GB2590475A

GB2590475A - An Expandable transducer

Info

Publication number: GB2590475A
Application number: GB1918858.0A
Authority: GB
Inventors: Bond Andrew; Mathieson Andrew
Original assignee: Thales Holdings UK PLC
Current assignee: Thales Holdings UK PLC
Priority date: 2019-12-19
Filing date: 2019-12-19
Publication date: 2021-06-30
Anticipated expiration: 2039-12-19
Also published as: GB2590475B; GB201918858D0

Abstract

An expandable transducer 100 comprising a scaffold of shape memory material which can transition from a first configuration to a second configuration, one or more transducers (222 figure 2) attached to the scaffold to be moved between a stowed configuration (figure 1a) and a deployed configuration (figure 1d) with the scaffold. The scaffold may comprise a network of interconnected members (218a-d figure 2) which may form tessellating polygons (figure 4). The shape memory material may provide a hinged connection 14 between at least two of these members. One or more interconnected member may comprise a heating element which, when electric current is supplied to, causes the scaffold to transition between the first and second configuration. The transducer may be a sub-aquatic piezoelectric transducer transmitting and/or receiving between 1-50 kHz.

Description

An Expandable Transducer

Field of invention

The invention relates to a transducer which is expandable from a stowed state to a deployed operative state. The transducer may, in some examples, use a shape memory material to induce the movement from a stowed state to a deployed state, or vice-versa. The expandable transducer may be particularly suited to communications and/or monitoring purposes. The expandable transduced may be particularly suited to low frequency subsea communications and/or monitoring.

Background

The use of underwater communication and monitoring systems is well known. These communication and monitoring systems (referred to collectively as communications below) can be used in military and commercial environments and provide communication links between any two transceivers or monitoring of communication or other signals. Such transceivers may be carried by unmanned vehicles, vessels, scuba divers, communication buoys, and countermeasures (in military applications). Deploying underwater communication systems at depth and in a rapid manner is often a requirement.

One limitation of present underwater communication systems relates to the required size of the transducers which may be prohibitive for smaller carriers such as a diver or a communication buoy. Larger transducers are generally required to transmit at lower acoustic frequencies or high power to obtain a required transmission range.

The present invention seeks to provide a transducer which is more readily deployable. The transducer may be used for communications (and monitoring), or may be more generally applicable.

Summary

The present invention provides an expandable transducer according to the appended claims. The expandable transducer may be a communications transducer.

The present disclosure provides an expandable transducer comprising: a scaffold of shape memory material which is transifionable (i.e. expandable or collapsible) from a first configuration to a second configuration, and one or more transducers attached to the scaffold so as to be moved between a stowed configuration and an in-service deployed configuration with the transition of the scaffold from the first configuration to the second configuration.

Providing a scaffold of shape memory material which is transitionable between first and second configurations (which may correspond to a stowed configuration and a deployed configuration) allows the transducer to be more readily transportable to a location of use prior to being expanded. This is particularly advantageous for larger transducers which are either of the volumetric or large planar type.

The scaffold may comprise a network of interconnected members and at least one of the interconnected members comprises shape memory material member. The network of interconnected members may be parts of a sheet of shape memory material. The members may be defined by transducer elements. The members may represent fold lines in the sheet. The transducer elements may be inflexible (relative to the shape memory material).

The shape memory material member may provide a hinged connection between at least two of the interconnected members. The hinged connection may be provided by a fold line in the shape memory material which is configured to straighten upon activation of the shape memory material. All of the members of the scaffold comprise shape memory material members.

The transducer may further comprise one or more interconnecting platforms extending between opposing members of the scaffold. Adjacent interconnecting platforms may define the hinge portions therebetween. The one or more transducers are mounted on the one or more interconnecting platforms.

The network of interconnected members may comprise a tessellation of polygonal substructures. Each substructure may comprise one platform. The substructures may comprise a triangular arrangement of interconnected members The scaffold may comprise at least one heating element. At least one of the interconnected members may comprise a heating element. The heating element may be at least one interconnected member. The interconnected member may comprise conductive material. The conductive material may be configured to provide sufficient Joule heating upon application of a suitable driving current.

