Mechanically coupled energy harvester array

Abstract

A piezoelectric energy harvester is provided that is arranged to share a support having a wide operating frequency range. The piezoelectric energy harvester comprises a plurality of piezoelectric beams arranged along one direction having different natural frequencies; a fixing member that fixes both ends of the plurality of piezoelectric beams; and a plurality of mass bodies connected corresponding to each of the plurality of piezoelectric beams.

Description

Technology Field

[0001] The present invention relates to a resonant piezoelectric energy harvester having a wide operating frequency range, and more specifically, to a piezoelectric energy harvester capable of generating electrical energy over a wide frequency range through constructive interference by sequentially arranging piezoelectric energy harvesters having different natural frequencies and connecting both ends with supports to induce coupling between resonants. Background Technology

[0003] Along with the increasing use of electricity in sectors that have traditionally utilized it, areas such as transportation, heating, and cooking, which previously did not use power, are also rapidly shifting from fossil fuels to electricity. Consequently, while more power generation is required, the construction of additional large-scale power facilities using existing fossil fuels or nuclear power is difficult due to policy constraints; thus, the trend is toward meeting the increased demand with new and renewable energy sources.

[0004] Under these circumstances, the development of energy harvesting technologies that convert solar, wind, wave, thermal, and kinetic energy into electrical energy is accelerating in order to secure future energy resources stably and respond to increasing electricity demand.

[0005] Among various energy harvesting technologies, a piezoelectric energy harvester is a device that converts mechanical energy into electrical energy by inducing physical deformation of a piezoelectric material from the external environment, and is a type of energy generation device capable of utilizing wasted energy from the surroundings, such as shock, pressure, and vibration, as electrical energy. In particular, with the recent development of low-power sensors and the widespread adoption of IoT sensors due to the Fourth Industrial Revolution, energy harvester technology is gaining significant attention as a standalone power source that eliminates the need for power cord connections or battery replacements.

[0006] In the case of a piezoelectric energy harvester using vibration, maximum power generation can be achieved only if the structure is designed to maximize the displacement generated by matching the frequency of the vibration source with the natural frequency of the device. Generally, piezoelectric energy harvesters using vibration have a cantilever structure in which one end is fixed (fixed support) and the other end vibrates freely (free end), or a two-ends fixed beam form in which both ends are fixed.

[0007] In this case, if the frequency of the vibration source deviates from the natural frequency of the device, the generated displacement decreases significantly, resulting in a substantial reduction in piezoelectric output. Therefore, conventional piezoelectric energy harvester devices, which have a fixed natural frequency and a narrow range, have limitations in application to environments where the frequency range of the vibration source is wide or where the vibration frequency changes continuously, such as in automobile or airplane engines. To enhance the performance and usability of piezoelectric energy harvesters utilizing such vibration energy, energy harvesting must be possible across a wide frequency band. [Prior Art Literature] Prior Art Literature 1: Published Patent Application No. 10-2020-0086951 (July 20, 2020) Prior Art Literature 2: Published Patent Application No. 10-2020-0025111 (March 10, 2020) The problem to be solved

[0009] The present invention is designed to solve the above-mentioned problems and aims to provide a piezoelectric energy harvester capable of having enhanced energy output and a wide operating frequency bandwidth by fixing piezoelectric beams arranged with different natural frequencies to the same support, thereby causing neighboring piezoelectric beams to operate together when a specific piezoelectric beam operates at a single frequency. means of solving the problem

[0011] A piezoelectric energy harvester according to one embodiment of the present invention may include: a plurality of piezoelectric beams arranged along one direction having different natural frequencies; a fixing member that fixes both ends of the connection so that the plurality of piezoelectric beams are coupled to each other and vibration is well transmitted; and a plurality of mass bodies connected to each of the plurality of piezoelectric beams so that the plurality of piezoelectric beams have different natural frequencies.

[0012] Here, the plurality of piezoelectric beams can be arranged to enable the transfer of mechanical vibration energy to one another through structural coupling.

[0013] And when one piezoelectric beam having a natural frequency corresponding to an external input frequency operates by resonating with the plurality of piezoelectric beams, the remaining piezoelectric beams can also operate together through the coupling.

