanisms on each of the pawls. These have two stable unpowered positions: pawl-down and pawl-up. This can be achieved by any of the many latching mechanisms known in the art. These latching mechanisms are then controlled by at least one but preferably two SMA wire actuators each (one SMA wire actuator can be used if a pull-on/pull-off type of latch is used. Two SMA wire actuators are used if a separate latch-wire and unlatch-wire are provided).
  • a two-SMA-wire driven latching mechanism is preferred, as these provide a definitely-known state (definitely on, or definitely off), whereas if using a single-wire pull-on/pull-off system, the initial state of the system cannot be known at first power- on without using a separate sensor subsystem.
  • latching pawl lifts one of the LSSAs can be mechanically decoupled from the shuttle by a single short electrical pulse to its latched pawl-lift SMA-wires and thereafter will consume zero power, until it subsequently is needed to drive the shuttle in the opposite direction which is achieved by one more short electrical pulse to the pawl-lift SMA-wires (whereafter the other LSSA is similarly put out of action until next required).
  • the maximum rate of stepping of a linear actuator as described is limited by the thermal time constant of the SMA wire actuators used to control the various movements of the pawls. In general this can be maximised by using the thinnest possible SMA wire (shortest thermal time constant) consistent with a given force output.
  • More force at the same speed can be achieved by using parallel pairs or multiples of thin SMA wires in place of each single SMA wire actuator.
  • Shorter stepping times may also be achieved by improved electronic control which can deliver a high power pulse for a short time at the initial heating phase of an SMA wire, the pulse delivering enough energy to match the thermal energy capacity and latent heat of phase- change of the wire to very rapidly raise the temperature of the SMA material and convert the Martensite material of the SMA to Austenite, without over-raising the temperature of the material.
  • Such techniques give very fast 'rise-times' for the phase-change and thus pulling force of the SMA wires. However, these techniques cannot assist with the 'fall-time', which is limited by natural cooling rates.
  • the type of indexed linear stepper - the BSA as described above - can be used to increase actuator step-speed (and thus actuator output speed) by providing additional stepper-pawls operating in parallel with each other along the length of the shuttle 3, each with an associated mechanism including SMA wire actuator and drive control.
  • the method is as follows:
  • a second additional stepper-pawl SMA actuator is actuated at a time t c /2 after activation of the first stepper pawl. This then drives another step in the same direction while the first actuator is still cooling, and because of the ratchet operation of the pawls, the two actuator cycles do not interfere with each other.
  • adding a second stepper-pawl mechanism doubles the speed of stepping and thus of actuator output (and also doubles the average maximum power
  • This technique is easily extended to three or more such stepper-pawl mechanisms, three giving a speed three times as great as one, etc.
  • a second (or third, or more) row of ratchet teeth may be provided in parallel with the first on the shuttle, and the multiple ratchet pawls are divided amongst the parallel sets of shuttle teeth as best suits the mechanical layout. These will operate in parallel with significant integral speed up factors.
  • the shuttle teeth width may be made greater than (multiples of) the pawl teeth width, and a pair of pawls (or more) may then share the same position along the shuttle but sit on different portions of the shuttle’s teeth width.
  • stepping rate of a single SMA wire actuator limits the stepping rate of a single SMA wire actuator to roughly five to fifty steps per second (one step per 200ms to 20ms) depending on the ambient conditions, wire parameters, any wire-heatsink methods or apparatus used, and mode of electronic drive used.
  • Adding a second parallel stepper pawl mechanism will increase this step rate to ten to one hundred steps per second (one step per 100ms to 10ms), and adding a third can achieve fifteen to one-hundred-and-fifty steps per second (one step per 67ms to 6.7ms).
  • Still more parallel steppers may be used if necessary.
  • Such a speed-up technique is not available with simple (non stepping) SMA wire linear actuators.
  • SMA wire actuators used to move the stepper pawls e.g. pawl 5
  • their associated springs e.g. spring 6
  • SMA wires have to be physically stretched back to their original length after they have been heated through the Austenite phase, otherwise they will remain at least partly contracted even when cooled and e.g. spring 6 serves this function, amongst others).
  • this can be as much as 40% of the rated load of the SMA wire.
  • the device can be modified by removing the return spring of the stepper pawl’s SMA wire, and replacing this with another length of SMA wire connected in its place between the pawl and the stator /base, so as to act in opposition to the stepper pawl’s first SMA wire actuator.
  • the stepper pawl can now be pulled in two opposite directions, one for each SMA-wire attached.
  • the first (original) SMA wire is actuated by heating and thus contracts which pulls the pawl in the direction of contraction of that wire, while the second SMA wire is unheated and remains at or near ambient temperature, and the actuator steps.
  • the second SMA wire actuator is heated and thus contracts, pulling the pawl in the opposite direction and in so doing stretching the first SMA wire back to its original unheated length. Once that point is reached, the second SMA wire actuator is unheated and begins cooling, to complete a stepper cycle.
  • This method of operating the stepper pawl SMA wire actuators results in significantly more of the wire’s rated force loading to be used to move the external load of the linear stepper actuator, at the cost of additional SMA wire, and higher electrical power consumption as well as a slight increase in complexity of the electronic controller driving the actuator, but can be useful in certain applications.
  • the actuator 3000 of figures 3 and 4 is broadly similar to the actuator 100 described above, with additional components to allow fast slewing back to a previous indexed output position, in one of the possible actuator directions.
  • the actuator 3000 is configured so as to provide a fast reverse slew-back operation to an indexed position.
  • This sort of movement scenario is important for certain applications, and can be referred to as a reverse slew-back to indexed position.
  • the upper and lower stators 3001 , 3002 are the same as the previously described stators 1, 2, and in this variation are shown connected by a further base component 3041 which supports the stators 3001 , 3002 and rigidly connects them.
  • a cover piece 3040 forms a rigid base extension over the top of and guiding the shuttle 3003.
  • an additional pair of pawls 3046, 3047 are slidably positioned on the shuttle, 3003, locating against the right-hand edges of stators 3001 , 3002.
  • the pawls 3046, 3047 are normally (in normal bidirectional stepping operation of the linear actuator) held apart and off shuttle 3003 by the additional bent wire spring 3048 which applies a separating force to pawls 3046, 3047.
  • Pawl 3046 meshes with the upper ratchet teeth 3102a of shuttle 3003, and is also mechanically coupled to one end of a long tension spring 3045 whose other end is rooted in the base at 3046.
  • This tension spring 3045 provides a pulling force on pawl 3046 in the direction along the line of the shuttle, to the left in the drawing, and in normal bidirectional stepping operation, ensures that pawl 3046 is held tight against the adjacent edge of stator 3001 which is a mechanical reference point for this pawl.
  • the connection between spring 3045 and pawl 3046 is not completely rigid, but does provide some guidance to the alignment of the pawl and maintains its orientation such that its row of ratchet teeth are approximately parallel to those of shuttle 3003.
  • ratchet teeth on pawls 3046, 3047 may each fully mesh with the nearest ratchet teeth on the sides of shuttle 3003.
  • a compression spring may be used instead of tension spring 3045 by suitable rearrangement of attachment points and positioning.
  • a compression spring has the advantage of most likely providing a more compact arrangement, given the same force and spring-constant requirements. However, a compression spring will also likely require additional mechanical guidance to prevent it buckling, which may be achieved simply by, e.g. embedding it into a loose-fitting slot in the base 3041 or indeed in the shuttle 3003.
  • Spring 3048 acts to hold apart the two pawls 3046, 3047 so that they have no contact with the teeth of the shuttle 3003. However, they may also be pulled towards each other against the separating force of spring 3048 by the action of an additional SMA wire actuator 3049, which mechanically links these two pawls, and when heated to the Austenite phase, pulls both pawls into contact with shuttle 3003, as shown in figure 3.
  • the normal position of these two pawls (with the SMA actuator wire 3049 unpowered) is away from and off the shuttle, and the position shown in Figure 3 is the position they occupy when SMA wire 3049 is actuated.
  • Pawls 3046, 3047 can be referred to as 'floating-pawls' because they are not anchored directly to either the shuttle or the stator and may move significantly relative to both of these primary components.
  • FIG. 5 Another view of the fast-slew mechanism of the actuator 3000 is shown in figure 5, where can be seen a clearer view of SMA wire actuator 3049 that straddles pawls 3046, 3047 and which when actuated pulls those pawls towards each other and into teeth-meshing contact with the shuttle 3003.
  • the entry points 3050, 3052 in the stators 3001 , 3002 are chamfered, which helps to ensure clean re-entry of the pawls 3046, 3047 at the end of a fast reverse slew back of the shuttle, so that the pawls locate properly against their reference edges in the stators 3001 , 3002.
  • Figure 6 shows a view of the linear actuator part way through an indexed movement to the right, the fast reverse slew back mechanism engaged at some position along the stepped movement. It will be seen that the pawls 3046, 3047 have now been carried along with the shuttle 3003 also to the right, as they are locked to the shuttle through the action of the actuated SMA wire actuator 3049, and that this movement has in turn stretched the long tension spring 3045, priming it for action on the fast reverse slew-back at then end of the stepped/indexed stroke.
  • SMA wire actuator 3049 is unheated / de-actuated and spring 3048 holds pawls 3046, 3047 off the shuttle teeth.
  • Tension spring 3045 pulls pawl 3046 back to its reference position against base 3001 , and the linking action of spring 3048 tends to pull pawl 3047 also back against base 3002 although this is not critical for this operation.
  • the stepping motion of the actuator commences as described above.
  • the shuttle begins its indexed motion starting from position N1 , moving to the right towards N2.
  • SMA wire actuator 3049 is heated / actuated pulling pawls 3046, 3047 into tight contact with the shuttle 3003 and the ratchet teeth of pawl 3046 intermesh with those of the shuttle and lock this pawl into position N3 on the shuttle.
  • the long tension spring 3045 is extended to the right by (N2-N3) steps (teeth-lengths) and applies a restoring force to the left, to the shuttle via pawl 3046 which is still locked to the shuttle.
  • This causes the shuttle to rapidly accelerate to the left, until pawls 3046, 3047 come into contact with the stators 3001 , 3002 which occurs when the shuttle reaches position N3 (the position where pawls 3046, 3047 were initially locked to the shuttle).
  • Overshoot of the shuttle due to its inertia (and inertia of the external load) is prevented primarily by pawl 3047 which prevents further leftward relative movement of the shuttle.
  • the fast reverse slew is now complete and the actuator may be stepped normally in either direction from this new starting position. It is preferable to provide some additional mechanical buffering and/or damping to reduce the impact force when the shuttle does a rapid relatively uncontrolled return under the action of the long tension spring.
  • a compliant end-stop may be adequate.
  • More velocity control may be achieved by e.g. by a gas-damper connected between the shuttle and the stator, which can conveniently and cheaply be incorporated into the body of the stator (e.g. a long blind hole in the stator parallel to the shuttle movement direction, open at the end of the actuator, and a long piston fitting into that hole attached to the shuttle - a small leak-hole then providing the damping rate).
  • a gas-damper connected between the shuttle and the stator, which can conveniently and cheaply be incorporated into the body of the stator (e.g. a long blind hole in the stator parallel to the shuttle movement direction, open at the end of the actuator, and a long piston fitting into that hole
  • the shuttle itself may be used as such a piston if the base/stator is arranged to enclose the end of the shuttle near the end of its stroke in a nearly airtight manner - e.g. by assuring close clearance.
  • the slew-back spring 3045 must be suitably pre-tensioned at this left-most position to ensure adequate return force against external loads and internal actuator forces.
  • Additional support structure can be provided to maintain the pawls 3046, 3047 in their locations on the shuttle during a stepped stroke when fast reverse slew-back is engaged.
  • FIG. 7 An example of this additional support is shown in the embodiment of Figure 7, where the actuator 701 is substantially similar to that described above and shown in figures 3, 4, and 5, except with the addition of side wings 761 , 762 added to the shuttle 703.
  • the wings 761 , 762 are located below the two moveable pawls 746, 747 to support them against movement parallel to the ratchet teeth when they are extended beyond the base/stator.
  • the V-shape of the wings fits into a V-groove in the base 741 , acting as a guide to the shuttle clear of its ratchet teeth.
  • FIG. 8 An alternative means of supporting the moveable pawls 846, 847 is illustrated in the embodiment of figure 8.
  • the pawls have wings 870 and 871 which wrap around the top and bottom sides of the shuttle 803. With the pair of pawls 846, 847 pulled together by their SMA actuator wire, and thus locked onto the ratchet teeth of shuttle 803, the wings 870, 871 hold the pawls 846, 847 firmly in place, eliminating any remaining degrees of freedom
  • the wings can be used with the bidirectional version of the fast reverse slew-back mechanism without interfering with it.
  • a small notch in base 841 around the shuttle entry point gives clearance for the pawl wings when the pawls are docked in their reference position against the base.
  • Electrical connections (not shown in the figures) to the SMA actuator wires connecting the moveable pawl pairs can be provided by a pair of lightweight flexible insulated and preferably stranded conductive cable, one wire to each end of such an actuator wire, with enough of a free length of this flexible wire to avoid any restriction to movement of the pawls on and along with the shuttle.
  • a flexible printed circuit can be used.
  • SMA wire actuator 3049 If a slow release of the floating-pawls’ SMA wire actuator 3049 is acceptable, this SMA wire can be air-cooled and therefore little static power is required. However, for applications which demand a very fast release of the floating pawls then a modified scheme may be employed. Here the floating pawls are held together by a latching actuator which is pulled ON (i.e.
  • a mechanical latching mechanism (of any suitable form of the very many known in the art) which incorporates a spring stressed (compressed or expanded) by the latching event and which in turn continues to apply meshing force between the floating-pawls and the shuttle, even after the first SMA actuator is released (de-actuated).
  • the floating pawls then continue in this meshed state until at a later time a second SMA wire actuator upon actuation unlatches this latched actuator, and may then be immediately released again.
  • both the first and second SMA actuators just described need be actuated only transiently (to latch, or unlatch the floating pawls) their static actuation power is unimportant and only the transient actuation energy is of concern.
  • these two SMA wire actuators for latching/unlatching may preferably be heat-sinked to the surrounding mechanical structures (as described hereafter), thus ensuring fast de-actuation times.
  • latch mechanisms require just one actuation device (e.g. SMA-wire) and operate in a push-on/push-off manner. Such a device could be used here. However, it is not preferred, as it is not possible to know the state of such a latch after first power-on, which is undesirable.
  • a dual actuated latch as described is highly preferable.
  • the additional two pawls, their associated SMA-wire actuator, and separator spring are not present in this variation.
  • the long tension spring is connected directly to the shuttle such that it provides a return force to the shuttle in all stepper actuator positions.
  • An end-stop is rigidly fixed to the shuttle (or the shuttle is formed with an integral end-stop) that limits the return stroke of the shuttle to the zero position by coming into contact with reference location(s) on the base components, in the same or a similar manner to the pawls in the variation described above.
  • all of the pawls may be lifted off the shuttle by their associated SMA wires, and the long tension spring will then apply a restoring force to the shuttle which will very rapidly return to the zero position when the end-stops will hit the“buffers” on the base.
  • the tension spring always loads the stepper actuators and reduces the maximum available output force (whether or not slew-back is to be used), and;
  • the total stepper actuator power consumption is lower because the slew- back mechanism no longer has an SMA-wire actuator for pawl-clamping to be powered during the stroke.
  • stepper motor mechanism for one of the two directions can be removed completely (e.g. the two pawls 24, 26, and their associated springs, plus the SMA wire actuator 22 and its connecting mechanism 21 , 23) and the slew-back mechanism alone is used for the return stroke.
  • the shuttle 903 extends from both sides of the base / stator components 901 , 902, 941 and two additional pawls 960, 961 are provided, each meshing with one set of ratchet teeth on shuttle 903, these pawls being sprung apart by a bent wire spring 962, and capable of being pulled towards each other to grip the shuttle by another SMA wire actuator 964.
  • the fast release version of the floating pawls using two SMA wire actuators may similarly be used for both directions of fast slew-back if desired.
  • Figure 10 shows a size comparison of a practical example with 100pm step-size, and a bidirectional travel of ⁇ 11mm (i.e. 22mm total stroke).
  • An American dime is shown drawn to scale.
  • dimension W is 3.9cm
  • dimension X is 1 2cm
  • dimension Y is 1.1cm
  • dimension Z is 2mm.
  • the rate of cooling after actuation ends (and with heating turned off) is determined by the thermal conductivity and thermal capacity of the surrounding air, and the proximity of other significant heat-sinks (e.g. the stator body).
  • Convection can play a significant part in cooling (particularly vertical) linear-actuator wires if their on-time is large (e.g. multiple seconds).
  • stepper-actuators e.g. the stepper-pawl SMA wire actuators described herein
  • Radiation effects are generally less than 1%.
  • One effective and simple way to greatly increase the cooling rate without significantly impeding the motion of the SMA-wires is to embed them in a heatsink-compound such as a standard silicone grease or thermally-conductive but electrically insulating grease or silicone polymer. This can reduce SMA wire cooling-times by a factor of ten, or more.
  • the thermal conductivity of air is ⁇ 0.02W/m/K
  • for standard (lubricating) silicone grease is ⁇ 0.18 W/m/K and for these types of thermal heatsink compounds it is ⁇ 1 to >2W/m/K.
  • Such active cooled SMA wires enables this technology to be effectively used for space -borne equipment, such as moving lenses and mirrors, tuning RF filters for communications, and for phase-shifters for microwave antennas.
  • Figure 11 shows an alternative arrangement where the stepper-pawl 1105 is on the opposite side of its adjacent passive-pawl 1104.
  • the effect of this is that the SMA- wire actuator 1111 for stepper-pawl 1105 no longer needs to pass through the passive-pawl 1104.
  • the pawls 1104, 1105 are now held in contact with the shuttle by forces provided by springs 1106, 1109 as before but in this implementation these are compression springs for mechanical convenience (although it should be noted that any suitable form of spring would suffice).
  • the pair of pawls are liftable together (off the shuttle teeth 1102a) by the action of SMA-wire actuator 1120, in a similar manner to that already described above.
  • SMA-wire actuator 1111 is now mounted in a groove 1120 in stator 1102 and this groove surrounding the SMA-wire is filled with heatsink-compound (not shown, for clarity) which tightly thermally couples actuator 1111 to the thermal compound itself, and then to stator 1102, enabling it to cool to ambient temperature very quickly and thus facilitating fast step-rates.
  • Groove 1120 is sufficiently deep to give adequate mechanical clearance between the SMA wire 1111 and stator 1102 when the stepper pawl is in the lifted state (i.e. off the shuttle teeth).
  • pawl- lift SMA-wire actuator 1120 also now is sited within a narrow groove 1102 in the stator (between the position reference blocks 1101) and so similarly may also be thermally coupled to the stator with heatsink compound, allowing fast cycling.
  • the actuator is constructed so that the heatsink compound is contained in the grooves around the SMA-wires, and egress of the compound is prevented.
  • a convenient way to resolve this dichotomy is to prevent the elastomer bonding to the side walls of the surrounding cavity, either by choice of material, or by applying a suitable coating, or by loosely line the cavity surrounding the SMA wire with a very thin elastomer sheet of high compliance material, and then to fill the remaining space to and around the SMA wire with the elastomer compound and allow it to set/cure. Then the slug of cured elastomer wrapped on one or more sides by the thin sheet, is able to contract and expand longitudinally (parallel to the wire contraction direction) without being impeded by the local cavity wall (e.g. parts of the stator) in which it is contact, but without any adhesion.
  • the local cavity wall e.g. parts of the stator
  • a simple way to decrease the SMA wire turn-on time is to drive it with an initially high voltage to increase the initial rate of heating and then to lower the voltage to a level enough to merely maintain the temperature, or indeed with this stepper actuator, to then simply turn off the drive voltage.
  • the microprocessor (or other pulse source) driving the SMA element should“freeze” /“stick-high” / crash or suffer a software error that can allow the drive line to hold in the high state for much longer than the intended short pulse drive time, then the SMA element can overheat, and in extreme cases suffer irreversible thermal and possibly mechanical damage, rendering the actuator useless.
  • This situation may be avoided by driving the SMA element via a capacitor (ac drive) rather than with direct dc drive.
  • one or more of the SMA active elements of the SMA-stepper-actuator is electrically driven by an electrical pulse via a series capacitor, Cs, whose capacitance value is chosen such that the energy passed through the capacitor to the SMA element when the pulse is applied is sufficient to heat the SMA element through its Martensite/Austenite transition.
  • each pulse of shorter duration than the single pulse drive-method requires.
  • the series capacitor can be very approximately Np times smaller in value than for a single pulse, with the same supply voltage. Using such a method allows the use of a very small 10pF capacitor.
  • the pulse-mode of driving the SMA element is relevant to stepper actuators.
