Vibrational energy projection devices and systems

Abstract

Some embodiments relate to an energy transformation device or apparatus. An exemplary device or apparatus includes a piezoelectric transducer, an electrical conductor electrically coupled to the piezoelectric transducer, and an axially aligned magnet assembly arranged to apply a static compressive force to the piezoelectric transducer, the magnet assembly having one end coupled to a base and an opposite free end. The magnet assembly is coaxial with the piezoelectric transducer, and at least a portion of the magnet assembly is concentric with the piezoelectric transducer. The magnet assembly defines a gap between axially adjacent portions of the magnet assembly, the gap being dimensioned such that the magnet assembly is small enough to apply a static compressive force to the piezoelectric transducer, but large enough to allow axial movement of the piezoelectric transducer without closing the gap.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE The embodiments relate generally to vibrational energy transformation devices and systems, and in particular to vibrational energy projection or detection devices and systems. In particular, the embodiments relate generally to a novel arrangement of a magnet and a piezoelectric transducer, which is configured to hold the piezoelectric transducer in compression. [Background technology]

[0002] Recent advances in materials technology have made new piezoelectric crystal materials available. Examples of such materials include relaxor ferroelectric single crystal (RFSC) materials. Although such materials can be used in vibration energy harvesting and ultrasound projection devices, such materials do not last long when placed under tension due to internal defects that cause stress concentrations and / or crack propagation.

[0003] It would be desirable to address or ameliorate one or more of the drawbacks or shortcomings associated with previous vibrational energy conversion devices, or at least provide a useful alternative thereto.

[0004] Any discussion of documents, acts, materials, devices, articles or the like which has been included in this specification should not be construed as an admission that all or any part of such content formed part of the prior art document existing prior to the priority date of each of the appended claims or was common general knowledge in the art relevant to the present disclosure.

[0005] Throughout this specification, the word "comprise" or variations such as "comprises" or "comprising" will be understood to mean the inclusion of a stated element, component or step, or group of elements, components or steps, but not the exclusion of any other elements, components or steps, or group of elements, components or steps. Summary of the Invention

[0006] Some embodiments provide an energy conversion device, comprising: base, a first magnet coupled to or comprising a base; a piezoelectric transducer disposed adjacent to the first magnet; a magnet array coaxial with a piezoelectric transducer, the magnet array being disposed opposite or at least partially around the piezoelectric transducer, or the piezoelectric transducer being disposed opposite or at least partially around the magnet array, the magnet array being polarized such that a first end of the magnet array is attracted to a first magnet; a second magnet polarized to be attracted to a second end of the magnet array opposite the first end; a vibratable mass coupled to or including a second magnet; an electrical conductor electrically connected to the piezoelectric transducer for conducting electrical current between the piezoelectric transducer and an external circuit; the first magnet, the piezoelectric transducer, the magnet array, and the second magnet are substantially coaxial; the first magnet, the second magnet, and the magnet array cooperate to maintain the piezoelectric transducer in compression; The vibrational motion of the second magnet is directly related to the compression of the piezoelectric transducer and the flow of current in the electrical conductor, The device is configured to convert electrical current in an electrical conductor into vibrations of a vibrable mass in the frequency range of about 300 Hz to about 100 kHz, thereby functioning as an acoustic projector.

[0007] In various embodiments, the magnet array and the second magnet are configured to exert a substantially static compressive force on the piezoelectric transducer of about 5 Newtons (N) to about 50 Newtons. In some embodiments, the static compressive force is between about 90 N and about 400 N. In some embodiments, the static compressive force is between about 50 N and about 500 N.

[0008] The magnet array may be disposed at least partially around the piezoelectric transducer. The vibratable mass may include a resonant mass.

[0009] The piezoelectric transducer may include a relaxor ferroelectric single crystal (RFSC). The piezoelectric transducer may include a binary or ternary piezoelectric single crystal. The piezoelectric transducer may be a PMN-PT or PZN-PT crystal. The piezoelectric transducer may be a PIN-PMN-PT or PMN-PZT crystal. The piezoelectric transducer may be a Mn-PIN-PMN-PT crystal or a Mn-PMN-PZT crystal. Alternatively, the piezoelectric transducer may be or include a piezoelectric ceramic material (e.g., PZT) or a piezoelectric polymer material (e.g., PVDF-polyvinylidene fluoride or polyvinylidene fluoride).

[0010] The piezoelectric crystal of the piezoelectric transducer is

[0011] and arranged to operate in a lateral extensional (3-2) mode, with the two axes of the piezoelectric crystal being substantially coaxial with the first magnet, the magnet array, the spacer, the second magnet and the vibrable mass.

[0011] The first magnet, the magnet array, and the second magnet may be rare earth magnets. The apparatus may further comprise an impedance matching layer and / or an acoustic lens disposed at an outer end of the second magnet.

[0012] The apparatus can include a first thin shim disposed between a first magnet and a first end of the piezoelectric transducer and a second thin shim disposed between a second magnet and an opposing second end of the piezoelectric transducer. The first thin shim and the second thin shim can be formed of a machinable glass-ceramic material.

[0013] The piezoelectric transducer may include a spacer disposed between the first magnet and the second magnet. The spacer may be significantly more compressible than the magnet array and the piezoelectric transducer. The spacer may define an opening for receiving the piezoelectric transducer therethrough. The spacer may have an axial thickness between about 1 mm and about 3 mm when the vibratable mass is at rest. The spacer may have an axial thickness between about 2.4 mm and about 2.8 mm when the vibratable mass is at rest.

[0014] The magnet array can define a passage through which the piezoelectric transducer extends, and the magnet array and the piezoelectric transducer may not contact each other within the passage. The magnet array can be symmetrical about multiple axes. The magnet array can include a single magnet body. The magnet array can include a plurality of magnet bodies fixed in position relative to each other. The axial spacer can be disposed between two of the plurality of magnet bodies. The apparatus can further include a coaxially disposed alignment disk disposed between two of the plurality of magnet bodies, the alignment disk can define an alignment opening in a center of the alignment disk for receiving and axially aligning the piezoelectric transducer. The alignment disk can be formed of a magnetically inert material. The magnet array can be substantially cylindrical.

[0015] The spacer may include a plurality of compressible ligaments arranged to separate the magnet array and the second magnet, and an axial length of the piezoelectric transducer is substantially the same as a combined axial length of the spacer and the magnet array.

[0016] In an alternative embodiment, the device may be configured to convert vibrational energy of a vibrable mass into electrical current in an electrical conductor, thereby functioning as an energy harvesting device.

[0017] Some embodiments relate to an aircraft or vessel that includes a device installed and / or attached to the aircraft or vessel to project vibrational energy from a component such as a mounting body of the aircraft or vessel. Some embodiments relate to a vessel that includes a device attached to the vessel to project vibrational energy from the vessel when the vessel is in use.

[0018] The magnet array may be disposed concentrically with the piezoelectric transducer.

[0019] The piezoelectric transducer may at least partially surround the magnet array. The piezoelectric transducer may include a plurality of stacked piezoelectric transducer elements. The magnet array may be a cylindrical magnet, in contact with either the first magnet or the second magnet, but not with both; and The cylindrical magnet may include one of: a cylindrical magnet in contact with a thin bonding layer that bonds the cylindrical magnet to the first magnet or the second magnet.

[0020] The combination of the first magnet, the magnet array, and the second magnet can be configured to exert a substantially static compressive force on the piezoelectric transducer of about 50 Newtons to about 500 Newtons. In some embodiments, the static compressive force is between about 5N to about 50N.

[0021] The static compressive force and the piezoelectric transducer motion can be aligned in the same axial direction.

[0022] The device can be configured to convert vibrational energy of the second magnet into electrical current in an electrical conductor, thereby functioning as an energy harvesting device.

[0023] The device may be configured to convert electrical current in the conductor into vibrations of a second magnet in the frequency range of about 300 Hz to about 100 kHz, thereby functioning as an acoustic projector.

[0024] Some embodiments provide an energy-transforming device, comprising: Piezoelectric transducer, an electrical conductor electrically coupled to the piezoelectric transducer; an axially aligned magnet assembly disposed to apply a static compressive force to the piezoelectric transducer, the magnet assembly having one end coupled to the base and an opposite free end; the magnet assembly is coaxial with the piezoelectric transducer, and at least a portion of the magnet assembly is concentric with the piezoelectric transducer; The magnet assembly defines a gap between axially adjacent portions of the magnet assembly, the gap being dimensioned so that the magnet assembly is small enough to apply a high static compressive force to the piezoelectric transducer, yet large enough to allow axial movement of the piezoelectric transducer without closing the gap.

[0025] In some embodiments, the static compressive force is between about 5 Newtons and about 50 Newtons. In alternative embodiments, the static compressive force is between about 50N and about 500N, optionally between about 90N and about 400N.

[0026] The gap may define an axial separation of between about 0.2 mm and about 1.0 mm between axially adjacent portions of the magnet assembly.

[0027] Some embodiments relate to an acoustic projection system that includes a plurality of the apparatus, or devices, described herein mounted to one or more mounting bodies for projecting vibrational energy from the one or more mounting bodies.

[0028] Some embodiments relate to an acoustic detection system that includes a plurality of the apparatus, or devices, described herein, mounted to one or more mounting bodies and configured to detect vibrational energy when each of the apparatus or devices is not being used for acoustic projection.

[0029] In various embodiments of the acoustic projection or detection system, the apparatus or devices may be positioned at spaced locations on one or more mounting bodies.

[0030] In various embodiments of the acoustic projection or detection system, a plurality of the apparatus or devices are arranged in an array or bank on one or more mounting bodies.

[0031] In various embodiments of an acoustic projection or detection system, multiple ones of the apparatus or devices are arranged to face in the same direction.

[0032] In various embodiments of an acoustic projection or detection system, multiple ones of the apparatus or devices are arranged to face in different directions.