[0014] In addition, the above one direction is a horizontal direction, and the plurality of piezoelectric beams may be arranged in a structure along the horizontal direction.

[0015] In addition, the above-mentioned fixing member may be formed with a thickness of less than 5 mm.

[0016] In addition, the plurality of mass bodies are connected to the upper and lower ends of the corresponding plurality of piezoelectric beams, and each of the plurality of mass bodies vibrates together with the piezoelectric beam according to a change in frequency, thereby inducing the generation of electrical energy of the piezoelectric beam.

[0017] Additionally, the piezoelectric beam may include an elastic beam and a piezoelectric element that receives a bending moment from the elastic beam, and the piezoelectric element may be arranged in a combination including a first electrode, a piezoelectric material located on the first electrode, and a second electrode located on the piezoelectric material.

[0018] In addition, the above piezoelectric material is Pb(Zn 1 / 3 Nb 2 / 3 )O3-PbTiO3(PZN-PT), [Pb(Mg 1 / 3 Nb 2 / 3)O3]-[PbTiO3](PMN-PT), (Na x K 1-x It may include at least one of crystalline materials such as NbO3(NKN), polymer materials such as PVDF, PVDF-TrFE, and thin film materials such as ZnO, CdS, and AlN.

[0019] In addition, the piezoelectric beam may further include a protective substrate positioned on the piezoelectric element to protect the piezoelectric element. Effects of the invention

[0021] A piezoelectric energy harvester according to one embodiment of the present invention has piezoelectric beams coupled to each other by a support, so that when one piezoelectric beam operates, surrounding piezoelectric beams are vibrated together, thereby enabling the piezoelectric energy harvester of the present invention to operate over a wide frequency band and simultaneously produce enhanced electrical energy.

[0022] Accordingly, the piezoelectric energy harvester according to one embodiment of the present invention can be applied anywhere in an environment where variable vibration or vibration over a wide frequency range is applied, and can be used as a power source for low-power sensors for the implementation of future ubiquitous sensor networks (USN). Brief explanation of the drawing

[0024] FIG. 1 is a conceptual diagram of a piezoelectric energy harvester array according to one embodiment of the present invention. FIG. 2 is a conceptual diagram of a piezoelectric beam applied to a piezoelectric energy harvester array according to one embodiment of the present invention. FIG. 3 is an example photograph of an actual piezoelectric beam applied to a piezoelectric energy harvester array according to one embodiment of the present invention. Figure 4 is a graph of the behavioral characteristics of the piezoelectric energy harvester array of Figure 2. Figure 5 is a graph comparing the performance of a piezoelectric energy harvester array according to one embodiment of the present invention with that of a conventional single energy harvester. FIG. 6 is a model designed to calculate the behavior of a piezoelectric energy harvester array according to one embodiment of the present invention through numerical analysis. FIG. 7 is a graph showing the behavior of a piezoelectric energy harvester array according to one embodiment of the present invention calculated by numerical analysis. FIG. 8 is a graph showing the behavior of a piezoelectric energy harvester array according to one embodiment of the present invention calculated by numerical analysis according to the thickness of the fixing member. Specific details for implementing the invention

[0025] The following detailed description of the invention refers to the accompanying drawings, which illustrate specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Various embodiments of the invention are different but need not be mutually exclusive. For example, specific shapes, structures, and characteristics described herein may be implemented in other embodiments without departing from the spirit and scope of the invention in relation to one embodiment. Additionally, the location or arrangement of individual components within each disclosed embodiment may be changed without departing from the spirit and scope of the invention. Accordingly, the following detailed description is not meant to be limiting, and the scope of the invention is limited only by the appended claims, including all equivalents to those claimed in the claims. Similar reference numerals in the drawings refer to the same or similar functions in various respects.

[0026] The terms used in this specification have been selected to be as widely used and general as possible, taking into account their functions; however, these may vary depending on the intent or convention of those skilled in the art or the emergence of new technologies. Additionally, in specific cases, terms have been selected at the applicant's discretion, and in such cases, their meanings will be described in the relevant explanatory sections of the specification. Therefore, the terms used in this specification should be interpreted based on their actual meaning and the overall content of the specification, rather than merely their names.

