Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
  • A61N1/00—Electrotherapy; Circuits therefor
  • A61N1/18—Applying electric currents by contact electrodes
  • A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
  • A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
  • A61N1/372—Arrangements in connection with the implantation of stimulators
  • A61N1/378—Electrical supply
  • A61N1/3787—Electrical supply from an external energy source
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
  • A61N1/00—Electrotherapy; Circuits therefor
  • A61N1/18—Applying electric currents by contact electrodes
  • A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
  • A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
  • A61N1/372—Arrangements in connection with the implantation of stimulators
  • A61N1/37205—Microstimulators, e.g. implantable through a cannula
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N35/00—Magnetostrictive devices
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
  • A61N1/00—Electrotherapy; Circuits therefor
  • A61N1/18—Applying electric currents by contact electrodes
  • A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
  • A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
  • A61N1/372—Arrangements in connection with the implantation of stimulators
  • A61N1/37211—Means for communicating with stimulators
  • A61N1/37217—Means for communicating with stimulators characterised by the communication link, e.g. acoustic or tactile
  • A61N1/37223—Circuits for electromagnetic coupling

Definitions

• This invention relates to apparatus and methods for harvesting energy from the environment and other sources external to the harvester and converting it to useful electrical energy.
• the present invention generally relates to implantable stimulator systems and methods, and more particularly relates to implantable stimulator systems and methods utilizing one or more implantable microstimulators for direct electrical current.
• PME implantable stimulator systems and methods
• the delivered therapy will be effective for continuous or temporary, as needed (PRN) therapeutic intervention.
• Energy harvesters are known that convert vibrational energy into electrical energy.
• the electrical energy produced can then be stored or used by other devices.
• the vibrations of an air conditioning duct can be converted into electrical energy by an energy harvester and the electrical energy then used to power a sensor that measures the air temperature in the duct.
• the sensor does not require electrical wiring to a remote source of power or periodic battery changes.
• vibrational energy harvesters While each of the known types of vibrational energy harvesters have different advantages, they also have drawbacks such as: the need for heavy, powerful permanent magnets (in the case of inductive energy harvesters) to produce a sufficiently large flux density; an auxiliary source of power, such as a battery (in the case of capacitive harvesters); the need for large vibration frequencies and/or a heavy inertial mass to generate sufficient vibrational energy for harvesting (for all types of vibration energy harvesters); undesirable levels of damping and noise generation from interaction between the locally generated magnetic field and nearby metallic parts (for inductive harvesters); and other disadvantages such as size or weight that make them unsuitable for use in a remote or generally inaccessible location.
• a typical magnetic device 2 to harvest vibrational energy consists of a permanent magnet 3 (an internal local field source) attached to a housing 7 and connected by a spring 4 to a passive magnetic field sensor 5 (e.g., an induction coil or a passive magnetostrictive/electroactive field sensor). External vibrations cause a relative motion of the magnet 3 and sensor 5, producing an electrical voltage across a load 8 and a current through the load.
• a local magnetic field source e.g., a permanent magnet disposed adjacent to the field sensor
• these devices also typically include an inertial mass 6 (also known as a proof mass) to increase the vibrational energy generated.
• the inertial mass may be rigidly attached to the sensor (as shown), may be the same or separate from the permanent magnet, or may comprise part of the sensor itself.
• the magnet may comprise part of the moving proof mass, as opposed to being fixed to the housing. In each case, the inertial mass and the permanent magnet increase the size and weight of the device.
• an apparatus for harvesting energy from the environment or other remote sources and converting it to useful electrical energy.
• the harvester does not contain a permanent magnet or other local field source but instead relies on the earth's magnetic field or another source of a magnetic field that is external to the sensing device.
• One advantage of these new harvesters is that they can be made smaller and lighter than energy harvesters that contain a magnet. Another advantage is that they do not require vibrational energy to function.
• the harvester differs from those of the prior art by the absence of a permanent magnet or other local (internal) field source.
• a change in the state of magnetization of the sensing element may be achieved in one (or both) of two general ways: 1.
• the magnetic flux density in the sensing element may be altered by changes in the orientation of the sensor (movement of the sensor) with respect to a static (non-changing) external field.
• the magnetization vector M of the sensing element may rotate due to changes in the orientation of the sensing element with respect to the earth's field.
• Such movement of the sensing element may be achieved by attaching the sensing element to a piece of rotating machinery or a rotating part on a vehicle.
• the sensing element may be suspended on its axis and allowed to rotate (due to external vibrations), the rotation causing a change in its orientation in the earth's field. 2.
• the sensing element may remain stationary and be operated on by a remote changing magnetic field from any of a variety of sources.
• the remote changing magnetic field can be produced by an electrical transformer, motor, electronic device, moving machinery or inductive wire or coil which is relatively remote (acting at a distance or through a non-magnetic barrier) on the sensing element.
• the changing (e.g., alternating) magnetic field source can be designed to couple with a remote sensing element efficiently in terms of frequency, distance, field orientation and magnitude to deliver power remotely to the sensing element.
• the power harvested from a remote field source will be measured in microwatts per centimeter cubed ( ⁇ W/cm 3 ), as opposed to milliwatts per centimeter cubed (mW/cm 3 ) for energy harvesters that include a strong magnet.
• ⁇ W/cm 3 microwatts per centimeter cubed
• mW/cm 3 milliwatts per centimeter cubed
• the power harvested can be considerably greater because the strength of such fields is often considerably greater than the earth's magnetic field (H ea r th is approximately 0.3 Oe or 3 micro-Tesla).