[0033] In further detail below, embodiments are described, by way of example, with reference to the accompanying drawings in which: [Brief description of the drawings]

[0034] [Figure 1] FIG. 1 is a schematic exploded perspective view of an energy harvesting device according to some embodiments. [Diagram 2] FIG. 1 is a schematic block diagram illustrating an environment in which a vibration energy harvesting device can be used. [Diagram 3] 1 is an exemplary plot of frequencies at which a vibration energy harvesting device may be effective for generating electrical energy for some applications. [Figure 4] FIG. 1 is a schematic diagram of a piezoelectric transducer that can be used in a vibration energy harvesting device according to some embodiments. [Diagram 5] FIG. 1 illustrates a perspective view of a spacer used in a vibration energy harvesting device according to some embodiments. [Figure 6] FIG. 2 is a side view of a vibration energy harvesting device according to some embodiments, showing a magnet array having an example configuration. [Figure 7] 1 illustrates an alternative magnet arrangement for a vibration energy harvesting device. [Figure 8]1 is a schematic representation of a side view of a vibration energy harvesting device according to some embodiments. [Figure 9A] A top view taken from the inside of a vibration energy harvesting device showing a magnet arrangement around a piezoelectric transducer according to some embodiments. [Figure 9B] FIG. 2 is a top view of a vibration energy harvesting device according to another embodiment, showing an alternative magnet arrangement around a piezoelectric transducer. [Figure 10] 13 is a 3D plot to show the magnetic permeance of a magnet array versus the diameter and length of the magnet array for three different gap configurations. [Figure 11] 1 is a plot of the demagnetization field and magnetic flux density at a particular temperature for a magnet array. [Figure 12] 1 is a plot of magnetic force versus separation gap with a spacer plotted for various magnet outer diameters. [Figure 13] 1 is an exemplary plot of magnetic force versus outer diameter of a magnet. [Figure 14] 1 is a schematic diagram of an electro-acoustic transducer device according to some embodiments. [Figure 15] 1 is a schematic diagram of an electro-acoustic transducer device according to some embodiments. [Figure 16] 1 is a schematic diagram of an electro-acoustic transducer device according to some embodiments. [Figure 17] 1 is an exemplary plot of measured impedance versus frequency from an exemplary electro-acoustic transducer device. [Figure 18] FIG. 2 is a schematic diagram of a sine wave tone burst. [Figure 19] FIG. 1 is a schematic diagram showing the through-transmission of conventional air-coupled ultrasound. [Figure 20] FIG. 1 is a schematic diagram showing air-coupled ultrasound transmission from a transmitter and receiver on the same side of a transmission medium. [Figure 21] 1 is a schematic diagram of an exemplary craft carrying an electroacoustic conversion device, according to some embodiments. [Figure 22]1 is an exemplary plot of head magnet length and magnetic force for selected axial gap spacings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] The embodiments relate generally to high frequency vibrational energy conversion devices and systems. The embodiments include a vibratable mass as part of the device. In particular, the embodiments relate generally to novel configurations of magnets and piezoelectric transducers intended to hold the piezoelectric transducers in compression. For example, some embodiments can apply a static compressive force to the piezoelectric transducers in the range of about 5 Newtons (N) to about 50 Newtons or about 50 Newtons to about 500 Newtons.

[0036] Some vibrational energy conversion embodiments are optimized for the collection of vibrational energy by converting it to electrical energy, while other embodiments are optimized for the generation of pressure waves by converting electrical energy to (kinetic) vibrational energy. Embodiments optimized for the generation of pressure waves by converting electrical energy to (kinetic) vibrational energy can be described as electroacoustic conversion (or "acoustic projection") devices. Many of the same energy conversion principles and device design considerations apply to both forms of conversion.

[0037] Embodiments of vibration energy conversion devices and techniques optimized for harvesting vibration energy, but also suitable or modifiable for generating pressure waves, are first described with reference to figures 1 to 13. Figures 1 and 6 show in detail the arrangement of components of a vibration energy converter optimized as a vibration energy harvesting device 100 according to some embodiments. Figure 8 is a schematic cross-sectional view of a vibration energy harvesting device 800 having the same components and configuration as the device 100, but with an alternative magnet arrangement. The embodiments of the vibration energy harvesting devices 100, 800 are generally arranged as an axial stack of coaxial components. This means that vibrations only along an axis perpendicular to the axis of the energy harvesting device 100, 800 excite the energy harvesting device 100, 800 in a negligible or not at all.

[0038] The vibrational energy harvesting device 100 includes a base 110 secured, coupled, or otherwise connected to a vibratory host structure 210 via a mount 215 (see FIG. 2 ). As used herein, the term proximal refers to a direction toward the base 110 and the term distal refers to a direction away from the base 110. The vibratory host structure 210 may form part of, for example, a plant, equipment, vehicle, or craft 200. The craft 200 may include an aircraft, such as a helicopter, and the vibratory host structure 210 may include, for example, a gearbox. In some embodiments, the base 110 may be omitted.

[0039] In some vibrational energy harvesting applications, it is beneficial to match the resonant frequency of the vibrational energy harvesting device to the resonant frequency of the host structure 210. In other applications, it may be preferable for the resonant frequency of the vibrational energy harvesting device to not match the resonant frequency of the host structure 210.

[0040] The vibration energy harvesting device 100 further includes a first magnet 112, a second magnet 150, and a magnet array 130 between the first magnet 112 and the second magnet 150. Also interposed between the first and second magnets 112, 150 are first and second shims 115a, 115b, a spacer 140, thin adhesive layers 114, 116, 117, and optionally an alignment disk 135. Also disposed between the first magnet 112 and the second magnet 150 and at least partially surrounded by the magnet array 130 is a piezoelectric transducer 120. These components of the vibration energy harvesting device 100 are housed within a housing 170. The components of the vibration energy harvesting device 100 are generally aligned along a single central axis 165. The axis 165 also corresponds to a proximal-distal direction as described herein. The magnet array 130 defines a passage through which the piezoelectric transducer 120 extends, and the magnet array 130 and the piezoelectric transducer 120 do not contact each other in the passage.

[0041] As used herein, the term magnet array is intended to describe an array that includes one magnet or a combination of magnets that cooperate to achieve a described function. A magnet assembly as described herein is intended to describe a combination of multiple magnets that are physically and / or magnetically coupled together. A magnet array may include a magnet assembly, and a magnet assembly may include a magnet array. However, certain embodiments described herein contemplate a magnet assembly that includes a magnet array. For example, vibration energy harvesting devices 100, 800 include a magnet assembly that includes a magnetic head and tail mass and a magnetic array between the head and tail mass.

[0042] The first and second magnets 112, 150 are preferably rare earth magnets, which have a strong attraction to magnetic materials. The first magnet 112 is magnetically and / or mechanically coupled to the base 110 proximal to the first magnet 112. The first shim 115a is disposed distal to the first magnet 112 and is adhered thereto by adhesive layer 114. The adhesive layers 114, 116, and 117 may include, for example, a suitable epoxy adhesive, such as CB359. The first and second shims 115a, 115b may be, for example, machinable glass ceramic shims. An exemplary material for such shims is a machinable glass ceramic material commercially available under the Macor brand sold by Corning, Inc. Such shims may be suitable because they may allow for a small amount of surface deformation. This may provide a slightly softer surface than most rare earth magnets, reducing the likelihood of breakage forming in the piezoelectric transducer (if formed as a crystal). This is due, for example, to the relatively high static compressive forces applied to the piezoelectric transducer by the magnet assemblies described herein. However, in some embodiments, other similarly deformable materials can be used in place of the shims 115a, 115b. Such similar materials can be provided, for example, as a coating, layer, layer with a material composition gradient, or thin sheet disposed on the distal side of the first magnet 112 or the proximal side of the second magnet 150. Such similar materials can include, for example, a magnet-glass composite with a higher glass concentration at the surface intended to contact the piezoelectric transducer 120.

[0043] The magnet array 130 is disposed on the distal side of the first shim 115a and is adhered thereto by the adhesive layer 116. Thus, the proximal end of the magnet array 130 is bonded to the distal face of the first shim 115a. The magnet array 130 is generally cylindrical with an annular cross-section defining an internal bore or hollow for receiving the piezoelectric transducer 120 therein. The magnet array 130 shown in FIGS. 1 and 6 is composed of a plurality of axially stacked concentric magnetic annular portions 131. Each of the annular portions 131 may be adhered to adjacent distal and proximal axial structures by the adhesive layer 116. Each of the magnetic annular portions 131 is preferably a rare earth magnet.

[0044] The purpose of the magnet array 130 is to surround or at least partially surround the piezoelectric transducer 120 while exerting strong magnetic attraction on axially adjacent components so that a compressive force is applied to both ends of the piezoelectric transducer 120. This strong magnetic attraction is due to the small spacing between adjacent magnets and the selection of magnet materials such as those used in rare earth magnets. The piezoelectric transducer 120 is held under compression due to the strong magnetic attraction between the components of the magnet array 130 and / or the first and second magnets 112, 150. For some piezoelectric materials such as piezoelectric ceramics or piezoelectric crystals, which are the preferred form of the piezoelectric transducer 120, allowing such materials to be subjected to tension can rapidly result in structural failure of the material.

[0045] The presence of the spacer 140 within the axial stack of magnets that make up the magnet array 130, and the first and second magnets 112, 150 aligned along axis 165, ensures that there is a small axial gap (occupied by the relatively compressible spacer) that allows some relative axial movement of the tip mass 160 relative to the base 110 or at least the first magnet 112. This relative axial movement is made possible by the spacer 140 having an effective spring constant that is at least one or two orders of magnitude less than the spring constant of the first and second magnets 112, 150 and the magnet array 130, and at least one or two orders of magnitude less than the spring constant of the piezoelectric transducer 120. This allows the spacer 140 to experience small axial compressions and expansions when the host structure 210 (to which the base 110 is coupled) vibrates. The mount 215 that couples the vibration energy harvesting device 100 to the host structure 210 can have its own spring constant that factors into the transmission of vibrations, but generally, the spring constant of the mount 215 is intended to be one or two orders of magnitude higher than the spring constant of the spacer 140. Due to the inertia of the tip mass 160, vibrations transmitted through the base 110 tend to result in repeated compression of the spacer 140 and simultaneous repeated compression of the piezoelectric transducer 120.

[0046] The spacer 140 has a plate-like base 141 that defines a central opening 142 sized to allow the piezoelectric transducer 120 to pass through. The central opening 142 may be, for example, slightly larger than 4 mm by 4 mm. The spacer base 141 has a series of radially oriented ligaments 144 projecting upwardly therefrom. Each of the ligaments 144 has the same height so that the spacer 140 can remain equidistant from its proximal side to its distal side during vibration. The spacer 140 is formed of a material, such as a suitable plastic material, having a spring constant on the order of 1 / 10 or less of the spring constant of the piezoelectric transducer 120. The gap maintained by the spacer 140 may be, for example, on the order of about 2.6 mm when the resonating tip mass 160 is at rest. The described arrangement allows for approximately 10 microns of axial movement and compression of the piezoelectric transducer 120 during vibration.