[0027] FIG. 1 is a conceptual diagram of a piezoelectric energy harvester array according to one embodiment of the present invention.

[0028] FIG. 2 is a conceptual diagram of a piezoelectric beam applied to a piezoelectric energy harvester array according to one embodiment of the present invention.

[0029] FIG. 3 is an example photograph of an actual piezoelectric beam applied to a piezoelectric energy harvester array according to one embodiment of the present invention.

[0030] Referring to FIGS. 1 and 2, the piezoelectric energy harvester array (1) means a structure in which a plurality of piezoelectric beams (10) are fixed to a fixed member (140).

[0031] Here, the piezoelectric beam (10) refers to a structure including an elastic beam (110), a piezoelectric element (120), and a mass (130). A plurality of piezoelectric beams may be in a form that extends along a first direction (D1). Additionally, a plurality of piezoelectric beams (10) may be arranged side by side along a second direction (D2) that is perpendicular to the first direction (D1). The spacing between the arrangement of the plurality of piezoelectric beams (10) may be the same, but is not limited thereto. Here, the second direction (D2) may be a horizontal direction as shown in FIG. 1, and the plurality of piezoelectric beams (10) may be in a structure arranged in a plane. However, the number and arrangement direction of the plurality of piezoelectric beams (10) are not limited to those shown in FIG. 1, and the second direction (D2) may be a vertical direction.

[0032] Multiple piezoelectric beams (10) can be arranged side by side and fixed at both ends to a fixed member (140). Multiple piezoelectric beams (10) can be vibrated along a third direction (D3) which is vertical while fixed at both ends to the fixed member (140). Multiple piezoelectric beams (10) can generate voltage through upward and downward vibration.

[0033] As illustrated in FIG. 2, an individual piezoelectric beam (10) is composed of an elastic beam (110), a piezoelectric element (120), and a mass (130). Here, the piezoelectric element (120) includes a piezoelectric material, an electrode, and a protective substrate. The piezoelectric element (120) may be positioned above or below the elastic beam (110). Additionally, the piezoelectric element (120) may be provided in multiple numbers. It may be composed of a first piezoelectric element (120) and a second piezoelectric element (120) positioned symmetrically above and below the elastic beam (110) with one or more piezoelectric elements (120) in between. However, it is not limited thereto, and multiple piezoelectric elements (120) may be positioned sequentially on the elastic beam, and may be implemented in various forms depending on the usage environment and design purpose. In this embodiment, considering that the piezoelectric beam (10) undergoes a large displacement due to the resonance frequency, the elastic beam (110), which has excellent mechanical strength, may be made of a metal material and connected to a fixed member (140). The elastic beam (110) may have a large aspect ratio and may be a cantilever suitable for a vibrating environment. The elastic beam (110) may be bent at a predetermined curvature, and may distribute physical force to the piezoelectric body (120) and provide a restoring force to restore it to an initial state. A voltage may be induced in the piezoelectric unit element constituting the piezoelectric body (120) according to the position change of the elastic beam (110).

[0034] Here, the piezoelectric beam (110) can be prepared with various stiffness and thickness through the configurations described above. Additionally, since the generated voltage may be reduced by potential difference attenuation when the neutral axis, which becomes zero stress when the piezoelectric beam (110) is bent, is formed in the piezoelectric body (120), the neutral axis of the piezoelectric beam (110) can be configured to be formed in the elastic beam (110).

[0035] The piezoelectric element (120) may be positioned above or below the elastic beam (110) to receive a bending moment from the elastic beam (110). The electrodes, piezoelectric material, and protective substrate of the piezoelectric element (120) may have a structure in which they are sequentially stacked.

[0036] The electrode may be a piezoelectric electrode that transmits piezoelectric energy to the outside when the piezoelectric material generates it, and may include a conductor having high electrical conductivity.