• a preferred sensing element for use in the present invention is based on a class of passive magnetostrictive electroactive (PME) magnetic field sensors that produce a voltage when exposed to a changing magnetic field.
• the sensing element is preferably a layered structure (e.g., sandwich) of magnetostrictive material bonded to an electroactive material, the latter being poled in a direction preferably parallel to the plane of the magnetostrictive layer(s).
• An external magnetic field causes a magnetization change in the magnetostrictive layer(s), which respond(s) with a magnetoelastic stress. Part of the stress is transferred to the electroactive layer that responds by producing a voltage given by V 1 ⁇ g 11 O 1 L 1 .
• L 1 is the distance between the electrodes across which the voltage V, is measured
• ⁇ 7 is the stress transferred to the electroactive component
• g u is the stress-voltage coupling coefficient.
• the principal stress and induced voltage may lie in orthogonal directions (e.g., 1-3 operation), or the principal stress and voltage may act along different axes (e.g., 1-5 operation).
• the energy harvester of the present invention is more than a simple passive magnetostrictive/electroactive (PME) field sensor.
• a simple PME field sensor is comprised of materials and dimensions designed preferably to produce a large voltage across a high impedance circuit, the voltage being) indicative of the field of interest.
• the electronic circuit for a simple PME sensor is designed to register a field value.
• the PME energy harvester of the present invention is comprised of materials and dimensions designed preferably to produce a voltage and current that match the impedance of the load to be driven.
• the PME energy harvester is coupled to an electronic circuit that converts the PME output to power for immediate use or storage.
• the PME element is preferably optimized to respond to the field strength of the intended environment, which would generally be much greater than that of a pure field sensor.
• suitable applications may include wireless monitoring applications, wherein wireless monitoring is meant to include self powered sensing of local conditions and processing of the sensor output and self powered wireless communication to a central data processing point.
• wireless monitoring is meant to include self powered sensing of local conditions and processing of the sensor output and self powered wireless communication to a central data processing point.
• suitable applications might include wireless transfer of electrical power over a small distance to a location inaccessible via electrical leads or not convenient for battery replacement. More specifically, these applications may include supplying power for:
• HVAC heating, ventilation and air conditioning
• applications of the new energy harvester are not limited to vibration rich environments.
• a simple repetitive motion or rotation of the more sensitive PME devices as described herein allows them to operate from the earth's magnetic field. They can be placed in physically inaccessible locations and activated from a remote field source that is either present in the environment or placed there for the purpose of energizing the device.
• an energy harvester without a local field source comprises: a magnetic field sensing element including one or more layers of magnetostrictive material having a magnetization vector that responds to variations in an applied magnetic field by generating a stress, and one or more layers of electroactive material, mechanically bonded to the layer of magnetostrictive material, that responds to the stress by generating a voltage; and a circuit coupled to the sensing element that converts the voltage to electrical power for immediate use or storage, wherein the sensing element either: a) moves relative to a remote static external magnetic field, such that changes in orientation of the sensing element with respect to the external field generates the voltage; or b) is stationary with respect to a remote changing external magnetic field, wherein the changing external field causes the sensing element to generate the voltage.
• the electrical power comprises a voltage and current suitable for an intended application
• the magnetostrictive material layer has a magnetization vector that responds to variations in the magnetic field by rotating in a plane and wherein the electroactive material is poled in a direction substantially parallel to the plane in which the magnetization vector rotates;
• the sensing element is mounted to an object that moves relative to the applied magnetic field; [0020] the variations in the applied external field are in one or more of magnitude and direction of the field;
• the sensing element is mounted such that local vibration changes its orientation with respect to the applied magnetic field; [0022] the sensing element includes electrodes for measuring the voltage generated and wherein the electrodes are configured such that the distance between the electrodes and cross sectional area between the electrodes are tailored to produce a desired electrical power;
• the magnetization vector rotates relative to the electrode axis due to changes in the orientation of the sensor in the applied external field
• the remote magnetic field is generated by one or more of an electrical transformer, motor, actuator, switch, electronic device, moving machinery or inductor;
• the inductor is a wire or coil through which an alternating current is flowing, to produce the remote changing external magnetic field
• the sensing element is rigidly attached to an inertial mass
• the sensing element includes an inertial mass; [0029] the changing external field or sensing element movement is at vibration or power transmission frequencies of no greater than 1 kHz;
• the changing external field is at a resonance frequency in the range of that of the sensing element
• the changing external field is in a range of 20 to 50 kHz; [0032] the external field frequency is equal to or close to the resonance frequency of the sensor, which varies roughly according to the equation
• L is a characteristic length of the sensor and E ⁇ ff and p e tf are the elastic modulus and mass density appropriate to describe the composite magnetostrictive/electroactive sensor properties; [0033] the changing external field and sensing element are within a resonant frequency range;
• the circuit is within the resonant frequency range; [0035] the external changing field is outside a human or other animal body and the sensing element is inside the body.
• a method of harvesting energy comprises: [0037] providing a magnetic field sensing element including one or more layers of magnetostrictive material having a magnetization vector that responds to variations in an applied magnetic field by generating a stress, and one or more layers of an electroactive material, mechanically bonded to the layer of magnetostrictive material, that responds to the stress by generating a voltage; wherein the voltage is generated by either: moving the sensing element relative to a remote static external magnetic field, such that changes in orientation in the sensing element with respect to the external field generates the voltage; or the sensing element is stationary with respect to a remote changing external magnetic field, and the changing external field causes the sensing elemenet to generate the voltage; and converting the generated voltage to electrical power for immediate use or storage.
