Energy harvesting and sensing device

Abstract

An energy harvesting sensor device comprising at least one elastically deformable membrane having a suspended portion and a peripheral anchoring portion, a magnetic assembly attached to the suspended portion of the at least one membrane, the magnetic assembly configured to undergo reciprocal motion in response to an externally applied force, at least one coil arrangement positioned proximate to the magnetic assembly and configured to generate electrical current in response to the reciprocal motion of the magnetic assembly, a stopper mechanism configured to limit displacement of the at least one membrane, and circuitry electrically connected to the at least one coil arrangement and configured to store electrical energy generated by the at least one coil arrangement and generate data / signals indicative of the reciprocal motion of the magnetic assembly.

Description

[0001] ENERGY HARVESTING AND SENSING DEVICE

[0002] TECHNOLOGICAL FIELD

[0003] The present invention is generally in the field of motion / vibration detection and particularly relates to self-powered vibrations detection and monitoring.

[0004] BACKGROUND ART

[0005] References considered to be relevant as background to the presently disclosed subject matter are listed below:

[0006] [1] R. N. Dean, Jr., A. Luque, “Applications of Microelectromechanical Systems in Industrial Processes and Services,” IEEE Transact, on Industrial Electronics, vol. 56, no. 4, pp. 913, April 2009.

[0007] [2] Correa, J.C.A.J.; Guzman, A.A.L. Mechanical Vibrations and Condition Monitoring; Academic Press: Cambridge, MA, USA, 2020.

[0008] [3] T. D. Popescu, D. Aiordachioaie, A. Culea-Florescu, “Basic Tools for Vibration Analysis with Applications to Predictive Maintenance of Rotating Machines: An Overview,” The Int. J. of Advanced Manufacturing Technology, vol. 118, pp. 2883-2899, 2022.

[0009] [4] M. Romanssini, P. C. C. de Aguirre, L. Compassi-Severo, A. G. Girardi, “A Review on Vibration Monitoring Techniques for Predictive Maintenance of Rotating Machinery,”

[0010] [5] L. Hou, and N. W. Bergmann, “Novel Industrial Wireless Sensor Networks for Machine Condition Monitoring and Fault Diagnosis,” IEEE Transact, on Instrumentation and Measurement, vol. 61, no. 10, pp. 2787-2798, October 2012

[0011] [6] S. Gao, X. Zhang, C. Du, Q. Ji, “A Multichannel Low-Power Wide-Area Network With High- Accuracy Synchronization Ability for Machine Vibration Monitoring,” IEEE Internet of Things Journal, vol. 6, no. 3, pp. 5040-5047, June 2019.

[0012] [7] H. Toshiyoshi, S. Jub, H. Honma, C-H. Ji, H. Fujita, “MEMS vibrational energy harvesters,” Science and Technology of Advanced Materials, vol. 20, no. 1, pp. 124-143, November 2019.

[0013] [8] C. Shearwood, R.B. Yates, “Development of an Electromagnetic Micro-Generator,” Electron. Lett., vol. 33, pap. 1883, 1997.

[0014] [9] Y.S. Tan, Y. Dong, X.H. Wang, “Review of MEMS Electromagnetic Vibration Energy Harvester,” Journal of Microelectromechanical Systems, vol. 26, no. 1, pp. 1-16, February 2017. BACKGROUND

[0015] This section intends to provide background information concerning the present application, which is not necessarily prior art.

[0016] In various systems, ranging from consumer products to industrial and aerospace applications, edge sensing, connectivity, and computing enable rapid response from critical process points. These operations demand power, but current solutions are often too bulky or limited for integration at these edges. Hence, there's a need for compact, efficient energyharvesting solutions. Some environments require robust designs to withstand extreme conditions like temperature variations, harmful chemicals, high pressure, and vibrations. An ideal solution may not only survive these challenges, but also harnesses them to efficiently harvest energy with a minimal footprint, addressing edge sensing limitations. This includes integrating multi-sensing capabilities into a single device, achieving high performance at low power, and ensuring cost-effective manufacturing.

[0017] Wireless / remote devices are typically powered by batteries, which may be replaceable and / or chargeable, and yet suffer many disadvantages, inter alia, relatively high costs, limited lifespan, limited power supply, energy / power-to-size / weight tradeoff, environmental pollution if improperly handled. Alternative power sources, such as solar and wind energy harvesting means depend on various environmental conditions and geographical constraints, and thus cannot guarantee continuous power supply. In applications involving continuous vibratory motion, vibration energy can be converted into electric power by magnet-coil harvesting arrangements, which typically can guarantee long lifespan, high power density, and geometrical dimensions suitable for replacing traditional batteries.

[0018] Some vibration energy harvesting solutions known from the patent literature are briefly discussed hereinbelow.

[0019] Chinese Patent Publication No. 105242623 discloses a vibration type self-energy- supply ground monitor system, comprising N nodes, M branch base stations, a main base station and a computer. The node comprises a vibration type electromagnetic energy collection device, an energy storage member, a detection module, a microcontroller, a transceiver and an antenna. The vibration type electromagnetic energy collection device collects vibration energy and vibration signals and transmits the vibration energy to the energy storage member; the energy storage member supplies power to the micro controller and the transceiver; the vibration type electromagnetic energy collection device transmits the vibration signal to the detection module; the detection module determines the strength and the type of the current vibration signal; if the current vibration signal achieves the detection intensity, the micro controller controls the transceiver to transmit an invasion signal through the antenna; the branch base station receives the invasion signal transmitted from the corresponding node and transmits the invasion signal to a main base station; and the main base station transmits the signal to the computer for processing.

[0020] Chinese Patent Publication No. 102497133 discloses an electromagnetic vibration generating device of a permanent magnet and application thereof in a vibration detection system, and relates to a device for recycling energy from mechanical vibration to realize energy utilization. The electromagnetic vibration generating device of the permanent magnet is composed of two outer cylinder end covers, a columnar hollow shaft, an inner side coil, a columnar inner cylinder, two fixed annular permanent magnets, a moving annular permanent magnet, a columnar outer cylinder and an outer side coil.

[0021] US Patent Publication No. 2011227545 suggests vibration power generator for electricity generation by a vibration power generator, a rectifier circuit bridge, an output controlling circuit, a load detecting circuit, a frequency detecting circuit for detecting a frequency of the vibration power generator and then controlling an impedance of an output controlling circuit depending on the frequency.

[0022] German Patent Publication No. 102014112604 discloses an energy recovery device for recovering energy from exhaust gas, with a membrane which can be attached to an opening of an exhaust system and can be made to oscillate by the exhaust gas flowing through the exhaust system, the membrane having a pickup of a magnet coil device is connected so that an electric current is induced in the magnet-coil device.

[0023] GENERAL DESCRIPTION

[0024] Self-powered motion detection techniques are disclosed that can be used for detection and / or monitoring (e.g., vibratory / oscillatory / rotatory) motion of objects (or body organs). Such self-powered detection means can be used in plethora of different applications requiring (e.g., vibratory / oscillatory / rotatory) motion detection, such as, but not limited to, monitoring of machinery during its operation (e.g., power hammers / drillers, disk cutters, borehole drillers), monitoring infrastructures exposed to repeated vibratory motion (e.g., bridges, production lines, floating / fixed wave breakers, wind blades, scaffolding, or suchlike), tremors monitoring applications such as required for monitoring Parkinson's disease patients (e.g., as a wearable, attachable or implantable device). Such self-powered detection means can be configured to implement tamper-proof (e.g., vibrations) monitoring devices accessible by authorized personals for obtaining motion events information recorded therein.

[0025] In a broad aspect the present disclosure is directed to motion energy harvesting techniques and implementations utilizing one or more membranes suspended by at least some peripheral / circumferential portion thereof to one or more support members (e.g., forming an elastically deformable / deflectable surface) and having a magnetic assembly attached to the one or more membranes and serving as a mass-load for causing / inducing reciprocal motion of the magnet assembly and membrane arrangement in response to externally applied forces. One or more coils mounted above and / or below the one or more membranes can be used to generate electrical current due to movement of the membranes and the magnetic assembly attached thereto.

[0026] The motion energy harvesting techniques / implementations disclosed herein can be effectively used to implement various self-powered motion detection applications, such as required in embodiments of the present application. The motion energy harvested and sensed in implementations of embodiments hereof can be due to any type of movement thereby experienced, such as, but not limited to, rotary motion, vibratory motion, oscillatory motion, or due to any other periodic or intermittent motion or external force.

[0027] Optionally, but is some applications preferably, at least one of the membranes has a substantially ring / annular anchoring rim configured for attachment to one or more support members and forming a substantially circular suspended and deformable / deflectable membrane portion to which the magnet assembly is attached for inducing / affecting the reciprocal motion.

[0028] In some implementations one or more stopper elements are fixedly coupled in proximity to the one or more membranes to at least partially limit / restrain the motion of the membranes and magnet assembly attached thereto in response to the externally applied forces. In some applications, one or more stoppers are configured to increase the out-of-plane stiffness of the at least one of the membranes (for example and without limiting, by up to 100 times) after coming into contact with the stoppers. The one or more stoppers are configured in some applications to surround some portion of the suspended one or more membranes carrying the magnetic assembly, so as to guarantee that the magnet assembly does not contact the one or more stopper elements while the one or more membranes and the magnet assembly attached thereto are in motion e.g., due to the externally applied forces.

[0029] Alternatively, or additionally, stiffness of the one or more membranes is increased by an air film layer defined within a closed housing in which the one or more membranes are mounted. In some embodiments the stiffness of the membrane(s) is increased by air / gas confined within one or more cavities formed in the housing / device e.g., between upper and bottom membranes and corresponding coils e.g., PCB (z.e., coil(s) printed on a printed circuit board) coils. This way, the air / gas within the volume of the one or more cavities acts as a stiffener as it is become compresses due to the membrane(s) motion.