[0047] The gap maintained by the presence of the spacer 140 is selected, for example, such that the compressive force due to magnetic attraction is between about 50 Newtons and about 500 Newtons (N). The spacer 140 can have an axial thickness of between about 1 mm and about 3 mm when the resonating tip mass 160 is at rest. In some embodiments, the spacer can have an axial thickness of between about 2.4 mm and about 2.8 mm when the resonating tip mass 160 is at rest.

[0048] In some embodiments, the spacer 140 is axially disposed between the two annular portions 131 of the magnet array 130. In other embodiments, the spacer 140 may be disposed distal to the magnet array 130 such that the spacer 140 is axially disposed between the magnet array 130 on its proximal side and the second magnet 150 (and second shim 115b) on its distal side. The second magnet 150 is magnetically or mechanically coupled to a resonating tip mass 160 distal to the second magnet 150.

[0049] The resonant tip mass 160 is only coupled to the second magnet 150, or possibly an intervening structure, proximal to the tip mass 160. The distal end of the resonant tip mass 160 is not fixed in position and is free to move axially. In some embodiments where the vibration energy harvesting device 100 is disposed within a housing, the housing allows some freedom of lateral and / or axial movement, for example on the order of 2-5 mm, before the resonant tip mass 160 contacts the housing wall. The resonant tip mass 160 may be formed primarily of tungsten carbide, for example.

[0050] The first and second shims 115a, 115b are selected to have a relatively low Young's modulus so as to be soft enough to allow the piezoelectric transducer 120 (if formed as a crystal) to be less than perfectly axially aligned during manufacture or use of the vibrational energy harvesting device 100, 800. The shims 115a, 115b may have a thickness of, for example, less than 1 mm. Otherwise, the crystal structure of the piezoelectric transducer 120 may be prone to fracture and / or excessive wear during vibration under compression. For such reasons, shims having similarly low Young's modulus are used in other energy transducer device embodiments described herein, such as electroacoustic conversion devices, examples of which include the sound projectors 1400, 1500, 1600.

[0051] In some embodiments, a thin alignment disk 135 may be present in the center of the axial stack of annular portion 131 of magnet array 130. Alignment disk 135 defines a central opening 136 sized slightly larger than the outer periphery of piezoelectric transducer 120. Alignment disk 135 serves to aid in positioning piezoelectric transducer 120 in axial alignment with magnet array 130. An opening 142 in spacer 140 also serves a similar alignment function as alignment disk 135. Both spacer 140 and alignment disk 135 may be formed, for example, of a suitable polycarbonate material.

[0052] Figure 3 is an exemplary plot of power spectral density (PSD) for frequencies up to 3 kHz. Figure 3 shows the power spectral density of acceleration measurements made on top of the resonating mass 160 with the base 110 driven by a broadband vibration in the range of 30-3000 Hz. The peak shown in the 2000-2500 Hz region is the resonant region, indicating that the response is relatively broadband, in this case over a band of about 500 Hz.

[0053] FIG. 4 is a diagram of an exemplary piezoelectric transducer 120 in the form of a piezoelectric crystal. The piezoelectric transducer 120 can be formed of other suitable materials, such as, for example, a piezoelectric ceramic, such as lead zirconate titanate (PZT), or a piezoelectric polymer material, such as PVDF (polyvinylidene fluoride). Certain piezoelectric crystals may be more effective as transducer devices than others. For example, piezoelectric crystals that are mechanically soft and anisotropic in their axis may be preferred to allow the vibration energy harvesting device 100, 800 to resonate at lower frequencies. Preferred materials for the piezoelectric transducer 120 include single crystal ferroelectric materials. Ferroelectric single crystals convert mechanical energy into electrical energy and vice versa. This makes them candidates as active materials for energy harvesting devices. By utilizing the direct piezoelectric effect when machinery is available from the environment, machinery can be converted into charge polarization of relaxor ferroelectric single crystal materials, and useful amounts of energy can be obtained.

[0054] A currently promising class of materials for energy harvesting are relaxor ferroelectric single crystals (RFSCs). These materials are single crystals of ferroelectric materials (e.g., known as lead zinc niobate-titanate, PZN-PT). These materials have been shown to provide relatively high output voltages with higher efficiency when the crystals are exposed to stress. In some ferroelectric crystal material compositions, for example, certain compositions of ternary indium niobate-lead magnesium niobate-lead titanate (PIN-PMN-PT), the crystal material undergoes a phase transformation when exposed to a critical amount of stress from an external source.

[0055] Relaxor single crystals exhibit both linear piezoelectric effect and nonlinear electromechanically coupled phase transitions. The linear piezoelectric effect of relaxor single crystals has been observed to be approximately six times that of ceramic lead zirconate titanate (PZT). Reversible stress- and temperature-induced phase transformations are associated with spontaneous charge generation in relaxor single crystals. These phase transformations can increase the energy density per cycle for mechanical energy harvesting by more than an order of magnitude. By utilizing this phase transformation behavior, stress-biased energy harvesting devices can take full advantage of the phase transformations of relaxor single crystal materials.

[0056] Lead zirconate titanate (Pb[Zr x Ti 1-x ]O 3 Pb(ZnT, or PZT) materials typically exhibit a piezoelectric charge constant, d, in the range of 150-500 pC / N and an electromechanical coupling coefficient, k, of about 0.3 to 0.7. RFSC materials can exhibit significantly larger charge constant, d, and coupling coefficient, k, parameters. For example, the first generation RFSC material Pb(Zn 1 / 3 Nb 2 / 3 )O 3 (PZM-PT) and Pb(Mg 1 / 3 Nb 2 / 3 )O 3 (PMN-PT) have electromechanical coupling coefficients exceeding 0.9 and piezoelectric charge constants that can be an order of magnitude larger than PZT. These improved coefficients exist in relaxor ferroelectric compositions close to the morphotropic phase boundary (MPB). The first generation materials are not without their drawbacks. For example, the coercive field of PMN-PT is much smaller than that of PZT (E C Approximately 8~15kVcm -1 ) is smaller than that of (E C Approximately 1.8kVcm -1 ). The rhombohedral-tetragonal phase transition temperature PMN-PT is low (T RT 85°C), which means that such materials may not be compatible with high temperature applications. 1 / 2 Nb 1 / 2 )O3 -Pb(Mg 1 / 3 Nb 2 / 3 )O 3 -PbTiO 3 Second generation RFSC materials such as PIN-PMN-PT have relatively high transition temperatures (T RT Approximately 120°C to 140°C) and approximately three times the coercive field (E C The properties of the materials, such as d ~ 5.5 kV / cm, show promise for use in energy harvesting devices. They also have piezoelectric charge constants that can be orders of magnitude higher than PZT (e.g., d ~ 1000-5000 pC / N).

[0057] More recently, third generation manganese modified Pb(Mg 1 / 3 Nb 2 / 3 )O 3 -Pb(Zr,Ti)O 3 (Mn-PMN-PZT)

[0011] poled single crystals have been reported to have power densities more than five times that of PZT4 ceramics. Third generation relaxor ferroelectric single crystals have shown improved fracture toughness and coercive field, as well as higher Curie and phase transition temperatures.

[0058] An additional advantage of RFSC materials for energy harvesting is their anisotropic material parameters, with the electromechanical compliance s and charge constant d being able to vary significantly with crystal orientation. d 32 The transverse extension mode (or "3-2 mode") is particularly useful for energy harvesting applications. When used with polarized RFSCs, the "3-2 mode" allows the design of harvesting devices to: (i) have a large d for improved electromechanical transduction compared to PZTs; 32charge constant, (ii) a large coupling coefficient k ≈ 0.9 to similarly improve transduction efficiency, and (iii) the ability to exploit the mechanically soft “2” axis of the

[0011] PIN-PMN-PT. The “2” axis of the

[0011] PIN-PMN-PT is significantly larger than its “1” axis and has much greater compliance than PZT, allowing the resonant frequency of the harvesting device to be lowered by a factor of 3 to 2 for ideally sized transducer elements. In addition to these three advantages of “3-2 mode” transduction, there is evidence that

[0011] poled RFSC materials are more resistant to large cycle induced degradation than

[0100] poled materials. These advantages mean that “3-2 mode”

[0011] poled PIN-PMN-PT single crystals may be suitable for use as piezoelectric transducers in vibration energy harvesting devices.

[0059] FIG. 5 is a perspective view of a spacer 140 according to some embodiments. While various configurations can be selected to achieve similar functionality, the illustrated embodiment of the spacer 140 has been shown to have the effect of providing a compressible gap between axially adjacent magnetic components of the axial stack, thereby allowing for variable compression of the piezoelectric transducer 120 (positioned and aligned with the aperture 142) depending on the vibrations undergone by the vibration energy harvesting device 100. The upper surfaces 146 of the ligaments 144 can be made generally coplanar and bonded, for example, to the proximal surface of the annular portion 131 or the second shim 115b. Advantageously, an array of radially oriented ligaments 144 spaced around the distal surface of the spacer base 141 allows electrical conductors to pass through the spaces 143 between the ligaments 144, so that their electrical conductors (e.g., 811a, 811b, FIG. 8) can be coupled to the opposite conductive surfaces of the piezoelectric transducer 120. The piezoelectric transducer 120 may have a conductive epoxy 122 on its opposing side to easily allow the conductors 811 a, 811 b to be electrically coupled to the piezoelectric transducer 120.

[0060] The ligaments 144 are formed such that their combined mechanical stiffness is much less than that of the piezoelectric transducer 120, so as not to interfere with the primary resonance of the energy harvesting device 100, 800, which is ostensibly determined by the effective spring constant of the piezoelectric transducer 120 and the size of the resonating tip mass 160. The spacer 140 should have an effective mechanical stiffness less than 10 times that of the piezoelectric transducer 120, so that any secondary resonances resulting from spacer / resonating mass interaction are sufficiently removed from the primary frequency of interest of the energy harvesting device 100, 800. Additionally, an approximate 10:1 ratio of transducer to spacer stiffness ensures that magnetic compression forces act primarily through the piezoelectric transducer 120, maximizing magnetic compression of the piezoelectric transducer 120 and minimizing the possibility of tension during resonant motion.