  • wire temperature has to be maintained continuously for as long as actuator output position is to be maintained, in which case short-pulse drive is inappropriate, and the use of high thermal-conductivity material surrounding the wire (to increase speed of de actuation) with continuous drive current, causes unacceptably high quasi-continuous power loss.
  • the SMA element is a 25pm SMA wire (not shown) with a roughly 130hm cold resistance surrounded by medium-thermal-conductivity (0.2W/m.K) silicone rubber.
  • the waveforms show the effect of driving the SMA element from a 5V pulse burst source of 50 pulses of duration100ps each and 200ps apart, via a 10pF capacitor.
  • Fig.14 the top chart shows the pulse burst drive voltage waveform, with 'time elapsed' shown in the x-axis in ms. Below that is the voltage across the 10pf capacitor.
  • the third chart in the figure is the wire current which will be seen to quickly become -symmetrical about zero.
  • the bottom chart in the figure shows the wire temperature initially rising steeply, then at a slower rate as the Martensite/Austenite transition occurs, and after ⁇ 8ms reaching the full Austenite temperature and shortly thereafter beginning to cool quite rapidly (-40C within about 30ms of start of heating in this example) due to the silicone rubber surrounding the wire, ready for another actuation cycle.
  • a directional ratchet and pawl combination is used, one for each direction of travel.
  • the shuttle 1203 has on one edge one set of teeth 1203a which are symmetric and bidirectional so that an engaged pawl with meshing teeth will block relative motion in both directions, in contrast with the double-edged shuttle described in the previous embodiments.
  • the teeth on both pawl and shuttle preferably have a primary tooth slope of angle alpha, where this angle is chosen to be steep enough that an engaged pawl blocks shuttle motion with a small pawl-shuttle contact force, but not so steep that meshing of teeth is difficult.
  • an angle of ⁇ 83degrees is used, which gives a roughly 10:1 ratio of pawl-shuttle force to shuttle blocking-force assuming moderate inter-tooth friction.
  • the shuttle teeth can have vertical sides, but these are difficult to mesh, so the arrangement described above is preferred.
  • pawl teeth and the shuttle teeth preferably have rounded tips, as shown in figure 12. With rounded teeth, on an attempted meshing of pawl to shuttle, the teeth slide easily together even when there is misalignment. The entire tooth profile may be curved.
  • the stepper-pawl has a pair of SMA wire actuators for stepping the shuttle (one for each direction).
  • the other pawl is a passive pawl which lifts on and off the shuttle to lock it in place.
  • Both pawls have springs which push the pawls into mesh with the shuttle (but which can be overcome by the SMA-wire actuators that lift the pawls). However, these springs are omitted in the drawings for clarity.
  • the passive pawl is free to move towards and away from the shuttle but has essentially no movement parallel to the shuttle’s travel direction, being limited in this direction by adjacent walls of stator acting as end-stops.
  • the active pawl is similar except that it may move in the latter direction by more than one tooth length (and less than two, and preferably less than 1.5, or even less still).
  • the passive pawl is much as previously described apart from its tooth profile and is not shown in Figure 12.
  • a step-right cycle comprises the following steps:
  • stepper-pawl by actuating the stepper-pawl’s lift SMA-wire actuator); [t on ]
  • stepper-pawl left (i.e. actuate the SMA wire actuator that pulls pawl to left); [t on ]
  • stepper-pawl i.e. de-actuate stepper-pawl’s lift SMA-wire actuator
  • step-left SMA wire and simultaneously lift passive-pawl i.e.
  • stepper-pawl right (i.e. actuate the SMA wire actuator that pulls pawl to right); [t on ]
  • the power-stroke i.e. when the shuttle is moved to the right
  • step 6 where the stepper-pawl is meshed with the shuttle and pulled to the right by one of its SMA wires.
  • This mechanism works whether the load is passive, or is actively pulling in either direction, as long as the load’s pull is small enough to be overcome by the SMA-wire actuator’s pull.
  • step 5 For example, if the load is pulling to the right for the duration of this cycle then no shuttle movement will occur until step 5, due to the fact that prior to that the shuttle is locked by the passive pawl. Thereafter, the load might pull the shuttle (and the meshed (dropped) stepper pawl) to the right before step 6 has started or completed, but either way it cannot move much further than a single step because of the meshed stepper pawl hitting its end-stops. This has no consequence for the stepper SMA- wire(s) as they can be pulled/pushed either way when in the de-actuated state.
  • step 5 an additional action is to simultaneously in step 5 partially actuate the SMA wire actuator that pulls the pawl to the right by enough to shorten it under zero load. This will prevent this wire from buckling if the load over-drives the actuator.
  • a step-left cycle comprises the following steps:
  • Lift stepper-pawl i.e. actuate stepper-pawl’s lift SMA-wire actuator
  • stepper-pawl right (i.e. actuate the SMA wire actuator that pulls pawl to right);
  • stepper-pawl i.e. de-actuate stepper-pawl’s lift SMA-wire actuator
  • step-right SMA wire and simultaneously lift passive-pawl i.e. actuate passive-pawl’s lift SMA-wire actuator
  • stepper-pawl left (i.e. actuate the SMA wire actuator that pulls pawl to left);
  • the embodiment as shown in figure 12 has additional features to allow heatsink- compound cooling of the SMA wires to be used without applying potentially damaging forces to the SMA wires.
  • stepper SMA wires 1210, 1211 are connected to a cage 1213 surrounding pawl 1212 on 4 sides.
  • Cage 1213 can, if made of suitable conductive material, e.g. phosphor bronze, brass or stainless steel, serve as a common electrical termination for these SMA wire ends.
  • Cage 1213 is just wide enough to allow pawl 1212 to slide freely vertically (to and away from the shuttle) but eliminates any significant lateral motion of the pawl within the cage.
  • the cage 1213 in turn may slide freely laterally (parallel to the direction of motion of the shuttle) but is prevented from moving vertically by the pair of extended wings 1216, 1217 which slide in grooves in stator 1202. The effect of this
  • SMA wire 1214 - the pawl lift wire - pulls directly on rod 1219 which passes freely through a hole in pawl 1212, and whose length is such that the ends of the rod just clear the walls of stator 1202 at either end, but are close enough to prevent any significant sideways movement of the rod (and thus of the SMA wire 1214).
  • the pawl 1212 is pulled by either of the stepper wires 1210, 121 1 pulling on the cage, the pawl slides along rod 1219 without transmitting its lateral motion to SMA wire 1214, which again might otherwise risk shearing the wire in the presence of surrounding thermal-compound.
  • FIG 13 A different view of the embodiment shown in figure 12 and described above is shown in figure 13.
  • the stepper-cage 1213 and shuttle 1203 are removed (in the figure, but not in the operational device) to show more clearly some of the internal arrangements, in particular the two (stepper-pawl) stepper SMA-wire actuators 1210, 121 1 can be seen to be deeply set into two grooves 1221 , 1220 in stator 1202.
  • Rod 1219 coupling the lift wire to pawl 1212 can be seen to be closely fitting (with clearance) between the adjacent walls of stator 1202, to prevent substantial movement in the direction parallel to the shuttle movement.
  • the passive pawl for this version of the actuator is essentially the same as for the previously described actuators except for the modified tooth shape (similar to that of pawl 1212 in figures 12, 13).
  • This pawl may be fitted either side of the stepper-pawl, preferably far enough along the shuttle not to interfere with the stepper pawl’s SMA stepper SMA wires.
  • the shuttle 1203 now needs teeth on only one edge, as only two pawls in total are needed and they both interface with the same set of teeth on the shuttle.
  • the lock-pawl may be placed on the opposite side of the shuttle to engage with a second set of rack teeth on the opposite edge of the shuttle from those shown in fig.12.
  • a fast return mechanism (or fast slew-back) as previously described can be added to this version of the stepping linear actuator as before, except that one of the moving pawls (the one on the edge of the shuttle with no teeth) is replaced by a smooth slider.
  • teeth as shown can be added to both edges of the shuttle, and then both fast-slew-back pawls can mesh with the shuttle teeth and apply bidirectional locking forces.
  • the long- tension spring can attach to both pawls, as neither will now slip when pulled by the spring.
  • stepper actuators described above that use a thermal- compound to enhance cooling time and thus increase the stepping speed, it is not always necessary to add one or more additional parallel stepper pawls (to be actuated sequentially and overlapping as described previously) to speed up the actuator, since the fast cooling times are usually adequate to produce the desired output shuttle speed.
  • An additional parallel stepper pawl assembly may still be added, as this allows the electronic controller to leave the second stepper-pawl assembly de-actuated in normal use, and to monitor the currents in the SMA-wires of the first stepper-pawl assembly. Should the electronic controller detect an open circuit (suggesting a broken wire) or a short circuit (suggesting some other kind of fault) then it can seamlessly cease driving the first pawl’s SMA wires and instead switch over to the second stepper assembly and use that instead, and carry on functioning without a pause. The controller can also then report back to a higher-level controller that a possible fault has been detected, so that the stepper motor can be repaired at the next service opportunity. In some implementations the same measure of
  • redundancy/enhanced reliability may be achieved by adding a second SMA-wire in parallel to the existing SMA-wire on the stepper-pawl, with at least one end of each of the two wires electrically insulated from each other. In this case an additional pawl is not required - instead sensing a break in the current drive wire will cause the controller to switch over to driving the second wire instead.
  • Typical values of tan A to be used can be in the range of 5 to 10, whereas mu is limited to a maximum value of one.
  • the overload safety factor can be designed in almost entirely by a suitable value for A since for A >45 degrees the tan A factor will dominate. That is for example if A ⁇ 83degrees then tan A ⁇ 8, which is very much greater than an average friction coefficient of 0.5.
  • this form of overload protection may be added by ensuring that the steepest part of any tooth profile (shuttle or pawl) is restricted to a maximum slope angle A ⁇ 90 degree chosen as appropriate (in conjunction with the pawl restoring force Fs) for the degree of protection required.
  • any of the variants of the BSA described above may be converted easily from a linear stepper motor to a rotary stepper motor by engaging a pinion gear with the teeth on one edge of the shuttle.
  • the teeth shape are ratchet teeth (asymmetrical) then it is preferable to engage a pair of pinions, one to each set of teeth on either shuttle edge, these two pinions then linked together by a further pair of passive pinions inter-meshing with each other and one to each of the first pinion pair, to guarantee non-slipping drive in both directions.
  • one or more of the sliding components of any of the stepper actuators described herein can be replaced with a similar component that instead of sliding on or against or within the body of the actuator or within another component thereof, is instead supported by one or more flexures capable of supporting it and guiding it in its direction of travel without direct supportive contact from the other surrounding components.
  • a similar component that instead of sliding on or against or within the body of the actuator or within another component thereof, is instead supported by one or more flexures capable of supporting it and guiding it in its direction of travel without direct supportive contact from the other surrounding components.
  • multiple parallel leaf flexures are useful for all spring functions in the stepper actuators described herein, in that they may have slender flexures allowing large deflections without plastic deformation of the flexure material and yet substantial return force because of the additive force effect of the multiple parallel leaves.
  • a pawl may be supported by a single leaf spring which is pre-stressed such as to push the pawl into contact with the shuttle (or away from it against an end- stop) with a certain required force, in such a way as there is no friction produced when the pawl moves.
  • the shuttle may be supported within/adjacent to the body of the actuator by one or more flexures, but more typically two or more flexures, which also provide a returning force, holding the shuttle at (typically) one end of its range of travel against an end-stop (although the reference point might in some cases be an intermediate position which would then be less precisely defined).
  • the shuttle During actuation via the stepper and lock pawls the shuttle would then be coerced to move away from this reference position against the spring force of the flexure(s) but substantially without friction. Such elimination of friction not only improves the reliability of this type of actuator, but also substantially eliminates wear, and the associated creation of particulates.
  • a moving component supported by one or more flexures is also the mechanical terminating point for one or more SMA actuation wires, then if one or more of the flexures is made of conductive material (e.g.
  • each such flexure can be used as an electrical connection to that end of the one or more SMA wires, eliminating the need for“flying-lead” connections to moving components.
  • the flexures are made of suitable material, especially metals and more especially phosphor bronze or stainless steel, then a part of the flexure material may be formed into a crimp structure to allow direct mechanical and electrical connection to the SMA wire and the moving component, greatly simplifying the overall structure of the actuator.
  • the fixed end of the flexure may then be mounted to the body of the actuator directly, or if the body is electrically conductive and the flexure connection needs to be electrically isolated from the body then instead it may be mechanically connected to the body via an insulated component, typically polymer and the electrical connection made at this fixed end by any convenient means.
  • One convenient means is for the body of the actuator to be a printed circuit board (PCB) in which case at least part of the fixed end (root) of each flexure may be mechanically and electrically attached to conductive pads on the PCB that connect it appropriately to the rest of the circuit, providing electrical and some mechanical support. The majority of mechanical support may be provided directly between the root of the flexure and the PCB itself.
  • PCB printed circuit board
  • stepper actuators made them highly resistant to the effects of g-forces directed at right-angles to the direction of shuttle motion (lateral g-forces).
  • lateral g-forces As long as the gross structure of the actuator is not damaged by them then even very high lateral g-forces have essentially zero effect on the actuator position because the pawls and their springs may be made to have very little mass, and so inertial forces induced by stator accelerations will be small compared to the related spring forces holding those components in place.
  • external g-forces parallel to the direction of shuttle motion can seriously effect the positional stability of the stepper-actuator because such forces magnify the apparent load mass.
  • the actuator can accurately move and hold the load in a stable position. If the body of the actuator is then subject to e.g. ⁇ 3g acceleration (i.e. ⁇ 30m/s 2 ), then the effective mass of the load becomes anywhere between 2gm and 4gm (depending on the orientation of the actuator in the 1g Earth’s gravitational field) and the actuator is now“out of spec”. So the load (relative to the actuator) is likely to move and positional accuracy is lost.
  • a second shuttle parallel to the first, capable of freely sliding parallel to the first, and caused to move in the opposite direction and by the same amount as the first by some sort of mechanical linkage.
  • a linkage could be for example a swing arm pivoted at a point midway between the shuttles and rotatably connected to each at either side of the pivot (e.g. via a pin protruding from each of the shuttles at the same distance from the pivot point, passing through slotted holes in the arm) to act like a see saw. In this way as one shuttle moves, the other shuttle is forced to move equally in the opposite direction.
  • Another mechanism would be to use inextensible cords or cables passing around pulleys beyond each end of the shuttles, the pulley diameters being the same as the separation of the shuttle centres, and the ends of the cables being connected to the ends of the shuttles. So when one shuttle moves one of the cords/cables would be placed in tension and would pull around its pulley onto the closest end of the other shuttle causing it to move the same amount in the opposite direction.
  • One type of dual-cog, balanced shuttle arrangement is to place a cog between a set of identical rack teeth on each facing edge of the two shuttles and engaging with those teeth.
  • the cog rotates about a central bearing fixed to the actuator body midway between the two shuttles. Movement of one shuttle causes the meshed cog to rotate and it in turn then causes the other shuttle to move the same distance in the opposite direction to the first. It is most preferred that one of a pair of such cogs is placed near to both ends of the shuttles (but always remaining meshed with the rack teeth over the entire range of allowable shuttle movement), to better balance the forces on the shuttles and prevent jamming. With this arrangement, linear motion of the shuttle is simultaneously converted to rotary motion of the cog(s).
  • any fast-slew-back springs from the shuttle to the cog(s), and to replace linear tension or compression springs attached between the stator and shuttle with spiral clock-springs attached between the stator and non central portion of the cog(s), which may provide a more compact arrangement. That is, the fast slew-back springs for each direction can be fitted one to each of two such cogs to provide a more compact arrangement.
  • Figure 15 shows schematically an implementation of a dual-cog, balanced shuttle arrangement.
  • the remainder of the SMA stepper actuator (which could be any of the variations described herein), is not shown in Fig.15, where 1503a is a shuttle of an SMA stepper actuator as already described, bearing a set of teeth along one long edge.
  • Cogs 1510, 1511 , and a balancing rack 1503b (the mass of which is arranged to be identical to the mass of the shuttle 1501a and any load connected thereto) are also shown.
  • the cogs have stub shafts 1505, 1506 which bear in the stator (not shown) and upon which they rotate freely.
  • the intermeshing of the cogs with the shuttle teeth and balancing rack teeth cause the balancing rack to move an equal and opposite distance to the shuttle, whenever the shuttle moves along the direction of its gear teeth.
  • an external force causes the stator (not shown) to accelerate (i.e. an external g-force)
  • this will cause the cog shafts to accelerate similarly and the balancing inertial forces of the shuttle and rack on opposite sides of the cogs will cancel out producing no net rotation of the cogs and thus no movement of the shuttle relative to stator.
  • This arrangement thus renders the actuator virtually immune to external g- forces.
  • the second shuttle s own mass to be the same as that of the first shuttle+load instead of adding a separate load mass to the second shuttle,. This allows it to be made more compact. If“gearing” is used then the balancing mass need not be the same as that of the first shuttle+load. For example if a 4:1 gear ratio is used by interspersing an odd number of cogs/gears in series, with a 4:1 overall ratio between the shuttles, then the 2nd shuttle mass need be only one quarter that of the first shuttle+load, and can be slightly less still because of the inertial effects of the gears.
  • An escapement is a mechanism well known in the art, that controls the movement of a carriage or wheel by a small fixed amount, when the carriage or wheel is being urged to move by some external force.
  • Rotary forms are found in clocks and watches. Linear forms are found on typewriter carriages.
  • An escapement may be used in another variant of the SMA stepper actuator, instead of the arrangement of one or more pawls described above.
  • the advantage of using an escapement over multiple pawls is that movement of the same single mechanical component (the verge) acts to position the shuttle at the end of a step, as well as to guarantee that only a single step occurs, under all within-specification load conditions. If the verge is spring-loaded in one direction of its movement, and SMA- wire driven in the other, then a step cycle may be controlled in exactly one SMA heat/cool cycle, allowing for relatively fast stepping compared with more complex multi-pawl-movement mechanisms.
  • An inverse escapement mechanism is also well known in the art. This type of mechanism not only controls the movement of a carriage or wheel by a small fixed amount as per an escapement, but in addition drives the motion as well. That is, there need not be any additional driving forces on the moving member.
  • the moving member is the shuttle.
  • the verge of the inverse escapement is arranged to mesh with the shuttle in such a way as to always limit the motion of the shuttle to a single step at a time, under the control of the position of the verge, and to also push or pull the shuttle along its direction of travel by means of the meshed contact points, by precisely one step during one cycle of movement of the inverse escapement mechanism.
  • FIG 16. An example of this mechanism suitable for use with the embodiments of linear actuators of the present invention is shown in figure 16.
  • the basic mechanism of rotary inverse escapement is already known in the art, but the example shown is modified and improved for the purposes of the present invention.
  • the rotary inverse escapement of figure 16 is shown in two of many possible positions.
  • the verge 1611 pivots about a pin 1612 fixed to a stator 1615, and is able to rock back and forth about that axis, and in so doing a pair of teeth 1617 and 1618 distal from the axis interface with the teeth of a ratchet wheel 1610.
  • the verge 1611 can be rotated anticlockwise about the pin 1612 by a first SMA actuator 1614 connected between a pin 1613 which freely rotates in the verge, and the stator 1615.
  • actuator 1614 When actuator 1614 is not pulling anticlockwise, the verge is stably held in the position shown in the right-hand view of figure 16, by spring 1616 connected between pin 1619 which freely rotates in the verge, and the stator 1615.
  • the arrangement of the verge teeth and its rocking motion driven by successive cycles of activation and deactivation of SMA actuator 1614 cause the ratchet wheel to rotate clockwise by precisely one tooth width on each cycle, and because at all times at least one of the verge teeth 1617, 1618 are engaged with the ratchet wheel teeth, the rotation of the wheel is completely under the control of the verge and actuator/spring combination.
  • the rotary inverse escapement as described above can also be combined with parts of the balanced shuttle mechanism shown in figure 15, to drive a linear SMA stepper actuator.
  • the mechanism as shown in figure 16 and as described above can be mounted such that its ratchet wheel 1610 is coaxial to and/or mounted to the same shaft as one of the cogs (e.g. cog 1510 of the embodiment shown in figure 15), such that a cycle of the escapement turns the ratchet wheel and thus the cog clockwise by one tooth width. This will then cause the shuttle 1503a to advance to the right by one tooth width. No other stepper mechanism would be required to move the shuttle 1503a.
  • a bidirectional stepper mechanism becomes available, providing that also an additional facility is included to allow one of the escapements to disengage from the linear stepper when the other is engaged and stepping (since both escapements block rotation in both directions when engaged and not stepping).
  • Such a dual inverse escapement driven linear stepper provides a fast mechanism, as a complete step cycle involves only a single SMA element contraction/expansion (heating/cooling) cycle-time.