• the invention disclosed and claimed herein addresses the above and other needs and provides means and systems for acutely stimulating a nerve root(s), spinal nerve(s), organs, soft tissue, incision site or similar, with a miniature implantable neurostimulator(s) that can be implanted via a minimal surgical procedure and powered by an external magnetic field.
• This invention describes a means of delivering power wirelessly from outside the body to inside the body for the therapies described above.
• the means of wireless power delivery consists of a passive magnetostrictive/electro-active (PME) magnetic-field sensor as the main component of a small implantable device that will receive a changing magnetic field from an external alternating magnetic field source external to the body.
• This field source may be a hand-held device or a small antenna affixed to the wearer's skin, clothing or accessories.
• the external field may be generated by a source planted in a chair, desk, car seat or table that the recipient frequents.
• the AC magnetic field excites the implanted PME sensor, which generates a voltage and current that can be used to provide therapeutic relief by stimulating nerve.
• the therapeutic system can also be used to minimize tissue damage, reduce tumor size and burden, or stimulate bone or cartilage growth in the appropriate space.
• An AC magnetic field is a more efficient means of transmitting power than an AC electric field because of the greater attenuation of electric fields by body fluids.
• the proposed system would include an external source of alternating magnetic field close to the recipient or in a wearable device that is made up of a power source (line power, battery, rechargeable battery or energy harvester) and electronics to control the signal generated by the wearable antenna.
• the antenna is connected to the wearable device with a wire and affixed to the skin or cloth in the area of interest to perform two functions: First, the antenna transmits data to communicate with the implanted devices. Second, the antenna transmits a signal that is converted by the implanted PME sensor/harvester (part of the implanted device) into useful power for the entire implanted device.
• the implanted PME provides a tiny implant that may be millimeter scale in size that can be driven by an external magnetic field applied only on an as needed basis.
• patients with migraine headaches can be treated with therapeutic electricity applied to the occipital nerve.
• the patient does not however express this headache chronically, rather the headache appears only on an intermittently acute basis. Therefore applying the magnetic field during the earliest (prodromal) period of the headache can prevent conversion to a migraine headache. This would be one therapeutic embodiment of the technology.
• Stimulation and control parameters of the implanted micro-stimulator are preferably adjusted to levels that are safe and efficacious with minimal patient discomfort.
• Different stimulation parameters generally have different effects on neural tissue, and parameters are thus chosen to target specific neural populations and to exclude others.
• large diameter nerve fibers e.g., A-. alpha, and/or A-.beta. fibers
• small diameter nerve fibers e.g., A-.delta. and/or C fibers.
• Stimulation patterns for non neural therapy are delivered at the range of therapeutic efficacy.
• the microstimulator used with the present invention preferably possesses one or more of the following properties: at least one PME for applying stimulating current to surrounding tissue and acting as a sensor for determination of therapeutic efficacy and time constants related to the flow of current; electronic and/or mechanical components encapsulated in a hermetic package made from biocompatible material(s); a coil that generates an AC magnetic field to deliver energy and/or information to the implanted PME wirelessly; a means for receiving and/or transmitting signals via telemetry; means for receiving and/or storing electrical power within the microstimulator; and a form factor making the microstimulator implantable via a minimal surgical procedure.
• a microstimulator may operate independently, or in a coordinated manner with other implanted devices, or with external devices.
• a microstimulator may incorporate means for sensing pain, which it may then use to control stimulation parameters in a closed loop manner.
• the sensing and stimulating means are incorporated into a single microstimulator.
• a sensing means communicates sensed information to at least one microstimulator with stimulating means.
• the present invention provides a therapy for chronic pain that utilizes one or more miniature PME's as neurostimulators and is minimally invasive.
• the simple implant procedure results in minimal surgical time and possible error, with associated advantages over known treatments in terms of reduced expense, reduced operating time, single implant surgery, and therapy provided on an as needed basis.
• Other advantages, inter alia, of the present invention include the system's monitoring and programming capabilities, the power source, storage, and transfer mechanisms, the activation of the device by the patient or clinician, the system's open and closed-loop capabilities and closed-loop capabilities coupled with sensing a need for and/or response to treatment, coordinated use of one or more stimulators, and the small size of the stimulator.
• FIG. 1 is a block schematic diagram of a prior art energy harvester device having a permanent magnet and inertial mass
• Fig. 2 is a schematic diagram of an energy harvester according to one embodiment of the invention, in which the harvester is attached to a moving part and is actuated by its motion in the earth's magnetic field;
• FIG. 3 is a schematic diagram of another embodiment of the energy harvester of the invention, in which a stationary harvester is actuated by a changing external field (H ea rth-mod ⁇ fied), the external field being that of the earth's field changed in magnitude or direction by a moving object in its path;
• H ea rth-mod ⁇ fied a changing external field
• FIG. 4 is a schematic diagram of another embodiment of the invention in which a stationary harvester device is activated by a remote external changing magnetic field H ext, where H ext is due to a permanent magnet affixed to a moving part exterior to the harvester;
• Fig. 5 is a schematic diagram of one construction of a sensing element useful in the present invention.