[0061] The spacer 140 can be formed of a magnetically passive material, such as, for example, aluminum, polycarbonate, or similar materials. Some embodiments can use a spacer 140 that includes a ferromagnetic material, provided that such material has a suitably low spring constant and does not have the effect of reducing the magnetic attraction between adjacent opposing magnetic components of the spacer 140. The spacer 140 needs to be durable under dynamic loads to ensure a long operational life of the harvesting device 100, 800. Furthermore, the mechanical and material properties of the spacer 140 should not change significantly at high temperatures. The spacer 140 can be designed to protect the piezoelectric transducer 120 from mechanical bending stresses when the harvesting device 100, 800 is oriented horizontally or when there is a lateral component to the host vibration. Due to the low aspect ratio of the spacer 140 (τ=length / outer diameter), it is estimated that the spacer 140 fabricated from 3D printed polycarbonate will only tolerate small static deflections, on the order of a few μm, which is unlikely to be enough to damage the piezoelectric transducer 120.

[0062] FIG. 7 shows a hollow cylindrical magnet as an example of a magnet arrangement 730 that can be used in place of the magnet arrangement 130. The magnet array 730 can be a single continuous body. The outer diameter (OD) of the magnet array 730 can be approximately the same as the outer diameter of the magnet array 130 and can be approximately the same as the outer diameter of the first and second magnets 112, 150. The magnet array 730 also has an inner diameter (ID) that defines an inner axial bore 732 large enough to accommodate the maximum dimension of the piezoelectric transducer 120 without contacting the piezoelectric transducer 120 during normal operation. The magnet array 730 has an axial magnetization M that is aligned with the inner bore of the magnet body. The length (L) of the magnet array 730 is approximately the same as the length of the piezoelectric transducer 120 minus the axial length of the spacer 140. In other words, the axial length of magnet array 730 (and 130) plus the axial length of spacer 140 and optional alignment disk 135 (if present) approximately equals the length of piezoelectric transducer 120. Magnet array 730 defines a passage through which piezoelectric transducer 120 extends, and magnet array 730 and piezoelectric transducer 120 do not contact each other at the passage.

[0063] In some embodiments, the piezoelectric transducer 120 can be an RFSC with dimensions of about 4 mm x 4 mm (width and depth) and a length of about 12 mm. For a piezoelectric transducer 120 in the form of an RFSC, the crystals are about 2x2 mm. 2 and about 5x5mm 2 The length of such crystals may be between about 5 mm and about 10 or 12 mm, for example up to about 15 or 20 mm or even 75 mm.

[0064] FIG. 8 is a schematic cross-sectional view of a vibration energy harvesting device 800 of the same configuration as the vibration energy harvesting device 100, except that the device 800 uses a magnet array 730 with a spacer 140 disposed between the magnet array 730 and the second magnet 150. The adhesive layers 114, 116, 117 are optional but are not shown to avoid unnecessarily obscuring FIG. 8. Similarly, shims 115a, 115b are not shown in FIG. 8 but are present between the first magnet 112 and the piezoelectric transducer 120 and between the second magnet 150 and the piezoelectric transducer 120. For example, FIG. 8 shows electrical conductors 811a, 811b, which may be in the form of thin wires extending through the gaps between the ligaments 144 of the spacer 140 to contact and electrically couple opposite sides of the piezoelectric transducer 120.

[0065] Figures 9A and 9B show alternative magnet configurations. Figure 9A shows a top view of a continuous cylindrical magnet array 730 looking proximal from the second magnet 150 as shown in Figures 7 and 8. The magnet array 730 can have an outer diameter substantially the same as the outer diameter of the first magnet 112 and / or the second magnet 150.

[0066] FIG. 9B shows an alternative configuration of the top view, looking proximal from the second magnet 150, where the magnet array partially but not completely surrounds the piezoelectric transducer 120. For example, a magnet array partially surrounding the piezoelectric transducer 120 may include at least two magnetic bodies 931, 932 arranged on opposite sides of the piezoelectric transducer 120 (e.g., laterally rather than axially). More than two magnetic bodies can be aligned or arranged, such as three, four, five, six, or more, to at least partially surround the piezoelectric transducer 120. As shown in FIG. 9B, at least two magnetic bodies 931, 932 can be arranged such that there is at least one axis of symmetry when viewed from above. The configuration of the magnet array in the vibration energy harvesting device 100, 800 can be changed if a suitable spacer can be accommodated to separate axially adjacent magnetic components by a small distance so that the strong magnetic attraction between the axially adjacent magnetic components can be used to provide a relatively strong magnetic compressive force on the compressible (soft) shaft of the piezoelectric transducer 120.

[0067] Conversely, in other alternative configurations, the vibrational energy converter may include at least two piezoelectric transducer bodies arranged on opposite sides of a central or intermediate magnetic body. More than two piezoelectric transducer bodies may be aligned or arranged, such as three, four, five, six or more, to at least partially surround the central or intermediate magnetic body. The at least two piezoelectric transducer bodies may be arranged such that there is at least one axis of symmetry when viewed from above.

[0068] In embodiments of vibrational energy harvesting devices 100 and 800, the magnetic components 112, 130, 730, 150, spacer(s) 135 and 140, tip mass 160 and piezoelectric transducer 120 are coaxial along a single axis 165 extending between the proximal and distal ends of the device 100, 800. Preferably, the magnetic components 112, 130, 730, 150, spacer(s) 135 and 140, tip mass 160 and piezoelectric transducer 120 are concentric. In the rest (non-vibrating) position of the vibrational energy harvesting devices 100 and 800, each component is in contact with another axially adjacent component. The vibrational energy harvesting devices 100 and 800 have no air gaps other than the hollow bores of the spacer 140 and magnet array 130, 730.

[0069] The compressive force applied to the piezoelectric transducer 120 (in the form of any suitable crystal described herein) by the combination of the second magnet 150 and the magnet array 730 has been estimated using the process described below.

[0070] A set of typical anticipated shapes for magnet array 730 are detailed in Table 1. [Table 1]

[0071] For an ideal permanent magnet, the magnetization M is independent of the magnetic field H, resulting in a linear flux BH demagnetization curve in the second quadrant. The magnetization M of the cylindrical magnet array is required for the calculation of magnetic force, not the magnetic flux B. For an ideal permanent magnet, M is independent of H, so if the magnet is ideal (i.e. for a N38H magnet, M r =1.26T / μ 0 Approximately 1.003MA / m, μ in the formula 0 is the permeability of free space (approximately 4π×10 -7 H / m), M inside the cylinder is the residual magnetization M r The value of M is somewhat lower because we do not assume an ideal magnet but use the actual BH / MH properties of the material.

[0072] Permeance coefficient P to determine the slope of the load line C =[1-N z ] / N z When determining the magnetic operating point through the cylinder shape demagnetization factor N z Table 2 shows examples of permeance coefficients for various cylindrical shapes.

[0073] [Table 2]

[0074] For the purposes of calculating the permeance, an operating temperature of 100°C was assumed. A conservative estimate of the magnetic permeance of the cylindrical magnet array was made taking into account the tubular nature of the magnet array 130, 730 and also the additional spacing provided by the machinable glass shims 115a, 115b. The second magnet 150 was not included in the magnetic permeance estimate, adding to the conservative nature of the estimate. FIG. 10 shows a plot 1000 of the predicted magnetic permeance as a function of geometry, with the minimum permeance P c It shows about 1.5H.

[0075] Using this conservative estimate of magnetic permeance, we mapped a magnetic load line (i.e., with a slope equal to a permeance of 1.5) onto a data sheet for a typical high-temperature neodymium-boron-iron magnet (N38H). This allowed us to determine the BH operating point and from there estimate the magnetic polarization J (see plot 1100 in Figure 11, adapted from a plot in a document provided prior to March 5, 2020 at https: / / www.eclipsemagnetics.com / media / wysiwyg / brochures / neodymium_grades_data.pdf / ). Knowing the magnetic polarization J, we can calculate the magnetization M, which is then used to calculate the magnetostatic energy constant K d This K d is conservative and valid for all magnetic geometries and temperatures considered (up to 100°C).

[0076] Calculated K d By substituting into the following equation (taken from equation 4 in David Vokoun, Marco Beleggia, Ludek Heller, Petr Sittner, “Magnetostatic interactions and forces between cylindrical permanent magnets”, Journal of Magnetism and Magnetic Materials, 321 (2009) 3758-3763), we can calculate an estimate of the magnetic force:

number

[0077] 12 and 13 show plots 1200 and 1300 of magnetic compression force as a function of gap (determined by the axial thickness of the spacer 140) and outer diameter OD, respectively. For larger magnets, forces in the range of 100N are expected, and compression of 400N is easily achievable. It is estimated that forces in the range of about 50N to about 500N can be achieved with the described axial arrangement of the vibration energy harvesting device 100, 800. A compression force of 400N is the force required to generate mechanical compressive stresses in the range of, for example, 20MPa, which is necessary to exploit the phase transition mechanism of RFSC in a resonant harvesting device such as the vibration energy harvesting device 100, 800. Operation of an energy harvesting device as described herein near the phase transition may lead to higher energy harvesting efficiency, but such operation is not necessary and energy harvesting efficiency in other piezoelectric states is still acceptable.

[0078] Exemplary design features of the magnetic preloading approach are shown in Figures 1, 6, and 14. According to some embodiments, the magnetic support structure including the magnet array 130 or 730 is shown generally as a series of ring magnets around a rectangular piezoelectric plate element such as the piezoelectric transducer 120. Figures 12, 13, and 22 show estimated or plotted relationships of device parameters (magnet outer diameter, gap, head mass length, etc.) based on example device dimensions and configurations described immediately below. In such an example embodiment, the ring magnets may have an outer diameter rm-OD and an inner diameter rm-ID, each ring magnet having a height of about 1.65 mm and an overall height rm-H of the ring magnet. The same rm-OD can be applied even if a single cylindrical magnet 730 is used instead of stacked ring magnets. The (distal) head magnet 150 is attracted to the magnetic support structure 130 or 730 and exerts compression on both the piezoelectric ceramic element 120 and the spacer 140, with an outer diameter similar to r-OD, and a height hm-H of about rm-OD / 2. An additional head mass (e.g., 160 in FIG. 1 or 6) can be included, having a diameter similar to the rm-OD and a height selected to tune the resonant frequency of the device, if desired. The tail magnet 112 completes the magnetic circuit and has a diameter similar to the rm-OD and a height similar to that of the head mass 150 (hm-H).