  • the verge contains at least two separate drive“teeth” mechanically connected together, and the arrangement of the verge teeth and their directions of motion are such that at least one of the two verge teeth is always engaged with teeth on the shuttle to be moved. Furthermore, when one of the verge teeth is engaged with the shuttle and causes the shuttle to move, then before that tooth disengages from the shuttle, the verge’s other tooth will have already engaged with the“next” tooth-pair along the shuttle from the tooth-pair it was previously engaged with, prior to the start of the verge movement cycle.
  • an inverse escapement mechanism driven in at least one direction of its cyclic movement by an SMA-wire actuator engages with the teeth of the shuttle in such a way as to cause the shuttle to move in the desired direction by just one step while preventing any further movement independently of the nature of the within- specification forces applied externally to the load of the stepper- actuator.
  • the return motion of the verge can be provided by a spring, or by a second SMA-wire actuator.
  • Such a device has minimal hardware, is very simple to drive electronically, and can step very rapidly, especially if the SMA wires are embedded in a thermal heat- conducting compound in the manner described herein.
  • the shuttle of the actuator is fixed, and the body of the actuator moves relative to the shuttle.
  • any of the actuators described so far may be converted into a crawler actuator, by reversing the physical arrangement of the pawls and shuttle teeth, such that the shuttle is now on the outside of the actuator with the shuttle teeth facing inwards, and the teeth of the pawls press outwards and onto the inside teeth of the shuttle when engaged with it.
  • the interfacing surface of the shuttle external body of such a crawler actuator is located inside a tube or pipe (either synthetic, or a component of an animal/human body).
  • placing two or more step-pawls opposite each other e.g. disposed at roughly 180deg, 120deg, etc around a circle inside the pipe
  • the contact force between the pawls and shuttle allows the contact force between the pawls and shuttle to be generated independently of gravity by squeezing the pawls roughly radially outwards into the inside of the pipe at (opposite) points around a circular section of the pipe, thus allowing the pawls to grip the inside of the pipe (by pushing outwards against each other) in order to provide the axial force needed for movement.
  • Such a device would be capable of insertion into a bodily aperture (such as a nostril) and then allowed to move itself along the passage (e.g. nostril-air-passage - trachea - bronchial etc into the lungs), and given adequate motive actuator force could pull a cable, catheter or delivery- pipe, waveguide or other flexible device along behind it. Signals on the cable could be used to power and control the actuator.
  • the catheter could deliver drugs to a target reachable via the pipe.
  • the delivery-pipe could deliver friction reducing fluid to the crawler head.
  • the waveguide could transmit radiation to such a target.
  • the crawler could be fitted with a miniature camera so that a surgeon could see what was ahead of the crawler and to control treatment processes and targets.
  • the delivery-pipe could deliver fluid to clean the camera lens. If more than one set of drive pawls were fitted to the actuator, and/or were the pawls to be individually controllable, then the lateral direction of the crawler could be controlled - i.e. it could be steered or navigated along the tube it was inside - and for example determine which branch to follow where the tube branched.
  • the shuttle can be curved or even circular in a plane through the set of teeth, but of such large radius that on the scale of a tooth size it is nonetheless essentially straight, thus forming a large diameter gear wheel (possibly of contrate gear form as well as pinion form), with number of teeth N.
  • an actuator could operate as described on this circular shuttle and upon each step advance the gear wheel by one tooth and thus rotate it through 2pi/N radians.
  • Such a device can be referred to as a Rotary SMA Stepping Actuator.
  • the shuttle is mechanically blocked (e.g. by external load overload) when a step-cycle is executed, then the step-cycle will necessarily fail to complete correctly, and the shuttle may not move at all.
  • a blocked step-cycle event is problematic.
  • the following two options are available: 1) Detect the blocked cycle (and so account accordingly for the current position; 2) include a return-to-reference-position facility (a return-to-zero, or RTZ, although it should be noted that zero does not need to be the actual reference position), so that when required, e.g. periodically or when some sort of fault condition is detected, the shuttle may be returned to some known reference position, independent of its actual current position.
  • RTZ return-to-zero
  • Blocked cycle detection is best done by sensing the motion (or lack of it) of the shuttle, for example by adding a step-sense mechanism that gives a distinctive yes/no signal when a step is successfully or unsuccessfully (respectively) completed, then the actuator control system can take account of the blocking, in its position counting (and can also be used to report error conditions if more blocks occur in a given stepping sequence than is deemed permissible).
  • the teeth on the shuttle provide a convenient mechanism for this to be achieved. When the shuttle successfully completes a step, a whole tooth will pass by any point adjacent to the shuttle.
  • a metal leaf spring of suitable length projects radially into the gaps between adjacent teeth, then during a step-cycle such a spring will be deflected by the motion of a tooth going by, and will then flick back as it rides over the tooth and into the next gap.
  • This will produce a particular characteristic motion of the leaf (slow deflection one way and then very rapid reverse motion) which can be detected for example by a simple capacitive sensor with the leaf spring forming one element of the capacitor, and transduced into an electrical signal, and then signalled to a processor capable of distinguishing slow from fast motion signals.
  • a typically blocked cycle will produce little or no motion and so little or no signal.
  • a half- blocked and then reversed step will typically produce slow motion in both directions and yet a different characteristic signal.
  • RTZ may be simply implemented by mounting one or more“limit- switches” which are actuated by the motion of the shuttle preferably when it reaches one end or the other (or both) of the allowable shuttle travel. The operation of the switches may then be detected electrically and e.g. sensed by a microprocessor GPIO pin, used to halt further motion in that direction, and to reset the position counter to the now known position of the shuttle.
  • RTZ limit-switches which can be galvanic switches, magnetic or optical sensors, resistive pressure sensors, or any other suitable form of sensor
  • Another way to achieve this result is to ensure that there are one or more mechanical end-stops which guarantee that the shuttle cannot move past them.
  • a “blind” position-reset may be attempted by repeatedly driving the shuttle at one or other of the end-stops a sufficient number of step-cycles that were it not to be blocked then it would definitely have reached the end stop (with a significant number of over-steps to allow for miss-steps or blocked steps, if required). In this way there is a high probability that the shuttle will be at the end stop.
  • SMA stepper actuator A specific implementation of the SMA stepper actuator is described below, and shown in figures 51 , 52, and 53.
  • directional indications e.g. left, right, up down, etc
  • This embodiment of the stepper actuator is configured to have a stroke of ⁇ 19mm; a step size of ⁇ 300micron; and a step number of 64. It has been found that a stepper actuator according to this embodiment has a positional precision of ⁇ 10micron; a positional stability of ⁇ 10micron, lasting approximately 24hrs, with or without power; a maximum working load of Igramme; an overload tolerance of 25gramme; a maximum step rate >10 steps/sec, and; an energy consumption per step of ⁇ 15mJ.
  • the SMA stepper actuator 5100 is formed by stacking a number of punched, stamped, etched or laser/ion-beam (or other suitable high resolution cutting process) cut thin layers of stainless-steel sheet, each between 200 and 300 micron thick, the layers assembled over a printed-circuit-board (PCB) base.
  • PCB printed-circuit-board
  • Each separate component has guide holes formed through it, that are aligned with a series of pins 5040 mounted in the PCB base. These serve to align all the components in the assembly.
  • the PCB provides mechanical support, rigidity, and placement precision (along with its guide pins 5040) for all of the other components, as well as providing electrical connections to the SMA wires.
  • the top plate 5041 is shown uppermost in figure 51.
  • a small portion of a fast slewback return spring 5031 Extending from the right-hand end in this particular implementation can be seen the overload protection spring 5029 for the SMA drive wire 5025 (shown on figure 53).
  • the overload protection spring 5029 is shown in the un-pretensioned state and has not yet been assembled to the SMA drive wire 5025 in this illustration.
  • the first metal layer directly above the PCB is shown in detail in figure 52 and figure 53.
  • the first metal layer directly above the PCB is the primary functional layer, containing the drive-pawl 5012 and lock-pawl 5001 , their associated leaf springs 5011 , 5002, guides for controlling the range of possible movement of the shuttle 5003, 5004, as well as cavity space for the two SMA wires 5020, 5025.
  • the shuttle
  • the next layer above the first metal layer preferably contains the overload-protection spring 5029 for the drive-pawl SMA-wire 5025 (or spring 5029 may alternatively be sited beneath this layer, in another layer, or even externally as seen in figure 51 in its un-pretensioned state).
  • This layer also acts as a spacer between the functional layer and the fast-slew-back return spring
  • the functional components are interlinked as required between layers by fold-down or fold-up tabs which extend out of the plane of the layer in which they originate, through holes in any intervening layers, and interlock with matching holes or slots in the other layer they connect to.
  • the final layer 5041 is a cover layer that keeps dirt out and keeps in any lubricating materials and heat-sinking materials.
  • All components which move within a layer e.g. pawls, springs, levers, shoes
  • FIG 52 shows the primary functional layer only.
  • the multiple parallel-leaf spring 5002 extends downwards and rightwards from the top portion of stator. Extending downwards (in the drawing) from spring 5002 is the lock-pawl 5001 , which carries a set of downwards facing triangular teeth that mesh with similar teeth on the shuttle 5030 which is shown out of position in this figure, for clarity.
  • the natural position of the leaf spring is as shown (i.e. the position as manufactured). However, insertion of the shuttle 5030 between the shuttle guide faces 5003 and 5004 lifts up the lock-pawl 5001 against the pressure of its leaf spring 5002, providing the required
  • the pawl 5001 , its leaf spring 5002 and the adjacent section of the stator 5000 are all one piece of material, which could be etched out of a thin sheet of stainless steel (or 3D printed), as a single component. No assembly is required of these separate parts. It will be seen that this method of fabrication enables the pawl and its spring to be made as just one integral part with the surrounding frame/spacer, enabling very low manufacturing and assembly costs.
  • an unlock lever system that comprises an unlock lever arm 5005 which is driven by the unlock SMA actuator wire 5020 (shown in figure 53), so as to lift the lever 5005 against the spring force of the long supporting arm or body of the lever 5005 when the wire 5020 is actuated.
  • the unlock lever system is integral with the frame 5000 of this layer, connecting to the frame 5000 via the spring arm body of the lever arm 5005, allowing the left-hand end of the lever arm 5005 to swing up and down.
  • a peg 5006 on the left-hand end of the lever arm 5005 fits loosely in a slot 5007 on the right-hand edge of the drive-pawl 5001.
  • the width of the slot 5007 is such that when the shuttle 5030 is assembled into the actuator the drive pawl 5001 is free to move up and down, driven by the shuttle teeth meshing and un-meshing with the pawl teeth, when the shuttle moves left or right without interfering with 5005.
  • the unlock SMA wire 5020 is actuated this pulls the unlock lever 5005 upwards, sufficiently far that the peg 5006 engages with the upper edge of the slot 5007 and lifts the drive-pawl 5001 completely clear of the shuttle teeth.
  • the unlock lever 5005 With the unlock lever 5005 in this actuated position, the shuttle is free to move left or right - i.e. is unlocked.
  • a drive-pawl 5012 extends upwards from the bottom portion of stator 5010, the drive- pawl mounted upon a multiple parallel-leaf spring 5011.
  • Pawl 5012 carries a set of upwards facing triangular teeth capable of meshing with similar teeth on the lower edge of the shuttle 5030 (when assembled).
  • the natural position (as manufactured) of the leaf spring 5011 is as shown in figure 52.
  • the un-activated SMA drive wire 5025 (not shown in figure 52, shown in figure 53) when assembled is attached to the right edge of the drive-pawl 5012 and wire 5025 pulls rightwards on this pawl 5012 and is held in sufficient tension by the then pre-tensioned leaf spring 5011 to pull the drive-pawl 5012 upwards and rightwards (because of the direction of the spring leafs of 5011) such that the teeth of the pawl 5012 are positioned just below but completely clear of those on the shuttle lower edge (after assembly as shown in Figure 53).
  • the action of the parallel leaf spring 5011 is to keep the row of drive-pawl teeth at all times parallel to the row of shuttle teeth.
  • the drive wire 5025 When the drive wire 5025 is actuated it shortens, and pulls the drive-pawl 5012 further to the right and further upwards, engaging its teeth with those on the shuttle, and because of the carefully arranged relative phase of the two sets of teeth, by the time the sets of teeth are fully meshed, the drive-pawl 5012 has pulled the shuttle 5030 more than half a tooth length to the right, against the external load force, internal friction forces, and the forces imparted on the shuttle by the lock-pawl. Because the shuttle 5030 has moved more than half a tooth length under the action of the SMA drive wire 5025, the lock-pawl 5001 has by now just lifted over the shuttle teeth previously immediately on the left of its teeth, and begun its descent sliding down their LH sides.
  • the drive wire 5025 is de-actuated and as the drive wire 5025 cools and re-expands under the return force of the drive-pawl spring 5011 , the drive pawl 5012 disengages from the shuttle teeth and the lock-pawl 5001 under the pressure of its leaf spring 5002 pushes down onto and into mesh with the teeth of the shuttle, moving it rightwards the rest of the whole tooth-length, and then locks it firmly and precisely into place, exactly one tooth further to the right.
  • the bottom end 5013 of the drive pawl leaf spring 5011 is firmly anchored into the stator 5010, and is in the most preferred form an integral part of this component so as to avoid separate parts and an assembly step.
  • stator 5010 in this layer of the actuator also forms a reference position for the“fixed” end of the drive SMA wire 5025.
  • Both sections 5000, 5010 of the stator in this layer are fitted with guide holes 5015 which upon assembly locate the stator sections over guide pins (not shown) fixed in the base plate of the actuator (not shown), to ensure precise relative positioning of parts.
  • Figure 53 shows the same layer of the actuator in assembled form.
  • the shuttle 5003 is now located slidingly between the upper 5003 and lower 5004 edges of stator parts 5000 and 5010, and is in full tooth-mesh contact with lock-pawl 5001.
  • the unlock SMA wire 5020 can be seen between its crimp contacts 5022 and 5021 which locate in the unlock-lever 5005 and stator 5000 respectively.
  • Wire 5020 is held taut when de-actuated by the prestress spring force in the deflected unlock lever 5005 which is held by wire 5020 just clear of the shuttle upper teeth.
  • an additional level of protection for the SMA drive wire 5025 is provided by the use of a pre-tensioned overload spring 5029 (not shown in this figure) which firmly pushes the right-hand terminal 5026 (which is slidingly mounted in slot 5027 of stator 5010) of SMA drive wire 5025 against an end-stop 5028 integrated into stator 5010, with a force Fovl, where Fovl ⁇ Fwmax, Fwmax being the maximum tolerable wire tensile force.
  • Fovl Fovl ⁇ Fwmax, Fwmax being the maximum tolerable wire tensile force.
  • the overload spring 5029 will allow the terminal 5026 to move left with the wire tension now being a function of the overload spring 5029 pre tension force, it’s spring-rate, and the amount of leftwards movement. With suitable values of these parameters, the SMA drive wire 5025 can be maintained at a safe tension ⁇ Fwmax under all conditions.
  • the method of fabrication described above enables the pawl 5012 and its spring 5011 to be made as just one integral part with the surrounding frame/spacer 5010, enabling very low manufacturing and assembly costs. It is also possible where the materials of the actuator are electrically conductive (e.g. stainless steel, phosphor bronze) to integrate at least one of the SMA wire terminals of each wire 5020, 5025, with the relevant part of the actuator assembly, preferably via a crimp terminal also integral with the structure. For example, for the drive wire 5025 it may be most convenient to integrate the left-hand terminal 5031 of wire 5025 with the drive pawl 5012, relying on the metal frame of the actuator to provide a return path for electrical heating current of the wire 5025.
  • electrically conductive e.g. stainless steel, phosphor bronze
  • the moving end 5022 may also be crimped directly to unlock lever 5005 with an integral crimp formed out of the same material as the lever.
  • the other ends 5026, 5021 may conveniently be crimped directly to electrically isolated crimps mounted on the base (e.g. a PCB) to complete the electrical circuits of these SMA wires without additional wires.
  • the base e.g. a PCB
  • an overload protection spring is used (as described for SMA drive wire 5025) the material of the overload protection spring 5029 itself used to provide a conduction path from terminal 5026 (then integrated with moving end of spring 5029) to the fixed end of spring 5029 which itself is then conveniently mounted into the PCB for external connection via a conductive PCB track.
  • a step of the shuttle may be achieved simply by pulsing on the drive SMA wire for a short time and then turning it off, the final part of the stroke happening automatically under control of the lock-pawl spring. This provides a very fast step cycle.
  • stepper actuator is resistant to external overload force damage because in un-actuated mode, excess load force simply pushes the shuttle harmlessly beneath the spring-loaded lock-pawl’s teeth.
  • the lock pawl and drive pawl may be placed either on opposite sides or the same side of the shuttle as convenient, in the latter case only one set of shuttle teeth then being required.
  • assembly reversed L to R may be fitted on either side of the shuttle wherever teeth are provided, which then allows full bidirectional operation of the shuttle (so long as simultaneous drive of both drive pawls is avoided). Again in this case no SMA unlock drive wire is necessary.
  • This particular form of the SMA linear stepper actuator lends itself particularly well to conversion into a rotary actuator: if the straight shuttle is replaced by a toothed cog, and the lock-pawl and drive pawl(s) are disposed around the cog so as to not interfere with each other, but to otherwise interact with the cog as previously they did with the toothed shuttle (in the previous configuration described above wherein all the pawls were on just one side of the shuttle), and, where the drive and lock pawl(s) are modified in shape to allow their set of one or more teeth to wrap around the cog and appropriately mesh with multiple teeth, then, the configuration with one lock pawl (no unlock SMA wire) plus one drive pawl is capable of continuously stepping the cog in the same direction, providing a unidirectional rotary SMA stepper motor; if a second drive pawl is added driving in the reverse direction around the cog, then a fully bidirectional rotary SMA stepper motor results; if a lock-pawl unlock assembly with an unlock S
  • Figure 54 shows a form of SMA rotary stepper actuator, similar in operation to the optimised SMA linear actuator just described, except that the linear shuttle 5030 has been replaced by a rotary cog 6000 rotatably mounted in stator 6050 and the remaining mechanism has been modified accordingly, as described below.
  • An anticlockwise drive pawl 6001 with teeth capable of meshing with those of cog 6000 is mounted on leaf spring 6005, which is pre-tensioned by connecting wire 6014 and anticlockwise SMA drive wire 6008, is held just completely clear of cog 6000 when SMA wire 6008 is unheated/deactivated.
  • a clockwise drive pawl 6003 is mounted on leaf spring 6007 and held just clear of cog 6000 by tension in connecting wire 6015 and clockwise SMA drive wire 6009, when 6009 is un activated.
  • connecting wires and SMA wires are mechanically linked by slidably mounted crimp blocks 6012 and 6013 which transmit tension freely between the wires and are merely guided by slots fixed to the base 6050.
  • Both drive pawl leaf springs are firmly rooted at their base ends 6016, 6017 to the actuator base/stator 6050.
  • the connector wire and connector block arrangement shown is optional and is here in this embodiment to keep the SMA wires moving substantially in a straight line during a step cycle, via guide holes in stator 6050 (not visible in figure 54) so that active cooling techniques may be applied over the length of each SMA wire to speed up the step cycle. Otherwise the SMA drive wires may be connected directly to the drive pawls.
  • 6009 can be made by e.g. flexible flying leads or via the pawls and leaf-springs to which they are mechanically and optionally electrically connected (and thus most conveniently connected to the stator 6050 as a common ground connection).
  • connecting wire 6014 in a direction so as to first engage its teeth with those of the cog 6000 and then as it progresses towards full mesh it pushes the cog teeth it contacts in an anticlockwise direction around the cog shaft, rotating the cog by greater than half a tooth width.
  • each SMA drive wire 6008, 6009 may be mechanically connected directly to each of the two drive pawls in place of the connecting wires 6014, 6015, and the connecting wires and guide holes dispensed with.
  • a wire mount 71 is mechanically coupled to one end of a pre stressed tension spring 73 via a first pin 72 that is securely coupled to mount 71.
  • the spring 73 is stretched so that its other end may be coupled to a second pin 74 which rests in slots 78 in the mount 71 , the pin being held in those slots by the pre stressed tension Fm in the spring 73.
  • a wire terminal 75 with crimp-end 76 is mechanically attached to pin 74.
  • the SMA-wire 77 of the actuator is crimped within the crimp-end 76 of the terminal 75. It can be seen that while the tension in wire 77 is smaller than Fm then pin 74 will not move away from mount 71 , so the effect is that SMA-wire 77 is for all intents and purposes rigidly attached to mount 71 , specifically in the direction of tension along the wire. When the tension in wire 77 exceeds Fm then spring 73 will stretch beyond its pre-stressed length allowing pin 74 and the attached terminal 75 and thus SMA-wire 77 end to move away from mount 71 , the spring-rate of spring 73 determining the distance moved for such forces greater than Fm.