The heating element may be coated and/or encapsulated with a water impermeable membrane. The water impermeable membrane may cover or encapsulate the transducer.

The transducer may further comprise a restraint to restrain the scaffold in the first configuration. The restraint may be a clamp. The restraint may be water soluble.

The transducer may comprise a sonic transducer. The transducer comprises a piezoelectric material, however, other transducer or sensor types may be used The scaffold may span a distance of at least 1m or has a volume of 0.005m3 or lower when deployed.

The transducer may be configured to transmit or receive at a frequency range of between 1kHz and 200kHz. In some embodiments, the frequency range may be between 1kHz and 50kHz. In some embodiments, particularly passive monitoring embodiments, the frequency range of a receiver may be lower than 1kHz.

The present disclosure provides a sub-aquatic transducer comprising the expandable transducer as described herein.

The present disclosure provides a method of deploying a transducer as described herein, comprising: locating the transducer in a desired location whilst in the scaffold is in the first configuration; causing the scaffold to transition between the first configuration and second configuration such that the transducers move from a stowed configuration to a deployed configuration.

The transducer may further comprise supplying electric current to the heating element.

Locating the transducer may comprise submerging the transducer in water.

The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the aspects, examples or embodiments described herein may be applied to any other aspect, example, embodiment or feature. Further, the description of any aspect, example or feature may form part of or the entirety of an embodiment of the invention as defined by the claims. Any of the examples described herein may be an example which embodies the invention defined by the claims and thus an embodiment of the invention.

Brief Overview of Figures The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figures la to id shows a schematic representation of the deployment stages of an expandable transducer; Figure 2 shows a sub-element of an expandable transducer; Figures 3a to 3c shows a schematic representation of the deployment stages of an alternative communications transducer; Figures 4a and 4b show a side view and plan view of an alternative communications transducer; and, Figure 5 shows a flow diagram of the deployment stages of a communications transducer.

Figure 6 shows a communications transducer system.

Detailed description

The transducers of the present disclosure overcome issues in existing solutions which may be too large or do not generate the sound power levels required for low frequency subaquatic applications. Although small transducers do exist, they may be susceptible to cavitation at high drive levels placing a fundamental limit on their performance. The present disclosure provides a transducer which may be folded into a relatively small volume for storage and transportation and expanded upon deployment to allow low frequency/long communications without the limiting power input or cavitation issues that could be experienced at high drive levels for smaller devices. It is of note that large transducers are generally better suited to receiving low frequency communications. As noted above, communications and communicating may be interpreted as including

monitoring only applications in this disclosure).

Thus, the expandable transducers of the present disclosure may find particular application for low frequency communications in which the size of the required transducer is prohibitively large for some platforms to carry. The range of frequencies at which the expandable transducer can be operated will depend on the carrier, but the present disclosure is envisaged as being employed for communication frequencies in the order of 50kHz or lower. In some examples, the transducer may operate at frequencies as low as 1kHz or 500Hz. In other examples, the frequency range may be as high as 200kHz. In some examples, the frequency range may be between 45kHz and 8kHz.

The size of the deployed transducers may be smaller than 0.005m3 in volume. In some applications, the transducers may comprise a large array of transducer elements which may be greater than 1m2 in a deployed state. The large array may be a receiver array and may comprise a flat panel.

The term transducer is used herein to relate to any device which converts a communication signal of one sort to another. Thus, the transducer may be an electromagnetic antenna for receiving and/or transmitting radio waves, or a sonic transducer for receiving and/or transmitting sonic waves, for example. The transducer may comprise a plurality of elements to provide an arrayed transducer, such as a phased array. Thus, the transducer may be comprise a single transducer (or transducer element) or an array of transducers (or transducer elements) and may be configured to transmit and/or receive signals. The term 'expandable transducer' can be interpreted as being the device including the one or more transducers or transducer elements.