[0079] An exemplary spacer 140 is shown in Figure 5, where the vertical ligaments are designed to have approximately one-tenth the mechanical stiffness of the (crystalline) piezoelectric transducer 120. The spacer 140 creates a gap in the magnetic circuit with a height gap -H. A thin disk 114 of machinable glass (e.g., made of Macor™) with a height MH = 0.8 mm, which protects the piezoelectric transducer 120 from damage during mechanical loading, can be placed between either end of the piezoelectric element 120 and, optionally, the ring magnet 130.

[0080] The total height of the ring magnet is rm-H=(piezoelectric transducer length)+(2*glass disk height)-gap-H. If necessary, small variations in height can be accommodated by placing a very thin disk layer of polymer, such as polycarbonate, between adjacent ring magnets. An exemplary embodiment uses a 12mm x 4mm x 4mm RFSC element as the piezoelectric transducer 120. The proof mass can consist of the head magnet and a single ring magnet, with shims 114 and other insignificant masses not significantly affecting the resonant frequency of the device.

[0081] According to one embodiment of the vibration energy harvesting apparatus of devices 100, 800, 1400, an approximate static compressive magnetic force of 50 N can be applied to the piezoelectric transducer 120 with rm-OD=20 mm, rm-ID=10 mm, gap-H=4 mm, rm-H=(12+2*0.8)-4=9.6 mm, hm-H=10 mm, under vibration with a maximum frequency of approximately 4.5 kHz.

[0082] According to another vibration energy harvesting apparatus embodiment of devices 100, 800, 1400, an approximate static compressive magnetic force of 500 N can be applied to the piezoelectric transducer 120 with rm-OD=50 mm, rm-ID=25 mm, gap-H=3 mm, rm-H=(12+2*0.8)-3=10.6 mm, hm-H=25 mm under vibration (i.e., only the head magnet as proof mass) with a maximum frequency of approximately 1.2 kHz.

[0083] For an Acoustic Projector embodiment of devices 100, 800, 1400 with a maximum drive frequency of 45 kHz (i.e., only head magnet 1450 as proof mass), an approximate static compressive magnetic force of 45 N can be generated with rm-OD=20 mm, rm-ID=10 mm, gap-H=1 mm, rm-H=(12+2*0.8)-1=12.6 mm, hm-H=1.5 mm. A further example modeled Acoustic Projector embodiment (a single 12x4x4 mm magnet generating a DC displacement of 2 microns under 90 N compression) 3Modeling with RFSC indicates that for a vibration (drive) frequency of 8.75 kHz with a drive voltage of 5V, a static compression force of about 31.5 N is required, for a vibration frequency of 17.5 kHz with a drive voltage of 5V, a static compression force of about 15.8 N is required, for a vibration frequency of 42.2 kHz with a drive voltage of 5V, a static compression force of about 6.5 N is required, for a vibration frequency of 45 kHz with a drive voltage of 5V, a static compression force of about 6.1 N is required, for a vibration frequency of 45 kHz with a drive voltage of 50V, a static compression force of about 61.3 N is required, and for a vibration frequency of 42.2 kHz with a drive voltage of 50V, a static compression force of about 65.3 N is required. Such modeled embodiments indicate that for a vibration frequency of about 50 kHz or greater with a drive voltage of 5V, a static compression force of about 5 N is required. Moreover, such modeled embodiments indicate that static compressive forces in the vicinity of about 50 N are feasible for vibration frequencies between about 300 Hz and about 8.75 kHz with drive voltages of 5 to 50 V.

[0084] Such exemplary embodiments are presented to illustrate some exemplary device configurations and to show how different device configurations can result in different static compression forces and operate under different vibration or drive frequencies. A variety of other device configurations are possible based on the principles described herein and illustrated in the figures without departing from the described embodiments.

[0085] 2, some embodiments relate to a movable craft or stationary plant 200 having a vibration host structure 210 with a vibration energy harvesting device 100, 800 attached in fixed relationship thereto via a mount 215. The craft or plant 200 may have multiple such vibration energy harvesting devices 100, 800 attached to the same or different host structures 210. The craft or plant 200 may have one or more sensors 230, for example, for monitoring machine conditions. The energy output of the one or more vibration energy harvesting devices 100, 800 may be provided to one or more batteries 220 (or other electrical energy storage devices) electrically coupled to the one or more sensors 230. The one or more sensors 230 may then provide an output to, for example, a monitoring system 240 using electrical energy from the batteries.

[0086] Some embodiments of the vibrational energy harvesting devices 100, 800 are designed to be able to operate effectively at somewhat higher temperatures to enable them to function properly at conditions typically experienced in the operating plant of the plant or craft 200. For example, the vibrational energy harvesting devices 100, 800 may be designed to be able to operate with greater efficiency at temperatures between 80 and 120 degrees Celsius.

[0087] 14 to 20, embodiments of a conversion device optimized for electroacoustic conversion (including acoustic projection), but also suitable or modifiable for energy harvesting, will now be described. FIG. 14 is a schematic diagram of a vibration energy converter optimized as an acoustic projector device 1400, which has similar components and design principles as the vibration energy harvesting apparatus 100, 800, except that the acoustic projector 1400 is designed to convert electrical energy from a current source 1455 into vibration energy for generating an output pressure wave 1460. An embodiment of the acoustic projector 1400 can also be used as a sensor device when it is not actively generating pressure waves. When functioning as a sensor device, the acoustic projector 1400 can convert vibrations into electrical signals in the manner described above for vibration energy harvesting, and the electrical signals can be processed by a separate processing device or circuitry associated with the acoustic projection system. Thus, the acoustic projector 1400 is an example of an electroacoustic conversion device that can, for example, emit pressure waves and receive (detect) pressure waves at different times.

[0088] The sound projector 1400 includes a base 110, a magnetic tail mass similar to the first magnet 112, thin shims 115a, 115b, a piezoelectric element 120 at least partially surrounded by a magnetic support structure (such as magnet array 130, 730), a spacer 140, and a head mass 1450. An alignment disk 135 may also be included in the axial stack of projector components in a manner similar to the vibration energy harvesting device 100 made possible by the shape of the magnetic support structure. Such components are contained in a housing 1470.

[0089] The housing 1470 may include a case for enclosing and holding the components of the Sound Projector 1400 together. The housing 1470 may also include a decoupling material between the case and the head mass 1450. In some embodiments, a soft sealing outer case, such as a rubber casing, surrounds some or all of the housing 1470. The housing 1470 may be a ferromagnetic material, such as steel, mu-metal, or iron, for example, to complete a magnetic circuit with the components of the magnetic assembly, including the magnetic tail mass 112, the magnet arrays 130, 730, and the head mass 1450.

[0090] In some embodiments, the head mass 1450 functions as both a distal magnet and a head mass. However, in some embodiments, the head mass 1450 includes a magnet as shown in FIG. 14 and an additional non-magnetic mass, such as, for example, a tungsten carbide mass. The head mass 1450 may also have an impedance matching layer 1458 and / or an acoustic lens disposed on or adjacent its outer distal surface 1452. Alternatively, the impedance matching layer 1458 and / or an acoustic lens may be used in place of the tungsten carbide mass.

[0091] The spacer 140 used in the sound projector 1400 may be located more proximally, but is substantially the same as the spacer 140 used in the vibration energy harvesting devices 100, 800. For example, the spacer 140 and sound projector 1400 may be located axially between the magnet array 130, 730 and the magnetic tail mass 112. A shim 115a may be located between the spacer 140 and the magnetic tail mass 112. As with the vibration energy harvesting devices 100, 800, the piezoelectric element 120 passes through an opening in the spacer 140 and contacts the shim 115a, whereby the piezoelectric element 120 is compressed at its proximal end by an axial force due to magnetic compression. At its distal end, the piezoelectric element 120 is adjacent to a distally located shim 115b, which is bonded to the head mass 1450.

[0092] The Sound Projector 1400 applies an alternating current source 1455 to the piezoelectric element 120 (which may be formed of any of the piezoelectric crystal materials described above) to cause axial expansion and contraction at frequencies ranging from about 300 Hertz to about 100 kHz. This small axial expansion and contraction is due to the selected orientation of the flexible axis of the piezoelectric crystal selected for the piezoelectric transducer 120. The resulting displacement of the piezoelectric transducer 120 may be on the order of 1 or 2 microns to about 100 microns, depending, for example, on the mass of the magnets in the magnet assembly plus any additional head mass. Any of the piezoelectric materials discussed above in connection with the vibration energy harvesting device 100 may be used for the piezoelectric element 120 of the Sound Projector 1400.

[0093] The motion of the piezoelectric transducer 120 under the influence of current from the AC source 1455 causes axial displacement of the magnetic head mass 1450 at a frequency determined by the frequency of the alternating current. Because the magnetic head mass 1450 is the free end of the Sound Projector 1400 (as opposed to the magnetic tail mass 112 and base 110 which are coupled to the housing 1470 and host structure), the vibratory axial displacement of the outer distal surface 1452 of the magnetic head mass 1450 propagates a pressure wave 1460 in a distal direction away from the Sound Projector 1400. Depending on the medium, substance, or material at the distal end of the magnetic head mass 1450, the radiation impedance 1456 of the pressure wave 1460 may vary at the distal end of the Sound Projector 1400. In some embodiments, an impedance matching layer 1458 may be placed at or adjacent to the outer distal surface 1452 to maximize the amplitude of the pressure wave in the target propagation medium. In such embodiments, the impedance matching layer 1458 may have variable properties or may include a lens or lens system for aligning or focusing acoustic energy.

[0094] Similar to the vibration energy harvesting devices 100, 800, the sound projector 1400 relies on the magnetic compression of the piezoelectric transducer to apply a static compressive load (e.g., between about 5N and about 500N, between about 5N and about 50N, between about 50N and about 500N, or between about 90N and about 400N) to operate the piezoelectric transducer 120 in a mode that provides efficient electrical-to-vibrational energy conversion. The spacer 140 serves to slightly separate the magnet array 130, 730 that at least partially surrounds the piezoelectric transducer 120 from the magnetic tail mass 112 (or, in other embodiments, the head mass 1450) so that the magnets are separated by a small gap that generates a strong magnetic attraction to provide a relatively high compressive force on the piezoelectric transducer 120.