  • the wire-overload protection assembly is made up of a number of parts. For large wires this is practical. However, for smaller wires in particular, it is possible to combine all of these functions into one component, as shown in figure 18.
  • the terminal 85 is extended away from its crimp-section 86, with the SMA-wire 88 attached as described in the previous embodiment.
  • the extended section of 85 is bent to form a serpentine tension spring 82, loops of which are shown.
  • An extended loop nearest to the crimp-end allows for extension of the spring portion of 85 in the direction of the wire.
  • the end of terminal 85 farthest from the crimp-end 86 is the attachment point for the mounting 81.
  • Mounting 81 in this schematic embodiment has been modified to provide an end-stop for the spring portion of terminal 85 which holds the spring in tension against its installed pre stressed force - i.e.
  • the spring portion as shown is already stretched from its natural length with a pre-stress force Fm as before, and is held in tension against this force by two different sections of the rigid mount 81.
  • Pin portion 82 of mount 81 holds the distal end of the spring portion of terminal 85, and another portion of mount 81 is inserted within the extended loop in line with the line of the SMA-wire, to hold that end in place against the spring tension.
  • the entire pre-stressed- spring overload protection device can easily, simply and cheaply be fabricated from the same piece of material (e.g. phosphor bronze or stainless steel) used to crimp the wire end, and this single component can thus provide electrical connectivity, rigid mechanical anchorage for the wire, as well as stress-overload protection.
  • the embodiment shown in figure 19 is a variation of the embodiment of figure 18, optimised for insertion directly into a printed circuit board (PCB).
  • a single piece of flat metal in the preferred embodiment a phosphor bronze or stainless steel, although other suitable metals can also be used
  • a serpentine tension spring some loops of which are designated 93.
  • the tension spring section is stretched into some restraining mounts (to pre-stress the spring) and held in place by the pins 91 , 92.
  • the SMA-wire 97 is crimped into the crimp-end 96 and excess tension in the wire (i.e tension above the pre-stress put into the tension spring), then causes the spring to stretch further thus providing overload protection for the SMA-wire.
  • Figure 20 shows the one-piece terminal and protection spring of figure 19 inserted into a PCB, with pin 91 inserted under tension into a tight-fitting hole, and preferably soldered to a PCB track (not shown) to provide additional mechanical and excellent electrical connection.
  • Pin 92 is inserted into a slot 500, one end of which provides an end-stop for the pre-stress tension in the spring while the rest of the slot allows clearance for the spring to stretch further in overload situations.
  • the slot 500 should be long enough to provide complete clearance for the pin 92 under the maximum overload anticipated.
  • figure 21 shows detail of the location of the hole 501 for pin 91 in the PCB and a clearer view of the slot 500, giving clear space for the pin 92 to move freely under overload conditions, constrained only by the force of the spring.
  • the SMA-wire overload protection invention as applied to a bowstring actuator is shown in figure 22.
  • an SMA-wire 600 crimped at both outer ends to mechanical and electrical connections engages with a load-attach-pin 60 at or near the wire’s centre.
  • the load attach pin 60 is mechanically connected to the push-rod 61 of the actuator (the moving part, to which the external load is coupled) via a connecting member 64 and pin 68 which in turn engage with a spring mechanism 63 whose other end is mechanically connected to the push-rod 61.
  • the spring mechanism 63 is pre-stressed with a force Fm to hold pin 68 firmly in the push-rod, until such time as the tension of the wire is great enough to pull the load attach pin 60 with a force greater than Fm (an overload situation).
  • Fm is set at a value guaranteed to keep the SMA-wire at a tension level smaller than its safe maximum working tension at all actuation positions of the wire.
  • the connecting member 64, pin 68, spring mechanism 63 and load-attach-pin 60 are all made from the same contiguous piece of material (preferably metal or polymer) for simplicity, low cost and ease of assembly.
  • FIG 23 An actuator using a double bowstring SMA-wire is shown in figure 23, with both SMA wires protected from overload by pre-stressed spring terminations as described above.
  • FIG 24 An alternative embodiment of actuator using a double bowstring SMA-wire is shown in figure 24, this embodiment using a common overload spring.
  • a fast cycle-time dual SMA actuator is shown in figure 25.
  • the SMA actuator wire 257 pulls load 25150 in opposition to SMA wire 25107.
  • Both SMA wires 257 and 25107 have one of their ends mechanically attached to base 1 via pre-stressed springs 2523 and 25123 respectively, whose pre-stress forces F2 and F1
  • wire 25107 is heated very rapidly (for very high speed actuation), wire 25107 becomes rapidly converted to austenite, gets stiff and short, and pulls load 25150 towards the spring 25123, and in so doing pulls the load-end of wire 257 (cool, martensite, and less stiff) with it. If at any time during this transition, the tension in the wires exceeds a certain threshold force F1 , then spring 25123 with pre-stress force F1 will start to expand, allowing the end of wire 25107 to move away from its end stop, relieving excess tension in the wire. The load reaches its destination position and if external load forces are in spec ( ⁇ F1) then spring 25123 will again hold crimp end 25106 against its backstop.
  • Wire 257 is then very rapidly heated (again as described above), even if wire 25107 is still hot / mainly or wholly austenite and stiff and short. Wire 257 pulls with a force Fw >F1 and in fact sufficiently hard to move the load 25150 (and if necessary pull the SMA-wire-end of spring 25123 with it) until the load reaches it’s final position. If at any time during this transition, the tension in the wires exceeds a certain threshold force F2, then spring 2523 with prestress force F2 will start to expand (in which case spring 25123 will already be expanded as it’s pre stress force F1 ⁇ F2), allowing the end of wire 257 to move away from its endstop, again relieving excess tension in the wire.
  • Fw force
  • spring 2523 with prestress force F2 will start to expand (in which case spring 25123 will already be expanded as it’s pre stress force F1 ⁇ F2), allowing the end of wire 257 to move away from its endstop, again relieving excess tension in the wire.
  • the springs 2523 & 25123 will contract and once again hold the SMA wire crimps against the end stops, ready for another bi directional cycle.
  • the cycle-cycle time of this actuator is determined by the sum of the heating times of both wires plus the cooling time of the slowest to cool wire (usually the second-to-be-heated wire).
  • the pull-one-way then pull- back-the-other-way cycle-time itself can be much shorter and is equal to just the sum of the heating times of both wires.
  • the cycle-cycle time in free air may be as long as 100ms or more; however, the cycle-time itself can be as short as 1 ms-5ms.
  • FIG. 26 shows a double bowstring SMA-wire actuator.
  • SMA wire 267 is the first wire of a first bowstring actuator, with its ends crimped at 2620, 2621 into mechanical and electrical terminals with pre-stressed overload protection spring 263.
  • SMA-wire 26151 is the second, opposed, bowstring actuator and similarly overload protected with its own separate protection spring.
  • FIG 27 shows a double bowstring SMA-wire actuator.
  • SMA-wire 277 is a first SMA wire of a first bowstring actuator, with its ends crimped at 2720, 2721 into mechanical and electrical terminals with shared pre-stressed overload protection spring 273a.
  • the second SMA-wire 27151 of a second, opposed, similarly overload protected bowstring actuator with a protection spring 273b is also shown.
  • the external load (not shown) is connected to the junction of springs 273a, 273b.
  • 'pawl' is used in this specification, this should be taken to mean a mechanical component that moveably engages with a set of teeth on another component that may lock or at least resist relative movement in at least one direction.
  • This definition should be taken to include pawls with single or multiple hook means including teeth, that can lock or partially resist motion in one or both directions, and which may be additionally slidably mounted or free-floating relative to a stator.
  • 'ratchet tooth' is used in this specification, this should be taken to mean a gear tooth having one side radial and the other inclined so that a pawl will catch firmly on the former and slide over the latter.
  • This definition should be taken to also include ratchet-teeth on a straight rack of teeth (instead of teeth around a gear) where 'radial' then can be taken to mean 'normal to the line of teeth', and 'inclined' can be taken to mean an angle of less than 90deg to the line of teeth.
  • 'Ratchet- teeth should also be taken to mean asymmetrical mechanical teeth such that when engaged they grip in one direction more strongly (the grip- direction) and slip in the other direction more easily (the slip-direction).
  • the embodiments of the invention as described above help to overcome the long term positional stability issues of SMA linear actuators, including the position sensitivity to mechanical load, as well as providing a precise, stepped linear motion.
  • a true zero- power fixed-position capability is also provided so that power is consumed only when the actuator is changing its position.
  • These embodiments also provide an actuator where the power consumption is not related to the total actuator stroke, and which for most applications will require significantly lower power than standard SMA-wire linear actuators with similar performance.
  • the wire being the effective output port of the actuator, made of material with linear coefficient of thermal expansion a P
  • the length of the push-rod between the connection of the push-rod to the SMA-wire, and the actuation point (i.e. the load to be moved) is D;
  • the wire being the effective output port of the actuator, made of material with linear coefficient of thermal expansion a P ;
  • the push-rod is oriented more or less orthogonal to the line through the crimp- ends of the SMA-wire;
  • the wire when held taut by orthogonal thrust from the push-rod, the wire forms a V-shape (hence the name“Bow-string”), with the push-rod connection to it at the point of the V, and the wire-ends at the two tips of the V.
  • the point of the V is either on the same side ( Case - 1) of the line through the wire-ends as the load-end of the push-rod, or the opposite side (Case- 2).
  • a technique called plated-through-hole (PTH) is used to interconnect any set of contiguous layers (i.e. not necessarily from the top copper layer all the way through to the bottom copper layer).
  • the term 'via generally refers to such a PTH that goes all the way through from top to bottom, providing direct electrical connectivity. For DC and low frequencies this works in the same manner as a wire.
  • the spacing between vias is «wavelength, then the "wall of vias" acts like a contiguous metal sheet" completely screening one side of the wall from the other at such high frequencies (in a similar manner to how a wire mesh acts like a continuous conductive surface on some antennas).
  • the present invention can be used to overcome issues of miniature-camera zoom- function actuation.
  • An alternative arrangement can use one of the SMA rotary stepper actuators described herein, to turn a lead-screw to which the optical element(s) of the miniature camera are attached by a nut which moves axially along the lead screw when the screw rotates.
  • one of the bidirectional forms of the SMA stepper actuators described herein may be used as the mover of optical element(s).
  • a possibly less convenient option is to use a uni-directional linear stepper-actuator with a“fly-back” mechanism (generally a return spring and a lock-pawl release actuator, which when activated causes the linear stepper to return quickly under spring return-force, to its nominal; zero position) as are also described herein.
  • this differential motion of the 2 or more lenses may be achieved by coupling the two or more optical elements via a mechanical
  • linkage/mechanism that compels each of the elements to move relatively as desired when any one of them is caused to move by an outside influence
  • an SMA stepper actuator as described above.
  • a suitable SMA stepper actuator for zoom implementation on a miniature camera is potentially very small and lightweight, it may in fact be advantageous to dispense with one or more such mechanical linkages between optical elements, and drive each element (or group of elements) independently each via their own connected SMA stepper actuator. This has the advantage of adding a degree of freedom of placement of the two (or more) separate stepper actuators, and elimination for any mechanical coupling between the optical elements themselves.
  • a miniature camera comprises at least one optical element capable of movement substantially along the optical axis of the camera and mechanically directly connected to the moving shuttle or output node of an SMA linear stepper actuator as described in any of the embodiments herein, wherein the body of said actuator is fixed relative to the body of the camera, the direction of motion of the shuttle of the actuator is substantially aligned with the optical axis of the camera, such that actuation of the actuator causes the at least one optical element to move along the optical axis of the camera.
  • the at least one optical element is indirectly connected to the moving shuttle of the SMA linear stepper actuator via a linkage mechanism, and the orientation of the movement axis of the actuator shuttle need not be aligned with the camera optical axis, the linkage being such that movement of the actuator shuttle along the actuator movement axis causes via the linkage, movement of the at least one optical element along the camera axis.
  • a miniature camera comprises at least two optical elements or groups of elements capable of movement substantially along the optical axis of the camera, each element or group thereof mechanically directly connected to the moving shuttle or output node of a different independently controlled SMA linear stepper actuator as described in any of the embodiments described herein (i.e. one actuator per element or group thereof), wherein the body of said actuators are fixed relative to the body of the camera, the directions of motions of the shuttles of the actuators are substantially aligned with the optical axis of the camera, such that independent actuations of the actuators causes the optical element or groups thereof connected to each actuator to move independently of each other along the optical axis of the camera.
  • any one or more of the SMA linear stepper actuators in any of the three previously described aspects of the miniature camera optics inventions is replaced by an SMA rotary stepper actuator connected to a leadscrew either directly or via a gearing or belt so as to rotate the leadscrew when the stepper actuator rotates, and where the leadscrew is fitted with a nut that moves axially along the leadscrew when the leadscrew rotates, and wherein the at least one optical element or group thereof is connected directly or via a linkage to the nut, instead of (as previously) to the linear stepper actuator shuttle.
  • Standard prior-art SMA linear-actuators capable of precision positioning to multiple different positions (as opposed to on-off actuators with essentially just two fixed positions) essentially rely on a continuously powered length of SMA material (most conveniently in the form of a Nitinol wire or tape or strip).
  • stepper-actuators described and shown in this specification were initially designed for use with Phase or Frequency Tuneable RF Devices, and are particularly suited for this purpose.
  • rotary electric motors may be used but these motors are costly, bulky and require a significant amount of electronic control, and frequently also require a position sensor with related electronics to provide an accurate indication of the position of the moving component.
  • Rotary electric motors also require some form of rotary-to-linear motion converter as well as a gearbox to produce the required component motions at the right speed, all of which add to the cost, size, weight and unreliability of the solution.
  • brushed electric motors are inherently unreliable and produce conductive particulate pollutants, whereas brushless motors are significantly more expensive and require more elaborate electronic control. Where a given tuneable filter has multiple tuning elements (often five or many more are required for high-performance) the cost of separately driving each of these elements is often prohibitive.
  • SMA actuators for these functions are an SMA wire actuator where the contraction of a long thin wire of SMA material is used to provide a pulling force upon heating of the wire above its Austenite start temperature.
  • SMA wire actuators we refer hereafter to such actuators very broadly as SMA wire actuators.
  • SMA material in an actuator in forms other than wires, e.g. strips, sheets or even rods and bars.
  • SMA wire For convenience of description we include all such SMA actuator forms in the term“SMA wire” hereafter.
  • conventional tuning screws are replaced by moveable and/or deformable elements actuated by SMA wires.
  • capacitive and inductive tuning elements are used, and we tune not only the resonators to shift centre- frequencies, but also tune input-output (I/O) couplings, inter-cavity couplings, as well as the phase angle of predominantly phase-shifting elements.
  • one small SMA actuator (each with one or more wires, and where there is only one SMA wire in an actuator it is to be understood that some sort of mechanical spring force is used to achieve a return stroke, as is well known in the art of SMA actuators) to control each tuneable element separately, we avoid complicated and unreliable mechanical mechanisms, gears and levers otherwise needed to keep multiple tuning elements in synchronisation (in sync). Instead the synchronisation is done entirely in electronics and/or software for maximum flexibility and minimum complexity.
  • SMA actuators assist with resolving these issues.
  • These SMA actuators have: zero-power position hold; required total SMA wire-length is independent of actuator stroke; near-ideal short- and long-term positional stability, unaffected by material ageing and fatigue; very high positional precision; simple electronic control with no need for precision ADC and DAC components.
  • Algorithms and/or look-up-tables (LUTs) in a controller determine how each tuneable element and its associated actuator needs to be moved or deformed to achieve the desired filter performance and then further algorithms are used to separately control all of the actuators in parallel to provide optimum performance. By having the same controller monitor the temperature inside the tuneable cavities and modulate the actuator control algorithms accordingly, the control system is also able to
  • tuneable filter Within the tuneable filter are one or more components or elements whose properties may be changed by moving or deforming them, or both. These are generically designated as tuneable elements hereafter.
  • a tuneable element may be a component specifically introduced solely to tune another electromagnetic component (such as a resonator, or a coupling device or a tapping point), or may be one of these electromagnetic components themselves in the case that the electromagnetic properties of that component may be changed by an external effect (e.g. mechanical force, which might be used to move or deform the electromagnetic component).
  • the SMA actuators themselves can be small and can be very low-cost, may require no lubricants, are highly reliable, are frequently silent and generate no significant magnetic fields.
  • Such an SMA actuator may be mounted outside an RF cavity and control its respective tuneable element via a mechanical connection to the tuneable element inside the cavity; alternatively the tuneable element itself may be extended to protrude through the cavity to the outside and become an integral part of the external actuator.
  • the SMA actuators may advantageously be positioned right inside the RF cavities or waveguides if suitable precautions are taken, and the SMA actuator can then be designed to be mechanically integral with the tuneable element to be controlled.
  • the total volume of an SMA wire actuator made from even a 20mm length of 25im wire is less than 1/100th of a cubic millimetre, i.e.
  • Such an actuator can pull a ⁇ 10gm to15gm load a distance or stroke of 0.75mm or more, which stroke can be greatly increased by use of suitable mechanical leverage techniques such as for example those described for the actuators above, which in some forms may reduce the force by the same ratio.
  • suitable mechanical leverage techniques such as for example those described for the actuators above, which in some forms may reduce the force by the same ratio.
  • Such tiny, relatively high-force, actuators positioned within the RF cavities can be highly beneficial in terms of reducing overall filter size, reducing the RF leakage otherwise encouraged by moving mechanical devices penetrating the walls of the RF cavities, reducing the amount of structure necessary to support and house the actuators (i.e.
  • this structure By suitably shaping this structure to produce capacitive and inductive sections an integral RF choke can be created that will completely eliminate such RF leakage.
  • the resonators and couplings are mechanically fixed shaped components with galvanic contacts implemented for electrically connecting the tuning pins, and generally only the positions or rather the lengths of the tuning elements, if anything, changes.
  • the provision of small internal (to the cavities) SMA actuators or actuator wires allows the resonator and tuning element components themselves to be mechanically deformed by the contraction and expansion of SMA wires when suitably arranged and attached.
  • a resonator e.g.
  • an RF filter has one or a plurality of stages, and the filter is either: i) tuneable between upper and lower frequency limits and is a low-pass, band-pass, band-stop or high-pass configuration, or ii) produces a tuneable phase shift, or iii) both of these.
  • the RF filter adjacent stages are electromagnetically coupled.
  • the filter is either constructed of two or more spaced preferably parallel conductive ground planes (though non-parallel ground planes can also be used) with solid conductive joining walls connecting between the conductive planes and/or with conductive vias positioned between the conductive planes, and has inside and between the ground planes one or a plurality of separate cavities separated by either solid conductive partitions or by walls formed by a plurality of conductive vias positioned between the conductive planes or by both, and in each of those cavities is zero, one or a plurality of resonators.
  • the resonators may be either conductive or dielectric or some combination of these.
  • Each of any conductive resonators in a cavity may be either connected to ground at one end only or connected to ground at each end or connected to ground in the middle or connected to ground at one or more half wavelength intervals or not be connected to ground at all resulting in a floating conductive resonator.
  • One or more of the cavities has each either one or more mechanically moveable or deformable resonators, or one or more deformable or movably mounted tuning elements penetrating into or wholly contained within the cavity such that the deformation or movement of the tuning element changes the electromagnetic characteristics of the cavity.
  • the moveable or deformable resonators are caused to move or deform each by an associated SMA-wire actuator.
  • the tuning element or elements are caused to deform or move each by an associated SMA-wire actuator.
  • the spacing between the vias is chosen to produce the required degree of coupling including zero coupling between any cavities separated by the vias or between any cavities and the outside of the filter delineated by the vias.
  • Each of the conductive vias between the ground planes may be either connected to a ground plane at each end or connected to one ground plane at one end only resulting in a blind via with one end left open-circuit or be connected to no ground plane at either end resulting in a buried floating via (with both ends left open-circuit).
  • a tuneable cavity either contains one or more tuneable resonators thereby giving that cavity a degree of tuneable frequency selectivity, or instead, a tuneable cavity contains no resonator in which case it can have very high Q and be very frequency selective.
  • a tuneable cavity may advantageously be used as a tuneable phase-shifter by incorporating one or more tuneable reflector elements instead, which may be tuned by movement or deformation thereof.
  • each stage is implemented by one or more tuneable cavities there is generally one primary path through the filter stages in a certain sequence from the input port to the output port, although in more complex filters there may also be secondary signal paths as well.
  • Stages or cavities which are sequential along that primary signal path are referred to here as path-adjacent stages or path-adjacent cavities, to distinguish them from merely physically-adjacent (here called adjacent) stages or cavities.