• Fig. 6 is a schematic diagram of a circuit for converting and changing electrical output of the harvester to a DC electrical signal, conditioning, storing and providing the resutling electrical energy to a load;
• Fig. 7 is a graph of PME voltage output versus field at 20 Hz for one embodiment of the invention.
• FIGs. 8a-8b are schematic diagrams of two embodiments of an energy harvester wherein an external changing magnetic field generated by a coil is transmitted through tissue to an embedded PME sensor;
• Fig. 9 is a graph of PME power versus load at 1 Oe and 29 kHz according to another embodiment of the invention.
• Fig. 10 is a block schematic diagram of a passive magnetostrictive/electroactive sensor constructed in accordance with one embodiment of the invention.
• Fig. 11 is a schematic of the invented system of wireless power transmission for implanted devices; external power source energizes flat "patch" coil antenna that emits magnetic-rich electromagnetic wave; implanted passive magnetostrictive/electro-active (PME) sensor/transducer receives and converts the AC magnetic field to AC voltage that is processed to produce the power needed for the particular application;
• PME passive magnetostrictive/electro-active
• Fig. 12 is a schematic of the PME-33 showing poled electro-active element with magnetostrictive outer layers bonded to the electro-active component and end electrodes providing for cf ⁇ operation; photo at right is of prototype PME-33 made by Ferro Solutions;
• Fig. 13 is a graph showing sensor voltage output (mV) vs. magnetic field (mOe) in an early (2002) Ferro Solutions prototype PME-33 sensor with a sensitivity of 0.06 V/Oe; and
• Fig. 14 is a plot of Eq. 3 showing decrease in field-per-Ampere with distance b along the normal to the coil.
• Fig. 2 illustrates a first embodiment of an energy harvester device according to the invention, wherein a static external magnetic field, here H earth (the earth's magnetic field), acts at a distance (or through a non-magnetic barrier) on a sensor whose orientation in the field changes with time.
• H earth the earth's magnetic field
• Fig. 2 illustrates this with a non-magnetic barrier 14 separating the energy harvester 12 on the left, attached to a moving object (rotating machinery part 16), from the source of external field 18 on the right.
• the arrow 26 extending across the width of sensor 12 represents the plane of the magnetization vector M.
• the arrow 20 illustrates rotation of sensor 12 from a first position 22 (labeled X) to a second position 24 (labeled X').
• the sensor can be attached to a rotating part on a vehicle, a door, or other object that moves relative to the earth's field.
• the sensor may also be suspended on its axis such that linear vibration acting on the sensor changes its orientation in the earth's field.
• the change in sensor orientation requires some asymmetry in the suspension for the vibrations to cause rotation of sensor about its axis. It is preferable that the change in sensor orientation be such that the axis between its electrodes changes orientation relative to the static field direction.
• FIG. 3 A second embodiment of the invention is shown in Fig. 3, wherein a changing external field, H ea r th - m od i f i e d, acts at a distance (or through a non-magnetic barrier) on a stationary sensor 32.
• a changing external field H ea r th - m od i f i e d
• H ea r th - m od i f i e d acts at a distance (or through a non-magnetic barrier) on a stationary sensor 32.
• H ea changing external field H ea r th - m od i f i e d
• a permanent magnet 42 is affixed to a rotating or moving object 44 remote from the sensor 48.
• the change in position of the magnet 42 relative to the stationary sensor 48 causes a changing field (see field lines 46 of H ext ) that acts on the static sensor 48.
• Arrow 45 illustrates rotation of the magnet to a second position (shaded area 42' at the bottom of rotating disk 44) and the changing field as dashed lines 46'.
• Other sources of changing or alternating magnetic field can be found near electrical transformers, motors, actuators, switches, many electronic devices, inductor wires or coils, and near areas of high vehicle traffic or moving machinery.
• the remote changing magnetic field source can be designed to couple with the sensor efficiently in terms of frequency, distance and magnitude to deliver power remotely to the sensor.
• FIG. 5 is a schematic illustration of a preferred sensor configuration 50 for use in the present invention.
• a central layer of an electroactive (e.g., ceramic, polymer or single crystal piezoelectric; or a relaxor ferroelectric) material having a polarization vector P is shown, sandwiched between two layers 54, 56 of magnetostrictive material (e.g., of a soft ferromagnetic material having a non-zero magnetostriction) on opposing faces of central layer 52.
• Each magnetostrictive layer has a magnetization vector M which is caused to rotate in the plane of the magnetostrictive layer by an applied field H.
• a pair of electrodes 58 are disposed at opposite ends of the piezoelectric, the axis between the electrodes being parallel to the plane in which the magnetization vectors rotate.
• the voltage V generated in the piezoelectric, resulting from the magnetoelastic stress generated in the magnetic layers and transferred to the piezoelectric, can be measured in a circuit coupled to the electrodes attached to the piezoelectric layers.
• the materials and configuration of the sensor may vary depending upon the particular application. While it is generally desirable to use a magnetic material with large magnetostriction for the magnetic layer(s), it is generally more important (for optimum power delivery) that the magnetostrictive material have a large product of a magnetostrictive stress and stiffness modulus (see “Novel Sensors Based on Magnetostrictive/Piezoelectric Lamination,” J. K. Huang, D. Bono and R. C. O'Handley, Sensors and Actuators 2006). This insures that the magnetic layer(s) more effectively transfer stress to the piezoelectric material.
• FeCo(Hyperco) shows a relatively large magnetostriction (approaching 100 ppm) and is extremely stiff, the product of these parameters translates to a magnetostrictive stress of 1.2 MPa.