[0030] In yet other possible implementations, the one or more stopper elements are configured to define a peripheral membrane band portion surrounding the magnet assembly that does not contact the one or more stopper elements. This configuration can guarantee continuous (e.g., oscillatory) and restrained motion of the magnet assembly and membrane(s) in relatively high angular frequencies with relatively high displacement amplitudes, in response to the externally applied forces. In some applications the magnet assembly has a substantially rectangular / square geometry. The one or more stopper elements can be accordingly configured to define a corresponding substantially rectangular / square peripheral membrane band portion that surrounds the magnet assembly and does not contact the one or more stopper elements during the reciprocal motion of the magnet assembly.

[0031] In one aspect there is provided an energy harvesting sensor device (also referred to herein as motion detection device) comprising at least one elastically deformable membrane having a suspended portion and a peripheral anchoring portion, a magnetic assembly attached to the suspended portion of the at least one membrane, at least one coil arrangement positioned proximate to the magnetic assembly and configured to generate electrical current in response to the reciprocal motion of the magnetic assembly, a stopper mechanism configured to limit displacement of the at least one membrane, and circuitry electrically connected to the at least one coil arrangement and configured to store electrical energy generated by the at least one coil arrangement and generate data / signals indicative of the reciprocal motion of the magnetic assembly. The magnetic assembly can be configured to undergo reciprocal motion in response to an externally applied force. The stopper mechanism can be configured to increase an effective stiffness of the membrane upon contact therewith.

[0032] The stopper mechanism comprises in some embodiments one or more stopper elements configured to define a non-contact zone surrounding the magnetic assembly, such that a peripheral membrane band portion surrounding the magnetic assembly does not contact the at least one stopper element during the reciprocal motion. The stopper mechanism may comprise a frame-shaped element having an opening larger than the magnetic assembly. Alternatively, or additionally, the stopper mechanism comprises an air film layer obtained within one or more cavities formed in the device. Optionally, the air film layer is implemented by confining air (or any other gas or a liquid) within cavities defined between at least one membrane and a corresponding coil (or array of coils).

[0033] The device may comprise two or more membranes. Magnet elements of the magnet assembly can be positioned above, below, or between the one or more membranes. Optionally, the at least one stopper element comprises a top stopper element positioned above the membrane and / or a bottom stopper element positioned below the membrane. The top and / or bottom stopper elements can be aligned to sandwich the membrane therebetween with predefined gaps. The predefined gaps can be set to suitable values depending on design specifications . The effective stiffness of the membrane can be increased through contact with at least one stopper element, with the degree of increase determined by the specific technical requirements. The device may comprise air-filled cavities between the at least one membrane and the at least one coil arrangement. Air confined within the cavities may provide additional nonlinear stiffness during operation.

[0034] In some embodiments the magnetic assembly comprises a two-dimensional array of magnetic elements arranged in an alternating polarity pattern. The alternating polarity pattern can form a checkerboard pattern.

[0035] The at least one coil arrangement may comprise a first array of coils positioned above the magnetic assembly and / or a second array of coils positioned below the magnetic assembly. Each array of coils may comprise multiple coil cells. Each coil cell can be aligned with a corresponding magnetic element of the magnetic assembly. Each array of coils can be a multilayered array of coils.

[0036] The at least one membrane comprises in some embodiments two or more membranes having the magnetic assembly attached thereto so as to prevent tilting of the magnetic assembly during reciprocal motion. The membranes can be spaced apart by appropriately selected gaps depending on the specific application needs.

[0037] The circuitry comprises in possible embodiments: an energy storage unit configured to store the electrical energy, a counter unit configured to count motion events, and a memory unit configured to record motion event data. The circuitry can comprise a wireless communication unit configured to transmit the recorded motion event data to an external device. The wireless communication unit comprises in possible embodiments a near-field communication (NFC) interface configured to be powered by electromagnetic signals from the external device. The circuitry comprises in some embodiments a rectifier circuit configured to convert AC current from the at least one coil arrangement to DC current. Optionally, a voltage threshold detection circuit is used to enable recording of motion events when stored voltage exceeds a predetermined threshold.

[0038] In some applications the peripheral anchoring portion of the membrane may be circular, with a diameter determined based on design or functional needs. The membrane may comprise at least one layer of polymeric material selected from polyethylene terephthalate (PET), polycarbonate (PC), polyimide (PI), or polyamide. In some embodiments a thickness of the membrane can be tailored to match the frequency range required for efficient energy harvesting.

[0039] The magnetic assembly and / or membrane arrangement can be configured to exhibit nonlinear stiffness characteristics enabling broadband frequency response. The nonlinear stiffness characteristics may result from mechanical contact between the membrane and the at least one stopper element and / or compression of air in cavities adjacent to the membrane.

[0040] In yest another aspect there is provided a vibration monitoring system comprising the energy harvesting sensor device of any of the embodiments disclosed herein and a reader device configured to receive from the circuitry of the device the generate data / signals thereby generated. The system can be configured to analyse the data / signals generated the circuitry of the device and register a motion event whenever the data / signals are indicative of a predefined motion pattern.

[0041] In yet another aspect there is provided a self-powered vibration sensor comprising: a housing having top and bottom support elements; a membrane suspension system comprising at least one circular membrane clamped at its periphery between membrane support frames; a checkerboard-magnetized permanent magnet assembly attached to a central region of the membrane suspension system; top and bottom arrays of planar coils fixedly mounted to the respective top and bottom support elements and positioned proximate to the magnet assembly; top and / or bottom stopper mechanism configured to limit out-of-plane displacement of the membrane suspension system; an energy harvesting circuit connected to the coil arrays and configured to convert induced electrical current to stored electrical energy; and a motion event recording circuit powered by the stored electrical energy and configured to count and store vibration events.

[0042] The top and / or bottom stopper mechanism comprises in possible embodiments movement limiting elements configured to maintain a non-contact operational zone of at least one of the membranes defined around the magnet assembly. The membrane can be comprised of three parallel membranes separated by spacers, with the magnet assembly positioned between and attached to the membranes to prevent tilting during vibration. In yet another aspect there is provided an energy harvesting device for vibration monitoring comprising: a membrane for elastic deformation; a rectangular magnetic assembly attached to a central portion of the membrane; a frame-shaped stopper element surrounding the magnetic assembly with a clearance zone, wherein the stopper element is positioned at a defined distance above or below the membrane surface, and wherein contact between the membrane and the stopper element creates a nonlinear stiffness response enabling broadband vibration energy harvesting. The device can comprise coil arrays positioned above and below the magnetic assembly, wherein the coil arrays comprise serially connected planar spiral coils aligned with magnetic pole regions of the magnetic assembly.

[0043] In yet another aspect, there is provided a method of manufacturing a self-powered motion detection device, the method comprising: anchoring a peripheral portion of one or more elastically deformable membranes to a stationary support so as to define a suspended portion of the one or more elastically deformable membranes; attaching a magnetic assembly to the suspended portion of the one or more membranes; defining a stopper mechanism configured to limit displacement the one or more membranes; mounting at least one coil arrangement in proximity to the magnetic assembly such that reciprocal motion of the magnetic assembly induces electrical current in the at least one coil arrangement; and electrically connecting circuitry to the at least one coil arrangement for storing electrical energy generated thereby.

[0044] The defining the stopper mechanism may comprise positioning at least one stopper element at a predetermined distance from the one or more membranes. The positioning of the at least one stopper element comprises in some embodiments forming a frame-shaped stopper element having an opening larger than the magnetic assembly and aligning the frame-shaped stopper element such that a peripheral band portion of the membrane surrounding the magnetic assembly remains free from contact with the stopper element during operation. The positioning of the at least one stopper element may comprise positioning a top and / or a bottom stopper element with a defined gap from the membrane. The defining the stopper mechanism comprises in some embodiments defining an air film layer within one or more cavities formed in the device.

[0045] The magnetic assembly can comprise a plurality of magnetic elements. Attaching the magnetic assembly comprises is some embodiments arranging the magnetic elements in a two- dimensional array with alternating magnetic polarities, and securing the array of magnetic elements to the membrane to form a checkerboard magnetization pattern.

[0046] The method can comprise preparing the membrane from a sheet of polymeric material. The method comprises in some embodiments forming the membrane from three separate membranes spaced apart by defined gaps, attaching the magnetic assembly between the membranes to prevent tilting during reciprocal motion, and clamping peripheral portions of all three membranes together. The method may comprise positioning spacers between adjacent membranes to maintain the gaps.

[0047] The method comprises in some embodiments fabricating the at least one coil as planar coils formed in / on a printed circuit board (PCB), or by any other suitable method of additive (e.g., screen printing) or subtracting manufacturing, and mounting a first PCB with said at least one coil above the magnetic assembly and / or a second PCB with said at least one coil below the magnetic assembly. The fabricating of the planar coils can comprise forming rectangular spiral coils on the PCB, forming a plurality of electrically conducting vias in the PCB, and electrically connecting multiple coils in series by the plurality of vias. Each PCB coil may comprise an array of coil cells. The method may comprise aligning each coil cell with a corresponding magnetic element of the magnetic assembly.

[0048] The method comprises in some embodiments 3D printing top and bottom cover plates from polymeric material and integrating the stopper elements as integral components thereto. The method may comprise forming air cavities between the membrane and coil arrays to provide additional nonlinear stiffness through air compression.

