An inclined-plane amplitude-limiting and frequency-adjustable piezoelectric cantilever micro-vibration energy harvester and its working method

Abstract

The present invention discloses an inclined-plane amplitude-limiting and frequency-adjustable piezoelectric cantilever micro-vibration energy harvester and its working method. The piezoelectric resonator is arranged inside the packaging shell, and the packaging shell is arranged on the PCB bottom plate; one end of the piezoelectric cantilever is fixedly supported on the packaging shell, and the free end of the piezoelectric cantilever is connected to the middle part of the inner side of the bottom edge of the mass block; amplitude limiters are arranged on both the upper and lower sides of the mass block inside the cavity of the packaging shell, and the amplitude limiters are used to limit the amplitude of the end of the mass block close to the fixed end of the piezoelectric cantilever; the packaging shell can limit the amplitude of the end of the mass block far from the fixed end of the piezoelectric cantilever; a first permanent magnet is arranged on the outer side of the bottom edge of the mass block, and a second permanent magnet is arranged at the position opposite to the first permanent magnet inside the cavity of the packaging shell. The packaging shell and the second permanent magnet are connected through an adjusting mechanism, and the adjusting mechanism is used to adjust the distance between the second and first permanent magnets. The present invention has an inclined-plane amplitude-limiting structure composed of two amplitude-limiting points, which can prevent overload and expand the frequency through collision at the same time, and adjusts the resonance frequency by magnetic coupling.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy devices, and particularly relates to an inclined-plane amplitude-limiting and frequency-adjustable piezoelectric cantilever micro-vibration energy harvester and its working method. Background Art

[0002] With the rapid development of wireless sensor networks, a large number of sensors are distributed in the environment to be monitored. Although traditional batteries can be used to power the sensors, the battery life is short and they cannot work for a long time, requiring regular replacement. As an alternative and supplement to battery technology, vibration energy harvesting technology powers electronic devices such as wireless sensor nodes, playing an important role in the distributed micro-energy consumption self-powered scenarios in the Internet of Things era.

[0003] Currently, the technologies for vibration energy harvesting mainly include piezoelectric, electromagnetic, and electrostatic types. Among them, the piezoelectric vibration energy harvester has high energy harvesting efficiency, small volume, and simple structure, and can output energy at the milliwatt level, which is suitable for sustainable self-power supply of small systems such as wireless sensors. The classic structures of piezoelectric energy harvesting devices include cantilever beams, simply supported beams, fixed beams, disk types, cymbal types, and piezoelectric stacks, and their resonant frequencies increase in turn from low to high. When the piezoelectric vibration energy harvester is in the resonant state, the piezoelectric material has a large strain and a high power generation. Therefore, the resonant frequency of the piezoelectric vibration energy harvester needs to be designed to be close to the environmental excitation frequency. The environmental excitation frequency is often low-frequency and broadband, and the vibration amplitude is small. Therefore, once the resonant frequency of the designed piezoelectric vibration energy harvester deviates from the environmental excitation frequency, the output characteristics deteriorate sharply.

[0004] On the one hand, the design of the piezoelectric vibration energy harvester needs to make full use of the strain of the piezoelectric material to generate enough piezoelectric energy to approach the theoretical power generation limit, and on the other hand, it is also necessary to prevent stress overload failure. The linear vibration PVEH has a narrow resonant frequency and needs to have a tuning function to match the actual environmental excitation frequency. When the environmental excitation is not a fixed frequency and amplitude, and the PVEH also needs to have a frequency broadening and resonance effect, a reasonable design of the PVEH nonlinear vibration system is the key to realizing tuning and frequency broadening.