  • Path-adjacent cavities are coupled to each other by couplings where the strength of each coupling can be between zero (no coupling) and one (fully coupled).
  • the coupling is formed by one or more appropriate sized apertures cutting through that conductive partition and the coupling response is related to the cavity separation distance and size and shape of the coupling aperture(s).
  • the coupling is formed by strategically locating gaps and the sizes of gaps between these vias and the number, position and dimension of the vias around the gaps define the amount of coupling between adjacent cavities.
  • the coupling is formed by providing additional non-grounded conductive tracks printed on an insulating layer formed on the inside of one or both of the ground planes or cavity walls sandwiching the cavities to be coupled, and the conductive tracks protrude into both of the adjacent cavities without electrically connection to anything else.
  • the coupling is formed by non-grounded cross-coupling wires protruding into both of the adjacent cavities without electrically connection to anything else. Both of these couplings are capacitive in nature. If instead the tracks or wires are grounded at both ends then such a coupling becomes inductive instead coupling may also be achieved by some combination of these coupling techniques.
  • the resonators are made of conductive material or are made of low-loss dielectric material or are made of non-conductive material coated or plated with conductive material or are made of some combination of these.
  • the dielectric resonators are preferably made of high permittivity low loss RF ceramic.
  • One or more of the resonators are in the form of strips or T-shaped strips or rings or spirals or crosses or other shapes that resonate at the required frequency.
  • the cross-section of the resonator is such that it is easy to bend or flex elastically in at least one dimension, e.g. a thin strip of metal or metallised plastic or laminate.
  • a resonator has a geometry with several eigenmodes (e.g.
  • X- shaped or star-shaped then concurrent modes in the resonator may be suppressed by shorting to ground the corresponding ends or points of the branches of the resonator structure.
  • a more compact assembly can be achieved with a dual-mode resonator or a triple-mode resonator with a minimum of two or three mutually orthogonal branches with a single common point.
  • Such an orthogonal three branch resonator necessarily has a 3D configuration and in this case at least one of the three branches may protrude through one of the ground planes if their spacing is too close to fully contain the 3D resonator.
  • multi-mode waveguide cavities can also be employed where orthogonality of modes is enforced by the boundary conditions on the walls and the degree of symmetry in the cavity.
  • External signal connections are provided in the form of input and output tapping points to the first (input) and the last (output) cavity; where there is only one cavity, then it becomes both the input (first) and the output (last) cavity, i.e. the first is the same as the last.
  • the tapping point is preferably adjacent to that resonator; where there is no resonator in the cavity being tapped (e.g. if this is a phase- shifter cavity) then the tapping point is into the cavity itself, e.g. a waveguide port.
  • a tuneable filter has an input port, an input tapping point, one or more cavities at least one of which is tuneable, and where more than one cavity, then one or more couplings, zero or more resonators, an output tapping point, and an output port, which may be the same port as the input port.
  • At least one electromagnetic element (input tap, cavity, resonator, coupling, or output tap) of the tuneable filter is tuneable, either by physically changing its shape (by deformation), or by moving it relative to the filter body i.e. the ground planes, or by the provision of an adjacent changeable tuning element.
  • a tuning element operates to tune its associated electromagnetic element by moving relative to it, and it may do this either by whole-body movement of the tuning element or by deformation of the tuning element such that the portion of the tuning element close to the
  • electromagnetic element moves relative to it or relative to a ground plane, or to both.
  • an electromagnetic element or tuning element operates to tune by virtue of deformation
  • that element may advantageously be contained wholly within the cavity that it tunes, thus avoiding the need to provide for moving structures to penetrate the cavity walls.
  • tuning element operates to tune by virtue of movement relative to an electromagnetic element (input tap, cavity, resonator, coupling, or output tap) of the tuneable filter, then that tuning element is movably mounted and either penetrates into the cavity being tuned or is wholly contained within that cavity.
  • electromagnetic element input tap, cavity, resonator, coupling, or output tap
  • the tuning effect comes about because the movement changes the capacitive loading or inductive loading or both of the associated electromagnetic element.
  • a thin glass wafer is a suitable dielectric material in a suitable form for this function.
  • glass wafer thicknesses are limited to about 300um or greater because of manufacturing and handling issues.
  • An alternative and much superior effect can be obtained by making from aluminium, either the conductive part of the element to be tuned (or at least the portion of it adjacent to the tuning element) or instead, the tuning element itself, and growing a thin smooth crystalline layer of corundum (crystalline AI203) on the aluminium surface between the tuning element and element to be tuned.
  • Such layers may have useful thickness in the range 1 to 30um (thicker layers are possible but become increasingly difficult to maintain the quality of the dielectric), have typical dielectric breakdown voltage of >16KV/mm, high dielectric constant of ⁇ 9.8 (@1 MHz), and very low RF loss with dissipation factor as low as 0.0002. If the aluminium surface to be oxidised is first polished then the resulting corundum coating grown upon it also has an external surface of more or less the same surface finish (i.e. almost polished) which allows intimate and low friction contact between it and the adjacent element.
  • an electromagnetic element when self-tuned by deforming it the effectiveness of such tuning may be enhanced by the suitable insertion of a dielectric element, such as a glass wafer or corundum coating on one of the adjacent surfaces, between the moving part of the deformed element and an adjacent ground plane.
  • a dielectric element such as a glass wafer or corundum coating on one of the adjacent surfaces
  • any, some, or all of the electromagnetic elements of the filter may be provided with such a deforming or movably mounted tuning element, or alternatively may themselves be constructed so as to be easily deformable or moveable and be tuned by virtue of such
  • Each tuning element may have the shape of a flat strip, or a rod, or a bar, or a tube, or more generally a long prismatic section with flat or curved or corrugated surfaces, but preferably a shape such as a thin flat strip is used to reduce the mass and volume of the tuning element, making it both easier to move with a small SMA wire actuator, and easier to fit inside a compact filter structure with multiple tuning elements.
  • the tuning elements are made of conductive material or are made of low-loss dielectric material or are made of non-conductive material coated or plated with conductive material or are made of some combination of these.
  • Dielectric tuning elements are preferably made of high permittivity low loss RF ceramic or alternatively are made from a glass wafer.
  • a tuning element is preferably aligned in the same direction of greatest extension as the resonator it is tuning so that the gap between the tuning element and the resonator is also aligned with the resonator.
  • the associated tuning element would preferably be in the form of a thin strip having a width similar to the width of the resonator, be positioned close to and parallel to the wide face of the resonator, and have its long axis aligned parallel to the long axis of the resonator, so that progressive movement of the tuning element in this axial direction would cause progressively increasing or decreasing overlap of the resonator by the tuning element and thus increasing or decreasing capacitance. This affords a large range of tuneability with nearly linear tuning characteristics.
  • a resonator may have a longitudinal slot or slots in it into which a tuning element may fit without touching the resonator, to increase the variability of capacitance between the tuning pin and resonator.
  • a resonator may have a longitudinal slot or slots in it into which a tuning element may fit without touching the resonator, to increase the variability of self-inductance per unit of length of the resonator.
  • Each tuning element may either be entirely contained within the RF cavity, or alternatively may extend through an aperture in the cavity wall and even further to the outside region beyond.
  • RF choke an additional auxiliary fixed low-pass filter with a stop-band covering at least the entire operating bandwidth over the full tuning range of the main tuneable filter.
  • the one or more tuneable elements of the tuneable filter of the present invention are caused to move or deform (shape change) by one or more actuators (defined below), with one or more of the tuneable elements sharing an actuator, so that the number of actuators can vary from one, where all of the tuneable elements are moved by the same actuator, up to the number N of tuneable elements where each tuneable element is driven independently of all of the others by its own actuator.
  • actuators defined below
  • the number of actuators can vary from one, where all of the tuneable elements are moved by the same actuator, up to the number N of tuneable elements where each tuneable element is driven independently of all of the others by its own actuator.
  • there is a separate actuator provided to independently control each tuneable element, so that there are N Actuators.
  • An actuator is herein defined to be an SMA actuator, with the SMA material in the form of a thin wire, strip, or sheet.
  • the most preferable forms of SMA actuator are: i) any of the forms of SMA-Stepper-actuator described above; and ii) an SMA-wire actuator where the length of one or more sections of SMA wire are caused controllably to change by controllably changing the SMA wire temperature(s).
  • the temperature of an SMA wire may advantageously be changed by controlling the magnitude of electric current passing through the SMA wire. This electric current in turn is preferably under the control of a programmable device such as a
  • the length-changing SMA elements e.g. wire or wires, strips or sheets, or the body and output element of a SMA- stepper-actuator
  • the length-changing SMA elements are then mechanically connected either directly or indirectly between the filter body and the moveable or deformable tuneable elements of the tuneable filter, which causes the tuneable elements to move relative to the filter body or to change their shape (deform).
  • the length-changing SMA element(s) may instead be mechanically connected between two (or more) separate points on the deformable tuneable element itself, which causes the tuneable element to change its shape (i.e. deform).
  • the mechanical linkage of a tuneable element to its respective actuator may be direct and immediate, in which case there is no independent mechanical coupling component between the tuneable element and the actuator.
  • part of the tuneable element itself may be used as part of the actuator structure and there then will be no discernibly separate actuator and tuneable element, but instead a single component with moveable or deformable parts capable of changing the electromagnetic environment within a cavity or between cavities. So the tuneable element may optionally and preferably be integral with the actuator structure.
  • Each actuator connected to one or more of its respective tuneable elements may be positioned outside of the RF cavity or cavities of its tuneable element(s), or may instead be positioned within the walls of the RF cavity or cavities, or instead be placed partially or wholly within the RF cavity or cavities.
  • any tuneable element is made of a dielectric material and its associated actuator is not wholly separated from the inside of a respective cavity or cavities by the solid conductive wall of the cavity(s) it may be RF electrically isolated by the positioning suitably close to the tuneable element of one or more conductive vias connecting between the conductive walls of the cavity(s).
  • straddling the tuning element with conductive vias spaced closer than a half wavelength of the highest operational frequency of the filter in this way will eliminate RF leakage via the dielectric element.
  • any tuneable element is made of a conductive material and protrudes through a cavity wall then to prevent TEM mode propagation along the tuning element of RF energy from within the cavity to the outside of the cavity and towards its associated actuator
  • two or more buried vias are located adjacent to and along the longitudinal line of the tuning element and separated by the appropriate interval which is approximately a half-wavelength but corrected for the reactance introduced by the adjacent vias. This is sufficient for the propagation at this wavelength to be blocked by capacitively loading the leaking TEM mode, and will completely stop the leakage.
  • the synchronisation of the movements of all of the tuneable elements is electrically controlled by the synchronisation of the appropriate control signals to the plurality of actuators, for example by means of a pre-computed look-up table kept in the memory of the controller or by a real-time algorithm generating the actual required positions of all tuneable elements to achieve the required state of the filter.
  • each tuning element is associated with at least one SMA wire, and is mechanically connected directly or indirectly to that wire such that changes in length of the SMA wire caused by heating and cooling of the SMA wire cause changes in position or shape of the tuning element.
  • each SMA wire may be enclosed within a dedicated void in one of the one or more supports to ensure free movement of the SMA wire relative to the support.
  • Each tuning element is then positioned slidably in a channel through the support to ensure free movement of the tuning element while maintaining a precise gap between and accurate distance from the tuning element to the corresponding resonator, coupling or tapping point for all positions of the tuning element controlled by the actuator.
  • Each such actuator may be fully integrated into the filter, for example by being buried inside the support.
  • a resonator is preferably mechanically fixed relative to the ground planes and is not moveable.
  • a resonator may be movably mounted within a cavity and caused to so move by mechanical connection to an actuator in which case the resonator becomes itself a tuneable element.
  • a resonator may be constructed so as to be easily mechanically deformable and is caused to so deform by mechanical connection to an actuator which then applies stress to the resonator in which case the resonator becomes itself a tuneable element.
  • Viable deformable resonator forms include thin strips, flat-section spirals, flat-section helices, bellows and other shapes which have at least one direction of easy (low force) deformation.
  • any ground plane may contain one or more resonators tuned by one or more tuning elements actuated by actuators, and such cross-couplings themselves may also preferably be tuned by one or more tuning elements each actuated (to move or deform) by an actuator.
  • a filter so constructed within three or more ground planes is called a 3-D folded filter.
  • a folded filter where there is only one cross-coupling (i.e. through a ground plane) then the filter topology is no different to non-folded filters, and topologies are limited to Chebyshev filters (defined by a diagonal coupling matrix).
  • a 3D folded filter with more than one cross-coupling i.e. through a ground plane
  • topologies make the manufacture of these structures more compatible with 3D printing and with 2.5D processes such as PCB and microstrip technology and wafer level integration potentially allowing fully printed designs for dramatic cost saving.
  • Such topologies may also be manufactured by CNC machining in solid metal when high power handling and low PIM requirements dictate.
  • Using multiple stacked ground planes and multiply folded filters with several levels of cross-coupling may advantageously be used to modify the overall volume of a filter with given performance characteristic, and because of the greater flexibility in defining the elements of the coupling matrix can better optimise performance parameters such as group delay equalization.
  • the at least one SMA wires that change the position of that tuning element may be attached directly to it.
  • the at least one SMA wires that change the position of that tuning element may be attached to it via an electrically insulating structure, e.g. plastic or ceramic, to electrically isolate the SMA wire heating current from the tuning element.
  • the section of a tuning element outside a cavity may be RF isolated from the RF energy within the cavity by: an intrinsic RF choke formed along the length of the tuning element wherein the longitudinal extent of the element provides a series inductance and the proximity of the tail to adjacent ground planes provides a parallel capacitance; and/or an at least 2-section RF choke, similarly formed as in a) by shaping the profile of the tuning element in the tail region so that it comprises successive wider and narrower sections electrically in series along the length of the element, the wider sections being predominantly capacitive and low impedance, the narrower sections being predominantly inductive and high
  • the SMA wire or wires provided to cause motion of the tuning element may be attached to the low-impedance capacitive sections of the so-shaped tail so as to maximally isolate them from any RF energy transmitted from within the cavity; such series
  • inductive/capacitive/inductive/capacitive series sections effectively form a multi section RF choke or low pass filter.
  • the conductive ground planes are preferably parallel.
  • An actuator of the tuneable filter may advantageously be positioned partly or wholly within the cavity containing the tuneable element that the Actuator serves to move or deform.
  • the actuator is at least partly inside the RF cavity it is necessary to minimise the RF field coupling to the conductive SMA material (wires , strips or sheets) of the actuator.
  • the conductive SMA material wires , strips or sheets
  • one or more of the following approaches may be taken: for a straight-wire strip or sheet SMA actuator where the SMA material is very thin, e.g.
  • the SMA material may be located entirely on or within the electric wall of the cavity (or simply parallel to the electric wall for mode TE10), or alternatively, the line or plane of the SMA material should be positioned orthogonal to and symmetrical to the magnetic walls of the cavity; where the SMA material or the SMA material and its conductive electrical connections (e.g.
  • wires to an external SMA-actuator controller deviate from a straight line within the cavity then they should be constrained to lie in a plane and that plane positioned orthogonal to and symmetrical to the magnetic walls of the cavity; further isolation of the SMA material and connecting wires thereto from the RF field may be achieved by sandwiching the planar arrangement of SMA material and connecting wires between two thin low RF-loss glass wafers held parallel to the electric field of the cavity, which effectively“suck-in” the surrounding RF field greatly reducing its amplitude in the vicinity of the actuator structure.
  • These glass wafers may be arranged not to touch the static or moving parts of the actuator, but also may advantageously be used as support elements for the actuator structure and even as the primary mechanical static portions of the actuator; the SMA element(s) of the actuator may also be electrically screened from the RF fields by partially or wholly surrounding them with conductive surfaces preferably metal or metallised plastic.
  • a tuneable filter that is to act as a phase-shifter has a nominally constant amplitude and linear phase response across its passband, and when tuned it is predominantly the magnitude of phase-shift at each frequency within the passband that changes, not the centre frequency or edges of the passband.
  • Such a tuneable phase-shifter filter consists of one cavity or a plurality of coupled cavities each containing one or more movable elements.
  • a tuneable phase-shifter filter in its simplest form consists of a cavity in the form of a section of waveguide with conductive walls, open at one end and preferably partly or fully closed at the other, the open end serving as both the input-port and the output port, i.e. the I/O port.
  • the tuning element Within the cavity a moveable or deformable element, the tuning element, is constrained to at least in part move along the waveguide in a direction towards and away from the I/O port, with the movement or deformation caused by an actuator, situated within the cavity or external to it, as described above for general tuneable filters of the present invention.
  • the tuning element itself forms an electromagnetic discontinuity in the waveguide which thus reflects some of the RF energy back to the I/O port.
  • the tuning element reflects all of the incident RF energy and at least a portion of it may preferably take the form of a plane conductive sheet or plate or conductive plated surface of a plane insulator almost filling the cross-section of the waveguide but preferably without touching it, and preferably without making electrical contact with the electrically conductive waveguide walls, movably supported so as to allow it to travel along the direction of the waveguide towards and away from the I/O port.
  • the tuning element may consist of a shaped resonator with a broad resonance across the passband of the phase shifter, made out of metal or a printed conductive pattern on a dielectric substrate.
  • RF energy propagates down the waveguide (e.g. in TE10 eigenmode) from the input port, is reflected back from the moveable element, and then exits the waveguide at the output port, the phase of the output wave relative to the input wave being directly proportional to twice the length of waveguide extending from the I/O port to the current position of the moveable tuning element. Because of the reflective nature of this tunable phase- shifter configuration it has the advantageous property that the amount of phase difference dphi produced by moving the moveable element a distance x is:
  • the extra factor of 2 achieved by the reflection (rather than pass-through) of the wave thus requires only half of the movement of the moveable element otherwise needed for the same amount of phase shift change, and this can simplify and/or lower the cost of the actuator provided to move it.
  • the RF field behind the moveable tuning element i.e. on the opposite side of it to the I/O port
  • the actuator may be sited within the thickness of or outside of the cavity wall opposite the I/O port (or indeed outside any of the adjacent side walls) when again the low RF field within this portion of the cavity minimises RF leakage issues around any moving parts passing through the cavity walls, which can be reduced further by the introduction of in-line RF chokes again as described above.
  • the phase-shifter as described above advantageously can be modified to reduce the required movement of the moveable element to achieve a given phase shift, by partially filling the cavity with dielectric. For example by placing glass wafers or other high dielectric constant material on the inside walls of the cavity it is possible reduce the effective wavelength of propagation within the cavity, whereupon a given change in phase shift is produced with a reduced movement of the moveable tuning element.
  • the tunable phase shifter filter comprises not one but two co-moving tuning elements separated by a distance m along the waveguide, where m is approximately half a wavelength of propagation in the cavity at the mid range frequency of the phase shifter; the optimal separation m differs from an exact half wavelength due to the reactive conductance of the tuning elements, as well as the other structures within the cavity, primarily the actuator or actuator coupling mechanics that link an external actuator to the moveable member.
  • the beneficial effect of the second tuning element is an increase in bandwidth of the tuneable phase-shifter and an increase in reflectivity achieved and a reduction of RF losses.
  • the two tuning elements may be mechanically joined by a stiff strut attached between them, which is preferably made of low loss dielectric, e.g.
  • the actuator used to move the moveable elements is sited inside the cavity in the gap between them, and as described above the conducting SMA material of and to the actuator are held in the electric wall in the cavity to minimise coupling to the RF field.
  • the two tuning elements may be identical or be made to differ so that they introduce reactances of different sign, thus providing the possibility to control the dispersion of the phase shift, or otherwise the linearity of the introduced time delay over frequency within the passband, or alternatively, achieving more compact design with reduced distance between the tuning elements.
  • tuning elements may advantageously be mounted sandwiched between glass wafers with elements etched on both faces of the copper-plated glass wafer providing stable and well defined electrical distance between them and at the same time achieving economical design.
  • the tuning elements in each and all of the above aspects of the tuneable phase shifter can take the form of conductive rectangles, conductive squares, conductive rings or conductive crosses, each of which has its own advantages and
  • Narrow band phase shifters may employ resonant elements while more wideband devices will benefit from using non- resonant elements providing only capacitive or only inductive response.
  • a further aspect of the invention is a tuneable phase-shifter constructed as a waveguide cavity as described in all variants of two tuning element phase-shifter above with the difference that now both ends of the waveguide are open (i.e. there is now no closed end).
  • one end of the waveguide cavity acts as the input- port and the other end acts as the output port.
  • the reflections back to the input-port of the two tuning elements are now arranged to cancel each other at the input-port to minimize the in-band return loss.
  • the degree of coupling between the tuning elements will define the width of the passband, and consequently the amount of phase-shift in-band. Moving them simultaneously along the waveguide will not be useful in this configuration. Instead an actuator is used to controllably change the distance between them which controllably changes their coupling, and each moveable element will be independently tuned by an actuator (one per moveable element) to keep the elements tuned to the same central frequency. Thus this configuration will require at least three actuators.