[0049] BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings. Features shown in the drawings are meant to be illustrative of only some embodiments of the invention, unless otherwise implicitly indicated. In the drawings like reference numerals are used to indicate corresponding parts, and in which:

[0051] Figs. 1A to 1G schematically illustrate moving magnet configurations according to some possible embodiments, wherein Fig. 1A shows a perspective view of a possible moving magnet configuration, Figs. IB and 1C show sectional views of the moving magnet configuration, Fig. ID shows a side view of a (e.g., vibratory or oscillatory) motion energy harvesting device utilizing the moving magnet configuration with fixed coils, Fig. IE is a graphical plot of a stiffness profile of the moving magnet configuration with the implemented stoppers elements 35 and Fig. IF is a graphical plot of a stiffness profile of the moving magnet configuration with incorporated additional stiffness of the air film layer confined within the cavities between the upper and the bottom membranes and the corresponding coils PCB; Fig. 1G shows the cavities 40 between the upper and bottom membranes and the corresponding coils PCB, and air film layer (or any other suitable gas) confined within these cavities 40 and which adds additional stiffness.

[0052] Figs. 2A to Fig. 2H show simulation results of the moving magnet configurations shown in Figs. 1A to ID, wherein Figs. 2A to 2C depicts results of three-dimensional (3D) simulations carried out for three different vibratory / oscillatory motion frequencies, Fig. 2D is a graphical plot of estimated displacement of the moving magnet, and Figs. 2E to 2H are graphical plots of magnet displacements obtained for various different configurations.

[0053] Figs. 3A and 3B schematically illustrate magnet configurations according to possible embodiments, wherein Fig. 3A shows an array of magnet elements and Fig. 3B depicts a single magnet element;

[0054] Figs. 4A to 4C schematically illustrate coil array arrangements according to possible embodiments, wherein Fig. 4A schematically illustrates a coil array arrangement, and Figs. 4B and 4C show top and bottom side views of the coil array arrangement;

[0055] Figs. 5A and 5B schematically illustrate magnets and coils configurations according to other possible embodiments, wherein Fig. 5A shows proximally located two-dimensional arrays of coil elements and of magnet elements and Fig. 5B shows an EMF distribution obtained utilizing the coils and magnet arrays;

[0056] Figs. 6A to 6G are graphical plots of the electromotive force (EMF) obtained by the various magnet element and coils cell of the motion energy harvesting device;

[0057] Figs. 7A to 7E schematically illustrate a (e.g., vibratory or oscillatory) motion energy harvesting device according to possible embodiments, wherein Fig. 7A shows a sectional view of the motion energy harvesting device, Fig. 7B shows an exploded view of the motion energy harvesting device, Fig. 7C shows a perspective view of the motion energy harvesting device, Fig. 7D shows a sectional perspective view of the motion energy harvesting device and Fig. 7E shows a closer perspective sectional view of the moving magnet configuration, the stoppers and coils of the motion energy harvesting device;

[0058] Fig. 8A to 8J schematically illustrate membrane configurations of the moving magnet configuration according to possible embodiments, wherein Fig. 8A and 8B show sectional views of a multilayered membrane, Fig. 8C to 8F show 3D simulation results obtained for multilayered membrane structures for various different frequencies, Fig. 8G and 8H are graphical plots of displacement measured for different membrane configurations, and Figs. 81 and 8J are graphical plots of EMF measured using a membrane configuration according to possible embodiments; Fig. 9 schematically illustrates a motion detector device according to some possible embodiments;

[0059] Figs. 10A to IOC schematically illustrate a motion energy harvesting device according to possible embodiments, wherein Fig. 10A shows a sectional view of the device implemented with three membranes and a magnetic assembly attached to the membranes (dashed lines depict the device in a deformed configuration), Fig. 10B shows a checkerboard magnetization pattern of at least one magnetic assembly of the device (arrowed lines depict the magnetic field lines), and Fig. IOC shows an exploded view of the device assembly including cover plates, spacers, membranes, magnetic assemblies, and PCB coil arrays;

[0060] Figs. 11A to 11C depict finite element (FE) modelling and simulation results of a motion energy harvesting device according to possible embodiments, wherein Fig. 11A shows a 3D finite element model of the device built using ABAQUS software showing the mesh structure and boundary conditions and Figs. 11B shows time history plots of the magnet displacement under harmonic inertial actuation and two different acceleration amplitudes of a = 19 g ( showing smaller displacement) and a =31 g ( showing larger displacement), and Fig. 11C shows corresponding time history time history plots of the output voltage over one period for both acceleration cases;

[0061] Figs. 12A and 12B show photographs of the fabricated energy harvesting device components according to possible embodiments, wherein Fig. 12A shows the assembled membrane structure with the checkerboard pattern magnets attached to the central region of the circular membrane, and Fig. 12b shows the printed circuit board (PCB) with the fabricated array of planar coils and a magnified inset image showing the detailed structure of a single rectangular spiral coils;

[0062] Fig. 13 shows a photograph of an experimental setup for testing the energy harvesting device according to possible embodiments, including the electromagnetic shaker (Bruel & Kjaer LDS), mounting fixtures, the harvesting device under test, measurement connections, and associated instrumentation for vibration control and output voltage measurement; and

[0063] Fig. 14 exemplifies operation of the energy harvesting device according to possible embodiments, wherein Fig. 14A depicts measured output voltage as a function of acceleration amplitude for harmonic excitation at different frequencies (in Hz), Fig. 14B shows measured time history of the harvester output voltage (line 1); the rectified amplified DC voltage signal provided by the charge pump circuit (line 2) and the DC voltage used to power the controller and the EEPROM memory writing (ON and OFF threshold values are 3.5 Vdc and 2.25 Vdc, respectively), Fig. 14C and 14D show possible measurement scheme, and Fig. 14E graphically illustrates electrical charging and sampling.

[0064] DETAILED DESCRIPTION OF EMBODIMENTS

[0065] One or more specific and / or alternative embodiments of the present disclosure will be described below with reference to the drawings, which are to be considered in all aspects as illustrative only and not restrictive in any manner. It shall be apparent to one skilled in the art that these embodiments may be practiced without such specific details. In an effort to provide a concise description of these embodiments, not all features or details of an actual implementation are described at length in the specification. Elements illustrated in the drawings are not necessarily to scale, or in correct proportional relationships, which are not critical. Emphasis instead being placed upon clearly illustrating the principles of the invention such that persons skilled in the art will be able to make and use the motion detection / energy harvesting scheme, once they understand the principles of the subject matter disclosed herein. The disclosed subject matter may be provided in other specific forms and embodiments without departing from the essential characteristics described herein.

[0066] The present application provides techniques for converting motion into electric energy, and / or for recording, monitoring and / or reporting, (e.g. , vibratory or oscillatory) motion events. For this purpose, a small sized energy harvesting device has been designed for incorporation in machinery, tools, equipment or infrastructures, or any other object / article (e.g., as a detachable or wearable or implantable device), that generates or experience (e.g., vibratory or oscillatory) motion during operation and / or use thereof. The energy harvesting device is configured in some embodiments for powering one or more circuitries coupled or embedded therewith for providing one or more functions, including, inter alia, electrical power storage, electrical power supply of the stored electrical power to other circuities e.g., vibratory / oscillatory motion counting and / or recording circuitries, and / or data / signal communication with external devices. This way, small-sized and self-powered vibration monitoring and recording assemblies can be implemented utilizing embodiments hereof.

[0067] In some implementations the energy harvesting device is equipped with wireless communication means (e.g., BLE, Bluetooth, Zigbee, near-fi eld-communication - NFC, or suchlike) configured for exchanging data / signals with external devices (e.g., personal or laptop computer, smart device, such smartphone, tablet or smartwatch, or suchlike) to enable readout of the vibration / oscillatory motion events recorded therein. Optionally, but in some embodiments preferably, the energy harvesting device comprises an electromagnetic energy harvesting arrangement and data / signals readout circuities configured to fetch from the recording circuitry vibratory / oscillatory events records stored therein, and wirelessly transmit the same to one or more external devices upon request. The data / signals readout circuities can utilize a type of NFC implementation configured to be wirelessly powered by external electromagnetic (e.g., radio-frequency - RF) signals, power the readout circuitry to fetch the one or more vibratory / oscillatory motion events, and wirelessly transmit the same to the external device(s).

[0068] For an overview of several example features, process stages, and principles of the invention, the examples of motion energy harvesting configurations illustrated schematically and diagrammatically in the figures are intended for detection and / or monitoring vibratory / oscillatory motion events. These motion energy harvesting configurations are shown as one example implementation that demonstrates a number of features, processes, and principles used to detect and record motions, but they are also useful for other applications and can be made in different variations. Therefore, this description will proceed with reference to the shown examples, but with the understanding that the invention recited in the claims below can also be implemented in myriad other ways, once the principles are understood from the descriptions, explanations, and drawings herein. All such variations, as well as any other modifications apparent to one of ordinary skill in the art and useful in motion energy harvesting applications may be suitably employed, and are intended to fall within the scope of this disclosure.

[0069] Figs. 1A to 1G schematically illustrate moving magnet configurations 10 according to some possible embodiments, comprising a permanent magnet(s) assembly 12 attached to an elastically deformable membrane 17 configured to allow reciprocal (e.g., up-down) movement of the magnet assembly 12 with respect to an anchoring rim 17p of the membrane 17. One or more coils 33 can be fixedly attached in a vicinity of the magnet assembly 12 for inducing electric current therein in response to the movements of the magnet assembly 12 (z. e. , according to Faraday's law of electromagnetism). One or more circuitries 13 can be electrically connected to the one or more coils 33 for storing electrical energy induced in the coil(s) 33, and / or for carrying out other functions / requirements of devices comprising the moving magnet configurations 10.