• a high-magnetostriction material such as Fe 2 (Dy 2 /3Tbi/ 3 ) (known as Terfenol-D) on the other hand, is mechanically softer than FeCo but shows a much larger magnetostrictive strain and its magnetostrictive stress approaches 6 MPa.
• the magnetostrictive stress changes by the largest possible amount under the influence of the changing field strength available at the sensor.
• the magnetization vector of FeCo can be rotated in a field of a few tens of Oe (Oersteds) while the magnetization vector of Terfenol-D can be rotated in a field of several hundreds of Oe, provided in each case they are properly annealed and the aspect ratio of the material in the magnetizing direction is favorable.
• the class of magnetostrictive materials that can be magnetized in the weakest fields consist of a variety of amorphous alloys based on iron (Fe) (optionally in combination with nickel (Ni)) and with glass formers such as boron (B) (optionally with silicon (Si)).
• Electro-active materials such as the commercially available piezoelectric lead-zirconate-titanates (PZT) have stress-voltage coefficients, gi 3 and g 33 , with values approximately equal to 10 and 24 mV/(Pa-m), respectively.
• a stress applied to the piezoelectric parallel to the direction across which the voltage is measured is more effective in generating a voltage than a stress transverse to this direction (out of the plane in which the vector is rotated by the field).
• relaxor ferroelectrics have g, j values that can be three to four times those of piezoelectrics. Also useful in these applications are piezo fibers or manufactured piezo fiber composites.
• the piezoelectric material(s) may be advantageous in some applications.
• flux concentrators e.g., fan-shaped soft magnetic layers placed in series with the sensing element in the presence of the field.
• the sensor output can be adapted for immediate use or storage by coupling the sensor to an electronic circuit.
• One such circuit 70 is shown in Fig. 6.
• a PME energy harvester Y1 is shown on the left hand side.
• a diode bridge D1 is disposed in parallel across the harvester output.
• the full wave diode bridge converts the AC electric charge on the harvester to a DC charge.
• an energy storage capacitor C1 which stores the harvested energy as a voltage across it.
• Parallel to the capacitor is a limiter zener diode D2 which prevents overcharging of the capacitor C1 beyond its breakdown voltage.
• a voltage regulator U1 Next provided in parallel to the capacitor and diode bridge is a voltage regulator U1.
• the voltage regulating circuit reduces the capacitor voltage to a useful level for a load.
• the voltage regulated output across J1 is applied to the load, here represented as a load impedance Z1, which typically includes resistive and capacitive elements, and which uses the harvested energy to do useful work.
• Fig. 7 is a comparison of the PME output voltage signal (RMS voltage in millivolts) versus magnetic field strength (H in telsa).
• the changing external magnetic field is at a low frequency of 20 Hz.
• the PME voltage output linearly increases from 0 to 650 millivolts with increasing magnetic field strength from 0 to 2 Oe.
• the magnetic field can be static and the position of the PME varying.
• the substantially linear relationship between the PME voltage output and magnetic filed strength is representative for low frequency applications (where the field changes or the sensor motions are at low vibration frequencies or power transmission frequencies).
• a higher frequency external field can be used to obtain a greater level of power from the PME (compared to the low frequency operation of Fig. 7). This is illustrated with the embodiment and resulting power output shown in Figs. 8-9.
• Fig. 8a illustrates a means of delivering power inside a living organism (or any inaccessible or difficult to access location) without requiring the use of electrical wiring between the source of the power and the target device and without requiring (or with diminished need for) batteries.
• Fig. 8a shows an external loop antenna 80 generating an alternating magnetic field outside of the body. The magnetic field 84 generated by this loop antenna is transmitted through the skin and other tissue 82 to an embedded PME sensor 86 producing a resulting output voltage V.
• the power transmission here is achieved not by a high frequency microwave, RF or other electromagnetic wave, but rather by means of a relatively low frequency, benign, alternating magnetic field.
• Microwaves and other electromagnetic waves having a wavelength comparable to or less than the distance between the source and receiver are rapidly attenuated by water or metals, and thus would not be suitable in this application.
• the loop antenna produces a low-frequency, magnetic-rich waves which are left essentially unattenuated by tissue (assuming no intervening magnetic material), and which do not have problems with tissue heating that accompanies microwaves.
• the external source could be a core-filled coil antenna such as a solenoid coil with core 90 (Fig.
• the field generated by a loop, solenoid or core-filled coil antenna is richer in magnetic field strength than electric field strength within a range comparable to the wavelength of the radiation.
• ⁇ the speed of light in the medium
• f the frequency of the radiation.
• the implanted passive magnetostrictive/electroactive (PME) sensor/transducer 86 receives and converts the AC magnetic field 84 to an AC voltage that can be processed to produce power needed for a particular application.
• this apparatus can be used in powering internal pumps, sensors, valves and transponders in human and animals. More generally, it can be used to power devices which monitor health, organ function or medication needs, and for performing active functions such as pumping, valving, stimulation of cell growth or accelerated drug or radiation treatment locally.
• the described means of delivering power inside a living organism can be achieved without the use of electrical wires in between the source of the power and the target device and without the need, or diminished need, for batteries.
• the wireless power harvested for the remote application can be optimized, for example, if resonance is achieved at each stage of transduction.
• the external power source and the transmit antenna should be in resonance.