[0037] A piezoelectric material may include a material that generates voltage from an external force based on the piezoelectric effect. Dielectric polarization within the material is induced by mechanical distortion caused by stress transmitted to the piezoelectric material, which may generate a potential difference between the upper and lower parts of the piezoelectric material. A potential difference may be formed between the first electrode and the second electrode located above and below the piezoelectric material, and a voltage of a corresponding magnitude may be generated.

[0038] The piezoelectric material may include at least one from the group consisting of PZT, BaTiO3, PVDF, PVDF-TrFE, ZnO, CdS, and AlN. That is, the piezoelectric material is Pb(Zn 1 / 3 Nb 2 / 3 )O3-PbTiO3(PZN-PT), [Pb(Mg 1 / 3 Nb 2 / 3 )O3]-[PbTiO3](PMN-PT), (Na x K 1-x It may include at least one of crystalline materials such as NbO3(NKN), polymer materials such as PVDF, PVDF-TrFE, and thin film materials such as ZnO, CdS, and AlN, and may be configured in various forms such as thin film form, polymer-based film structure, and a mixture of nano / microstructured materials and polymers, but is not limited thereto.

[0039] In addition, a piezoelectric energy harvester array (1) according to one embodiment of the present invention as shown in FIG. 3 may further include a vibration source (2) capable of providing vibration so that a piezoelectric beam (110) can vibrate at a predetermined input frequency, an energy storage circuit (not shown) capable of rectifying and accumulating voltage generated from a piezoelectric body (120), and a housing (not shown) for housing each component of the piezoelectric energy harvester array (1).

[0040] Meanwhile, each of the plurality of piezoelectric beams (10) may have a different natural frequency. The natural frequency of the plurality of piezoelectric beams (10) ) can be defined by the following mathematical formula 1.

[0042] [Mathematical Formula 1]

[0043] ,

[0044] (Here, : Equivalent mass, : Equivalent spring constant, : Length of the piezoelectric beam, : Elastic modulus of a piezoelectric beam, : As the moment of inertia of the piezoelectric beam cross-section, : Mass per unit length of piezoelectric beam, : It is the weight of the verification mass, and ... holds true, where b represents the breadth of the piezoelectric beam cross-section and d represents the depth of the piezoelectric beam cross-section.

[0045] As illustrated in FIG. 1, a plurality of piezoelectric beams (10) may be composed of n beams, and the lengths of the n piezoelectric beams (10) may be equal to each other. The number and configuration of the plurality of piezoelectric beams (10) are exemplary, and the embodiments of the present invention are not limited thereto.

[0046] Multiple piezoelectric beams (10) may have different natural frequencies, and the weight of the mass (130) placed on the piezoelectric beam may be different from each other.

[0047] Each mass (130) can increase the deformation amount of each piezoelectric beam (10), thereby increasing the amount of electricity produced in the piezoelectric energy harvester array (1). The mass (130) may be located at the top or bottom of the piezoelectric beam (10), but is not limited thereto. The mass (130) is used to control the natural frequency of the piezoelectric beam (10), and in this embodiment, a metal with a relatively high density is used, but is not limited thereto.

[0048] A mass (130) can be coupled to a position on the piezoelectric beam (10) that can maximize the displacement of the piezoelectric beam (10). An input frequency can be provided from the outside to the piezoelectric energy harvester array (1), and the piezoelectric beam (10) can vibrate by the input frequency. If the external input frequency is within the natural frequency range of the piezoelectric beam (10), the piezoelectric beam (10) can resonate with the externally provided input frequency while connected to the mass (130), and the generated displacement of the piezoelectric beam (10) can be amplified, thereby generating more voltage.

[0050] FIG. 4 is a graph of the behavioral characteristics of the piezoelectric energy harvester array of FIG. 2. Beams 1 through 4 refer to the first piezoelectric beam (10) through the fourth piezoelectric beam (10), and the first through fourth piezoelectric beams are arranged in order from smallest to largest natural frequencies. As shown in FIG. 4, it can be confirmed that power is produced through vibration even at frequencies other than the natural frequencies of individual piezoelectric beams (10). That is, strong mechanical vibration energy coupling can occur between at least adjacent piezoelectric beams (10), and a dependent relationship of operation between them can be formed through this mutual coupling.