[0070] The magnet assembly 12 can be attached to the deformable membrane 17 using any suitable technique, such as by gluing using an appropriate adhesive. Alternatively, or additionally, magnet elements positioned on opposite sides of a single membrane element 17 can be held in place (e.g., without any adhesive) relying on the magnetic force and / or shear friction between the magnet surfaces and the membrane 17.

[0071] The moving magnet configurations 10 disclosed herein can be used for harvesting vibrational motion energy, converting the vibrational motion into electrical energy by the coil(s) 33, and powering one more circuitries 13 electrically connected to the coil(s) 33. The moving magnet configurations 10 can be embedded / coupled with the coil(s) 33 and circuitries 13 in any machinery, tool, equipment, infrastructure or object / item, experiencing and / or generating vibratory motion for harvesting the vibratory motion energy and / or monitoring and / or recording vibratory motion events thereby experienced and / or produced. In possible embodiments the moving magnet configurations 10 are configured as a detachable, wearable (e.g., wrist- worn) or implantable device.

[0072] Optionally, but in some embodiments preferably, the permanent magnet assembly 12 is engageable with one or more stoper elements 35 configured to at least partially limit the reciprocal movement of the membrane 17 with the magnet assembly 12 attached to it, and / or prevent and / or restrain tilts of the magnet assembly 12 during the reciprocal (e.g., up-down) movement of the membrane. Fig. 1A exemplifies a stopper element 35 configured for engagement with portions of the membrane 17 surrounding the magnet assembly 12. This stopper configuration can effectively restrain the reciprocal movement of the membrane 17, while leaving sufficient membrane portion Z3 about / around (i.e., surrounding) the magnet assembly 12 that is not engageable by the stopper 35, for guaranteeing continuous reciprocal motion of the membrane 17 with the magnet assembly 12 attached thereto.

[0073] It is noted that though a rectangular-shaped stopper element 35 is exemplified in the figures herein, the stopper element 35 can be similarly configured in any other suitable shape (e.g., any other polygonal shape, or circular, or by one or more discrete / point stopper elements arranged about a desired non-engageable membrane portion Z3).

[0074] As exemplified in Fig. 1A, in some embodiments the movable portions of the membrane 17 are defined within a ring / annular anchoring rim 17p configured for attachment to a corresponding ring / annular support (not shown), but any other suitable geometrical configuration of the anchoring rim 17p can be similarly contemplated per specific application requirements. In some embodiments the magnet assembly 12 is generally of a rectangular / square shape or cross-section, but any other suitable geometrical configuration of the magnet assembly 12 can be similarly contemplated per specific application requirements. The one or more stopper elements 35 can be configured to assume geometrical properties of the magnet assembly 12, and / or of the anchoring rim 17p, as long sufficient non-engageable membrane portions Z3 are obtained about / around the magnet assembly 12 to guarantee continuous motion of the membrane 17 and of the magnet assembly 12 attached to it.

[0075] For example, and without limiting, in possible embodiments the membrane 17 is made from one or more thin layers of elastic / flexible material, such as Polyethylene Terephthalate(PET), Polycarbonate (PC), Polyimide (PI), Polyamide (Nylon), Polyimide (PI)) or any other suitable polymeric or non-polymeric material configured in any suitable shape e.g., a polygonal or circular membrane (e.g., having a diameter D of about 15 to 45mm, optionally in a range of 25 to 35mm, or about 30mm). The anchoring rim 17p is made in possible embodiments of elastic / flexible material, such as for example but without limiting Polycarbonate (PC), Tritan (a type of copolyester), Polystyrene / Acrylonitrile Butadiene Styrene (PS / ABS), Polymethyl Methacrylate (PMMA), Polyether Ether Ketone (PEEK) or any other suitable polymeric or non-polymeric material. Alternatively, or additionally, the anchoring rim 17p is formed by layers of the membrane 17.

[0076] The magnet assembly can be implemented by one or more magnet elements configured to form a substantially square (or differently shaped) magnet assembly 12 (c.g, having a sidelength Z2 of about 7 to 22 mm, optionally in a range of 10 to 20mm, or about 15mm). In the embodiment exemplified in Fig. 1A the one or more stopper elements 35 are configured to surround the magnet assembly 12 and define a separation zone Z3 surrounding the magnet assembly 12 for preventing any contact between the magnet assembly 12 and the stopper elements 35 e.g., the stopper element 35 can be generally a rectangular / square frame-shaped element having a side-length (or cross-sectional area) that is greater than the side-length (or cross-sectional area) of the magnetic assembly 12.

[0077] Fig. IB shows a sectional view of a portion of a moving magnet configuration 10 comprising according to some possible embodiments two stopper elements: a top stopper element 35a; and a bottom stopper element 35b (collectively referred to herein as stopper element 35). In this non-limiting example, the stopper elements 35a and 35b are rectangular / square frame-shaped elements (e.g., having a width Z1 of about 1 to 3 mm, optionally about 2 mm). As seen, the stopper elements 35a and 35b can be aligned above and below the membrane 17 to substantially surround the magnet assembly 12, and define a separation zone Z3 (e.g., having a width Z3 of about 1 to 3 mm, optionally about 2 mm) surrounding the magnet assembly 12.

[0078] Fig. 1C shows a sectional side view of a portion of a moving magnet configuration 10 comprising according to some possible embodiments the two stopper elements 35a and 35b. In this non-limiting example the movements of the membrane 17 (e.g., having thickness T of about 0.01 to 1.0 mm, optionally in a range of 0.05 to 0.07 mm) is limited / restrained by top and bottom stopper elements 35a, 35b positioned some predefined distance from the surface of the membrane 17 (e.g., forming top and bottom gaps G between the membrane and the stopper elements of about 0.01 to 0.5 mm, optionally about 0.025 mm).

[0079] Fig. ID shows a side view of a (e.g., vibratory / oscillatory) motion energy harvesting device 16 utilizing the moving magnet configuration 10 with top and bottom stopper elements 35a and 35b, and fixed top and bottom coils, 33a and 33b (collectively referred to herein as coils 33), respectively located above and below the magnetic assembly 12. Fig. IE shows a graphical plot of a stiffness profile of a PET membrane (17) having thickness T of about 0.1 mm, limited / restrained by top and bottom stopper elements (e.g., 35a and 35b) forming gaps (G) of about 0.025 mm between the membrane (17) and the stopper elements (35), and a non- engageable membrane portion having a width Z3 of about 1mm. As seen, with this configuration, the displacements of the membrane (17) with the top and bottom stopper elements (e.g., 35a and 35b) is confined to about 0.1 mm for forces between 0 to about 0.75 kgf, and thereby provide significantly increased membrane stiffness by a factor of 100 (factor of 100 is given as an example and without limiting). In addition to the top and bottom stopper elements (e.g., 35a and 35b), the magnet motion can be also restricted by stiffness of the air film layer confined within the cavities between the (e.g., upper and the bottom) membrane(s) and the corresponding coils 33.

[0080] Figs. 2A to 2C show frequency analysis 3D simulation results of the moving magnet configuration 10 shown in Figs. 1A to ID, for vibration frequencies of 134 Hz, 267 Hz and 3000 Hz, respectively. As seen, in this non-limiting example, for vibrations frequency of 134 Hz (Fig. 2A) the reciprocal motion of the membrane 17 and magnet assembly 12 is such that the magnet assembly 12 moves substantially parallel to a plane defined by the anchoring rim 17p, for vibrations frequency of 267 Hz (Fig. 2B) the reciprocal motion of the membrane 17 and magnet assembly 12 is such that the magnet assembly 12 is tilted with respect to the plane defined by the anchoring rim 17p, and for vibrations frequency of 3000 Hz (Fig. 2C) the reciprocal motion of the membrane 17 and magnet assembly 12 introduces multiple deformations in the membrane projecting above and below the plane defined by the anchoring rim 17p.

[0081] Fig. 2D shows a plot of estimated displacements of the moving magnet arrangement 10 in a possible embodiment, which exhibits restrained motion of the magnetic assembly (12) after the membrane (17) contacts the stopper elements (35), after about 0.26 seconds of vibratory motion thereof. It is noted that in possible embodiments the frequency and amplitude of displacements, of the device’s membrane 17 and the magnet assembly 12 attached thereto, due to the mechanical vibrations, should be sufficiently large in order to obtain desired EMF values through the coil(s) 33.

[0082] For example, and without limiting, in case of harmonic vibrations in the linear approach with the constant stiffness, the displacements of the magnet assembly 12 can be expressed by the following equation - wherein u(f) designates temporal (z.e., as a function of time f) vertical displacements of the magnet assembly 12, m designates proof mass of the system, c is the damping factor, k is the out of plane stiffness of the system and F = —ma is the amplitude of applied external harmonic excitation force by means of acceleration of amplitude a, w is the circular / angular frequency, and t designates time. Steady state solution of equation (1) is u(t) = A ■ cos(wt — (p) where A is the amplitude of magnet displacement and (p is the phase delay from the applied harmonic excitation. Consequently, vertical velocity of the magnet assembly 12 can be calculated as follows:

[0083] In order to obtain maximal EMF the device configuration aims to obtain the maximum of the product A ■ w. Amplitude A can be expressed by the following equation:

[0084] (2)

[0085] - deflection under the static force F = —ma,

[0086] - undamped natural frequency,

[0087] - quality factor of the system,

[0088] - frequency ratio

[0089] From equation (2) maximum amplitude A can be reached at the following excitation resonant frequency: Further examination of equation (2) shows that for r namely for an

[0090] I 1 angular frequency w wres= w01 - - near resonance frequency, the reduction in

[0091] "\i 2Q amplitude A is dramatic and continues to decrease as the frequency moves further from the resonant frequency.