The invention finds particular application in sub-aquatic applications. However, this is not a limitation of the invention which may find application in other scenarios, such as on-land or air communication systems.

The term shape memory material should be taken to include any material which is capable of being restored to a pre-deformation state upon application of a required stimulus. The shape memory material may be a shape memory polymer or a shape memory alloy, for example. In one example, the shape memory material may be a nickel-titanium shape memory alloy such as commercially available Nitinol. The shape memory material may have one way shape memory or have two way shape memory. By one way shape memory material it is meant that the material is pre-stressed and moves back to an original shape upon activation. A two way shape memory material can be taken to be one which can be moved between two states, as is known in the art.

Figures la to id show the deployment stages of an expandable communication transducer 100. The expandable transducer 100 may comprise a scaffold of shape memory material which is transifionable from a first configuration to a second configuration. The first configuration is shown in Figure la with a second configuration being shown in Figure id. Figure lb shows the transition between the first and second configuration in which the scaffold is in an intermediate configuration between the first configuration and the second configuration.

One or more transducers, which may be referred to as transducer elements, may be attached to the scaffold so as to be moved from a stowed configuration in which the transducers are typically dormant, to a deployed configuration in which the transducers are ready for use, e.g. transceiving, transmitting or receiving. Hence, as the scaffold is moved from the first configuration to the second configuration, the transducers are moved from a stowed configuration to a deployed and operable configuration.

The scaffold may be moved between the first and second configurations via an actuator (or actuation mechanism which may be referred to as an activation mechanism or device in this disclosure). The actuator may comprise a shape memory material. The shape memory material may comprise all of part of the scaffold and may be configured such that, upon activation, the shape memory material causes relative movement between different parts of the scaffold.

The scaffold may comprise a plurality of members which are connected together in a network arrangement so as to provide a frame. The members may comprise sheets plates or rods which may be elongate and/or planar and which are connected at junctions (which may be referred to as nodes). The nodes may be formed from the terminal end of two or more members. The connection between two members may be provided by a hinge portion which is located between substructures. In some examples, the scaffold may be provided by a single sheet of shape memory material upon which the transducers can be mounted. The hinge portions may be provided by folds in the sheet of shape memory material between the transducers.

The network of members and/or transducer elements may be divided into sub-structures which are tessellated with each other to provide the expandable transducer.

The substructures may be distinguished from each other in that each substructure may be moved relative to the adjacent substructures with which it is bordered. Thus, as shown in Figure 1, there is an expandable transducer 100 which comprises first 10 and second 12 substructures which are configured to pivot relative to one another around a hinge portion 14.

In the first configuration the first and second substructures 10, 12 are arranged next to each other in a stacked arrangement. The stacked arrangement may place the substructures 10, 12 in a parallel relation to one another, where the hinge portion 14 and stowed configuration of the substructures 10, 12 allows. Upon actuation of the shape memory material, the substructures 10, 12 move away from one another by pivoting about the hinge portion 14 until the first 10 and second 12 substructures lie in an expanded state.

The representation shown in Figures la to id shows a simple arrangement of two substructures 10, 12 which are configured to open into a deployed configuration in which the two substructures may be placed in a common plane or along a common axis. However, it will be appreciated that in some examples, the substructures 10, 12 may not lie in a parallel relation to one another when stowed and may not lie in a common plane or along a common axis when in a deployed configuration. This is particularly so for expandable transducers comprise a quasi-curved profile when deployed.

The hinge portion 14 may comprise a pivotable mechanical connection which simply attaches the substructures 10, 12 together and/or may comprise the shape memory material upon which the transducers are mounted. In the case of the former, the hinge portion 14 may provide a fulcrum about which the substructures 10, 12 can pivot under the influence of the shape memory actuators which may be located elsewhere in the structure. In the case of the latter, the activation of the shape memory material forces the two substructures 10, 12 apart from within the hinge portion 14. It will be appreciated that the entire scaffold and/or substructure may comprise shape memory material.