[0005] Therefore, researchers have put forward requirements for the design of piezoelectric vibration energy harvesters with low frequency, broadband, and high power output. In order to improve the power density, methods such as increasing the additional mass and improving the electromechanical coupling coefficient are generally used; in order to increase the resonant frequency band, magnetic coupling frequency modulation and collision frequency broadening are generally used. However, at the same time, it is also necessary to consider that the maximum stress during the resonance of the piezoelectric beam should not exceed the allowable stress of the material. Summary of the Invention

[0006] To solve the above problems, the object of the present invention is to provide an inclined-plane amplitude-limiting and frequency-adjustable piezoelectric cantilever micro-vibration energy harvester and its working method. The present invention has an inclined-plane amplitude-limiting structure composed of two amplitude-limiting points, which can prevent overload and expand the frequency through collision while adjusting the resonant frequency by magnetic coupling.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] An inclined-plane amplitude-limiting and frequency-adjustable piezoelectric cantilever micro-vibration energy harvester, comprising a piezoelectric resonator, a packaging shell, and a PCB bottom plate. The piezoelectric resonator is arranged inside the packaging shell, and the packaging shell is arranged on the PCB bottom plate;

[0009] The piezoelectric resonator includes a piezoelectric cantilever and a mass block; one end of the piezoelectric cantilever is fixedly supported on the packaging shell, the other end of the piezoelectric cantilever is a free end, the overall shape of the mass block is a U shape, and the free end of the piezoelectric cantilever is connected to the middle part of the inner side of the bottom edge of the mass block;

[0010] Limiters are provided on both the upper and lower sides of the mass block in the inner cavity of the packaging shell. The limiter is located on the side of the mass block close to the fixed end of the piezoelectric cantilever, and the limiter is used to limit one end of the mass block close to the fixed end of the piezoelectric cantilever; the packaging shell can limit the end of the mass block far from the fixed end of the piezoelectric cantilever;

[0011] A first permanent magnet is provided on the outer side of the bottom edge of the mass block, and a second permanent magnet is provided at a position in the inner cavity of the packaging shell opposite to the first permanent magnet. The packaging shell is connected to the second permanent magnet through an adjusting mechanism, and the adjusting mechanism is used to adjust the distance between the second permanent magnet and the first permanent magnet.

[0012] Preferably, the mass block includes a first L-shaped mass block and a second L-shaped mass block arranged symmetrically. Both the first L-shaped mass block and the second L-shaped mass block include a first side and a second side connected perpendicularly. The first side of the first L-shaped mass block, the first side of the second L-shaped mass block, and the piezoelectric cantilever are parallel to each other. The second side of the first L-shaped mass block and the second side of the second L-shaped mass block are connected to form a U-shaped structure as a whole. The free end of the piezoelectric cantilever is inserted between the interfaces where the second sides of the first L-shaped mass block and the second L-shaped mass block are connected, and the second sides of the first L-shaped mass block and the second L-shaped mass block are connected to the substrate layer of the free end of the piezoelectric cantilever.

[0013] Preferably, the first L-shaped mass block is separated into a rectangular large mass block and a rectangular small mass block along the inner side surface of the first side and its extension surface. The centroid of the overall mass block is located at the intersection of the surface of the small mass block near the fixed end of the piezoelectric cantilever beam and the neutral layer of the substrate layer at the free end of the piezoelectric cantilever beam. The centroid of the large mass block of the first L-shaped mass block and the large mass block of the second L-shaped mass block is located on the neutral layer of the substrate layer of the piezoelectric cantilever beam and between the centroid of the overall mass block and the fixed end of the piezoelectric cantilever beam. The centroid of the overall mass block and the centroid of the large mass block of the first L-shaped mass block and the large mass block of the second L-shaped mass block satisfy the following relationship:

[0014]

[0015] where, l sm is the length of the small mass block along the direction parallel to the length of the piezoelectric cantilever beam, l bm is the length of the large mass block along the direction parallel to the length of the piezoelectric cantilever beam, l AB is the distance between the centroid of the overall mass block and the centroid of the large mass block of the first L-shaped mass block and the large mass block of the second L-shaped mass block, t bm is the thickness of the large mass block along the direction perpendicular to the piezoelectric cantilever beam, t sm is the thickness of the small mass block along the direction perpendicular to the piezoelectric cantilever beam.