[0095] 15 and 16 show schematic diagrams of an embodiment of an alternative energy conversion device in the form of an acoustic projector 1500, 1600. The acoustic projectors 1500, 1600 are examples of electroacoustic conversion devices. The acoustic projectors 1500, 1600 may be similar to the vibration energy harvesting device embodiments described herein, but are optimized as acoustic projectors. The acoustic projectors 1500, 1600 may also be suitable or modifiable for energy harvesting and / or detection purposes. In particular, the acoustic projector devices described herein, such as the acoustic projectors 1500, 1600, may be used as vibration detector devices. In such a situation, the acoustic projectors 1500, 1600 may be used to detect small and large pressure waves impinging on the distal projection / detection surface of the device by observing the fluctuations in the current of electrodes electrically coupled to the piezoelectric transducers of such devices.

[0096] Referring initially to FIG. 15, Sound Projector 1500 is similar in general design to Sound Projector 1400, except that it has a magnet 1530 located at its axial center while the piezoelectric transducer 1520 is coaxially and concentrically located around the magnet 1530. Sound Projector 1500 includes a magnetic tail mass 1512, shims 1515a, 1515b, and a magnetic head mass 1550 in a configuration similar to Sound Projector 1400. In Sound Projector 1500, no physical spacer is inserted between the central magnet 1530 and the tail mass 1512. However, there is still an axial gap 1540 (e.g., between about 0.2 mm and about 1 mm) defined between the central magnet 1530 and the tail mass 1512 to induce a static compressive force due to magnetic attraction.

[0097] The components of the Sound Projector 1500 may be wholly or at least partially housed in a housing 1570. The Sound Projector 1500 may also have an outer casing 1568 to cover at least its distally protruding surface, and optionally cover most or all of the housing 1570. The outer casing may comprise, for example, a thin rubber or silicone sheet material.

[0098] The magnet 1530 may include multiple magnet elements coupled together in a magnet array, or may include a single magnet body, for example. An electrical conductor (not shown) is coupled to the piezoelectric transducer 1520 for applying an excitation current from a varying current source, such as an AC source 1455. In addition to being coupled to the head mass 1550 by magnetic attraction, the magnet 1530 may be attached to the head mass 1550 by a suitable adhesive, for example.

[0099] The magnetic head mass 1550 may have an additional head mass 1560 coupled to a distal surface of the magnetic head mass 1550 to provide an additional resonating mass for frequency tuning or impedance matching. In some embodiments, the additional head mass 1560 may have a distal outer surface 1552 that is larger in surface area than the axial cross-section of the magnetic head mass 1550 or that is shaped as an acoustic lens to generate a larger acoustic wavefront than is possible with the magnetic head mass 1550 alone. In other embodiments, the magnetic head mass 1550 may define a distal outer surface 1552 and may be configured to have an increasing cross-sectional area in the distal direction to generate a larger acoustic wavefront.

[0100] The piezoelectric transducer 1520 may include multiple transducer elements 1522. The transducer 1520 may be disposed on opposite sides of or at least partially around the magnet array. In some embodiments, the piezoelectric transducer 1520 includes a series of axially stacked piezoelectric transducer elements 1522, generally in an annular or near-annular configuration, to extend completely or partway around the magnet 1530. In other embodiments, the piezoelectric transducer 1520 may include a ring-like or circumferentially spaced or positioned array of axially aligned single crystal transducer elements. The transducer elements of such an array may be wedge-shaped, for example, to allow them to easily fit together. Such a ring-like array may be similar, for example, to the array of ligaments 144 of the spacer 140 shown in FIG. 5. The ring-like or circumferential array may have the piezoelectric transducer elements tightly or loosely packed in a generally circular or nearly circular circumference around the magnet 1530. The ring or circumferential array is preferably symmetric about at least two axes orthogonal to the proximal-to-distal (aligned) axis of Sound Projector 1500. Piezoelectric transducer 1520 is positioned to have its central axis axially aligned with the remainder of Sound Projector 1500, including magnet 1530, tail mass 1512, and head mass 1550.

[0101] The material of the piezoelectric transducer 1520 and its constituent piezoelectric elements 1522 may be formed or constructed from one or more RFSC transducer elements, as described above in connection with vibration energy harvesting embodiments, or may include more conventional piezoelectric ceramics, such as Navy Type Lead Zirconate Titanate (PZT) compositions. If relaxor ferroelectric single crystals are used for the piezoelectric transducer 1520 or piezoelectric elements 1522, the crystals may be arranged in a d32 mode cylinder using a

[0011] polarizing material. In the illustrated piezoelectric transducer arrangement of the Sound Projector 1500, 1600 using an array of multiple RFSCs, a high applied excitation voltage may be applied via electrical conductors (not shown) to the radially inner piezoelectric surface, with the outer surface grounded and oriented radially outward from the inside of the ring in three directions, one aligned with the axial direction of the Sound Projector 1500, 1600.

[0102] The shims 1515a, 1515b are or can be formed of a thin (relatively soft), machinable ceramic material, such as Macor. The shims 1515a, 1515b differ from the shims 115a, 115b in that they are annular and define a central opening through which the magnet 1530 passes.

[0103] The shim 1515a is disposed proximally and is bonded to the tail mass 1512. The shim 1515a has the proximal end of the piezoelectric transducer 1520 adjacent to it. The material thickness and central opening of the shim 1515a are sized to allow the magnet 1530 to move partially in and out of the opening as the piezoelectric transducer 1520 undergoes axial expansion or contraction in response to a changing current from the AC current source 1455. Thus, the shim 1515a acts as a spacer and may have a thickness slightly greater than the expected axial deflection of the piezoelectric transducer 1520. For example, if the maximum expected axial deflection is 1.0 mm, the thickness of the shim 1515a may be approximately 1.2 mm.

[0104] Shim 1515b is disposed distally and is glued to the head mass 1550. Shim 1515a has the proximal end of the piezoelectric transducer 1520 adjacent to it. The thickness of the material of shim 1515b does not need to be the same as that of shim 1515a, the central opening defined by the ring of shim 1515b only needs to be sized to allow the magnet 1530 to pass through it. Both shims 1515a, 1515b should provide at least sufficient flat surface area to contact the end face of the piezoelectric transducer 1520.

[0105] 16, a further Sound Projector embodiment is shown as Sound Projector 1600. Sound Projector 1600 is the same as Sound Projector 1500, except that magnet 1530 is coupled to tail mass 1512 instead of head mass 1550, and the function and configuration of shims 1515a, 1515b are reversed. In other words, distal shim 1515b is provided with a material thickness and central opening sized to allow magnet 1530 to move partially in and out of the opening as piezoelectric transducer 1520 undergoes axial expansion or contraction in response to a changing current from AC current source 1455. Thus, in Sound Projector 1600, shim 1515b functions as a spacer and may have a thickness slightly greater than the expected axial deflection of piezoelectric transducer 1520. For example, if the maximum expected axial deflection is 1.0 mm, shim 1515b may be approximately 1.2 mm thick.

[0106] The shims 1515a, 1515b may be suitable as they may allow for a small amount of surface deformation, resulting in a slightly softer surface than most rare earth magnets, reducing the possibility of breakage forming on the piezoelectric transducer 1520 (when formed as a crystal or when including a series of crystals). However, in some embodiments, other similarly deformable materials may be used in place of the shims 1515a, 1515b. Such similar materials may be provided as coatings, layers, layers with material composition gradients, or thin sheets, for example, located on the distal side of the tail (first) magnet 1512 or the proximal side of the head (second) magnet 1550. Such similar materials may include, for example, magnet-glass composites with a higher glass concentration at the surface intended to contact the piezoelectric transducer 1520.

[0107] In the case of Sound Projector 1500, magnet 1530 may be in direct contact with head mass 1550 or separated therefrom by a sufficiently thin adhesive bonding layer such that the magnetic attractive forces between magnet 1530 and head mass 1550 are negligible. Similar to Sound Projector 1600, magnet 1530 may be in direct contact with tail mass 1512 or separated therefrom by a sufficiently thin adhesive bonding layer such that the magnetic attractive forces between magnet 1530 and tail mass 1512 are negligible.

[0108] In Sound Projector 1600, no physical spacer is inserted between the central magnet 1530 and the head mass 1550. However, there is still an axial gap 1640 (e.g., between about 0.2 mm and about 1.0 mm) defined between the central magnet 1530 and the head mass 1550 to induce a high (e.g., 5-500 N or 50-500 N) static compressive force due to magnetic attraction. In the case of Sound Projector 1500, 1600, no spacer is required because mechanical loads such as compression and bending are absorbed by the piezoelectric transducer 1520.

[0109] Otherwise, Sound Projector 1600 is the same as Sound Projector 1500. Components such as housing 1570, piezoelectric transducer 1520, tail mass 1512, head mass 1550, additional head mass 1560, and outer casing 1568 are indicated with the same reference numbers in Figures 15 and 16.

[0110] Embodiments of the sound projectors 1400, 1500, 1600, and other energy transforming devices described herein employ an arrangement in which the piezoelectric transducer 120, 1520 is coaxial with the magnet array 130, 730 (or 931, 932 in FIG. 9B) or magnet 1530. In some embodiments, the magnet array 130, 730 or 931 / 932 extends in a direction parallel to an axis, such as axis 165, along which the centers of components are aligned and disposed at one or more locations radially spaced (outside) from the central axis, and a piezoelectric transducer, such as piezoelectric transducer 120, is aligned with and extends along the central axis. In other embodiments, the radial positions of the magnet array or magnet and piezoelectric transducer are swapped. In these other embodiments, the piezoelectric transducer, such as piezoelectric transducer 1520, is disposed to have one or more components radially disposed outside a magnet, such as magnet 1530, aligned with and extending along the central axis. In this context, the term coaxial is intended to describe an arrangement in which the center of gravity of the magnet array or magnets is generally axially aligned with the center of gravity of the piezoelectric transducer, regardless of the exact form each magnet or piezoelectric component takes and the number of components that make up each magnet or piezoelectric component. The term coaxial also refers to the axial alignment of the piezoelectric transducer 120, 1520 and magnet array 130, 730 or magnet 1530 with other device components such as the tail mass 112, 1512, head mass 150, 1550, shims 115a, 115b, 1515a, 1515b, alignment disk 135 (if present), and spacer 140 (if present).