• the PME device should also be in resonance with the field it responds to, and the PME device should also be in resonance with the part of the circuit that receives the signal from the PME device. By careful design and material selection, it is possible for all three resonances to closely coincide.
• Fig. 9 illustrates one example of a PME power output (mW/cm 3 ) versus load (ohm) for one such resonant system operating at a frequency of 29 kHz and a field of one (1) Oe.
• the remote sensor can be used not only for powering internal pumps, sensors and transponders in humans and animals, but can be used to monitor the flow of things (people or inanimate objects) past gates (either for security or tracking purposed).
• Fig. 10 is a block schematic diagram of one embodiment of a passive magnetostrictive sensor useful in the practice of the invention.
• the sensor 400 comprises a magnetic layer 402 that is bonded to a piezoelectric layer 404 by a suitable non-conductive means, such as non-conductive epoxy glue.
• a suitable non-conductive means such as non-conductive epoxy glue.
• the magnetization vector 415 (M) of the magnetic material 402 rotates in the plane 416 of the magnetic layer 402 when an external magnetic field (H) is applied as shown by the arrow 414.
• the rotation of the magnetization vector M causes a stress in the magnetostrictive layer 402 which is, in turn, applied to the piezoelectric layer 404 to which the magnetic layer 402 is bonded.
• the direction of magnetization, M rotates in the preferred plane of magnetization, changing direction from being parallel to perpendicular (or vice versa) to a line joining the electrodes. This maximizes the stress change transferred to the electroactive element.
• the stress-induced voltage in the piezoelectric material 404 is measured across a pair of electrodes 406 and 407 of which only electrode 406 is shown in Fig. 10.
• the magnitude of the voltage developed across electrodes 406 and 407 is a function of the magnetic field strength for H ⁇ H a , the anisotropy field (at which M is parallel to the applied field) and can be utilized to power a device 410 that is connected to electrodes 406 and 407 by conductors 412 and 408, respectively.
• the sensor is constructed so that stress-induced voltage is measured in a direction that is parallel to the plane 416 in which the magnetization rotates.
• the stress is generated in the magnetic material 402, which responds to an external magnetic field 414 (H) with a magnetoelastic stress, ⁇ mag , that has a value in the approximate range of 10 to 60 MPa. Because the magnetic material 402 is bonded to a piezoelectric layer 404, the layer 404 responds to the magnetostrictive stress with a voltage proportional to the stress, ⁇ mag , transmitted to it. Piezoelectric materials respond to a stress with a voltage, V, that is a function of the applied stress, a voltage-stress constant, g, j , and the distance, / between the electrodes. In particular,
• ⁇ mag is the change in magnetic stress that is generated in the magnetic material by the field-induced change in its magnetization direction. A fraction,/ of this stress is transferred to the electroactive element. SV is the resulting stress- induced change in voltage across the electrodes on the electroactive element.
• the stress generated by the magnetic material 402 depends on the extent of rotation of its magnetization, a 90 degree rotation producing the full magnetoelastic stress.
• the extent of the rotation depends of the angle between the magnetization vector 415 and the applied magnetic field direction 414 and also depends on the strength of the magnetic field and on the strength of the magnetic anisotropy (magnetocrystalline, shape and stress-induced) in the magnetic layer.
• the fraction,/ of the magnetostrictive stress, ⁇ mag , transferred from magnetic to the piezoelectric layer depends on the (stiffness x thickness) product of the magnetic material, the effective mechanical impedance of the bond between the magnetic and electric elements (proportional to its stiffness/thickness), and the inverse of the (stiffness x thickness) of the piezoelectric layer.
• J Jos- m/A
• the characteristics of a suitable magnetostrictive material are preferably large internal magnetic stress change as the magnetization direction is changed. This stress is governed by the magnetoelastic coupling coefficient, B 1 , which, in an unconstrained sample, produces the magnetostrictive strain or magnetostriction, ⁇ , proportional to Bi and inversely proportional to the elastic modulus of the material. It is also important that the magnetization direction of the magnetic material can be rotated by a magnetic field of magnitude comparable to the applied field. In general, the magnetic material should also be mechanically robust, relatively stable (not prone to corrosion or decomposition), and receptive to adhesives.
• the magnetic material is electrically non-conducting, it can be bonded to the electroactive element with the thinnest non-conducting adhesive layer that provides the needed strength without danger of shorting out the stress- induced voltage developed across the electroactive element.
• the magnetostrictive layers not short out the voltage between the measuring electrodes. This can be accomplished by using a non-conducting adhesive to insulate the magneostrictive layer(s) from the electroactive element(s).
• Many known magnetostrictive materials can be used for the magnetic layer 402.
• amorphous-FeBSi or Fe- Co-B-Si alloys include various magnetic alloys, such as amorphous-FeBSi or Fe- Co-B-Si alloys, as well as polycrystalline nickel, iron-nickel alloys, or iron-cobalt alloys such as Fe 5 OCo 50 (Hyperco).
• Iron-nickel alloys with Ni between 40 and 70 at% with a preferred composition near 50% Ni can be used.
• iron- cobalt alloys with Co between 30 and 80% and a preferred composition near 55% Co (such as Fe 5 oCo 50 .) are also suitable.
• Terfenol-D ® (Tb x Dyi -X Fe y ), an alloy of rare earth elements Dysprosium and Terbium with the transition metal iron, manufactured by ETREMA Products, Inc., 2500 N. Loop Drive, Ames, Iowa 50010, among others.