Once in the deployed configuration, the transducer 100 is ready to send or receive signals, as represented by reference numeral 16. Each of the substructures 10, 12 may include individual transducer elements which may be used individually or as part of an collective array of transducers. The array of transducers may form an array, as noted above.

In some examples, the expandable transducer may include a staged deployment in which the expandable transducer includes a different configuration or shape at each stage of deployment and is operable to transmit and/or receive at each stage. Hence, there may be provided an expandable transducer which is operable at a plurality of different configurations or shapes. There may be a first deployment stage at which the transducer has a first configuration or shape and is operable at a first operating frequency, and a second deployment stage at which the transducer has a second configuration or shape and is operable at a second frequency. The different stages of deployment may alter the spacing between the transducer elements to allow for different operating frequencies. There may be a plurality to deployed configurations and a plurality of operating frequencies (beyond the two described above).

In order to provide the staged development, the expandable transducer may incorporate one or more actuators which are configured to provide different configurations. The one or more actuators may be selectively operated to move the transducer between two or more of the deployment stages. Alternatively, a sub-set of the one or more actuators may be configured to deploy the transducer from a first configuration to a second configuration, and a second subset of the one or more actuators may be configured to deploy the transducer from a second configuration to a third configuration, etc. Figure 2 shows an example of a substructure 200 of an expandable transducer. The expandable transducer may be similar to an expandable transducer as described above in connection with Figures la to id or elsewhere in this disclosure. The substructure 200 may be comprised from a plurality of elongate members 218a-d which are connected in an end to end relation to provide a closed loop. The shape of the substructure 200 when viewed in plan is polygonal having straight edges and apexes at the nodes, but this is not a limitation. The polygon may be four sided as shown in Figure 2, but any polygon may be used provided the shape is suitable for forming a tessellated structure which can be expanded from a collapsed configuration. In some examples, the substructure may be triangular, rectangular or a parallelogram for example. As shown, the members 218a-d of the substructures may be arranged in an opposing relation to one another.

The elongate members 218a-d may be located at and define the periphery of the substructure 200. When provided in a larger structure to form the expandable transducer, at least one side of each substructure 200 is connected to at least one side of another one of the other substructures (not shown in Figure 2). Some of the elongate members 218a-d may be shared between adjacent substructures such that a common elongate member provides a structural support and boundary of two substructures.

The members 218a-d of the scaffold may be distinct members which are joined at the nodes/terminal ends to provide the network of members, or they may be integrally formed as a homogeneous continuous structure. It will be appreciated that in the case of the scaffold comprising a sheet of shape memory material, the members 218 a-d may be defined by the presence of the platform 220 and/or transducer element 222.

The platform 220 or transducer 222 may have sufficient rigidity that it can remain in a generally undistorted shape upon activation of the shape memory material.

As noted above, the members 218a-d which define the substructure 200 form a closed loop across which a platform 220 may extend. A transducer 222 may be located on the platform 220. The platform 220 may be provided a membrane or substrate upon which the transducer 222 may be formed either during the fabrication of the transducer 222 or post fabrication. Alternative, the transducer 222 may be fabricated directly onto the shape memory material (with any necessary intervening insulating or conducting layer which may be required). The platform 220 and substructure 200 may be planar in construction. The platform 220 may extend across the substructure 200 so as to close the opening defined by the substructure 200. It will be appreciated that each substructure and/or platform 220 may comprise a plurality of transducer elements 222.

The substructure 200 may incorporate an activation element (which may also be referred to as an actuator or actuator mechanism) which is used to actuate the shape memory material. The activation element may be a heating element 224 in the form of a conductor, e.g. a metallic wire, which extends along the length of a shape memory material member 218a 218c. In the case where the shape memory material is a conductor having a suitable resistivity which will allow for Joule heating with the passing of a suitable driving current, the heating element 224 may be provided by the member itself and there may not be a discrete heating element 224. In some examples the heating element 224 may be provided by an ink based conductive track. The ink based conductive track may comprise graphene. The ink based track may be printed on to the substrate or shape memory material.