  • the two tuning elements are optimally separated by a distance m along the waveguide, where m is approximately one quarter of a wavelength of propagation in the cavity at the mid-range frequency of the phase shifter; the optimal separation m differs from an exact quarter wavelength due to the reactive
  • a phase shifter can be formed by two orthogonal transmission lines (Line V and Line H) supporting waves of orthogonal polarisations propagating in a direction P.
  • the two lines may each for example be formed by pairs of spaced parallel conductors.
  • a sliding plate placed orthogonal to the direction of propagation P and within the space between the four conductors forming the transmission lines contains a resonating structure formed by a metal structure layout on the plate surface resonating at the frequency of operation, to facilitate the reflection of an incoming wave.
  • These metal structures are designed to resonate at the operating frequency; for example - conductive strips forming dipoles may be used, one dipole in each of the two orthogonal directions.
  • the plate thus contains two types of structures - each designed to interact with the wave of corresponding polarization. This configuration of phase shifter provides dual polarized operation with identical phase shift introduced for Vertical and Horizontal polarizations supported by Lines V and H respectively.
  • a phase shifter for independent control of the two orthogonal polarizations is formed by two orthogonal transmission lines (Line V and Line H) supporting waves of orthogonal polarisations propagating in a direction P.
  • Two plates orthogonal to each other and lying parallel to the direction of propagation P are placed between the two transmission lines.
  • One plate is orthogonal to the walls of line V and the other orthogonal to line H.
  • a resonating structure designed to interact with one of the waves of each polarization is placed on each plate, one for each polarisation.
  • One structure on one plate interacts with the wave supported by Line V, and the other structure on the other plate interacts with the wave supported by Line H.
  • Each plate has independent freedom of movement in the direction of propagation P, and can be moved independently of the other with the help of dedicated slot in one plate that allows the other plate to move within it (in the slot) without mechanical interaction.
  • a slot can also be placed in both pates to achieve the same end.
  • Each plate is attached to a separate actuator capable of moving the plate far enough to achieve the desired range of phase-shift of the waves.
  • a tuneable RF filter comprises one or more resonant or reflective elements positioned in a waveguide with conductive walls and the one or more resonant or reflective elements are caused to move axially along the waveguide each by an actuator.
  • the waveguide conductive walls are formed from alternate metal and dielectric layers with adjacent metal layers joined together by rectangular arrays of conductive vias through the dielectric layers the rectangular arrays forming the walls of the waveguide whose axis is orthogonal to the metal and dielectric layers, and the waveguide cavity is formed by the removal of the dielectric and metal layers within and between the waveguide walls.
  • the waveguide conductive walls are constructed of conductive metal or conductively coated insulating material such as polymer, by, for example, metallising the polymer.
  • the one or more resonant or reflective elements are constructed so as to reflect as perfectly as practically possible all of the RF energy incident at one end of the waveguide back to that same end of the waveguide with a phase directly proportional to the axial position of the moveable elements along the waveguide thus providing a single-port reflective tuneable phase-shifting filter.
  • the length of the waveguide is at least half the wavelength within the waveguide of the waves of interest so that the reflected wave may be delayed by any phase angle between 0 and 360deg, allowing, for example, the construction of a phased-array antenna with an array of such phase-shifters.
  • the length of the waveguide is a multiple (greater than 0.5, and quite possibly >5 or >10 or even more)) of the wavelength within the waveguide of the waves of interest, so that the reflected wave may be delayed by a time anywhere between 0 and the time taken to traverse the waveguide in both directions, which may advantageously be many cycle- times of the wave, allowing, for example the construction of a true-time-delay-array antenna, with greater bandwidth than an otherwise similar phased-array antenna.
  • two resonant or reflective elements are constructed so as to reflect as little as practically possible of the RF energy incident at one end of the waveguide back to that same end of the waveguide such that nearly all of the RF energy emerges from the other end of the waveguide with a phase directly proportional to the axial positions of the moveable elements along the waveguide and wherein a second actuator is used to control the axial separation of the two resonant or reflective elements to optimise the input return loss with operating frequency thus providing a dual-port tuneable phase-shifting filter.
  • two separate sets of one or more resonant elements are positioned in the waveguide, each set independently of the other moveable axially along the waveguide by independently controllable actuators, and each set of resonant elements is responsive to only one of two different polarisations of waves incident on one end of the waveguide, for plane polarisation waves the different polarisations being orthogonal to each other, and for circular polarisation the different polarisations being of opposite sign.
  • a phase or frequency tuneable device (hereinafter Device A) comprises an RF cavity exploiting the thermo-mechanical properties of SMA material in the shape of wires or ribbons or sheets so arranged to form an actuator applied in such a way as to achieve controllable deformation or controllable movement of the walls of the RF cavity, or controllable movement or controllable deformation of additional electromagnetic structures in the vicinity of or inside the RF cavity, so as to affect the electric and/or magnetic components of one or several of the eigenmodes of electromagnetic field supported by the RF cavity.
  • an RF tuneable filter device (hereinafter Device B) comprises two or more phase or frequency tuneable devices A as just described wherein these two or more devices A are each electromagnetically coupled to at least one other of the plurality of such devices.
  • an RF tuneable filter device B as just described has at least one of the electromagnetic couplings between devices A in the form of an iris penetrating the solid walls or ground planes separating the phase or frequency tuneable devices or by an iris formed by a gap in a wall of conductive vias separating those devices.
  • an RF tuneable filter device B has at least one of the electromagnetic couplings between devices A formed by the provision of additional non- grounded conductive tracks formed (e.g. printed) on an insulating layer itself formed on the inside or outside of one or both of the ground planes sandwiching the cavities to be coupled, and wherein the conductive tracks protrude into both of the adjacent cavities of the devices A either without electrical connection to anything else or with both ends grounded.
  • an RF tuneable filter device B has at least one of the electromagnetic couplings between devices A formed by non-grounded cross coupling wires protruding into both of the cavities of the adjacent devices A through an iris either without electrical connection to anything else or with both ends grounded.
  • an RF tuneable filter device B of any of the variants described above has at least one of the electromagnetic couplings between RF cavities of the devices A tuneable by a tuning device comprising SMA material in the shape of wires or ribbons or sheets applied in such a way as to achieve controllable deformation or controllable movement of a conductive or dielectric tuning element in the vicinity of the electromagnetic coupling.
  • an RF tuneable filter device as in any of device A or device B variants described above comprises one or a plurality of stages, the filter either being of the low-pass, band-pass, band-stop, high-pass or phase-shifting configuration and further comprising two or more spaced conductive ground planes with joining walls connecting between the conductive planes and/or conductive vias positioned between the conductive ground planes, having inside between the ground planes one or a plurality of separate RF cavities separated by solid conductive partitions and/or by a plurality of conductive vias positioned between the conductive planes and in each of those cavities is zero, one or a plurality of resonators or electromagnetic reflectors, and where there is a plurality of cavities each cavity is electromagnetically coupled to at least one other cavity by an iris penetrating the solid walls or ground planes or by an iris formed by a gap in a wall of conductive vias between ground planes, and wherein one or more of the RF cavities has each one or more
  • a convenient and effective way to minimise RF/SMA interaction, when the SMA element is in the form of thin wires, is to firstly, use insulated SMA wire, and secondly to use the insulated SMA wire in the form of tightly twisted-pairs as are familiar to those practised in the electronics signal processing art as an effective way to cancel interactions between fields and wires.
  • a twisted-pair SMA insulated-wire element will contract upon heating and allow expansion upon cooling much as a single SMA wire will, but will provide approximately twice the pulling force, with little if any increase in cooling time constant.
  • the heating current to such an SMA element may be provided entirely from one end - where an SMA element has one fixed and one moving end (very common) then at the fixed end current may be supplied up one strand and down the other, and all that is necessary at the moving end is to connect the two strands to each other, and to nothing else. This eliminates the otherwise sometime difficult problem of creating a reliable current return from a moving component.
  • any actuator used near or within an RF environment, and especially within any of the tuneable RF devices described herein, is comprised of twisted-pair insulated SMA wire elements, with the length between successive twists at most half a wavelength of the RF energy of concern, and preferably much smaller than half such a wavelength.
  • insulated SMA wire for the SMA elements of any SMA actuators used to tune the RF devices described herein. And to avoid other interactions with RF currents flowing through the conductive structures of the RF devices being tuned, it is preferable in all cases to provide a return path for any SMA element heating current that is separate from the conductors of the RF energy.
  • Figure 35 shows a schematic section of a conventional solid wall cavity, with two opposing sections (the rest is not shown, for clarity) of solid conductive wall 3501 and 3502 parallel to each other containing in between them a resonator 3503 which is galvanically grounded at one end to wall 3502 and unconnected at its other end, which instead has a glass wafer 3504 attached to its surface. Also not shown (again for clarity) are the remaining conductive walls of the cavity that define its shape and volume.
  • a tuning element 3505 of the present invention nominally parallel to wafer 3504 penetrates wall 3501 through an aperture in that wall and is positioned a small precise orthogonal distance from glass wafer 3504, and is slidably mounted such that it can move in and out of the cavity formed between walls 3501 and 3502.
  • actuator 3506 which is shown only schematically, and is mechanically attached to actuator 3506 by link-pin 3507, so that when actuator 3506 moves the tuning element 3505 may be positioned at a range of distances along the end of resonator 3503. This has the effect of modifying the capacitance (primarily) at the end of resonator 3503 which in turn changes its resonant frequency, providing a tuning function.
  • Actuator 3506 is mechanically attached (not shown) to the outside walls of the cavity.
  • the tuning element 3505 is made of conductive material and extends through the cavity wall 3501 to the outside and provides an unwanted potential leakage path for RF energy from inside the cavity.
  • tuning element 3505 in the form of a series of wide (capacitive) and narrow (inductive) sections of the tuning element, formed by cutting notches one of which is shown at 3508 into either side of the element and spaced along the element in the direction along the tuning element. A further pair of notches similar to those visible at 3508 are cut into the portion of tuning element 3505 where it penetrates the cavity wall 3501 and which are thus not visible in this view.
  • the glass wafer 3504 could advantageously be replaced by a corundum coating on either of the two adjacent faces (i.e. resonator or tuning element) to act as a very high quality high dielectric-constant dielectric between them.
  • Figure 36 shows a schematic section of a cavity constructed between two parallel conductive ground planes 35010 and 35011 , only sections of which are shown for clarity) and which are electrically and mechanically connected to each other by a number of conductive vias 3509 most of which are not shown, for clarity.
  • the size and volume of the cavity are defined not only by the ground planes 35010 and 35011 but also by“walls” made up of suitably spaced conductive vias such as 3509 but these additional cavity“walls” are not shown in this figure, for clarity.
  • a resonator 3503 which is galvanically grounded at one end to a pair of vias 3509 and unconnected at its other end, which instead has a glass wafer 3504 attached to its surface.
  • a tuning element 3505 of the present invention nominally parallel to wafer 3504 penetrates into the cavity through an iris formed by an adjacent pair of vias 35096, the positioning and separation of which are chosen to minimise RF energy leakage from the cavity along the direction of the tuning element 3505.
  • the tuning element 3505 is positioned a small precise orthogonal distance from glass wafer 3504, and is slidably mounted such that it can move in and out of the cavity formed between ground planes 35010 and 35011.
  • Actuator 3506 which is shown only schematically, and is mechanically attached to Actuator 3506 by link-pin 3507, so that when Actuator 3506 moves the tuning element 3505 may be positioned at a range of distances along the end of resonator 3503. This has the effect of modifying the capacitance (primarily) at the end of resonator 3503 which in turn changes its resonant frequency, providing a tuning function.
  • Actuator 3506 is mechanically attached (not shown) to the outside of one of the ground planes.
  • the tuning element 3505 is made of conductive material and extends outside the cavity through the iris formed by two of the vias 35096 and could provide an unwanted potential leakage path for RF energy from inside the cavity.
  • Such leakage is prevented in this example by the integral RF choke built into tuning element 3505 as can be seen more clearly in the tuning pin drawing in Figure 35.
  • Such grounded capacitive elements i.e. like 350801
  • Figure 38 shows two coupled resonators 3503 and 35031 grounded at one end by vias 35093 and sandwiched between two parallel ground planes 35010 and 35011 as before in figure 36, except that ground plane 35010 has been removed in figure 38 to reveal the structures between them.
  • the two resonators have glass wafers 3504 and 35041 covering part of one face near the end opposite the grounded end, and the resonators are tuned by moveable grounded tuning elements 3505 and 35051 which are in turn moved by Actuators 3506 and 35061 which are shown only schematically.
  • the two resonators are electromagnetically separated from each other by a set of closely spaced vias 3509 lying between them and connecting at each end to the ground planes 35010 and 35011 , and this line of vias effectively forms one“wall” of each of the two cavities in which sit the resonators 3503 and 35031.
  • the remaining walls of these cavities which are similarly constructed of lines of closely spaced vias are not shown, for clarity.
  • this gap functions as the coupling iris which electromagnetically couples the two resonators 3503 and 35031.
  • notches some of which are indicated at 35081 forming the integral RF chokes in the tuning element 35051 can be clearly seen in this drawing, although only one notch at 3508 is visible in tuning element 3505 because the figure shows the capacitive cover plate 350801 grounded by the vias 35096 which normally covers all such notches in such integral RF chokes and is an integral part of the RF choke structure.
  • Other cover plates like 350801 have been removed in the drawings to more clearly show the structures beneath but it is to be understood that some conductive structure serving the same capacitive function would be expected to be present in all such integral RF chokes.
  • FIG 38 is a further development of the structure shown in figure 37 and is now in this drawing complete enough to form a fully functional tuned filter.
  • the additional elements will now be described.
  • the coupling iris between the two resonators 3503 and 35031 previously (in figure 37) formed between two vias 35091 and 35092 has now become a tuned coupling and is formed between via 35092 and conductive tuning element 35052 which is moved towards and away from via 35092 by actuator 35062 shown schematically only.
  • actuator 35062 shown schematically only.
  • the two resonators 3503 and 35031 may be independently tuned by actuators 3506 and 35061 , the coupling between them may also be independently tuned as well, by Actuator 35062, the action of which is to open and close the gap in the electromagnetic wall between the resonators, as tuning element 35052 moves.
  • An input port to the filter is formed by a stepped cylinder 350111 the function of which is to convert the impedance at the input end 350121 (e.g. typically 50ohm if this was a coaxial connection) to the impedance of the resonator 35031 to which impedance converter 350111 is electrically bonded (e.g. soldered).
  • This subassembly The overall function of this subassembly is to connect with low return loss an input signal into the cavity containing resonator 35031.
  • an output port is provided at the end 350120 of a stepped cylinder impedance converter 350110 electrically connected to resonator 3503 at the other end.
  • the output port 350120 might also be matched to a coaxial connector, e.g. at 50ohm impedance.
  • These two input/output ports are each separately tuned by grounded conductive tuning element 35053 (for the input port at 350121) and grounded conductive tuning element 35054 (for the output port at 350120) and the tuning is accomplished by moving these tuning elements towards and away from their respective stepped cylindrical impedance converters, the movement being produced by actuators 35063 and 35064.
  • These tuning elements 35053 and 35054 operate in magnetic mode rather than electric mode, and are grounded to the inside of the cavity by elements not shown for clarity.
  • Figure 39 illustrates an alternative arrangement of the components of the two- resonator tuneable filter shown in figure 38.
  • one of the resonators, 3503 has been flipped through 180 degrees end to end so that it still lies parallel to the other resonator 35031 but has its grounded end at the opposite side of the ground plane to the other resonator.
  • I/O port 350120 and tuning elements 3505 and 35054 (and associated components) have all moved with it, so that functionally this layout is more or less identical to that in figure 38.
  • this ability to flip resonator cavities gives great flexibility, particularly when building triple (or more) ground plane 3D filters.
  • Figure 40a illustrates a 3D folded tuneable filter with three ground planes 35010, 35011 , 35012, six resonators and with I/O ports at 350121. This is effectively a development of the complete tuneable filter shown in figure 38 and figure 39, now with six resonators (three between ground planes 35010, 35011 and three more between ground planes 35011 , 35012) and additional inter-cavity couplings between each pair of cavities adjacent to each other on opposite sides of the central ground plane 35011.
  • the following parts of Figures 40b - 40e show all this in more detail.
  • top ground plane 35010 has been removed to show the top layer internals, where three resonators 3503, 35031 , 35032 can be seen each situated in their own cavities defined by closely spaced walls of conductive vias connecting between ground planes 35010, 35011 not all of which are shown, for clarity.
  • Each resonator 3503, 35031 , 35032 is tuned respectively by tuning elements 3505, 35051 , 35052 themselves made moveable by actuators 3506, 35061 , 35062.
  • the tuning elements are RF isolated from their Actuators by integral RF chokes implemented as a sequence of wide and narrow sections along the length of the elements and these sections are capacitively coupled to ground by grounding sections not all of which are shown for clarity.
  • An I/O port 350121 can be seen to couple into the cavity containing resonator 3503 and this coupling is magnetically tuned by tuning element 35056 moved by actuator 35066.
  • the coupling between the cavities of resonators 3503, 35031 is tuned by tuning element 35057 moved by actuator 35067 and that between the cavities of resonators 35031 , 35032 by tuning element 35058 moved by actuator 35068.
  • the cavity of resonator 35032 is coupled through an aperture or iris in ground plane 35011 (not visible in this view), to the cavity beneath it between ground planes 35011 , 35012 and this coupling is tuned by tuning element 35059 (only the far end of which is visible in this drawing where it is connected to its associated actuator 35069).
  • FIG. 40c is a close-up view of the through-plane iris 350200 coupling the cavities of resonator 35032 and 35033.
  • Resonator 35032 which lies between planes 35010, 35011 as can be seen in figure 40b has been removed in this drawing to reveal the coupling iris 350200 beneath it, which coupling can now be seen to be tuned by grounded conductive tuning element 35059 (also beneath resonator 35032) moved by actuator 35069.
  • Resonator 35031 which is parallel and adjacent to (removed in the drawing) resonator 35032 is shown in the drawing.
  • the iris-end of tuning element 35059 has a tab or ridge 350280 on it which is narrower than the iris slot 350200 so that when element 35059 partially covers iris 350200 it forms a ridge-loaded waveguide between the cavities on either side of plane 35011 which assists coupling and tuneability.
  • a ridge-loaded waveguide section is therefore formed inside or in the vicinity of the coupling iris 350200 (i.e. a waveguide loaded with a ridge in the middle) and this structure has the lowest cut-off frequency which is strongly dependent on the ridge and the shape of the waveguide, and in particular on the gap between the ridge tip and the opposite wall of the coupling waveguide. Even when the ridge does not fill the entire thickness of the iris 350200 it will strongly affect the coupling value.
  • a possible variant (of the structure shown in figure 40c) has a coupling pin with a thicker tip protruding through the entire thickness of the iris 200.
  • the resonator 35033 in the cavity below plane 35011 is mostly hidden from view by ground plane 35011 although a portion of it closest to iris 350200 is visible through the iris.
  • the capacitive grounding plate 350802 of the tuning element 35052 which is used to tune resonator 35032.
  • tuning element 35058 moved by actuator 35068 which tunes the coupling iris between the cavities of resonators 35031 and 35032 (latter not shown for clarity).
  • FIG 40d is another close up of this through-ground-plane iris 350200 where the centre ground- plane 35011 has now also been removed to reveal the structures beneath.
  • the iris 350200 is shown in outline directly beneath the tip 350259 of iris coupling tuning element 35059. Now also visible is tuning element 35053 (moved by actuator 35063) which in conjunction with dielectric element 35043 tunes resonator 35033, several conductive vias 3509, as well as actuator 35062 which moves tuning element 35052 which tunes resonator 35032.
  • FIG 40e shows a variant on the coupling tuning element of figure 40c, where a true ridged waveguide between the two coupled cavities is formed.
  • Tuning element 35059 now has an extra thickened tab 3502591 which can be seen more clearly in the disassembled tuning element 35059A.
  • Element 35059 moves in the direction shown by the arrow 001 over the surface of ground plane 35011 so that the thickened tab 350259 now fills the full thickness of the iris 350200 in ground plane 35011 so that a true ridged waveguide is formed.
  • a copy of 35059 is shown at 35059A to clearly reveal the shape of the modified tab end 350259, 3502591.
  • the actuators have been sited either outside of the RF cavities or in some cases merged with them, and in general could be any suitable type of actuator, though as aspects of the present invention, as mentioned above, they are any sort of SMA actuator, suitably configured to give enough stroke with adequate load-force capability.