• Terfenol-D ® can generate a maximum stress on the order of 60 MPa for a 90-degree rotation of its magnetization. Such a rotation can be accomplished by an external applied magnetic field on the order of 400 to 1000 Oersteds (Oe).
• highly magnetostrictive alloys such as Galfenol ® , Fei -x Ga x .
• Softer magnetic materials such as certain Fe-rich amorphous alloys mentioned above, may achieve full rotation of magnetization in fields of order 10 Oe, making them suitable for the magnetic layer in a sensor for sensing weaker fields.
• nanocrystalline magnetic materials it is possible to use certain so-called nanocrystalline magnetic materials. In these polycrystalline materials, it is generally that case that the magnetization can be rotated as easily as it can be in amorphous materials. But nanocrystalline materials can sometimes be engineered to have larger magnetoelastic coupling coefficients than amorphous materials.
• a suitable electroactive layer for the sensor devices are primarily that they have a large stress-voltage coupling coefficient, g 33 .
• they preferably should be mechanically robust, receptive to adhesives, not degrade the metallic electrodes that must be placed on them (this is most often easily achieved when the electrodes are made of noble metals, such as silver or gold).
• the electroactive material is chosen on the basis of having a value of g ti greater than 10 mV/(Pa-m).
• the electroactive layer can be a ceramic piezoelectric material such as lead zirconate titanate Pb(Zr x Tii -x ) ⁇ 3 , or variations thereof, aluminum nitride (AIN) or simply quartz, SiO x . In some applications a single crystal (as opposed to a ceramic or polycrystalline) piezoelectric material may be advantageous. Alternatively, a polymeric piezoelectric material such as polyvinylidene difluoride (PVDF) would be suitable for applications where the stress transferred from the magnetostrictive material is relatively weak. The softness of the polymer will allow it to be strained significantly under weaker applied stress to produce a useful polarization, or voltage across its electrodes.
• PVDF polyvinylidene difluoride
• electroactive material such as an electrostrictive material (for example, (Bio 5 Nao 5 )i- ⁇ Ba ⁇ ZryTii -y ⁇ 3 ) or a relaxor ferroelectric material (for example, Pb(Mgi/ 3 Nb2/3)3).
• electrostrictive material for example, (Bio 5 Nao 5 )i- ⁇ Ba ⁇ ZryTii -y ⁇ 3
• relaxor ferroelectric material for example, Pb(Mgi/ 3 Nb2/3)3
• Piezoelectric materials typically have g 33 ⁇ 4 x g 31 and g 33 « 20 to 30 mV/(Pa-m) which is about 10 x d 3 i.
• Model predictions and experimental results shown in Table 1 compares the parameters g y , in mV/m-Pa, the electrode spacing / in meters, the maximum stress per unit field (Bi/ ⁇ 0 H a ) in Pa/T, and calculated field sensitivity in nV/nT and the observed field sensitivity, dV/dB.
• the values tabulated for a g 33 device using a relaxor ferroelectric are based on the data observed with a piezoelectric based sensor and using a ratio of g 33 for typical relaxors/piezoelectrics.
• Piezo/magnetic sensors 9u £ stress CaIc. Obs. d 3 i sensor 11 10 "3 10 8 10 4 280 d 3 i sensor 11 10 "3 10 8 10 4
• Relaxor/magnetic sensors d 33 relaxor/mag sensor 60 10 -2 10 s 10 6 (10 5 )
• Bi is the magneoelastic coupling coefficient, a material constant that generates the magnetic stress in the magnetostrictive material, ⁇ m , which was used in earlier equations.
• Chronic pain is usually a multidimensional phenomenon involving complex physiological and emotional interactions.
• CRPS complex regional pain syndrome
• RSD reflex sympathetic dystrophy
• the pain is considered “complex regional” since it is located in one region of the body (such as an arm or leg), yet can spread to additional areas.
• CRPS typically affects the sympathetic nervous system, which in turn affects all tissue levels (skin, bone, etc.), many symptoms may occur. Pain is the main symptom. Other symptoms vary, but can include loss of function, temperature changes, swelling, sensitivity to touch, and skin changes.
• FBSS chronic pain, failed back surgery syndrome
• Arachnoiditis a disease that occurs when the membrane in direct contact with the spinal fluid becomes inflamed, causes chronic pain by pressing on the nerves. It is unclear what causes this condition.
• Chronic pain may occur in any area of the body. For many sufferers, no cause is ever found. Thus, many types of chronic pain are treated symptomatically. For instance, many people suffer from chronic headaches/migraine and/or facial pain. As with other types of chronic pain, if the underlying cause is found, the cause may or may not be treatable. Alternatively, treatment may be only to relieve the pain.
• Chronic pain though the primary indication for neurostimulation, is not the only disease entity in the human body that can benefit from neuromodulation.
• Treatment of acute stroke, sleep apnea, cancer, migraines, bone and joint disease and various types of primary brain disorders such as depression, epilepsy and mood disorders would benefit greatly from neuromodulation. These therapeutic areas are currently being researched heavily.
• TENS transcutaneous electrical nerve stimulation
• Implantable, chronic stimulation devices are available, but these currently require a significant surgical procedure for implantation.
• Surgically implanted stimulators such as spinal cord stimulators, have been described in the art. These spinal cord stimulators have different forms, but are usually comprised of an implantable control module to which is connected a series of leads that must be routed to nerve bundles in the spinal cord, to nerve roots and/or spinal nerves emanating from the spinal cord, or to peripheral nerves.