Any of the shape memory material members 218a-d, heating element 224, platform 220 and transducer 222 may be coated in one or more protective layers (not shown).

The protective layer may be a water impermeable membrane formed from a suitable polymer. In addition to or alternatively, the heating element 224 may be separated from the elongate member 218a-d and/or a shape memory material by a protective layer. The protective layer may be a dielectric material to prevent the driving current in the heating element 224 flowing into the member.

The scaffold may be configured to expand and be deployed upon application of heat, or may be collapsible upon the application of heat.

Each substructure 200 may additionally include one or more electrical connectors and connecting wires to send or receive power or signals to the various elements of the substructure (not shown). Each substructure 200 may include an electrode which is in electrical connection with the heating element 224 such that a suitable driving current may be provided when required. Similarly, one or more further electrodes may be provided on or adjacent to the platform 220 and be in electrical communication with the transducer element 222 for the receipt or transmission of signals to or from the transducer element 222.

In some situations it may be advantageous to restrain the movement of the substructures of the expandable transducer until they are required for use in a deployment location. Figures 3a to 3c show a schematic representation of an alternative expandable transducer 300 which comprises first and second substructures 310 and 312, a hinge portion 314 and a restraint 326. The expandable transducer 300 may be similar to the expandable transducer 100 of Figure 1 and/or have the substructures described in connection with Figure 2 and corresponding features will not be described further.

The restraint 326 engages with the scaffold in two locations and/or at least to two substructures 310, 312 so as to restrict separating movement therebetween. The separating movement may be due to residual stress within the substructures 310, 312 provided by, for example, the hinge portion 314 or the elongate members, or may be provided to prevent an unintended deployment, for example, by knocking the scaffold during a transportation for deployment at a desired location.

The restraint 326 may be manually removable or configured to disengage upon activation of a disengagement mechanism. In one example, the disengagement mechanism may be provided by the material choice of the restraint 326 which may be, for example, water soluble such that deploying the expandable transducer 300 in a sub-aqua environment causes the restraint 326 to dissolve and release the adjacent substructures 310 312 so as to be expandable. Thus, as shown in Figures 3a -3c, the restraint may transition from an intact state, to a partially dissolved state 326' to a fully dissolved or released state 326" in which the substructures 310, 312 are free to move apart. Suitable water soluble materials are known in the art.

The restraint 326 may be any configuration which provides the required tethering of the substructures. Further, the restraint 326 may bind a plurality of substructures, specifically three or more, so that the plurality of substructures may be released at the same or approximately the same time. Hence, an expandable transducer of the present disclosure may include only one restraint, or may include a plurality of restraints. In some examples the restraints may be distributed to allow a phased deployment in which the release of different substructures 310, 312 is staged.

The restraint 326 may be located towards a distal end of the substructures 310, 312 (distal being with reference to the hinge portion 314), however this is not a limitation and the restraint 326 may be located anywhere on the scaffold. It will be appreciated that the choice of material and size of the restraint 326, e.g. the thickness and depth in the case of a band, will determine the duration of the dissolution such that a time delay may be incorporated into the release. A time delay may be useful where the transducer is to be deployed at depth, for example.

As shown in Figures 3a-c, the restraint 326 may be a band which encircles the substructures 310, 312. In some examples, the restraint 326 may be provided in other forms such as a clamp, bag, sock or net. In other examples, the restraint 326 may comprise a strap of which the free ends are connected together using a mechanical coupling, e.g. a clasp, which could be manually detached. In other examples, the restraint 326 may include a release actuator which is controlled to provide a release upon receipt of a signal or after a predetermined amount of time. The release actuator may comprise a heating element which is activated upon heating of the shape memory material, or may be some form of electromagnetic latch. The release actuator may be remotely operated.