[0092] There are two main ways to increase the product A ■ w when implementing the linear system with constant stiffness. The first method is to increase the excitation amplitude a which is not always possible as it depends on the excitation source. The second method is to always

[0093] I 1 operate at the resonance frequency wres= w01 — — but this is also problematic because "\l the excitation signal can be broadband. From equation (2) it can be observed that varying the out-of-plane stiffness of the membrane is not effective in increasing the product A ■ w under broadband excitation.

[0094] Since in some embodiments the device is designed for broadband excitation, to alleviate / resolve these problems, it is proposed to use in some embodiments a relatively soft membrane (for the proof mass around 2 g out of plane stiffness of the membrane can be for example and without limiting in the range 0.05 — 5 kgf / mm) and equip the device with one or more stoppers 35 e.g., as exemplified in Figs. 1A to ID, and 7A to 7E.

[0095] In some embodiments it is proposed to incorporate an additional stiffness of the air film layer confined within the cavities 40, as shown in Fig. 1G, formed between the upper and the bottom membranes 4c, 4d and their corresponding (e.g., PCB) coils 33. Implementation of the additional stiffness of the air film layer confined within the cavities 40 between the upper and the bottom membranes 4c, 4d and their corresponding coils 33 can be done together with the stoppers or on its own e.g., without the stoppers (35).

[0096] The concept of some of the embodiments hereof is based on that the membrane 17 is considered to be "soft" when its displacements are within the gaps G between the membrane 17 and the stopper(s) 35. When the displacements of the membrane 17 increases such that it contacts the stopper(s) 35, the working area of the membrane 17 will be reduced to the area confined by stoper(s) 35, and the stiffness of the membrane 17 will be consequently thereby increased dramatically for example but without limiting up to 100 times.

[0097] The concept of embodiments hereof that incorporate additional stiffness from the air film layer confined within the cavities 40 between the upper and bottom membranes 4c, 4d and the corresponding coil 33 is based on the isothermal process equation for the air (or any other suitable gas) in the cavities 40 in the form of PV = const. This equation provides a nonlinear contribution to the out-of-plane effective stiffness of the device, as shown in Fig. IF.

[0098] Embodiments with the stoppers 35 or / and with the additional stiffness of the air film layer confined within the cavities 40 between the upper and the bottom membranes 4c, 4d and the corresponding coils 33, serves for the similar purpose - to provide nonlinear effective stiffness properties to the membrane of the devise. Generic equation for damped system with nonlinear can be expressed by the following equation:

[0099] Here Fk(u) denotes nonlinear stiffness as a function of displacement u.

[0100] An equation of magnet motion for example but without limiting for particular case, taking into account the stopper(s) 35, can be expressed as follows: wherein ksdenotes the additional stiffness introduced by placement of the stopper(s) 35, and gsrepresent the distance G between the stopper(s) 35 and the membrane 17.

[0101] An equation of magnet motion, considering an additional stiffness of the air film layer confined within the cavities 40 between the upper and bottom membranes 4c, 4d and the corresponding coils PCB, can be expressed using Duffing's equation, without limiting to this particular case, as follows: Fcos(wt), (5)

[0102] Where a > 0 is a fitting coefficient.

[0103] The improvement obtained by introducing the stopper(s) 35 or / and stiffness of the air film layer confined within the cavities 40 between the upper and the bottom membranes and the corresponding coils (33) can be further demonstrated in the following example, in which the following embodiments are considered:

[0104] (i) a relatively soft membrane 17 without stopper(s) 35 (e.g., k = 0.42kgf / mm);

[0105] (ii) a relatively stiff membrane 17 without stopper(s) 35 (e.g., k = 15.54kgf / mm); and

[0106] (iii) a relatively soft membrane 17 with the stoppers 35a and 35b (e.g., k = 0.42kgf / mm, ks= 15.12kgf / mm, gs= 0.025mm).

[0107] (iv) a relatively soft membrane 17 with incorporated additional stiffness from the air film layer confined within the cavities 40 between the upper and bottom membranes 4c, 4d and the corresponding coil 33 (e.g., k = 0.42kgf / mm, knonUnerjrom airstarts from around 7 kgf / mm and reaches around ll kgf / mm at magnet displacement around 0.2 mm).

[0108] For all embodiments (i), (ii), (iii) and (iv) harmonic excitation is applied with frequency of 1000Hz and acceleration of 60g. The product of A ■ w obtained will be compared for each of the embodiments (i), (ii), (iii) and (iv). Figs. 2E to 2H show magnet displacements plots and the product A ■ w comparison for above-mentioned the embodiments (i), (ii), (iii) and (iv).

[0109] As seen in Fig. 2E, for embodiment (i) using a soft membrane 17 without stopper(s) 35, exhibits small reaction to excitation because the excitation frequency is significantly higher than the membrane natural frequency, for which a non-resonant frequency is behaviour. In turn, embodiment (ii) using a relatively stiff membrane 17 without stopper(s) 35, exhibits relatively small displacements, as seen in Fig. 2F, because the excitation frequency is less than the natural frequency of the membrane, for which a non-resonant frequency behaviour is observed. Embodiment (iii), using a soft membrane 17 with the stoppers 35a and 35b, exhibits much better behavior in terms of temporal displacements u(t) and the product A ■ w, as seen in Fig. 2G. Embodiment (iv), using a soft membrane and incorporated additional stiffness of the air film layer confined within the cavities 40 between the upper and the bottom membranes 4c, 4d and the corresponding coils 33 exhibits much better behavior in terms of temporal displacements u(t) and the product A ■ w, as seen in Fig. 2H.

[0110] These four examples (embodiments (i), (ii), (iii) and (iv)) show that the use of the stopper(s) 35 and / or additional stiffness of the air film layer confined within the cavities 40 between the upper and the bottom membranes 4c, 4d and the corresponding coils 33 can be used to effectively achieve relatively high temporal displacements u(t) and significantly improve the product A ■ w.

[0111] Embodiments (iii) and (iv) exhibit significantly better performance than (i) and (ii) due to the nonlinear effective stiffness of the device. As shown, unlike the linear case, the nonlinear resonant frequencies increase with amplitude. This phenomenon allows embodiments with nonlinear stiffness to consistently operate near the resonant frequency, if the excitation is sufficient (for example, not less than 30g)

[0112] Figs. 3A and 3B schematically illustrate magnet assembly configurations 12 according to possible embodiments. Fig. 3A shows an array 25 arranged to form a rectangular / square alternating grid of magnet elements 12e. As seen, in this alternating grid arrangement 25 each magnetic element 12e of a certain magnetic polarity (e.g., "N") that is not on the edge of the array 25 is located between horizontally- and vertically- adjacently located (i.e., four) magnetic elements 12e of the opposite polarity (e.g., "S"), and (z.e., four) diagonally-adjacent magnetic elements 12e of the same polarity (e.g., "N") i.e., located on the diagonals extending therefrom (not shown). Fig. 3B depicts a single magnet element 12e of the magnet array 25, shown that an inversed distribution of the magnetic polarities is obtained at the underside of the magnet array 25.

[0113] In some embodiments the magnet array 25 of magnet elements 12e is made of any ferromagnetic material(s) such as for example, but without limiting, Neodymium Iron Boron (NdFeB), Alnico (Aluminum -Nickel-Cobalt), Samarium Cobalt (SmCo), Ferrite (Ceramic), where each magnet element 12e has a thickness H3 of about 0.1 to 5 mm, optionally within the range of 0.3 to 0.5 mm, or either about 0.3 mm or 0.5 mm. The side length of each magnet element 12e is in some embodiments about 0.5 to 50 mm, optionally about 3 mm. The corners of magnet element 12e are rounded in some embodiments to assume a radius r e.g., in the range of 0.7 to 0.9 mm, optionally about 0.8 mm. Accordingly, in embodiments wherein the magnet array 25 is a 5x5 array the side lengths W1 and W2 of the array 25 are generally in the range of 0.5 to 250 mm, optionally about 15 mm.

[0114] Fig. 4A to 4C schematically illustrate coil array arrangements 20 according to possible embodiments. Fig. 4A shows the coil array arrangement 20 comprising coils cells 20c, wherein each cell 20c comprises at least one coil Li (where i>0 is an integer number) in each side of the cell 20c. In this specific and non-limiting example, the array of coils 20 comprises 5x5 coils cells 20c (i.e., l<z<50), each having a single top coil (e.g., Li l<z<25) and a single bottom coil (e.g., Li+25 l<z<25). Figs. 4B and 4C show top and bottom side views of the coil array arrangement 20, wherein the coils Li and Li+25 of each coils cell 20c are patterned / attached over two sides of a (e.g., circular) substrate (e.g., made of Copper (Cu), Aluminum (Al), Silver (Ag), Gold (Au), conductive polymer or any other appropriate materials) 21 e.g., in an overlapping relation. A connector sleeve 21s extending from the substrate 21 is used in some embodiments for connection pads 2a and 2b.

[0115] In this non-limiting example, the top and bottom coils Li and Li+25 of each coils cell 20c are serially connected (e.g., by vias) and configured such that the electric currents induced through them are in the same direction to provide for summation of said electric currents. In addition, the coils Li and Li+25 of each coils cell 20c are serially connected by conducting lines extending between them on the substrate 21. However, in possible embodiments parallel, or hybrid (serial and parallel) connections between the coils cells 20c can be alternatively used.