[0051] In FIG. 4, it can be seen that when the external input vibration is 60 Hz, the first piezoelectric beam (10) is in a resonant state and shows the largest output voltage, when the external input vibration is 70 Hz, the first piezoelectric beam (10) is in a resonant state and shows the largest output voltage, when the external input vibration is 80 Hz, the first piezoelectric beam (10) is in a resonant state and shows the largest output voltage, and when the external input vibration is 95 Hz, the fourth piezoelectric beam (10) is in a resonant state and shows the largest output voltage. Here, as can be seen from the fact that when the first piezoelectric beam (10), beam 1, is in a resonant state at 60 Hz, voltage is also output from the second to fourth piezoelectric beams (10), beam 2-4, it can be seen that voltage is output from other piezoelectric beams that are not in resonance.

[0052] Accordingly, when one piezoelectric beam (10) having a natural frequency corresponding to an external input frequency operates in resonance, the vibration is transmitted through the fixed member (140), and the remaining piezoelectric beams (10) can also operate together. Accordingly, the displacement generated by the piezoelectric energy harvester array (1) is further expanded, and more power can be generated. In addition, since the plurality of piezoelectric beams (10) have different natural frequencies, the piezoelectric energy harvester array (1) according to one embodiment of the present invention has an expanded operating frequency bandwidth, and can generate more power.

[0054] Figure 5 is a graph comparing the performance of a piezoelectric energy harvester array according to one embodiment of the present invention with that of a conventional single energy harvester.

[0055] FIG. 5 (a) is a graph showing the output voltage according to the frequency when an external input frequency of a certain magnitude is provided to a piezoelectric energy harvester composed of individual piezoelectric beams (10). FIG. 5 (b) is a graph showing the voltage generated from a piezoelectric body (120) according to a change in frequency when a plurality of piezoelectric beams (10) are coupled to a fixed member (140) to share mechanical vibration energy. FIG. 5 (a) provides an external input frequency from 20 Hz to 80 Hz to the piezoelectric energy harvester (10), and FIG. 5 (b) provides an external input frequency from 30 Hz to 90 Hz to the piezoelectric energy harvester array (1).

[0056] As shown in FIG. 5(a), when the external input vibration matches the natural frequency of each piezoelectric beam (10) and is in a resonant state, it exhibits the largest output voltage.

[0057] As shown in FIG. 5(b), when the external input vibration is 60 Hz, beam 1, which is the first piezoelectric beam (10), is in a resonant state and exhibits the largest output voltage. Here, unlike beam 1, which is the first piezoelectric beam (10), beams 2, 3, and 4, which are the second, second, and third piezoelectric beams (10), are in a non-resonant state and therefore should have almost no output voltage, but since they are coupled to each other by a fixed member (140), it can be confirmed that they vibrate in a quasi-resonant state and generate an output voltage.

[0058] FIG. 6 is a model designed to calculate the behavior of a piezoelectric energy harvester array according to an embodiment of the present invention by numerical analysis. FIG. 7 is a graph showing the behavior of a piezoelectric energy harvester array according to an embodiment of the present invention calculated by numerical analysis. FIG. 8 is a graph showing the behavior of a piezoelectric energy harvester array according to an embodiment of the present invention calculated by numerical analysis according to the thickness of a fixing member.

[0059] FIGS. 6, 7, and 8 are a schematic diagram of a model and a graph of the simulation results of a finite element simulation performed to provide a vibration with a constant input acceleration to a piezoelectric energy harvester according to the present embodiment and to investigate the output characteristics of the voltage according to the change in frequency. In FIG. 6, the piezoelectric beam (10) that resonates changes according to the change in frequency, and it can be seen that the beams surrounding the piezoelectric beam (10) where the greatest deformation occurs also vibrate under the influence. In FIG. 7, it can be seen that among the plurality of piezoelectric beams (10) arranged side by side according to the change in frequency, the piezoelectric beam that mainly generates power changes. In addition, it can be seen that each piezoelectric beam (10) generates power at frequencies other than the main resonant frequency. That is, each piezoelectric beam (10) has multiple resonant frequencies in addition to the main resonant frequency. As a result, it can be seen that stable power production is possible at a significantly wider frequency range compared to the narrow resonant frequency range of a conventional piezoelectric energy harvester.