• the implantable devices are relatively large and expensive. In addition, they require significant surgical procedures for placement of electrodes, leads, and processing units. These devices may also require an external apparatus that needs to be strapped or otherwise affixed to the skin.
• Drawbacks such as size (of internal and/or external components), discomfort, inconvenience, complex surgical procedures, and/or only acute or intermittent use has generally confined their use to patients with severe symptoms and the capacity to finance the surgery.
• Spinal cord stimulation (also called dorsal column stimulation) is best suited for back and lower extremity pain related to adhesive arachnoiditis, FBSS, causalgia, phantom limb and stump pain, and ischemic pain.
• Spinal cord stimulation is thought to relieve pain through the gate control theory described above.
• FBSS adhesive arachnoiditis
• phantom limb and stump pain and ischemic pain.
• Spinal cord stimulation is thought to relieve pain through the gate control theory described above.
• applying a direct physical or electrical stimulus to the larger diameter nerve fibers of the spinal cord should, in effect, block pain signals from traveling to the patient's brain.
• Shealy and coworkers first utilized this concept, proposing to place stimulating electrodes over the dorsal columns of the spinal cord. (See Shealy C. N., Mortimer J. T., Reswick, J. B., "Electrical Inhibition of Pain by Stimulation of the Dorsal Column", in Anesthesia and Analgesi
• the gate control theory has always been controversial, as there are certain conditions such as hyperalgesia, which it does not fully explain.
• the relief of pain by electrical stimulation of a peripheral nerve, or even of the spinal cord may be due to a frequency-related conduction block which acts on primary afferent branch points where dorsal column fibers and dorsal horn collaterals diverge.
• Spinal cord stimulation patients tend to show a preference for a minimum pulse repetition rate of 25 Hz.
• Stimulation may also involve direct inhibition of an abnormally firing or damaged nerve.
• a damaged nerve may be sensitive to slight mechanical stimuli (motion) and/or noradrenaline (a chemical utilized by the sympathetic nervous system), which in turn results in abnormal firing of the nerve's pain fibers. It is theorized that stimulation relieves this pain by directly inhibiting the electrical firing occurring at the damaged nerve ends.
• Stimulation is also thought to control pain by triggering the release of endorphins.
• Endorphins are considered to be the body's own pain-killing chemicals. By binding to opioid receptors in the brain, endorphins have a potent analgesic effect.
• the heart of the implanted power source is a high-sensitivity, passive magnetostrictive/electro-active magnetic field sensor, e.g. a Ferro Solution g ⁇ mode (PME-33) magnetic sensor depicted schematically in Fig. 12.
• Other magnetostrictive/electroactive devices e.g. gz ⁇ devices, could also work with this system.
• This magnetic field sensor converts magnetic field variations seen by the magnetic layer(s) to a magnetostrictive stress, ⁇ , some of which is transmitted to the electro-active element to which it is bonded.
• the stressed electro- active element develops a voltage across its electrodes.
• the coupling coefficient g ⁇ can have values ranging from about 0.015 V/m-Pa for ceramic PZT, to 0.1 V/m-Pa for single- crystal electro-active materials.
• g 33 is 3 or 4 times greater than g ⁇ used in all other reported, prior-art PME sensors. Magnetostrictive stresses can be as large as 60 MPa [for Terfenol-D, Fe 2 (Tb 1 Dy)].
• the PME-33 sensors have a theoretical limiting magneto-electric sensitivity of order 6 x 10 7 V/(m-T), much greater than that of a similar g 3 i device.
• prototype PME-33 devices similar to that shown in Figs. 12 and 13 linear response of 5 V/Oe has been measured and fields as small as 2 ⁇ T (20 mOe) have already been measured. It is possible to significantly enhance the sensitivity of this device by applying an AC bias to the magnetic layer(s).
• a magneto-electric sensitivity or quality factor, Q me can be defined for PME sensors.
• the magnetic field that drives this sensor (and thus makes it function as a remote energy harvester and/or voltage generator) is provided by an external power source that is connected to a small, flat-profile coil antenna.
• a small, flat-profile coil antenna Such an antenna generates a near field that is mainly magnetic in character.
• the PME sensor is essentially a capacitor that has a value of C typically in the range of 0.1 - 10 nF.
• the power stored on the capacitor under the action of a magnetic field alternating at the resonance frequency of the PME sensor typically 10 - 30 kH for cm-scale devices
• the power that can be drawn from the PME-33 estimated to be hundreds of mW based on the efficiency of these devices, can be used immediately or stored in a small implanted battery.
• the coil, the AC circuit powering it, the configuration of the PME-33 receiver and its power-conditioning circuit can each be modified to optimally meet the implant power needs.
• a very short pulse of high voltage at low current is needed.
• more current should be provided by the external power source and the coil should contain more turns of low-resistance wire to increase the field generated.
• the PME or PME like device either singular or multiple, would be placed adjacent to the therapeutic bed whether nerve, tissue, or solid organ. These pellets are charged with power transfer from an external coil. The pellets can assume varying charge either in a singular or plural form.
• Each PME can be an anode or a cathode (positive or negative) and each pellet can change its state by external signal from anode to cathode or vice versa.
• the PME can function as a sensor, therefore the movement of electrical power between the PME pellets can be determined as a function of time. This can allow for selective delivery of electricity to involved muscle groups while sparing body areas not involved in therapy providing a greater degree of therapeutic benefit.

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