[0116] Fig. 5A schematically illustrates a two-dimensional array of coil cells 22c of the array of coils 20 and a proximally located two-dimensional array of magnet elements 12e of the magnet assembly 12, according to possible embodiments of the motion energy harvesting device 16. As seen, the array of coils 20 is located above (or below) the magnet assembly 12 to define a gap G therebetween, within which the magnet array 25 can reciprocally (2c e.g., in up-down directions) move to induce EMF in the coils cell 22c of the array of coils 20. The magnet elements 12e can accordingly form an alternating grid of North ("N") and South ("S") poles, and each magnet element 12e of the magnet assembly 12 can be associated / aligned with a respective inferior (and / or superior) coils cell 22c of the coils array 20. Optionally, but in some embodiments preferably, the outer geometrical (in-plane) dimensions of each coils cell 22c approximately / substantially equal to the outer geometrical (in-plane) dimensions of the magnet elements 12e of the magnet assembly 12.

[0117] Fig. 5B shows an EMF spatial distribution obtained utilizing the array 20 of coils cells 22c and the array 12 of magnet elements 12e (the notations 2a, lb on Fig. 5B, and 2c on Fig. 5A, indicate that a, b and c are half the size of the corresponding sides of the magnet assembly in this non-limiting example. For the sake of simplicity, each magnet element 12e of the magnet assembly 12, and the coils cell 22c associated therewith, will be referred to hereinafter as magnet / coil cell 52. In addition: the magnet / coil cells 52 at the corners of the illustrated configuration are referenced as MOO; the magnet / coil cells 52 in the peripheral sides of the illustrated configuration, and that are not at the corners and not at the centers of the peripheral sides, are referenced as MOI; the magnet / coil cells 52 at the centers of the peripheral sides of the illustrated configuration are referenced as M02; the internal (z.e., not on the peripheral sides or comers) magnet / coil cells 52 that are on the diagonals, and not at the center, of the illustrated configuration are referenced as Mil; the internal magnet / coil cells 52 that are not on the diagonals, and not at the center, of the illustrated configuration are referenced as M12; and the internal magnet / coil cell 52 at the center of the illustrated configuration is referenced as M22. The contribution of each of the above-defined groups of magnet / coil cells 52 to the total EMF produced via the coil elements, relative to the EMF produced via the center magnet / coil cell M22, is as follows:

[0118] • the MOO magnet / coil cells contribute four (4) times positive EMF / current;

[0119] • The MOI magnet / coil cells contribute eight (8) times negative EMF / current;

[0120] • The M02 magnet / coil cells contribute four (4) times positive EMF / current;

[0121] • The Mil magnet / coil cells contribute four (4) times positive EMF / current;

[0122] • The M12 magnet / coil cells contribute four (4) times negative EMF / current; and

[0123] • The M22 magnet / coil cell contributes one (1) times positive EMF / current. The number of contributions from each cell 52 can be explained by the symmetry of the magnet design. The contribution of each cell 52 (M p, where 0<x<2 and 0<y<2 are integer numbers) corresponds to the number its instances in the checkerboard cell representation of Fig. 5B.

[0124] Figs. 6A to 6F are graphical plots of the EMF obtained by the various magnet / coils cell 52 (M p) of the motion energy harvesting device 16. In these plots the average spacing between layers of the coil elements Li and Li+25 in the coil array arrangements 20 is about 50pm. Fig. 6A depicts the EMF obtained by the magnet / coil cells MOO. Fig. 6B depicts the EMF obtained by the magnet / coil cells Mil. Fig. 6C depicts the EMF obtained by the magnet / coil cells MOI. Fig. 6D depicts the EMF obtained by the magnet / coil cells M12. Fig. 6E depicts the EMF obtained by the magnet / coil cells M02. Fig. 6F depicts the EMF obtained by the magnet / coil cell M22.

[0125] Fig. 6G graphically plot the total EMF produced by array of coils 20 according to possible embodiments. Based on these EMF plots:

[0126] - the peak-to-peak voltage expected from one array 20 of coils cells 22c is about 50 to 100 mV.

[0127] - the 4thlayer produces 30% less EMF that the 1stlayer, so that 10% of the EMF is lost in each layer due to the greater vertical distance from the magnet.

[0128] The total peak-to-peak voltage expected from 8 layers is about 680 - 340 mV.

[0129] It is noted that the number of coils / coil layers can be decreased or increased in accordance with a desired output voltage level e.g., the number of coils / coil layers is increased in order to increase the output voltage level).

[0130] Figs. 7A to 7E schematically illustrate a (e.g., vibratory and / or oscillatory) motion energy harvesting device 70 according to possible embodiments. Fig. 7A shows a sectional view of the motion energy harvesting device 70, comprising: top and bottom support elements, 31a and 31b respectively; top arrays of coils (only two are shown in Fig. 7E) 32a, 33a,... fixedly coupled to the top support element 31a and bottom arrays of coils (only two are shown in Fig. 7E) 32b, 33b,... fixedly coupled to the bottom support element 31b; top and bottom stopper elements 35a and 35b, each can be respectively fixedly coupled to the top and bottom arrays of coils 32a, 33a,. . . and 32b, 33b,. . . ; top and bottom membrane spacer 36a and 36b; and an elastically deflectable / deformable membrane 17 at least some peripheral portions thereof are sandwiched and anchored by the top and bottom membrane support frames 31a and 31b, so as to enable reciprocal movement of free portions of the membrane 17 located within the support element 31a and 31b. In this specific and non-limiting example the membrane 17 comprises a top magnet arrangement 12a attached over a top surface area of the membrane 17, and a bottom magnet arrangement 12b attached over a bottom surface area of the membrane 17. The support element 31a and 31b can be configured to form a (e.g., sealed) housing of the device 70.

[0131] In this non-limiting example, each one of the top and bottom stopper elements 35a and 35b can be fixedly attached to a respective one of the top and bottom arrays of coils 32a, 33a, . . . and 32b, 33b,... . In possible embodiments, each one of the top and bottom support elements 31a and 31b comprises one or more alignment elements 38 configured for precise alignment of the internal components of the motion energy harvesting device 70.

[0132] Fig. 7B shows an exploded view of the motion energy harvesting device 70. In various embodiments, the number and arrangement of stopper support elements (34) and spacer (36) may vary. The number of membranes (17) used can be two (2), three (3), or another quantity, as depicted in Fig. 10C. Additional magnets can be added to clamp the membranes (17) and enhance the magnetic field and resulting electromotive force (EMF), as also shown in Fig. 10C. Additional spacer elements (36) can maintain the distance between the membranes (17), as illustrated in Fig. 10C. In some embodiments, the number of coils (32, 33) may be increased to boost the EMF. As seen, each of the top 32a, 33a,. . . and bottom 32b, 33b,..., arrays of coils can be implemented by a coil array arrangement 20 such illustrated in Figs. 4A to 4C. Similarly, each of the top and bottom magnet arrangements 12a and 12b can be implemented by a magnet assembly such as illustrated in Figs. 3 and 5. Fig. 7C shows a perspective view of the motion energy harvesting device 70. Fig. 7D shows a sectional perspective view of the motion energy harvesting device 70. Fig. 7E shows a closer perspective sectional view motion energy harvesting device 70.

[0133] Fig. 8A to 8J schematically illustrate multilayered membrane configurations 17' according to possible embodiments. Fig. 8A and 8B shows sectional views of the multilayered membrane 17' comprising in some embodiments a central membrane layer 17b sandwiched between a top membrane layer 17a and a bottom membrane layer 17c. The membrane layers 17a, 17b and 17c, can be made from a thin layer of, for example, Polyethylene Terephthalate (PET), Polycarbonate (PC), Polyimide (PI), Polyamide (Nylon), Polyimide (PI), or any other suitable polymeric material, each having a thickness of about for example but without limiting 0.005-2 mm.

[0134] Fig. 8C to 8F show natural frequency analysis results obtained for single and multilayered membrane structures 17'. In Fig. 8C the natural frequency is 134 Hz for which membrane bending behavior is exhibited. In Fig. 8D the natural frequency is 267 HZ for which magnet assembly tilting behavior is exhibited. In Fig. 8E the natural frequency is 135 Hz for which membrane bending behavior is exhibited. In Fig. 8F the natural frequency is 965 Hz for which magnet assembly tilting behavior is exhibited.

[0135] Fig. 8G and 8H are graphical plots of displacement measured using a membrane configuration according to possible embodiments when a broadband excitation signal is applied to the membrane configuration.

[0136] Figs. 81 and 8J are graphical plots of the EMF measured using a membrane configuration according to possible embodiments when a broadband excitation signal is applied to the membrane configuration. The EMF measured is related to the displacement of membrane shown in Fig. 8G and 8H.

[0137] Fig. 9 schematically illustrates a motion monitoring system 60 utilizing a detector device 61 according to any of the embodiments hereof. The detector device 61 comprises a motion energy harvesting unit 62, which can be implemented by any of the embodiments disclosed herein, a counter unit 63 configured to generate information indicative of motion events actuating the harvesting unit 62, a storage (e.g., non-volatile memory, such as flash memory) 64 configured for recording the motion events information generated by the counter unit 63, and a reader unit 65 configured to fetch motion events information stored in the storage unit 62 and communicate the same to an external device 67. The harvester 62 is configured to generate electrical power needed for operating the counter 63 and storage 64 units.

[0138] Optionally, but in some embodiments preferably, the reader unit 65 comprises one or more antenna elements 65a configured to receive electromagnetic radiation from one or more antenna elements 67a of the external device 67, for wirelessly energizing the reader unit 65. This way the reader unit 65 can be configured to be wirelessly energized by the external device 67, for fetching the motion events information stored in the storage unit 62 and wirelessly transmitting the same to the external device 67.