Figures 3a to 3c show the expandable transducer 300 as comprising a pair of planar substructures 310, 312 gathered in a parallel relation to each other and bound by a restraint 326 in the form of a band of water soluble material located at a distal end, as described above. Advantageously, the restraint 326 may provide ballast such that the expandable transducer 300 can be ejected into a body of water and sink in a required orientation for deployment. Thus, the transducer 300 may be deployed on a seabed and vertically orientated during a descent. The orientation of the transducer 300 will be application specific and the vertical orientation provided in Figures 3a to 3c should not be seen as a limitation.

The expandable transducer can take any form that provides the required arrangement of individual transducer elements in use. The transducer may be two dimensional, e.g. a polygon, or three dimensional, e.g. a polyhedron. In the case of a three dimensional expandable transducer, the substructures may be geodesic elements of the three dimensional structure. For example, the sides of a three dimensional shape may comprise a tessellation of triangular, quadrilateral, heptagonal or hexagonal substructures for example, or any combination thereof The transducer may be provided in a collapsed cylinder, cuboid or sphere (or partial sphere) for example. Examples of possible structures may be provided by the art of origami such as the foldable triangulated cylinder described in Guest, S.D., and Pellegrino, S. (1994). "The Folding of Triangulated Cylinders, Part I: Geometric Considerations." ASME Journal of Applied Mechanics, 61, 773-777, which is incorporated herein by reference.

The expandable transducer may comprise sections which are moved relative to one another. As such, the transducer may be provided with one or more end caps which provide are moved apart linearly to elongate a cylinder from a collapsed state to an elongate cylindrical state. Such an example may be inspired by the elongated structure provided in "Packing and deploying Soft Origami to and from cylindrical volumes with application to automotive airbags", Jared T. Bruton, Royal Society Open Science, which is incorporated herein by reference.

The above provide just some examples of different shapes which may be useful in different applications. It will be appreciated that other configurations will be possible with only the geometric constraints which are suitably expandable with a shape memory material limiting the options.

Generally, the construction of the transducer can be carried out using known techniques found in the art. As noted herein, the scaffold may be a sheet of shape memory alloy which provides the frame of shape memory members. The construction of the scaffold may be achieved by providing a sheet of shape memory material such as nitinol, and disposing a transducer element, such as PZT, on the shape memory material. It will be appreciated that an electrical connection may be provided between the shape memory material and transducer where the shape memory material is suitably conductive, however, separate electrical connectors and insulating layers may be provided in some examples. In some examples, the transducer element may be provided on a separate substrate prior to being placed on the shape memory material. The substrate may be chosen to improve the acoustic performance of the transducer. The scaffold and transducer element(s) may be coated in an encapsulant which protects the arrangement from the ingress of water or other deleterious substance. The encapsulant may comprise a flexible coating and may comprise one or more of a rubber, polyurethane or silicone based material.

Figure 4a and 4b show an expandable transducer 400 in side view and plan view respectively. Thus, there is a shown an expandable transducer 400 comprising a plurality of substructures 410a-i which are arranged in a stack which can be seen to the left of arrow 428 which indicates the transition between the stowed and deployed states. The arrangement in the right hand side of Figure 4a shows the unfurling of the substructures which necessitates a rotation of the scaffold 430. The right hand side of Figure 4b shows the expandable transducer in a fully deployed configuration.

The substructures 410a-i may broadly correspond to the substructure described in connection with Figure 2. The substructures 410a-i may be in the form of a polygonal structures when viewed in plan and may, as shown in this example, be triangular. Each substructure 410a-i may be planar in form and comprise a plurality of elongate structural members 418 defined by the periphery of the substructures 410a-i, with a platform 420 extending therebetween. The transducer element (not shown) may be located on the platform 420 or may comprise the platform in its entirety.