  • a double-bowstring actuator will serve this purpose well as its stroke can be tailored within wide limits even in a compact actuator, as the forces required for tuning these tuned filters are small typically ⁇ 1 gram, and even a 25micron diameter SMA wire can pull nearly 15 gram and so quite high leverage can be applied to increase the stroke above that available directly from the contraction of a straight wire ( typically 3- 4%, but sometimes more, of its length).
  • Figure 41x is a development of the aspect of the invention shown in figure 38 with which figure 41 x should be compared.
  • the standalone actuator 3506 of figure 38 used to tune resonator 3503 has now been replaced with a completely integral actuator built in and around resonator 3503 in figure 41x.
  • SMA wire 350171 is mechanically anchored in an insulating member 350170 positioned on the grounded base end of resonator 3503 and is electrically terminated here to a wire (not shown) connecting it to a controller which supplies heating current to change the length of the SMA wire.
  • the other end of SMA wire 350171 is mechanically attached to grounded tuning element 3505 which is moveably mounted so as to be able to slide over thin dielectric layer 3504 (as before in figure 38) along the direction of the length of the resonator 3503.
  • This end of the SMA wire may also optionally be electrically bonded to grounded tuning element 3505 which then forms a return path without additional wires, for the SMA-wire heating-current.
  • tuning element 3505 When the SMA wire 350171 is heated by the controlled current and subsequently contracts, tuning element 3505 is pulled in the direction towards the resonator’s grounded base and in so doing more overlaps resonator 3503 increasing the capacitance between these elements and thus tuning the resonator. Also attached to tuning element 3505 is one end of a spring, a leaf spring 350172 in this variant, whose other end is attached to the base plate ground plane 35011 via some form of mechanical mounting, shown in figure 41x as pin 350173.
  • the spring force is arranged to oppose the pulling force of SMA wire 350171 such that when the heating current to the SMA wire is reduced, and the SMA wire cools, spring 350172 stretches the SMA wire back to its original (unheated) length, thus performing the return-stroke function of the actuator so formed.
  • An alternative to return spring 350172 is to add a second SMA wire capable of pulling 3505 in the opposite direction to SMA wire 350171.
  • both SMA-wires can have similar lengths and be nearly co-located so taking up very little extra space, but may operate as a push-pull pair of actuator wires as is known in the art.
  • tuning element 3505 is grounded and covered by grounding plate 350801 although it may also be arranged to be grounded by any other suitable means, to either of the adjacent ground planes of the filter (i.e. 35010, 35011).
  • grounding plate 350801 may also be arranged to be grounded by any other suitable means, to either of the adjacent ground planes of the filter (i.e. 35010, 35011).
  • One of the immediate advantages of this implementation of a tuning actuator may be seen to be that it is entirely enclosed within the RF cavity surrounding resonator 3503 and takes up hardly any additional volume, and also requires no RF chokes or other countermeasures to reduce RF energy leakage along mechanical linking structures. It might also be expected to cost less to implement than a separate actuator structure.
  • Figure 41a shows a close-up view of the grounded end of resonator 3503 from figure 41x, and illustrates the location of SMA wire 350171 sited in groove 350175 of the resonator 3503 and mechanically terminated on insulated mount 350170, and shows the electrical termination point 176 of the SMA wire.
  • the moveable tuning element 3505 can be seen at the opposite end of the resonator separated from it by dielectric layer 3504 together the latter’s grounding plate 350801.
  • dielectric layer 3504 together the latter’s grounding plate 350801.
  • Several conductive vias 3509 are also visible but note that the ground planes 35010, 35011 , 35012 are not shown in this drawing.
  • Figure 41b shows a close-up view of the non-grounded end of resonator 3503 from figure 41x now looking from the underside (i.e from the direction of ground plane 35011), and again illustrates the location of SMA wire 350171 passing along a groove in the surface of resonator 3503 and mechanically (and in this case electrically too) terminating in a conductive mounting point 350177 connected to tuning element 3505.
  • the return spring 350172 is clearly visible in this view attached at its free end to tuning element 3505 at point 350178 and at its fixed end to ground plane 35010 (not shown) via post 350173.
  • spring 350172 is significantly extended and SMA-wire 350171 significantly contracted (i.e. the SMA wire is hot) which causes tuning element 5 to significantly overlap resonator 3503 increasing its capacitive coupling to ground.
  • the SMA wire actuator integral with a resonator as illustrated in figures 41x, 41c, and 41b, may of course be used in any place in a tuneable filter of the present invention where a tuneable resonator or other form of tuneable or moveable element is required.
  • a tuneable resonator or other form of tuneable or moveable element is required.
  • One disadvantage of this particular arrangement shown is that a straight- wire actuator configuration is used. While the length of a resonator may be sufficient to house enough length of SMA wire in this way to achieve the required range of tuning (i.e.
  • Figures 42x, 42a, 42b, 42c, 42d and 42e show a tuneable filter where the phase is the primary parameter changed by tuning (a phase-shifter) which is one aspect of the present invention.
  • the top layer of metal 350510 can be seen to have an aperture in it of rectangular shape with rounded corners, exposing a portion of the dielectric 350511.
  • the other layers of metal are of similar shape.
  • the top metal layer 350510 is joined to the middle metal layer 350520 by a rectangular array of closely spaced conductive vias 3509 piercing the dielectric layer 350511 , two such vias being labelled 3509.
  • the diameter and spacing of the vias are chosen appropriately so as to form a waveguide for the RF frequency of interest, as is known in the art.
  • the second metal layer 350520 is similarly joined to the next metal layer 350530 by a further similar rectangular array of closely spaced conductive vias piercing the dielectric layer 350521 thus extending the waveguide so formed.
  • Each layer of dielectric 350511 , 350521 , 350522 has a rectangular slot 350519 cut through it somewhat smaller than the aperture in the metal layers in such a way as to minimize the impact to propagation conditions of the dominant operating mode of the waveguide.
  • a large slot aperture may eventually move the cutoff frequency upwards to the extent it reduces the operating frequency band.
  • the aperture size is chosen to ensure that this does not happen. In practice this is defined by the dielectric parameters of the manifold substrate and those of the structures supporting the resonators, and may require an additional dielectric filler in front of the resonator to keep the cut-off frequency within desired limits. This dielectric filler would then become another dielectric layer atop element 350512 and become part of the moving element of this filter.
  • the T shape of elements shown may advantageously be rotated through 90deg in the plane of its thickness and suitably re-scaled to extend to the limits of the support 350513 so that the stem of the T points along the height of the waveguide rather than its width.
  • the moveable element is caused to move by an actuator 350561 a small portion of which is visible beneath the bottom dielectric layer 350531.
  • the top aperture in metal layer 350510 is a waveguide I/O port and RF energy entering the port travels down the waveguide in both air (in the central cavity 350519) and dielectric (between the cavity walls and the walls of conductive vias 3509 surrounding the cavity), is reflected from the structures of the moving element (further described below) and returns to the I/O port with a phase proportional to the distance of resonator 350512 from the I/O port entry defined by the metal layer 350510.
  • the output phase of the phase-shifter is thus controlled by the position of the moveable element which in turn is controlled by Actuator 350561 , which may in turn be controlled by electronic / digital commands from a controller.
  • Figure 42a is a top view of the phase-shifter of figure 42x which now clearly shows the T shaped resonator 350512 supported by support 350513, and also visible is the small clearance gap between these moveable parts and the surrounding dielectric layers 350511 , 350521 , 350531.
  • the top metal layer 350510 with its round-cornered rectangular waveguide aperture cut through it is also clearly seen, as are the conductive vias 3509 connecting it to the metal layer 350520 below which form the walls of the waveguide.
  • Figure 42b is a cut away view of the phase-shifter where the dielectric layers 350511 , 350521 , 350531 have been removed to reveal the walls of vias 3509 connecting the metal layers 350510, 350520, 350530 forming the waveguide.
  • the resonator 350512 on the moveable element support 350513 is also just visible.
  • Figure 42c shows another cutaway view of the phase-shifter looking upwards from beneath, with all but the top layer of metal and vias removed, as well as the three dielectric layers removed, to reveal the moving element comprised of its support 350513 and resonators, the second of which 350514 can now be seen on the opposite side of 350513 to where resonator 350512 is positioned.
  • This pair of resonators 350512, 350514 are spaced apart in the direction of movement by a fixed distance chosen to maximise the reflection of RF energy back to the I/O port, and this distance is equal to half the wavelength of operation of the phase-shifter corrected for the reactance of the resonators.
  • the actuator 350561 (which is supported by the rear of dielectric layer 350531 not shown) is mechanically coupled to the moving element by a link 350515 made of any suitable non-conductive material.
  • Figure 42d shows a cutaway view of a slightly simplified version of the phase-shifter described above in figures 42x, 42a, 42b, and 42c, constructed by replacing the pair of resonators 350512, 350514 on the moveable element by a single conductive metal reflector or resonator, in which case the spacing support 350513 is no longer required, and the actuator 350561 may then be coupled directly to the first and only reflector 350512.
  • the resonator/reflector is shown as a self- supporting conductive (e.g.
  • T shape but this could be replaced by other shapes with the appropriate resonance and/or reflective properties, e.g. a flat rectangular conductive sheet filling the whole aperture through the dielectric in the waveguide except for a small clearance gap around the edges, or a conductive flat ring.
  • An alternative construction would have the conductive metal resonator/reflector etched or plated onto a thin dielectric backing support material.
  • Figure 42e is a more detailed development of the type of phase-shifter sketched in Figure 42d where we have shown more of the conductive metal layers 350510, 350520, 350530 and via waveguide walls 3509 (with some cut away for clarity).
  • the moveable resonator/reflector 350512 is now directly mechanically connected to the moving member 350568 of a double-bowstring SMA wire actuator comprised of base 350567, SMA wires 350562, 350563 terminated mechanically and electrically to pins 350564 fixed to base 350567 at their ends, and half-looped around pins 350565, 350566 fixed to moving member 350568.
  • the base 350568 is mechanically fixed to the body of the phase-shifter, e.g.
  • phase-shifter in this drawing could have one of the SMA actuator wires on either side of the resonator/reflector 350512 so long as these rules are adhered to. This makes for a more compact assembly.
  • Another variant has the base 350567 of the actuator extending (further left and right in the drawing) into and/or beyond the walls of conductive vias to allow longer SMA actuator wires and thus greater stroke to be achieved. It is only necessary to ensure that the SMA wires do not touch the grounded parts of the metalwork (vias or ground planes).
  • figure 43 shows a different aspect of the present invention in the form of a phase- shifting filter similar in many ways to that of figures 42x - 42e except that the device shown in figure 43 shows a through-waveguide phase- filter and not a reflective filter, where one end of the waveguide formed by the rectangular arrays of conductive vias 3509 is an input port (e.g. the top in figure 43) and the other end (e.g. the bottom in figure 43) is the output port.
  • the layers of dielectric in and around the conductive vias has been removed for clarity, and the metal layers 350510, 350520, 350530, 350540, 350550 too have been cut away to show the internals as have some of the arrays of vias.
  • actuators illustrated here in non-limitative fashion as double bowstring actuators, the top one comprising two SMA wires 350562, 350563 in a bowstring configuration (for example, and not in any limiting way), a moveable element 350569 connected mechanically to a top reflector/resonator element 350512 which it can move axially along the waveguide relative to actuator support structure 350567.
  • a second resonator/reflector element 3505121 is mechanically connected to Actuator support 350567 and this whole assembly of top actuator and both reflector/resonator elements is in turn caused to move axially along the waveguide by a second actuator below it in the figure, fixed to the phase-shifter body structure, for example to one of the dielectric layers of the stack.
  • This second lower actuator again shown for illustration only in this example has a pair of SMA wires 3505621 , 3505631 in a bowstring configuration which move a moveable element 3505681 which
  • the control wires (for heating the SMA wire) of the upper actuator can be either flexible (to allow free movement of this actuator) and constrained to the electric wall and led out of the sides of the waveguide though small apertures in the dielectric and between the walls of vias, or instead maybe led out to the lower actuator with flexible leads (to allow free relative movement) and then carried to the outside alongside the lower actuator’s control wires, again through suitable small apertures in the dielectric walls.
  • the purpose of the first actuator is to maintain the correct spacing between elements 350512, 3505121 for minimum reflection to input port at the operating frequency at any time.
  • the actuators are each sandwiched between a pair of dielectric (e.g. glass) wafers 350569, 350569A for the top actuator, and 3505691 , 3505692 for the bottom actuator, some of which have been cut away in the drawing to show the actuator structure within, and these dielectric wafers effectively“suck in” the RF field near the wires and so minimise its interaction with them.
  • dielectric e.g. glass
  • the two reflector/resonator elements 350512, 3505121 are no longer identical and their shapes and separation are chosen to minimise the reflection of RF energy back to the input port whilst achieving the required phase- shift at the output port at the operating frequency.
  • the upper actuator adjusts the axial separation of the reflector/resonators 350512, 3505121 and the lower actuator moves them both bodily along the waveguide axially.
  • figure 43 shows T-shaped resonator/reflectors, these may equally well be other shapes such as circular or elliptical rings, or cross-shaped elements; in fact any shape with the correct reflective and phase-shifting properties.
  • a further refinement is the provision of additional actuators and tuning elements (which could take the form of moveable capacitive elements, or inductive elements as described elsewhere above) for each of the reflector/resonators 350512, 3505121 to minimise reflections to input port right across the frequency band of interest, each of these being co- moving with their respective resonator/reflector element.
  • the two resonators 350512, 3505121 are each moved along the waveguide independently by separate SMA actuators, the actuators being mounted rigidly to the waveguide structure, thus allowing complete freedom of the absolute and relative positions of the two resonators provided they always remain on the same side of each other.
  • Figure 44 illustrates another aspect of the invention where the tuning elements, previously operable by moving relative to their target tuned element, now instead deform rather than move as a rigid body, the deformation being maximised in the region close to the tuned element.
  • the advantages of deformation instead of movement includes no sliding and so no friction, simplicity, potentially use of shorter SMA wire actuators which result in lower cost and reduced drive power, the elimination of the need for a separate return spring for the actuator (the deformed element itself provides that function), extreme compactness, highest reliability, and the ability to place the entire actuated tuning element right inside the waveguide to eliminate RF leakage to the outside.
  • SMA wire 350178 is mechanically terminated in an insulating mount 350177 and controlled heating current is fed into end 350176 by a control wire (not shown), the return current conveniently run through the grounded end of the wire at 350179. Only a short length of SMA wire 350178 is needed to produce significant bending.
  • the strip 35051 can be very thin, just a few multiples of skin-effect-depth (e.g. ⁇ 1um in copper at 5GHz) at operating frequency being adequate to produce insignificant losses, and the material of strip 35051 can be chosen for its mechanical properties alone (e.g. phosphor bronze, or a polymer) if it is plated or coated with a suitable conductive surface e.g. silver.
  • Figure 45 shows another example of the deformation-tuning technique described above and shown in figure 44.
  • the device shown in figure 45 shows an I/O port tuning element 35053 first seen in figure 38 where it was moved longitudinally towards and away from the I/O port components 350111 , 350121 by an external actuator 35063 and RF isolation was performed by an integral RF choke built into the stem of 35053.
  • the tuneable element 35053 comprises a thin, conductive, elastic flexible strip mechanically mounted and grounded at the end farthest from the I/O port 350111 , 350121 to be tuned, in this case by one or more conductive pillars 350971 , 350972 (which could be vias).
  • An SMA wire 350779 is mechanically and preferably electrically connected to an offset / out-of-plane tab 350578 of element 35053 on one side of 35053.
  • the other end of the SMA wire is mechanically mounted to an insulating mount 350777 attached to ground plane 35011 (not shown) and has an electrical connection point 350776 to which a control wire (not shown) is electrically connected.
  • the controlled heating current is passed through the SMA wire (using in this example the grounded end as return path) the wire heats and contracts controllably causing the thin conductive element 35053 to bend out of its natural plane and because of the offset position of the SMA wire (i.e.
  • element 35053 will twist and so also bend so that its top edge (where the SMA wire attaches) will no longer be parallel to the axis of I/O port components 350111 , 350121 which will have a strong tuning effect as this is a magnetic tuning element. Similar mechanical and conductivity considerations as applied to the bending element and SMA wire in 44 apply here too. The net result of this configuration is a very small low cost controllable tuning element that can fit right inside the waveguide allowing no leakage of RF energy.
  • Figure 46 illustrates another aspect of the present invention and shows a variant of part of the assembly of figure 38.
  • item 35031 is one of the resonators but now instead of being a solid rigid conductor it is instead a thin folded elastic conductive sheet comprising a long face of similar size to the resonator it replaces in figure 38, which has a grounded end (here by two vias 35093) and at that end it has also a folded side panel on which is mounted the I/O port assembly 350111 , 350121 again as before, which is folded around once more to rejoin the via 35093, the rigid U- section so formed designed to keep the location of the I/O port fixed in space.
  • the other end of the long main face has a twice folded over end inside of which can just be seen an insulating mounting point 3501030 which serves as a mechanical anchor for an SMA wire 3501010 which extends back to the base where the SMA wire it is again anchored on another mounting 3501040.
  • Wires carrying controlled heating current for 3501010 are attached to each end of SMA wire 3501010 the one from the ungrounded end of 31 being run down the inside face of 35031 to the grounded base-end where it is effectively Faraday shielded from the RF field on the outside face.
  • 47a illustrates another useful deformable form of tuneable resonator 35031.
  • This is made of thin folded elastic conductive sheet, e.g. thin metal, and consists of two curved surfaces with facing each other connected at the top (non-grounded end) and optionally also at the bottom (grounded end) with a further piece of the continuous thin conductive sheet.
  • An SMA wire runs up the centre of the inside of the structure and its bottom end 3501120 is just visible in its mechanical and electrical insulated mounting 3501140, while its top end (not visible in this drawing) is mechanically and electrically mounted to the centre of the top section of 35031 joining the top ends of the two curved surfaces.
  • the SMA wire When the SMA wire is controllably heated by a current applied to end 3501120 by a control wire (not shown) using return current path to ground via the body of resonator 35031 , the SMA wire within 35031 contracts which causes the flexible long curved walls to curve through a tighter radius and thus for the entire resonator structure envelope to shorten changing its inductance as well as its capacitance to the surrounding grounded components (not shown for clarity).
  • the SMA wire is symmetrically placed between the two curved walls and is effectively in a complete Faraday cage, completely isolated from the RF energy in the cavity as can be seen more clearly in the side view in Figure 47b.
  • the end result is a completely controllably tuneable resonator taking up no additional space (over and above that of a solid metal component), having lower mass, very high Q (e.g. the external portion of 31 could be silver plated to a few skin depths at negligible cost) and no leakage of RF energy to the outside of the cavity, and all at very low cost, and high reliability.
  • Another useful variant of this aspect of the present invention is to instead have the two curved surface curving outwards rather than inwards, when more use can easily be made of their capacitance to nearby ground planes for example.
  • FIG. 50 shows a phased array antenna comprised of a 2D array of phase shifters, which may be any of the types of phase-shifter actuated by an actuator, described herein.
  • An RF feeding system 3501401 irradiates the antenna array (in transmission mode, which will be described from hereon, but the same device also works similarly in receive mode).
  • Each array element is formed by the metal layout configuration that resonates at the frequency of operation to facilitate the strongest possible interaction with the incoming wave.
  • the elements are shown realised as dipoles 3501403 with geometrical dimensions chosen to obtain maximum interaction with the incoming wave.
  • the dipole metal structures may conveniently be laid out on the surface of a dielectric panel supporting the whole structure (not shown in figure 50).
  • Each dipole is connected to an independently variable length transmission line 3501404, designed to channel the energy received by the dipole to the reflector 3501405.
  • the reflected energy then returns to the dipole with a phase determined by the specific length of each transmission line.
  • the dipole than reradiates the energy with phase as determined by the length of its respective transmission line.
  • the length of each transmission line is independently changed by a mechanically connected actuator (not shown in figure 50).
  • the array of phase shifters (for each polarisation independently where dual polarisation structures e.g, as per figure 49, are used), can be individually positioned so as to form a directional beam of radiation of the reflected waves and form an antenna pattern 3501406, for example, as shown in figure 50, for one polarisation only for clarity - the other polarisation may also be formed similarly into a beam which is independently steerable from the first polarisation in the case of dual polarisation phase-shifters.
  • the direction and shape of the antenna pattern is adjustable by suitable positioning of each of the actuators connected to the phase- shifters.
  • the array as described may be improved by layering dielectric and metal layers behind all the other elements including the reflectors, to act as a shield and minimise back radiation, which metal layers may advantageously be interconnected with other structures in the array with vias through the thickness of the plane of the antenna.
  • a further variant of this phased array dispenses with the variable length transmission lines altogether and instead makes the individual dipoles independently moveable orthogonal to the plane of the array, the movement of each being controlled by a dedicated Actuator capable of moving the dipole precisely with 4-bit, or preferably 5- bit or more preferably 6-bit precision.