[0139] A possible implementation of a motion energy harvesting device incorporating advanced features for enhanced performance and manufacturability according to possible embodiments is described below with reference to Figs. 10 to 14. This and the other embodiments hereof demonstrate a robust and manufacturable design suitable for industrial vibration monitoring applications with integrated energy harvesting, storage, and wireless communication capabilities. The embodiment of Figs. 10 to 14 implements the motion harvesting principles described above with specific adaptations for industrial monitoring applications. Three-membrane configurations are exemplified, that provide enhanced stability while maintaining the reciprocal motion characteristics essential for energy harvesting. The checkerboard magnetization pattern of embodiments hereof represents one implementation of the alternating magnetic pole arrangement described in connection with Figs. 3A to 3B.

[0140] Embodiments hereof provide a combination of the electromechanical vibration sensor, energy harvester, energy storage, signal processing and wireless data transmission functions, provided in the same integrated device. The electromechanical core of the sensor shown schematically in Fig. 10A comprises a permanent magnet also serving as a proof mass, an elastic membrane suspension, and an array of planar coils formed on / in a print circuit board (PCB). To prevent the undesired tilting of the proof mass, the magnet is suspended using three circular, polymeric membranes, separated from each other by the gap e.g., of about 0.01 to 2 mm, optionally about 0.5 mm. In this non-limiting example, the thickness of the membranes is in a range of 10 to 4000 pm, optionally about 100 to 150 pm, and their diameter (e.g., clamped at the outer circumference) is in a range of 3-150 mm, optionally about 30 mm.

[0141] It is noted that more (or less) than three membranes 17 can be used to carry the magnet assembly 12. The magnet elements of the magnet assembly 12 can be positioned beneath, above, or between any of the adjacent membranes (layers) 17.

[0142] In this non-limiting example, the (e.g., 15 mm x 15 mm x 1.5 mm) magnetic mass is assembled out of three (e.g., 0.5 mm thick) magnet elements. In possible embodiments, during the assembly procedure, these three separate magnets are attached to each other. One of the distinguished features of the device architecture is the way in which the magnets are magnetized. Due to the checkerboard magnetization pattern, the magnetic field lines are predominantly oriented in the directions parallel to the magnet upper and bottom surfaces, as shown in Fig. 10B As a result, the field lines are directed perpendicular to the wires of the rectangular planar coils positioned in the proximity of the magnet.

[0143] It is noted that while certain analogy with the Halbach magnets array can be mentioned, the magnetic polarization here is different. The actual stack of the assembly in this example is shown in Fig. 10C, which incorporates two 3D printed cover plates (substrates), several (e.g, 27. 5 pm and 0.5 mm thick) spacers, providing the gap between the membranes and two or four custom-built printed circuit boards (PCB) with the serially connected planar coils. All the coils are connected in series e.g., the coil layers are connected using PCB vias. As seen, in this nonlimiting example the stopper mechanism is implemented without stopper elements (35), but rather utilizes an air film layer 33v defined within the device 61. In possible embodiments the stiffness of the membrane(s) is increased by air / gas film layers 33v confined within one or more cavities formed in the housing / device e.g., between the membranes 17 and corresponding PCB coils 32 of the device. In the framework of this example, the motion energy harvesting device (also referred to herein as sensor) is attached to a vibrating platform (e.g., the machinery to be monitored). The motion of the magnetic mass with respect to the coil’s wires induces an electric current in the coils, converting the kinetic energy of the proof mass motion into electric energy. This energy is stored in an integrated small battery and / or capacitor and / or super-capacitor.

[0144] The electric current can be rectified and amplified (e.g., circuitry 13 in Fig. 1A) using the Villard cascade switch capacitor (or any other rectifier and amplifier circuit). Once the switch capacitor voltage exceeds the threshold value sufficient for the memory (e.g., EEPROM) read / write operation, the power output is enabled by the ON / OFF switch circuit and the switching events counter value stored in the (e.g., EEPROM) memory is increased by one. This is accompanied by the decrease of the switch capacitor voltage.

[0145] The storage unit built-up voltage, which is related to the total accumulated energy, can be constantly / periodically monitored. Once the stored energy, and thus the stored voltage, reaches a threshold value, sufficient for the wireless transmission, a pulse is transmitted to an external receiver (e.g, 67 in Fig. 9). Since the stored energy is related to the vibrations of the tool the sensor is attached to, the number of the transmitted pulses per unit time can serve as a simple indicator of the tool usage intensity and therefore the machinery burnout and possible wear.

[0146] Among key requirements of the sensor implementations for industrial applications there is their manufacturability and high reliability combined with low price. For reduced costs, the devices can be fabricated using mainly polymeric materials, with the exception of the magnets and coil / wires. The processes commonly used for the fabrication of Si based MEMS devices requiring clean room environment were not involved. The cover plates were 3D printed out of polymeric material. The spacers serving for the membranes separation and clamping at the outer membrane’s circumference were cut out of polymeric material sheets and / or foils.

[0147] The assembly and attachment of the layers of the stack was carried out using simple clamping pins without use of adhesive layers. The checkerboard polarization scheme of each of the layers allowed simple magnetic attachment between each of the three layers of the magnets. Motion-limiting stoppers under the bottom and above the upper membranes are provided to prevent contact between the magnet and the coils wires e.g, forms as an integral part of the cover plates.

[0148] A main challenge of the device design is related to the requirement to achieve the level of the harvested and stored energy which would be sufficient for the wireless transmission of the data. In addition, the harvester is required to efficiently operate in a relatively broad range of frequencies. To achieve the desired performance by tailoring the design parameters, parametric studies were carried out using the three-dimensional numerical finite elements model of the device built using the ABAQUS package, as illustrated in Figs. 11A and 11B. In this example, the membranes were modeled using shell elements, the magnets were represented using two-dimensional (2D) rigid quadrilateral elements which simulate magnet’s boundaries, and their mass and moments of inertia has been modeled by concentrated mass and moments of inertia and large deflection option, taking into account geometric nonlinearity of the structure. The model incorporated an additional stiffness of the air film layer confined within the cavities between the upper and the bottom membranes and the corresponding coils PCB.

[0149] It was found that due to the presence of the air layer the effective stiffness of the device vibrating at the fundamental mode frequency increases by 57% for magnets’ relative displacement of 0.2 mm. Only the inertial external loading due to the platform vibration was incorporated into the model while the additional forces due to the interaction between the permanent magnets and the current induced in the coils were neglected. The finite element (FE) model was mainly used for the extraction of the equivalent stiffness and damping parameters of the device and construction of the compact nonlinear single degree of freedom reduced order (RO) model, which was then analyzed numerically in time domain. Once the amplitudes of the proof mass vibrations were found, the electric current in the wires was estimated analytically. The results depicted in Figs. 11B and 11C suggest that for the realistic acceleration levels e.g., of about ~ 31 g, the magnet vibrational amplitudes of up to 100 pm can be achieved, resulting in the induced voltage of up to 1 Vp (peak).

[0150] A possible assembly of the device is shown in Figs. 12A to 12C.

[0151] Experiments were carried out using the setup shown in Fig. 13. The devices were mounted on a shaker (Briiel & Kjaer LDS). Prior to the operation the shaker was calibrated using piezoelectric accelerometer (Columbia research labs). The shaker was operated at the frequencies between 860 and 950 Hz, in the vicinity of the device resonant frequency. The voltage signal was supplied by the arbitrary function generator. The output of the coils was directly connected to the oscilloscope.

[0152] The experimental results are shown in Figs. 14A, 14B and 14E. As seen in Fig. 14A, Output voltages of up to 1.2 Volts were registered at the accelerations of 31 g and frequency of 930 Hz. The values of the output voltages were generally consistent with the model prediction depicted in Fig. 11C. A discrepancy can be attributed to the approximate character of the air film related nonlinear damping calculation. Fig. 14A suggests that the dependence of the output voltage on the acceleration is not fully linear. The nonlinearity is attributed to the geometric nonlinearity of the membranes, of the confined air layer as well as nonlinear dependence between the induced current and the wire positions within the fringing magnetic field. It is noted that the use of nonlinearities was suggested to widen the bandwidth in vibration energy harvesters.

[0153] Fig. 14C demonstrates operation of a harvester / motion detection device 61 according to possible embodiments. The device 61 can be configured to be activated whenever the voltage thereby produced is greater than a defined voltage level V (si e.g., 3.5 Volt ). The circuitries / hardware (HW e.g., 13) can be then activated (s2) to record (s3) in its memory the motion event sensed by the device (e.g., counter increment). If the voltage produced by the device 61 is smaller than the defined voltage level then the HW / circuity is turned OFF (s4). Fig. 14C further demonstrates wirelessly reading the memory of the HW / circuity of the device 61 by an external (e.g., NFC) reader device 67.

[0154] Fig. 14D shows operation of a harvester / motion detection device 61 such that the operation of the device is terminated whenever the vibration ends (s5). In possible embodiments the system and / or device is configured to analyse the data / signals generated the circuitry of the device and register a motion event whenever said data / signals are indicative of a predefined motion pattern.

[0155] The sensor combined with the electronic circuit was operated in accordance with a sensing scenario. At this stage, to bypass the loading limitations of the shaker, the electronic circuitry, which was not integrated within the same package, was located outside of the shaker and was connected to the harvester by wires. The (e.g., EEPROM) data was extracted using an Android application configured to read the data by a smartphone by NFC. Three write / read events in 10 s were registered.

[0156] Terms such as top, bottom, front, back, right, and left and similar adjectives in relation to orientation of the described elements and components refer to the manner in which the illustrations are positioned on the paper, not as any limitation to the orientations in which the apparatus can be used in actual applications.