One side of each of the substructures may be connected to an adjacent substructure and may share one of the structural members 418. The substructures 410a-i may be arranged in a linear array with the each of the triangles inverted with respect to its adjacent neighbour so as to be provide a tessellated line with a linear top and bottom edge. It will be appreciated that the expandable transducer 400 may include more or less substructures than those shown and may be a two dimensional array (as opposed to a linear array). Other aspects of the construction of each of the substructures may be in keeping with the substructure described in Figure 2. In combination, the substructures 410a-i may provide the expandable transducer 400 with elongate side rails 432 having lateral members extending diagonally therebetween in the form of a warren truss (in plan).

As shown in the left hand side of Figure 4a, the collapsed structure may comprise a linear stack of the substructures 410a-i when viewed side on. Although the stack of substructures 410a-i is provided with each of the substructures being arranged vertically with respect to the side length and parallel to one another, these are not limitations and the stack may not comprise parallel substructures and any orientation may be possible.

Upon application of an activation means (not shown), such as the heating element, the substructures 410a-i expand away from each other so as to unfold linearly. Due to the nature of the structure, the expansion may necessitate some rotation of the structure as it unfolds, as shown by arrow 430. The expansion may be occur at a common rate for each pair of adjacent substructures 410a-i to provide a uniform expansion along the length of the structure.

Although the above illustrations generally provide a hinge portion with an axis of rotation coaxially aligned with the longitudinal axis of one of the elongate members, it will be appreciated that the hinge portion may be replaced and or added to be provided the shape memory material along the length of one of the structural members such that it can unfold lengthwise. In the example of Figures 4a and 4b, the side rails 432a,b may comprise shape memory material which is concertinaed when in the collapsed stack.

When activated, the side rails 432a,b may be induced to unfold and straighten into a deployed state. In such an example, the lateral members which extend between the side rails 432a,b may or may not be shape memory material and may provide structural reinforcement or may actively aid the deployment. Thus, the actuation required for deployment may be provided by the shape memory actuation of any of the members from which the scaffold is comprised, e.g. side rails. As noted above, the scaffold may be provided by a sheet of shape memory material with the various lateral members and side rails being defined by the presence of the transducers/substrates on the sheet.

Figure 5 shows a method 500 of deploying an expandable communications transducer.

The expandable communications transducer may correspond to any described in the present disclosure. The method 500 may comprise: providing the communications transducer in a desired location whilst in the scaffold is in the first, stowed, configuration 534 and causing the scaffold to transition between the first configuration and second configuration 536 such that the transducers move from a stowed configuration to a deployed configuration.

Once deployed, the communications transducer may be put into operation such that the transducer elements provided on each of the substructures can either transmit or receive 538 a desired signal, such as a pressure wave in the case of a sonic device.

As will be appreciated, the method of deployment may include activating the actuation means such that the substructures can expand, as described above. Hence, in one example, the method of deployment may comprise supplying an electric current to one or more heating elements which may be distributed throughout the scaffold or comprise the scaffold.

As noted above, the communications transducer may be submersible and the method may involve submersing the transducer prior to deployment. The submersion may be achieved by deploying the collapsed structure from a surface vessel or submarine or with a scuba diver. In other examples the communications transducer may be deployed from a surface structure such as a communications buoy or the like.

Figure 6 shows a communications transducer system 600 comprising an expandable transducer 601 and ancillary equipment which may be used as part of the deployment and use of the expandable transducer 601. The ancillary equipment may include one or more power sources 602 which can be used to power the activation actuation system for the shape memory material, such as a current source for driving a heating element and a controller 603. The power source 602 may be provided from one or more batteries and/or an energy harvester such as a solar panel. The controller 603 may include a processor and one or more memory units and be configured to control the activation of the shape memory material via the activation power source 602. The controller 603 may additionally or alternatively be configured to process any signals which are sent or received by the expandable transducer 601 when in service. The controller 603, power source 602 and transducer 601 may be collocated in a common housing and deployed with the expandable transducer.

The activation of the expandable transducer may be time based such that it is activated at a predetermined time (for example after a deployment time), via a switch which is operated by a deployment agent such as a scuba diver during deployment, or via a remote signal.