  • the dielectric panel supporting the whole structure may now be pierced with an array of slots in which the dipoles move and to which the Actuator stators may conveniently be mounted. Again it is advantageous to add a rear dielectric layer and behind that a plane metal layer, to minimise unwanted rear-radiation.
  • a phase or frequency tuneable device comprising an RF cavity exploiting the thermo- mechanical properties of SMA material applied in such a way as to achieve controllable modification of electric and/or magnetic components of one or several of the eigenmodes of electromagnetic field supported by the RF cavity.
  • Close integration of SMA actuation functions with the rest of the electromagnetic structure of the device is described, resulting in the capability of very high performance, low- RF-loss, high reliability, compact and low-cost fully tuneable RF filters and phase shifter.
  • one end of the wire is mechanically connected via a pre-tensioned or pre-stressed spring mechanism, rather than via a rigid connection.
  • a pre-stress force Fs in the spring mechanism, so that the spring mechanism does not change in length in the direction of tension in the SMA-wire while the magnitude of that tension is below the spring mechanism's pre-stress force Fs, thus providing a tight mechanical link to the SMA- wire.
  • the spring mechanism begins to change in length according to its spring rate k.
  • a spring rate k may be chosen such that the maximum tension ever experienced by the SMA-wire under overload conditions is always within the wire’s safe limit. Under these worst-case conditions, the spring mechanism will have extended a distance Xs and will thus exert a total force on the SMA-wire of FS+k.Xs and by design this force is kept lower than the maximum safe force capability of the SMA-wire, Fwmax.
  • One way to implement such a scheme is to use the spring mechanism to hold with a preset force at least one end of the SMA-wire against wire-end-stop means which may for example comprise part of, or be fixed to, the actuator base structure.
  • the wire-end-stop mechanism may be mechanically connected to the load to be moved by the actuator.
  • the spring force directed along the direction of wire tension has a magnitude and sign sufficient to hold the end of the wire against the wire-end-stop means for wire-tensions smaller than Fs.
  • the pre-stressed spring mechanism holds constant mechanical length until the force applied to it exceeds the pre-stress force level Fs. Thus the pre-stressed spring mechanism applies no retarding force to the SMA-wire during a normal (non overload) actuator stroke.
  • an SMA-wire actuator has at least one wire-end mechanically connected to its mounting (load-end or fixed end) via a mechanical pre-stressed spring mechanism with the magnitude of the spring mechanism pre-stress force component in the direction along the line of the wire no greater than the maximum safe working tension of the SMA-wire.
  • the actuators can use a pre-stressed spring-mounted SMA-wire mechanical terminal mechanism that holds the SMA wire-end(s) against a defined end-stop with a force less than or equal to the maximum safe tension force for the wire, such that when the tension in the SMA-wire rises above this pre-stressed spring-force, the spring changes length allowing the SMA wire-end to move away from the end-stop at least to a distance sufficient to allow the load to be prevented moving further by the load-end-stop, and the spring-constant is designed such as to keep the wire tension within safe limits during this change in length even when the SMA-wire is fully actuated in the fully austenite phase.
  • An SMA-wire actuator designed in this manner will have the spring mechanism pre stress force magnitude and spring mechanism spring-constant such as to keep the tension in the SMA-wire at or below the maximum safe working tension of the SMA- wire at all positions of the load between the mechanical load end-stops even when the SMA-wire is fully actuated, for example in the case of NiTi SMA, in the fully austenite phase.
  • the spring mechanism may be either a tension or compression spring mechanism, and may be embodied with coil-springs, leaf-springs, flexures, stretchable or compressible materials (e.g. rubber, polyurethane), or other mechanical spring forms, or even magnetic couplings. It is preferred that the spring mechanism is fabricated out of the same continuous piece of metal (e.g. phosphor-bronze, or stainless steel) that is used for the SMA-wire crimp terminal (where the wire is crimped) and is mounted to the base under pre-stressed tension or compression of a magnitude as described above.
  • metal e.g. phosphor-bronze, or stainless steel
  • An SMA-wire actuator has one or both of the SMA-wire ends crimped into a piece of metal for mechanical and/or electrical connection, and preferably the spring mechanism is fabricated out of the same continuous piece of metal used as the SMA-wire crimp. More preferably, the metal is phosphor bronze or stainless steel.
  • an SMA-wire bowstring-actuator has the actuator load connected to the centre region of the SMA-wire via a mechanical pre-stressed spring mechanism.
  • a load-attach pin mechanically connects with the SMA-wire of the bowstring actuator and is mechanically connected to the actuator load via a mechanical pre-stressed spring mechanism.
  • the spring mechanism pre-stress force Fs is set close to or above the rated actuator output force. Thus when the actuator is operating within its rated limits the pre-stressed spring mechanism does not change length.
  • the spring mechanism When the force exerted on the spring mechanism exceeds the pre-stress force, the spring mechanism changes length according to the value of its spring constant which is designed such that even when the SMA-wire of the actuator is fully actuated, and when the maximum rated overload force is present, the spring mechanism extends sufficiently to maintain the force on the SMA wire at or below its maximum safe operating tension.
  • the load-attach pin is slidably mounted - sliding in the direction of the load force - into the bowstring push- rod, and is held against push-rod-end-stop means on the push-rod by a pre-stressed spring mechanism, which holds the load-attach pin against the push-rod-end-stop means by a spring force of magnitude approximately equal to or greater than the rated output-load-force of the actuator.
  • a pre-stressed spring mechanism which holds the load-attach pin against the push-rod-end-stop means by a spring force of magnitude approximately equal to or greater than the rated output-load-force of the actuator.
  • the actuator configuration should be such that when the load has moved the push-rod to the push-rod’s mechanical limit end-stop, then the force applied to the load-attach pin is no more than the SMA-wire tension is safely able to apply even when in the full austenite (actuated) state.
  • the spring mechanism does not change length during a normal (non- overload) actuator cycle, and the spring mechanism provides no opposing force to the movement of the actuator load until overload-tension is reached.
  • An SMA-wire bowstring-actuator has the output load connected to the centre region of the SMA-wire via mechanical pre-stressed spring mechanism.
  • the pre-stress force magnitude in the direction along the line of the actuator load travel is close to and not much greater than the maximum safe output-force of the actuator, that the load mechanical travel is limited by load-travel mechanical end-stops, and that the spring mechanism pre-stress force magnitude and spring mechanism spring-constant are such as to keep the tension in the SMA-wire at or below the maximum safe working tension of the SMA-wire at all positions of the load between the mechanical load end-stops.
  • the spring mechanism pre-stress force magnitude and spring means spring-constant are such as to keep the tension in the SMA-wire at or below the maximum safe working tension of the SMA-wire whatever the actuation state of the SMA wire, and particularly when the SMA-wire is fully actuated in the fully austenite phase.
  • the spring pre-stress tension is Fp, produced by stretching or compressing the spring by the appropriate amount, and this Fp may be set at or slightly above the rated actuator output load force Fop (a design input specification).
  • Fop a design input specification
  • the spring mechanism has been stretched or compressed by an additional distance x because it is now in series with the load, not the wire as previously, and this additional stretch produces an additional spring force of FL - Fp.
  • the required spring-constant k of spring means is:
  • one or both of the bowstring actuators’ load- attach pins may be pre-stressed spring mounted and optionally slidably mounted on and spring loaded against the push-rod, as described above, thus protecting the whole double bowstring actuator against mechanical overload.
  • a double bowstring actuator may be constructed by combining any one or two of the overload-protected single bowstring actuators described above, and in the case of one of the above with a non-protected single bowstring actuator.
  • the overload protection device of the present invention minimises the total number of components in a mechanism, and in the overload protection device of the present invention this is done most conveniently by making the SMA-wire terminal and crimp out of thin sheet metal such as phosphor-bronze or stainless steel, and also fabricating the overload-protection spring mechanism from the same contiguous piece of metal, and if possible making the external electrical connection terminal also out of this same single piece of metal. This avoids multiple electrical and mechanical joints providing much higher reliability, and makes for a compact, light-weight and low-cost assembly.
  • thin sheet metal such as phosphor-bronze or stainless steel
  • a control system can be provided that is capable of measuring the position of the actuator output by the use of suitable position sensor.
  • the sensor can for example use electrical resistance measurement of one or more of the SMA-wires of the actuator embodiments, and from the measurement(s) of resistance the control system estimates the instantaneous length(s) of the SMA-wire(s), and from these length estimates together with knowledge of the specific actuator mechanical configuration and geometry the controller is capable of estimating the output position of the actuator and thus is able to accurately position the actuator output.
  • Very high speed actuation with SMA-wire is usually possible only in one direction - i.e. the heating phase of the whole cycle - because while it is easy in principle to apply heat arbitrarily quickly (e.g. by applying a large enough voltage Vto the ends of an SMA-wire and relying on the V ⁇ /R internal Joule-heating), it is far more difficult to induce very fast cooling as there is no equivalent internal method of cooling, and all the heat energy must be removed through the surface of the wire, primarily by conduction and convection. However, there are practical limits even to the allowable rate of heating without damaging the SMA-wire of the actuator.
  • This analysis defines the limits and thus describes the optimal heating method for fastest safe operation.
  • the analysis is applicable to any form of SMA-wire actuator, and is intended to apply generally to all such forms of SMA-wire actuator including the simple straight-wire actuator, and the bowstring-actuator, as specific cases.
  • the wire is coupled to a moveable load mass M L (including the mass of any push-rod and other co-moving coupling components).
  • M L including the mass of any push-rod and other co-moving coupling components.
  • a given SMA-wire will have some maximum safe operating load (tension) F wmax , repeated application above which load the wire properties will change, the actuator cease to operate according to specification, and if greatly exceeded, the wire will fail.
  • the intent is to show how to drive the wire’s temperature-time profile so as to move the load as quickly as possible, whilst at all times keeping the tension in the wire below or at the safe value F wmax .
  • F wmax F wmax (T).
  • F wmax F wmax (T)
  • the material of the SMA wire has a specific heat H s (typically H s ⁇ 3200J/kg.K for NiTi SMA), and latent heat of transformation (from martensite to austenite) H L (typically H L -24300 J/kg for NiTi SMA).
  • H s typically H s ⁇ 3200J/kg.K for NiTi SMA
  • H L typically H L -24300 J/kg for NiTi SMA
  • a small temperature change dT (within the range A s to A f ) will convert a fraction dT/T t of the wire into austenite and will produce a shortening of the wire of S w .dT/T t , where S w is the wire-stroke as defined above. This in turn will cause a movement of the actuator load of g s (x).S w .dT/T t .
  • the push-rod (if any) and actuator load necessarily have to slide on some bearing surface (unless the load is hanging freely & vertically in space), and be supported by that surface with a normal force component F n .
  • F n a normal force component
  • F f m-F n.
  • the result of interest is high-speed actuation, and therefore it can be assumed that the heat lost from the wire to ambient (at temperature T am ) during the actuation period is negligible, but this turns out not to be true, especially if the wire is pre heated to temperature - A f prior to the high-speed stroke because this is often enough to allow convection to come into play, so we will account for that here as well.
  • the SMA-wire has a heat transfer coefficient h (e.g. measured in [W/K]) which is a function of wire length, diameter and orientation.
  • h is itself a function of temperature T, h (T), because for very small DT temperature rises above ambient , the dominant heat loss is conduction not convection and h is small, whereas for larger DT convection dominates and h is larger, while for very large DT radiation may dominate.
  • T temperature
  • h a constant simplifies things and gives good accuracy, but the variation of h may be included in the analysis that follows if higher accuracy is needed.
  • the wire mass M w can be incorporated as an addition 6M L to the moving load mass M L where 6M L ⁇ V 4 M w / g s (x) 2 (because the average velocity of the wire is ⁇ 1 ⁇ 2 g s (x) times smaller than that of the load).
  • dT/dt (dE/dt - h.(T T amb ))/(H ws + HwJTt + (G f (x).F wmax - F f ).g s (x). S w /T)
  • R(T, ⁇ ) R M .(1-Q(t)) + R A .Q(t)
  • 6R M /5T and 6R A /6T are just the temperature coefficients of resistance b M and b A in the martensite and austenite states respectively, with approximate values:
  • 6R M /5 ⁇ and 6R A /6 ⁇ are the stress coefficients of resistance with experimental values:
  • 6R M /5 ⁇ 1.616 x10 4
  • 6R A /6 ⁇ 8.091 x10 5 .
  • P(T) POM ⁇ 1 + (T-TOM) M ⁇ 1-Q(t) ⁇ + POA ⁇ 1 + (T-T 0A ) A ⁇ Q(t)
  • the wire resistivity at time t is p(t) « p 0M ⁇ 1 + (T-T 0M ) b M ⁇ 1-0( ⁇ ) ⁇ + P OA ⁇ 1 + (T-T 0A ) b
  • V h (t) V ⁇ P(t).R(t) ⁇ . equnG5
  • a generic SMA-wire actuator with parameters as defined above is controllably heated at a rate T(t) as defined by equation G1 ( equnGI above).
  • power P(t) is controllably delivered to the wire of a generic SMA-wire actuator at a rate defined by equnG2.
  • the resistance of the wire R(t) of a generic SMA-wire actuator is controlled to change at a rate defined by equnG3.
  • the wire of an SMA-wire actuator is heated electrically by an electrical heating current l h (t) at a controlled rate defined by equnG4, or alternatively by a drive voltage at a controlled rate V h (t) defined by equnG5.
  • an electrical heating current l h (t) at a controlled rate defined by equnG4, or alternatively by a drive voltage at a controlled rate V h (t) defined by equnG5.
  • E h (t) H ws . T t F
  • _ t 2 /(M L . Ac. L tot ) [J] the energy required to transform the austenite fraction is E t (t) H WL F L t 2 /(M L .Ac. L tot ) the energy required to accelerate the load mass to velocity v(t) is
  • the wire resistivity at time t is p(t) « F L t 2 /(M L ./i.L tot ).p A + ⁇ 1-F L t 2 /(M L ./i.L tot ) ⁇ .p M
  • a simple straight-wire SMA-wire actuator with parameters as defined above is heated at a rate T(t) as defined by equation S1 ( equnSI above).
  • power P(t) is delivered to the wire of a simple straight-wire SMA-wire actuator at a rate defined by equnS2.
  • the resistance of the wire R(t) of a simple straight-wire SMA-wire actuator is controlled to change at a rate defined by equnS3.
  • the wire of a simple straight-wire SMA-wire actuator is heated electrically by an electrical heating current l h (t) at a rate defined by equnS4, or alternatively by a drive voltage at a rate V h (t) defined by equnS5.
  • an electrical heating current l h (t) at a rate defined by equnS4, or alternatively by a drive voltage at a rate V h (t) defined by equnS5.
  • a bowstring SMA-wire actuator with parameters as defined above is heated at a rate T(t) as defined by equnBI described above.
  • power P(t) is delivered to the wire of a bowstring SMA-wire actuator at a rate defined by equnB2.
  • the resistance of the wire R(t) of a bowstring SMA-wire actuator is controlled to change at a rate defined by equnB3.
  • the wire of a bowstring SMA-wire actuator is heated electrically by an electrical heating current l h (t) at a rate defined by equnB4 , or alternatively by a drive voltage at a rate V h (t) defined by equnB5.
  • an electrical heating current l h (t) at a rate defined by equnB4
  • a drive voltage at a rate V h (t) defined by equnB5.
  • a pair of opposed in-line simple straight-wire SMA actuators each with one end fixed to a base and each with the other end attached to an output-member via a pre-stressed spring device as described above for overload protection.
  • the output-member may be a discrete component, or may be the actuator output-load itself.
  • one of the wires WireP can pull the load in the positive x-direction
  • the other wire WireN can pull the load in the negative x-direction. It is desired to apply an accelerating force £F P
  • the pre-stress on the overload protection spring of WireP has magnitude at least F P
  • the load is positioned at nominal zero displacement position, which is the static position to which WireN when fully actuated would pull the load in the absence of dynamic forces or any force from WireP.
  • Both wires are originally at ambient temperature, or alternatively one or both of them may be pre-heated to temperature less than or not much more than A s - this latter has two useful effects but uses more power: firstly, there is smaller or no preheat delay required to get the wire or wires to temperature A s at which temperature the strokes begin; secondly, temperature A s may be high enough above ambient to start a significant convection flow around the heated wire(s) which will decrease the wire cooling time after the heating phase ends, and thus allow a faster cycle repetition rate.
  • the positive acceleration stroke is induced by heating WireP above temperature A s at a rate no faster than described above for safe-wire operation, and possibly all the way to temperature A f , while WireN is kept below or not much higher than A s .
  • Neither spring means will extend during this positive stroke if the forces produced by WireP remain below the prestress levels.
  • WireN must be capable of safely producing at least this much pulling force, and WireN' s overload protection spring must be pre-stressed to at least F 1 max .
  • WireP meanwhile must also be able to pull with at least this same force to maintain its fully austenite-phase position as the return stroke may have completed before WireP' s temperature has fallen below temperature M s . So the specification for the two actuator wires is stroke 3 S, and output force in the fully actuated state 3F 1 max .
  • wire-protection springs for that of WireP, prestress ⁇ 3 F P
  • the spring means prestress values are only approximate because if e.g. for WireP, prestress is slightly less than F P
  • WireN's protection spring will not stretch at all, so it is not strictly necessary - only the spring means on WireP is necessarily required for the mechanism to work as described.
  • the nature of this actuator arrangement is to drive the wires close to their safe limits, the extra protection provided by an overload protection string on WireN is well worth including since it guarantees the safe operation of both wires even in overload conditions.
  • an actuator is comprised of two SMA-wire actuators each
  • the mechanical connection to the load of at least one of them is via pre-stressed spring means.
  • the magnitude of the prestress force F PP of the at least one pre-stressed spring means is substantially equal to the maximum designed accelerating force to be applied to the load, or approximately F P
  • the spring constant KI of the at least one pre-stressed spring means is as defined by equnPI using F PP for the value of F wmax , so
  • Ki G s (S). F PP /S . equnHI
  • the mechanical connection to the load of both of SMA-wire actuators is via pre stressed spring means.
  • the magnitude of the prestress force F pm of the second pre-stressed spring means is given by

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Abstract

L'invention concerne un actionneur en alliage à mémoire de forme comprenant un corps de stator ; une navette, le corps de stator étant conçu pour recevoir la navette, la navette étant conçue pour se déplacer par rapport au corps de stator ; un mécanisme de déplacement et de verrouillage reliant le corps de stator et la navette conçu pour venir en prise avec la navette pour déplacer la navette par rapport au corps de stator ; le mécanisme de déplacement et de verrouillage comprenant des première et seconde parties de déplacement conçues pour venir en prise avec la navette et se dégager de cette dernière, la première partie de déplacement étant sollicitée hors de prise avec la navette, la seconde partie de déplacement étant sollicitée en prise avec la navette, et un actionneur d'élément en SMA conçu de sorte que l'actionnement amène la première partie de déplacement à venir en prise avec la navette pour déplacer la navette sur une première partie dans une première direction, la navette et la seconde partie de déplacement étant conçues de sorte que la libération de l'actionneur d'élément en SMA amène la navette à terminer le déplacement.
PCT/IB2019/060339 2018-11-30 2019-11-29 Actionneur en alliage à mémoire de forme WO2020110091A2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB2107163.4A GB2593618A (en) 2018-11-30 2019-11-29 A shape-memory alloy actuator

Applications Claiming Priority (12)

Application Number Priority Date Filing Date Title
GB1819638.6 2018-11-30
GBGB1819576.8A GB201819576D0 (en) 2018-11-30 2018-11-30 Improvements to SMA actuators #13
GB1819576.8 2018-11-30
GBGB1819638.6A GB201819638D0 (en) 2018-11-30 2018-11-30 Phase or frequency tuneable RF device exploiting properties of SMA #03
GBGB1903321.6A GB201903321D0 (en) 2018-11-30 2019-03-11 Phase or frequency tuneable rf device exploting properties of sma #03_2add
GB1903321.6 2019-03-11
GB1907426.9 2019-05-24
GBGB1907426.9A GB201907426D0 (en) 2019-05-24 2019-05-24 Improvements to actuators #15
GB1907437.6 2019-05-25
GBGB1907437.6A GB201907437D0 (en) 2019-05-25 2019-05-25 Improvements to actuators #16
GB1907823.7A GB2579425A (en) 2018-11-30 2019-06-03 Phase or frequency tuneable RF device exploiting properties of sma #03_3
GB1907823.7 2019-06-03

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WO2022263856A1 (fr) * 2021-06-17 2022-12-22 Cambridge Mechatronics Limited Ensemble actionneur en alliage à mémoire de forme (amf)

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