[0157] As described hereinabove and shown in the associated figures, the present application provides motion harvesting techniques and implementations usable for motion detection / monitoring applications, and related methods. While particular embodiments of the invention have been described, it will be understood, however, that the invention is not limited thereto, since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. As will be appreciated by the skilled person, the invention can be carried out in a great variety of ways, employing more than one technique from those described above, all without exceeding the scope of the claims.

Claims

CLAIMS1. An energy harvesting sensor device comprising: at least one elastically deformable membrane having a suspended portion and a peripheral anchoring portion; a magnetic assembly attached to the suspended portion of the at least one membrane, the magnetic assembly configured to undergo reciprocal motion in response to an externally applied force; at least one coil arrangement positioned proximate to the magnetic assembly and configured to generate electrical current in response to the reciprocal motion of the magnetic assembly; a stopper mechanism configured to limit displacement of the at least one membrane, wherein the stopper mechanism is configured to increase an effective stiffness of the membrane upon contact therewith; and circuitry electrically connected to the at least one coil arrangement and configured to store electrical energy generated by the at least one coil arrangement and generate data / signals indicative of the reciprocal motion of said the magnetic assembly.

2. The device of claim 1 wherein the stopper mechanism comprises one or more stopper elements configured to define a non-contact zone surrounding the magnetic assembly, such that a peripheral membrane band portion surrounding the magnetic assembly does not contact the at least one stopper element during the reciprocal motion.

3. The device of claim 1 or 2 wherein the stopper mechanism comprises a frame-shaped element having an opening larger than the magnetic assembly.

4. The device of any one of the preceding claims wherein the stopper mechanism comprises an air film layer obtained within one or more cavities formed in the device.

5. The device of claim 4 wherein the air film layer is implemented by confining air or any other gas, or a liquid, within cavities defined between at least one membrane and a corresponding coil, or array of coils.

6. The device of any one of the preceding claims comprising two or more membranes, and wherein magnet elements of the magnet assembly are positioned above, below, or between the one or more membranes.

7. The device of any one of the preceding claims wherein the at least one stopper element comprises a top stopper element positioned above the membrane and / or a bottom stopperelement positioned below the membrane, wherein the top and bottom stopper elements are aligned to sandwich the membrane therebetween with predefined gaps.

8. The device of any one of the preceding claims further comprising air-filled cavities between the at least one membrane and the at least one coil arrangement, wherein air confined within the cavities provides additional nonlinear stiffness during operation.

9. The device of any one of the preceding claims wherein the magnetic assembly comprises a two-dimensional array of magnetic elements arranged in an alternating polarity pattern.

10. The device of claim 9 wherein the alternating polarity pattern forms a checkerboard pattern.

11. The device of any one of the preceding claims wherein the at least one coil arrangement comprises a first array of coils positioned above the magnetic assembly and / or a second array of coils positioned below the magnetic assembly.

12. The device of claim 11 wherein each array of coils comprises multiple coil cells, each coil cell aligned with a corresponding magnetic element of the magnetic assembly.

13. The device of claim 11 or 12 wherein each array of coils is a multi-layered array of coils.

14. The device of any one of the preceding claims wherein the at least one membrane comprises two or more membranes having the magnetic assembly attached thereto so as to prevent tilting of the magnetic assembly during reciprocal motion.

15. The device of claim 14 wherein the membranes are spaced apart by gaps.

16. The device of any one of the preceding claims wherein the circuitry comprises: an energy storage unit configured to store the electrical energy; a counter unit configured to count motion events; and a memory unit configured to record motion event data.

17. The device of claim 16 wherein the circuitry further comprises a wireless communication unit configured to transmit the recorded motion event data to an external device.

18. The device of claim 17 wherein the wireless communication unit comprises a near-field communication (NFC) interface configured to be powered by electromagnetic signals from the external device.

19. The device of any one of claims 16 to 18 wherein the circuitry comprises a rectifier circuit configured to convert AC current from the at least one coil arrangement to DC current and a voltage threshold detection circuit configured to enable recording of motion events when stored voltage exceeds a predetermined threshold.

20. The device of any one of the preceding claims wherein the peripheral anchoring portion of the membrane is circular.

21. The device of any one of the preceding claims wherein the membrane comprises at least one layer of polymeric material selected from polyethylene terephthalate (PET), polycarbonate (PC), polyimide (PI), or polyamide.

22. The device of any one of the preceding claims wherein the magnetic assembly and / or membrane arrangement configured to exhibit nonlinear stiffness characteristics enabling broadband frequency response.

23. The device of claim 22 wherein the nonlinear stiffness characteristics result from mechanical contact between the membrane and the at least one stopper element and / or compression of air in cavities adjacent to the membrane.

24. A vibration monitoring system comprising the energy harvesting sensor device of any one of the preceding claims and a reader device configured to receive from the circuitry of the device the generate data / signals thereby generated.

25. The system of claim 24 configured to analyse the data / signals generated the circuitry of the device and register a motion event whenever said data / signals are indicative of a predefined motion pattern.

26. A self-powered vibration sensor comprising: a housing having top and bottom support elements; a membrane suspension system comprising at least one circular membrane clamped at its periphery between membrane support frames; a checkerboard-magnetized permanent magnet assembly attached to a central region of the membrane suspension system; top and bottom arrays of planar coils fixedly mounted to the respective top and bottom support elements and positioned proximate to the magnet assembly; top and / or bottom stopper mechanism configured to limit out-of-plane displacement of the membrane suspension system; an energy harvesting circuit connected to the coil arrays and configured to convert induced electrical current to stored electrical energy; and a motion event recording circuit powered by the stored electrical energy and configured to count and store vibration events.

27. The sensor of claim 26 wherein the top and / or bottom stopper mechanism comprises movement limiting elements configured to maintain a non-contact operational zone of at least one of the membranes defined around the magnet assembly.

28. The sensor of claim 26 or 27 wherein the membrane comprises three parallel membranes separated by spacers, with the magnet assembly positioned between and attached to the membranes to prevent tilting during vibration.

29. An energy harvesting device for vibration monitoring comprising: a membrane configured for elastic deformation; a rectangular magnetic assembly attached to a central portion of the membrane; a frame-shaped stopper element surrounding the magnetic assembly with a defined clearance zone, wherein the stopper element is positioned a defined distance away from the membrane surface, and wherein contact between the membrane and the stopper element creates a nonlinear stiffness response enabling broadband vibration energy harvesting.

30. The device of claim 29 further comprising coil arrays positioned above and below the magnetic assembly, wherein the coil arrays comprise serially connected planar spiral coils aligned with magnetic pole regions of the magnetic assembly.

31. A method of manufacturing a self-powered motion detection device, the method comprising: anchoring a peripheral portion of one or more elastically deformable membranes to a stationary support so as to define a suspended portion of said one or more elastically deformable membranes; attaching a magnetic assembly to the suspended portion of the one or more membranes; defining a stopper mechanism configured to limit displacement the one or more membranes; mounting at least one coil arrangement in proximity to the magnetic assembly such that reciprocal motion of the magnetic assembly induces electrical current in the at least one coil arrangement; and electrically connecting circuitry to the at least one coil arrangement for storing electrical energy generated thereby.

32. The method of claim 31 wherein the defining the stopper mechanism comprises positioning at least one stopper element at a predetermined distance from the one or more membranes.

33. The method of claim 32 wherein positioning the at least one stopper element comprises forming a frame-shaped stopper element having an opening larger than the magnetic assembly and aligning the frame-shaped stopper element such that a peripheral band portion of the membrane surrounding the magnetic assembly remains free from contact with the stopper element during operation.

34. The method of claim 32 or 33 wherein positioning the at least one stopper element comprises positioning a stopper element above and / or below the membrane with a defined gap from the membrane.

35. The method of any one of claims 31 to 34 wherein the defining the stopper mechanism comprises defining an air film layer within one or more cavities formed in the device.

36. The method of any one of claims 31 to 35 wherein the magnetic assembly comprises a plurality of magnetic elements, and wherein attaching the magnetic assembly comprises arranging the magnetic elements in a two-dimensional array with alternating magnetic polarities and securing the array of magnetic elements to the membrane to form a checkerboard magnetization pattern.

37. The method of any one of claims 31 to 36 comprising preparing the membrane from a sheet of polymeric material.

38. The method of any one of claims 31 to 37 further comprising forming the membrane from three separate membranes spaced apart by defined gaps, attaching the magnetic assembly between the membranes to prevent tilting during reciprocal motion, and clamping peripheral portions of all three membranes together.

39. The method of claim 38 comprising positioning spacers between adjacent membranes to maintain the gaps.

40. The method of any one of claims 31 to 39 comprising fabricating the at least one coil as a planar coil formed in / on a printed circuit board (PCB) and mounting a first PCB with said at least one coil above the magnetic assembly and / or a second PCB with said at least one coil below the magnetic assembly.

41. The method of claim 40 wherein fabricating the planar coils comprises forming rectangular spiral coils on the PCB, forming a plurality of electrically conducting vias in the PCB, and electrically connecting multiple coils in series by said plurality of vias.

42. The method of claim 40 or 41 wherein each PCB comprises an array of coil cells and wherein the method further comprises aligning each coil cell with a corresponding magnetic element of the magnetic assembly.

43. The method of any one of claims 31 to 42 comprising 3D printing top and bottom cover plates from polymeric material and integrating the stopper elements as integral components thereto.

44. The method of any one of claims 31 to 43 comprising forming air cavities between the membrane and coil arrays to provide additional nonlinear stiffness through air compression.

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