In the present disclosure, the shape memory material is generally described as being expanded from a stowed configuration to an expanded configuration. However, this may not be the case, and the shape memory material may be activated to return the expanded transducer to a stowed configuration. Thus, a thermally activated shape memory material may be heated in a deployed configuration causing it to fold in order to be clamped. When the clamp is removed, for example by dissolution, the expandable transducer would be free to return to its original shape. This cycle could be repeated by re-applying heat to return it to a collapsed configuration and re-clamped (or heat continually applied).

In one example, the transducer element may be fabricated from sheets of piezoelectric material connected electrically to allow a drive voltage to be applied. These sheets may be mounted upon a Nitinol structure which is capable of being folded into a stowed configuration. A heating element may be built into the transducer such that it can heat the folded Nitinol. The Nitinol will then return to its original shape, increasing the size of the transducer such that it can transmit at low frequency.

It will be understood that the invention is not limited to the examples and embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

Claims

CLAIMS: 1 An expandable transducer comprising: a scaffold of shape memory material which is transitionable from a first configuration to a second configuration; and, one or more transducers attached to the scaffold so as to be moved between a stowed configuration and an operable deployed configuration with the transition of the scaffold from the first configuration to the second configuration.
2 An expandable transducer according to claim 1 wherein the scaffold comprises a network of interconnected members and at least one of the interconnected members comprises shape memory material member.
3 An expandable transducer according to claim 2, wherein the shape memory material member provides a hinged connection between at least two of the interconnected members.
4 An expandable transducer according to any of claims 2 or 3, wherein all of the members of the scaffold comprise shape memory material members.
An expandable transducer according to any of claims 2 to 4, further comprising one or more interconnecting platforms extending between opposing members of the scaffold.
6 An expandable transducer according to claim 5, wherein the one or more transducers are mounted on the one or more interconnecting platforms.
7 An expandable transducer according to any of claims 2 to 6, wherein the network of interconnected members comprises a tessellation of polygonal substructures.
8. An expandable transducer according to claim 7 when dependent on claim 5, wherein each substructure comprises one platform.
9. An expandable transducer according to either of claims 6 or 7 wherein the substructures comprise a triangular arrangement of interconnected members.
10. An expandable transducer according to any preceding claim, wherein the scaffold comprises at least one heating element.
11. An expandable transducer according to claim 10 when dependent on any of claims 2 to 9, wherein at least one of the interconnected members comprises a heating element.
12. An expandable transducer according to claim 11, wherein the heating element is the at least one interconnected member.
13. An expandable transducer according to any preceding claim, further comprising a water impermeable membrane.
14. An expandable transducer according to any preceding claim, further comprising a restraint to restrain the scaffold in the first configuration.
15. An expandable transducer according to claim 14, wherein the restraint is water soluble.
16. An expandable transducer according to any preceding claim, wherein the one or more transducers are sonic transducers.
17. An expandable transducer according to claim 16, wherein the transducer comprises a piezoelectric material.
18. An expandable transducer according to any preceding claim, wherein the scaffold spans a distance of at least 1m or has a volume of 0.005m3 or lower when deployed.
19. An expandable transducer according to any preceding claim wherein the transducer is configured to transmit or receive at a frequency range of between 50kHz and 1kHz.
20. An expandable transducer according to any preceding claim, wherein the one or more transducers are configured to provide a transducer array.
21. An expandable transducer according to any preceding claim, wherein the one or more transducers are configured to transmit and/or receive.
22. A sub-aquatic expandable transducer comprising the expandable transducer of any preceding claim.
23 A method of deploying an expandable transducer according to any preceding claim, comprising: locating the transducer in a desired location whilst the scaffold is in the first configuration; causing the scaffold to transition between the first configuration and second configuration such that the transducers move from a stowed configuration to a deployed configuration.
24 A method according to claim 23, wherein the transducer is according to any of claims 10 to 21, further comprising supplying electric current to the heating element.A method according to claim 23, wherein the transducer according to claim 15, wherein locating the transducer comprises submerging the transducer in water.