[0060] As shown in FIG. 8(a), it can be confirmed that mechanical vibration energy sharing between piezoelectric beams (10) is effective when the fixed member (140) has a sufficiently thin thickness of 1.5 mm.

[0061] As shown in Fig. 8(b), it can be seen that when the fixed member (140) has a relatively thick thickness of 5 mm, there is almost no sharing of mechanical vibration energy between the piezoelectric beams (10).

[0062] In this embodiment, the fixed member (140) is made of a metal material with excellent mechanical strength, taking into account that a large displacement occurs due to the resonance frequency of the piezoelectric beam. Through the simulation results of FIG. 8, it was confirmed that vibrations are transmitted better in a thin fixed member.

[0064] Therefore, it is energy-efficient and has a wide operating frequency bandwidth, making it applicable to any real-life environment where variable vibrations are applied, and it can supply power to various sensors for the realization of future smart factories.

[0066] Although the invention has been described above with reference to embodiments, it should not be interpreted as being limited by such embodiments or drawings, and those skilled in the art will understand that various modifications and changes can be made to the invention without departing from the spirit and scope of the invention as described in the following claims. Explanation of the symbols

[0068] 1: Piezoelectric energy harvester array 10: Individual piezoelectric beams constituting a piezoelectric energy harvester array 110: Elastic beam constituting the piezoelectric beam 120: Piezoelectric elements constituting a piezoelectric beam 130: Mass constituting the piezoelectric beam 140: Fixed member constituting the piezoelectric beam

Claims

Claim 1 A plurality of piezoelectric beams arranged along one direction having the same length but different natural frequencies; a fixing member that fixes both ends by restraining both ends in the longitudinal direction of the plurality of piezoelectric beams connected so that the plurality of piezoelectric beams are coupled to each other and vibration is well transmitted; and a plurality of mass bodies that are mechanically independent of each other and connected to each of the plurality of piezoelectric beams so that the plurality of piezoelectric beams have different natural frequencies, wherein when one piezoelectric beam having a natural frequency corresponding to an external input frequency resonates and operates, the remaining piezoelectric beams whose ends are fixed together by the fixing member also operate together. Claim 2 In claim 1, the plurality of piezoelectric beams are arranged to enable the transfer of mechanical vibration energy to one another through structural coupling in a piezoelectric energy harvester. Claim 3 delete Claim 4 A piezoelectric energy harvester according to claim 1, wherein the one direction is a horizontal direction and the plurality of piezoelectric beams are arranged along the horizontal direction. Claim 5 In claim 1, the fixing member is a piezoelectric energy harvester formed with a thickness of less than 5 mm. Claim 6 A piezoelectric energy harvester according to claim 1, wherein the plurality of mass bodies are connected to the upper and lower ends of the corresponding plurality of piezoelectric beams, and each of the plurality of mass bodies vibrates together with the piezoelectric beams according to a change in frequency to induce the generation of electrical energy of the piezoelectric beams. Claim 7 In claim 1, the piezoelectric beam comprises an elastic beam and a piezoelectric element receiving a bending moment from the elastic beam, and the piezoelectric element comprises a first electrode, a piezoelectric material located on the first electrode, and a second electrode located on the piezoelectric material, arranged in combination to form a piezoelectric energy harvester. Claim 8 In claim 7, the piezoelectric material is Pb(Zn 1 / 3 Nb 2 / 3 )O3-PbTiO3(PZN-PT), [Pb(Mg 1 / 3 Nb 2 / 3 )O3]-[PbTiO3](PMN-PT), (Na x K 1-x A piezoelectric energy harvester comprising at least one of a crystalline material such as NbO3(NKN), a polymer material such as PVDF, PVDF-TrFE, or a thin film material such as ZnO, CdS, or AlN. Claim 9 In claim 7, the piezoelectric energy harvester further comprises a protective substrate positioned on the piezoelectric body to protect the piezoelectric body.

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