[0111] In some embodiments, the magnet or piezoelectric components will have a generally circular or circular array configuration. In such embodiments, and even in non-circular embodiments (such as shown in FIG. 9B), the magnet and piezoelectric components may also be described as concentric circles, with the magnet components disposed radially inward of the piezoelectric components, or the piezoelectric components disposed radially inward of the magnet components.

[0112] The Sound Projector devices described herein, such as Sound Projectors 1400, 1500, 1600, etc., can form part of a sound projection system that includes a combination of multiple such devices. Such multiple Sound Projector devices can be positioned adjacent to one another in an array or bank of such projectors, or they can be positioned at spaced apart locations. In such a system, multiple ones of the Sound Projectors can be pointed in substantially the same direction and / or multiple ones of the Sound Projectors can be pointed in different directions.

[0113] As described herein, various embodiments apply a compressive mechanical preload to the piezoelectric transducer elements of the Acoustic Projector. Some previous Acoustic Ultrasound Projector designs use an axial bolt / nut (otherwise known as a tie rod or sometimes called a stress rod) to provide a static compressive stress to the piezoelectric elements. The greater the prestress, the greater the amplitude of motion that is possible before the transducer is placed in tension, which typically results in failure of the transducer (because it is ceramic).

[0114] The arrangement of magnet combinations in the axial magnet assembly described herein provides an alternative source of static compressive stress on the tie rod. The described arrangement has the advantage of low damping and a wide range of unimpeded resonant motion since leaf springs are not required at the ends of the tie rod. The magnetic arrangement is not limited to a single cylinder surrounding the piezoelectric element, but can be configured to have various numbers of magnets and spacers of various shapes, examples of which are described above.

[0115] The results of the magnetic calculations shown in Table 1 demonstrate the large compressive forces that can be generated using a magnetic preload arrangement, which has several potential advantages for acoustic projection: Compact design for multiple applications, as single devices or in arrays, in areas such as structural health monitoring of air / land / water vehicles, in air-coupled and underwater systems, in sonic thermography, composite manufacturing, and as an exciter for various underwater applications. In general, the described acoustic projectors can be used wherever low frequency (300Hz+) acoustic projection is already used. Unhindered sympathetic movement of the head mass. Cleaner acoustic mode shapes as the head mass movement is not constrained in compression by a centrally located tie rod. ·More energy efficient operation due to inherently less resistance to movement than designs that use tie rods for compression. Efficient transmission and highly sensitive signal reception at the resonant frequency of the device (which can be modified to above approximately 300Hz with various design considerations). · A significant amount of pre-stress so that the transducer remains in compression, allowing the piezoelectric crystal to be driven with a strong electric field (crystalline ceramics are not durable when placed in tension). · The possibility of exploiting the relaxor ferroelectric phase transition available in certain crystal compositions to increase acoustic output (via a step change in crystal strain that occurs as the crystal undergoes a reversible transition).

[0116] [Table 3]

[0117] The results of the magnetic calculations shown in Table 3 indicate the large compressive forces that can be generated using the magnetic preload arrangement and the lowest resonant frequency that can be achieved.

[0118] The primary goal of a sound projector is to generate a relatively large mechanical displacement, which in turn radiates acoustic energy into the adjacent medium. For example, the dynamic strain of a vibrating piezoelectric bar can be approximated as:

number

[0119] where S is the dynamic strain, Q m is the mechanical quality factor, d ij is the piezoelectric coefficient and E is the applied electric field. In the proposed magnetic compression configuration, d 32 is chosen because of its compliant dual axis and the benefits it offers, such as lower operating frequencies and higher power density, which are beneficial for more efficient and / or portable designs. As an example, third generation RFSCs have a large, Q m (usually 1000), large d ij (typically 1000pC / N), and large E c (6 kV / cm), which allows for the generation of large dynamic strain.

[0120] Additionally, there are advantages to using first generation RFSCs over previously used piezoelectric ceramics. These advantages include lower modulus / higher compliance biaxially, higher coupling constant, and higher piezoelectric strain constant. Third generation RFSCs combine these advantages with an extra Q m So it is an ideal choice.

[0121] The dynamic strain prediction is shown in Table 4. The crystal unit dimensions are 4x4x12mm. 3 It is assumed that the maximum voltage is 0.4E C (for a distance of 4 mm in three directions). For demonstration purposes, only the transducer is considered and the effects of the surrounding projector structure are neglected. The potential effects of crystallographic phase changes are also neglected. [Table 4]

[0122] Table 4 shows that Mn-PMN-PZT is the most suitable choice for transmission / projection at least in air and shallow water. When Mn-PMN-PZT is used as an electrical to mechanical converter, the Q m The piezoelectric constant d is large, and the elastic modulus s E The low d and high degree of coupling k are advantageous for projection. PIN-PMN-PT has a larger piezoelectric constant d 32 The sensitivity afforded by the coupling k and may be practical for sensing applications. The sound projector devices 1400, 1500, 1600 described herein include both a magnet and a support structure that imparts additional mass, and the magnet acts as a spring in parallel with the crystal transducer, and thus may include additional mass or stiffness. This affects the overall mechanical quality of the device by the following equation:

number

[0123] where M is the mass, k is the spring constant, and D is the damping coefficient.

[0124] The proposed method of magnetic compression preload force, when combined with third generation piezoelectric elements, offers the advantages described below.

[0125] The compliant two-axis of the quartz transducer allows lower operating frequencies than devices fabricated using conventional piezoelectric ceramic transducers. Scattering losses typically increase as the fourth power of frequency, but when resonant conditions are required, the size of the projector is inversely proportional to the operating frequency.

[0126] The use of sinusoidal tone burst excitation (exemplified in FIG. 18) instead of a single rectangular or "spike" pulse allows the piezoelectric transducer 120, 1520 to respond resonantly, improving the signal projection efficiency and signal reception sensitivity of the device. After the four interfaces (from the probe to the transmission medium(s), to the desired location, and back again), only a small percentage of the original acoustic energy remains. This problem is partially mitigated by the resonant operation.

[0127] Lower transmission frequencies are useful for sonotrodes (i.e. ultrasonic machining, welding, and mixing), and as compact acoustic excitation devices for sonic thermography, for example, with the acoustic propagation advantages afforded by low operating frequencies, especially below 50 kHz.

[0128] The large static preload provided by the magnet arrangement allows the transducer to be compact and to withstand large electrical excitation voltages without being exposed to tension, which increases the operating capability and general durability of the system.

[0129] For acoustic projection devices, consideration is given to matching the acoustic impedance of the head mass to both air and water. When a sound wave passes through an interface between two materials, only a portion of the energy is transmitted, the rest is reflected or otherwise lost. The percentage of energy transmitted depends on how closely the acoustic impedances of the two materials are matched. Air frequency attenuation increases exponentially with frequency, so air-coupled ultrasonic devices operate below 1 MHz.

[0130] The reflection and transmission coefficients are given by the following equations (for wave excitation perpendicular to the plane under study):

[0131]

number

[0132]

number

[0133] where R is the reflection coefficient, T is the transmission coefficient, and the wave is subjected to an acoustic impedance Z 1 Acoustic impedance Z from the medium 2 It was transmitted to the media, Z i =ρ i xv i ,i=1,2,ρ i is the density, v iis the speed of sound in the medium. It is clear that the closer the two values ​​are to each other, the higher the transmission and the lower the reflection, and therefore, to improve the signal-to-noise ratio, the acoustic impedances should be as close as possible. Typical acoustic impedances for various commonly used materials are shown in Table 3.

[0134] The energy transfer coefficient from one medium to another is calculated by the following formula (which can be multiplied by 100 as a percentage of energy transfer):

[0135]

number

[0136] Table 5 shows the parameters of various materials that are useful in sound projection models, which can be used to estimate sound transmissibility (see, for example, Tables 6 and 7 below).

[0137] Tables 6 and 7 show the acoustic impedance advantages of matching the projector to the medium. One way to achieve impedance matching is to optimize the interface materials shown in Table 5. [Table 6] [Table 7]

[0138] An inherent weakness of air-coupled ultrasound is the low acoustic impedance of air, which is typically 10 times lower than that of other materials. 4(Compare Table 6 for air and Table 7 for water.) This results in smaller acoustic energy transfer values, reducing but not eliminating the effect of acoustic impedance matching, although the unhindered resonant motion of a device using magnetic compressive preload (rather than using tie rods) may counter this by resulting in a higher electrical efficiency relative to the mechanical efficiency.

[0139] A magnetic preload air-coupled acoustic projector can be used to generate Lamb / plate waves that can travel significant distances in suitable materials, especially at low frequencies. An exemplary through-transmission configuration using separate transmitters 1910 and receivers 1912 is shown in FIG. 19. It is possible to configure the measurement so that the air-coupled transmitters 1920 and receivers 1912 are on opposite sides of the test part as shown in FIG. 19, or on the same side of the test part as shown in FIG. 20. The air-coupled transmitters 1910 can measure lines instead of single points, greatly improving test speed in applications where precise imaging is not required. It is contemplated that in the configurations shown in FIGS. 19 and 20, the acoustic projector embodiments 1400, 1500, 1600 can be used for the transmitter 1910. It is also contemplated that such acoustic projector embodiments 1400, 1500, 1600 can be used in the acoustic detection mode of the receiver 1912 in the configurations shown in FIGS. 19 and 20. In some embodiments, the receiver 1912 may be or include a sensor (other than a vibrational energy transforming device as described herein) configured to directly or indirectly sense an output or effect from or induced by the transmitter 1910. Examples of such sensors include a thermal camera or a scanning laser vibrometer. In such embodiments, the acoustic energy from the transmitter may excite radiation, damage, or another thermally or optically detectable effect in the test part or other intervening medium that can be detected by the receiver 1912.

[0140] Underwater acoustic technology may be used for industrial and scientific purposes. Active sonar transmits and receives echoes returning from the target, whereas passive sonar only blocks noise radiated from an external target source. Examples of industrial and scientific applications include, but are not limited to: (i) a bathymetry sounder to measure water depth; (ii) Fisheries sounders designed to detect and locate aquatic organisms; (iii) Side-scan / multibeam sonar used for acoustic imaging of the seafloor; (iv) Sediment profilers, which are used to study the internal structure of the ocean floor; (v) Acoustic communication systems used for the transmission of digital data; (vi) a positioning system for locating the platform; (vii) Sonar velocity relative to a stationary medium, or acoustic Doppler systems used to measure water velocity relative to a stationary instrument; and (viii) Acoustic tomography used to assess hydrological perturbations.

[0141] In oceanography, a high-power, low-frequency projector is desirable. The low power output of the design can be compensated for by using multiple electroacoustic conversion devices, such as multiple individual acoustic projector devices 1400, 1500, 1600 in an array. An example of an oceanographic application is shown in FIG. 21 by a craft 2100, such as a ship, equipped with electroacoustic conversion devices. This can be, for example, acoustic projectors 1400, 1500, 1600, mounted on a mounting body, such as the underside of the hull 2110 of the craft 2100. The ship can include, for example, a boat, ship, or submarine. In some embodiments, multiple ones of the electroacoustic conversion devices (e.g., in the form of acoustic projectors 1400, 1500, 1600) can be mounted on one or more mounting bodies to project vibrational (acoustic) energy from the one or more mounting bodies. The one or more mounting bodies can include a hull 2110 and / or a mounting structure that is in turn mounted on the hull 2110. In other examples, the mounting body or bodies may include a movable craft other than a marine vessel, or one or more static mounting bodies such as a pylon, wall or fixed surface facing a volume of fluid such as water or air. Multiple electroacoustic transducing devices may be oriented to emit or detect pressure waves in or from the same or multiple directions. Such multiple transducing apparatus / device embodiments may form part of an acoustic projection or detection system (e.g., including or as part of the craft 2100) including the mounting structure / mounting body and appropriate control system and power source for operation of such a system.

[0142] The figure of merit (FoM) of a piezoelectric transducer for underwater applications is related to the initial acoustic velocity, d ij Q_m and / or k, which are related to the electroacoustic efficiency 2 Q m The already mentioned properties of the proposed magnet arrangement, especially the high Q m、 Considering the possibility of resonant motion and crystallographic phase changes, one can speculate as follows. High actuation forces enabled by a critical and compact preloading mechanism (not to mention the potential for crystallographic phase changes) keep the crystals in compression rather than reaching tension, allowing for strong signal emission. Some existing designs use tie rods to provide preload to the piezoelectric transducer, but tie rods are bulkier than the Sound Projector embodiments described herein and dampen the resonant response of the device. Q m The higher the , the narrower the bandwidth and the higher the power. Unhindered resonant movement of the head mass permitted by the design produces more efficient pressure wave transmission and greater sensitivity to incoming pressure waves. The simple design means manufacturing is simple and consistently repeatable with readily available materials.

[0143] The low power and low directivity of individual low-frequency projectors can be overcome by assembling several of them into dense arrays with appropriate control by a local controller controlling the excitation current to each Sound Projector. This can lead to larger source levels and improved directivity when compared to a single Sound Projector.

[0144] Arrays of Sound Projectors utilizing magnetic preload forces can be constructed such that separate housing cases are not required for each Sound Projector. Potentially, individual magnetically active Sound Projectors can be placed in appropriate magnetic circuits to optimize the preload force of each individual Sound Projector.

[0145] Tonpilz acoustic projectors can be used as underwater electro-acoustic transducers mounted on a vessel's hull, for example as shown in Figure 21. They utilize a stack of ring-shaped piezoelectric material with axial tie rods, the rings alternating in polarity along the length of the stack, interspersed with electrodes, bonded together and electrically connected in parallel. Tonpilz projectors are mounted in a rugged, waterproof housing, with the front emitting surface covered by an acoustically transparent rubberized "boot".

[0146] The resonant frequency of the Tonpilz transducer is higher than that of the barrel-stave flexural transducer, with examples being found to resonate above 1000 Hz. A Tonpilz example shown by Takeshi Inoue et al. (1990 Jpn.J. Appl. Phys.2956) (“Inoue et al”) has a resonant frequency of about 7300 Hz. A 2019 paper describing the design, optimization, fabrication, and characterization of a Tonpilz transducer for low frequency applications had a resonant frequency of about 4600 Hz.

[0147] The device presented by Inoue et al. is optimized for low operating frequencies. In their paper, the volume of the Tonpilz transducer (including everything except the housing case) is approximately 486 cm. 3 However, the volume of the Sound Projector Device 1400 (FIG. 14) with a 2 cm long tungsten carbide tip mass is approximately 27 cm 3 (5.6% of the volume of the Inoue et al. device). The mass of the prototype Sound Projector Device 1400 is about 6% of the Inoue et al. design, and the volume of the piezoelectric element is about 0.5% of the Inoue et al. design. This illustrates the compact shape that the proposed magnetic preload force arrangement allows.

[0148] The vibration energy conversion device according to the embodiments of the present disclosure advantageously does not use a non-magnetic mechanical compression mechanism to exert a static compression force, for example, the embodiments do not use (include) tie rods to apply a static compression force to the piezoelectric transducer 120.

[0149] It will be understood by those skilled in the art that numerous variations and / or modifications may be made to the above-described embodiments without departing from the broad general scope of the present disclosure, and the present embodiments are therefore to be considered in all respects as illustrative and not restrictive.

Claims

1. 1. An energy conversion device, comprising: base, a first magnet coupled to or comprising said base; a piezoelectric transducer disposed adjacent to the first magnet; a magnet array coaxial with the piezoelectric transducer, the magnet array being disposed opposite or at least partially surrounding the piezoelectric transducer, or the piezoelectric transducer being disposed opposite or at least partially surrounding the magnet array, the magnet array being polarized such that a first end of the magnet array is attracted to the first magnet; a second magnet polarized to be attracted to a second end of the magnet array opposite the first end; a vibratable mass coupled to or comprising the second magnet; an electrical conductor electrically connected to the piezoelectric transducer for conducting electrical current between the piezoelectric transducer and an external circuit; the first magnet, the piezoelectric transducer, the magnet array, and the second magnet are substantially coaxial; the first magnet, the second magnet, and the magnet array cooperate to maintain the piezoelectric transducer in compression; the vibrational motion of the second magnet is directly related to the compression of the piezoelectric transducer and the flow of current in the electrical conductor; The device is configured to convert electrical current in the electrical conductor into vibrations of the vibrable mass in a frequency range of about 300 Hz to about 100 kHz and function as an acoustic projector.

2. The apparatus of claim 1 , wherein the magnet array is disposed at least partially around the piezoelectric transducer.

3. The apparatus of claim 1 or claim 2, wherein the piezoelectric transducer comprises a relaxor ferroelectric single crystal (RFSC).

4. the piezoelectric transducer comprises a ternary piezoelectric single crystal; or the piezoelectric transducer is a PMN-PT or PZN-PT crystal; or the piezoelectric transducer is a PIN-PMN-PT crystal; or The device of claim 3 , wherein the piezoelectric transducer is a Mn-PIN-PMN-PT crystal or a Mn-PMN-PZT crystal.

5. the piezoelectric crystal of the piezoelectric transducer is polarized in [011] and arranged to operate in a transverse extensional (3-2) mode; The apparatus of claim 4 , wherein the two axes of the piezoelectric crystal are substantially coaxial with the first magnet, the magnet array, the second magnet and the vibratable mass.

6. 6. The apparatus of claim 1, further comprising a first thin shim disposed between the first magnet and a first end of the piezoelectric transducer, and a second thin shim disposed between the second magnet and an opposing second end of the piezoelectric transducer.

7. the piezoelectric transducer includes a spacer disposed between the first magnet and the second magnet, the spacer being significantly more compressible than the magnet array and the piezoelectric transducer; or the spacer defines an opening for receiving the piezoelectric transducer therethrough; or the spacer has an axial thickness between about 1 mm and about 3 mm when the vibratable mass is at rest; or the spacer has an axial thickness between about 2.4 mm and about 2.8 mm when the vibratable mass is at rest; 7. The device according to claim 1, wherein the at least one of

8. the magnet array defines a passageway through which the piezoelectric transducer extends, the magnet array and the piezoelectric transducer not contacting each other at the passageway; or the magnet array comprises a plurality of magnet bodies fixed in predetermined positions relative to each other, or the apparatus further includes a coaxially disposed alignment disk disposed between two of the plurality of magnet bodies, the alignment disk defining an alignment opening at a center of the alignment disk for receiving and axially aligning the piezoelectric transducer; or the alignment disk is made of a magnetically inert material, or the magnet array is substantially cylindrical; 8. The device according to claim 1 , wherein the at least one of

9. the spacer includes a plurality of compressible ligaments disposed to separate the magnet array and the second magnet; The apparatus of claim 7 , wherein an axial length of the piezoelectric transducer is substantially the same as a combined axial length of the spacer and the magnet array.

10. the magnet array and the second magnet are configured to exert a substantially static compressive force on the piezoelectric transducer of about 50 Newtons to about 500 Newtons; or the magnet array and the second magnet are configured to exert a substantially static compressive force on the piezoelectric transducer of about 5 Newtons to about 50 Newtons.

10. Apparatus according to any one of claims 1 to 9.

11. 11. The apparatus of claim 1, wherein the apparatus is configured to convert electrical current in the electrical conductor into vibrations of the vibrable mass in a frequency range of about 300 Hz to about 50 kHz and function as an acoustic projector.

12. The apparatus of claim 1 , wherein the magnet array is disposed concentrically with the piezoelectric transducer.

13. the piezoelectric transducer at least partially surrounds the magnet array; or the piezoelectric transducer comprises a plurality of stacked piezoelectric transducer elements; or The magnet array is a cylindrical magnet, in contact with the first magnet or the second magnet, but not with both; or a cylindrical magnet in contact with a thin bonding layer that bonds the cylindrical magnet to the first magnet or the second magnet; The apparatus of claim 12, wherein the at least one of

14. the combination of the first magnet, the magnet array, and the second magnet is configured to exert a substantially static compressive force on the piezoelectric transducer of about 50 Newtons to about 500 Newtons; or the combination of the first magnet, the magnet array, and the second magnet is configured to exert a substantially static compressive force on the piezoelectric transducer of about 5 Newtons to about 50 Newtons.

14. Apparatus according to claim 12 or 13.

15. an impedance matching layer disposed at an outer end of the second magnet; and / or an acoustic lens disposed at the outer end of the second magnet; 15. The apparatus of claim 1 , further comprising:

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