[0016] Preferably, the adjusting mechanism uses an adjustable bolt. The adjustable bolt is threadedly connected to the encapsulation housing. The nut of the adjustable bolt is located outside the encapsulation housing, and the threaded end of the adjustable bolt extends into the encapsulation housing and is connected to the second permanent magnet.

[0017] Preferably, the first permanent magnet is arranged in the middle of the outer side of the bottom edge of the mass block.

[0018] Preferably, the piezoelectric cantilever beam includes a upper piezoelectric layer, a substrate layer, and a lower piezoelectric layer arranged in sequence; the polarization directions of the upper piezoelectric layer and the lower piezoelectric layer are opposite, electrode layers are provided on both surfaces, and lead-out electrodes are connected to both. The surface of the substrate layer is connected to the upper piezoelectric layer and the lower piezoelectric layer through a conductive layer capable of conducting electricity.

[0019] Preferably, both the upper piezoelectric layer and the lower piezoelectric layer adopt PZT piezoelectric layers, the substrate layer adopts a copper substrate layer, and the surface of the substrate layer is connected to the upper piezoelectric layer and the lower piezoelectric layer through an epoxy resin layer capable of conducting electricity.

[0020] Preferably, the encapsulation housing includes an upper cover plate, an upper frame, and a lower frame. The lower end of the lower frame is connected to the PCB bottom plate, the upper end of the lower frame is connected to the lower end of the upper frame, the upper end of the upper frame is connected to the upper cover plate, and the piezoelectric resonator is disposed in a cavity formed by the upper cover plate, the upper frame, the lower frame, and the PCB bottom plate; the fixed end of the piezoelectric cantilever beam is fixed between the upper frame and the lower frame, and flexible lead electrodes are padded between the piezoelectric cantilever beam and the upper frame and between the piezoelectric cantilever beam and the lower frame.

[0021] Preferably, electrode lead grooves for embedding lead electrodes are formed on the upper frame 2, and the upper cover plate, the upper frame, the lower frame, and the PCB bottom plate are encapsulated with epoxy resin; the first permanent magnet and the mass block, as well as the second permanent magnet and the end face of the adjustable bolt, are bonded with ergo5800 glue.

[0022] The working method of a slant-limiting frequency-adjustable piezoelectric cantilever micro-vibration energy harvester as described above in the present invention includes the following processes:

[0023] When ambient vibration is applied, the PCB bottom plate is subjected to vibration excitation, the piezoelectric cantilever beam generates forced vibration. After the mass block collides with the limiter, the collision energy between the mass block and the limiter is converted into the bending moment of the free end of the piezoelectric cantilever beam. When the forced vibration of the piezoelectric cantilever beam continues to increase, the mass block can still contact the encapsulation housing, and at this time, the encapsulation housing can limit the mass block.

[0024] When it is necessary to make the resonance frequency of the slant-limiting frequency-adjustable piezoelectric cantilever micro-vibration energy harvester match the ambient vibration frequency, adjust the adjustment mechanism to adjust the distance between the first permanent magnet and the second permanent magnet until the resonance frequency of the slant-limiting frequency-adjustable piezoelectric cantilever micro-vibration energy harvester matches the ambient vibration frequency.

[0025] The present invention has the following beneficial effects:

[0026] In the inclined-plane amplitude-limiting and frequency-adjustable piezoelectric cantilever micro-vibration energy harvester of the present invention, by setting a first permanent magnet, a second permanent magnet and an adjustment mechanism, the axial force of the piezoelectric cantilever can be adjusted by adjusting the distance between the second permanent magnet and the first permanent magnet, thereby changing the stiffness and adjusting the resonant frequency of the resonator. When the resonant frequency of the PVEH needs to be decreased compared with the design value, the second permanent magnet and the first permanent magnet are opposite in the same pole; when the resonant frequency needs to be increased, the second permanent magnet and the first permanent magnet are opposite in the opposite pole. Through the encapsulation shell and the provided amplitude limiter, two amplitude-limiting points are provided on both sides of the piezoelectric cantilever in its vibration direction. The first amplitude-limiting point is the amplitude limiter, and the second amplitude-limiting point is the encapsulation shell. After the mass block at the free end of the piezoelectric cantilever collides with the first amplitude-limiting point, the collision energy can be converted into the bending moment at the free end of the piezoelectric cantilever, making the stress distribution at the free end of the piezoelectric cantilever more uniform, improving the structural electromechanical coupling coefficient, and the mass block contacts the second amplitude-limiting point only when the bending moment of the piezoelectric cantilever is large enough. Compared with the traditional single-point amplitude limiting, the two amplitude-limiting points form an inclined-plane amplitude-limiting structure, which can prevent the piezoelectric beam from being overloaded in an S shape under large excitation in the traditional frame plane amplitude limiting. The comprehensive frequency broadening of magnetic coupling and collision is easier to control the potential energy curve to achieve bistable frequency broadening with a low potential barrier. The frequency broadening based on tuning can obtain a wider resonant frequency band. The overall shape of the mass block is a U shape, and the free end of the piezoelectric cantilever is connected to the middle part of the inner side of the bottom edge of the mass block. The mass block of this structure ensures the realization of the above two-point amplitude limiting.

[0027] Further, the mass block includes a first L-shaped mass block and a second L-shaped mass block that are symmetrically arranged. The mass block of this structure makes the U-shaped mass block a split type, which is convenient for assembling with the piezoelectric cantilever.

[0028] Further, the center of mass of the mass block is located in the middle of the inner side of the bottom edge of the mass block, which can avoid the output energy being reduced due to the opposite charge polarities in some areas on the left and right sides of the center of mass of the piezoelectric layer when the center of mass of the piezoelectric cantilever is not at this point. Description of the Drawings

[0029] Figure 1 It is a schematic diagram of the overall structure of the inclined-plane amplitude-limiting and frequency-adjustable piezoelectric cantilever micro-vibration energy harvester of the present invention;

[0030] Figure 2 is Figure 1 A schematic diagram of the structure of the internal movable piezoelectric resonator;

[0031] Figure 3 is Figure 2 A schematic diagram of the piezoelectric bimorph in it;

[0032] Figure 4 It is a schematic diagram of the inclined-plane amplitude-limiting structure of the present invention;

[0033] Figure 5Schematic diagram of the magnetic coupling frequency modulation structure of the present invention;

[0034] Figure 6 Schematic diagram for comparing the output voltage of this embodiment when setting the inclined plane amplitude limit with that when setting the single-point amplitude limit;

[0035] Figure 7 Schematic diagram of the connection between the mass block and the piezoelectric bimorph in the embodiment of the present invention.

[0036] In the drawings: 1. upper cover plate, 2. upper frame, 3. lower frame, 4. PCB bottom plate, 5. lead-out electrode, 6. piezoelectric bimorph, 7. mass block, 8. PZT piezoelectric layer, 9. substrate layer, 10. electrode layer, 11. epoxy resin layer, 12. amplitude limiter, 13. permanent magnet, 14. adjustable bolt. Detailed implementation manners

[0037] The present invention will be described in detail below with reference to the drawings and specific implementation manners.

[0038] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, or a specific orientation structure and operation, and thus should not be construed as a limitation of the present invention.

[0039] Refer to Figures 1 to 5 , the inclined plane amplitude limit adjustable frequency piezoelectric cantilever micro vibration energy harvester of the present invention includes a piezoelectric resonator, a packaging shell and a PCB bottom plate 4. The piezoelectric resonator is arranged in the packaging shell, and the packaging shell is arranged on the PCB bottom plate 4. The packaging shell can be a fully enclosed shell structure or a shell structure without a bottom. Figure 1 , Figure 4 and Figure 5 The case where the packaging shell has no bottom is shown in. The shown packaging shell includes an upper cover plate 1, an upper frame 2, a lower frame 3 and a PCB bottom plate 4. The lower end of the lower frame 3 is connected to the PCB bottom plate 4, the upper end of the lower frame 3 is connected to the lower end of the upper frame 2, the upper end of the upper frame 2 is connected to the upper cover plate 1, and the upper cover plate 1, the upper frame 2, the lower frame 3 and the PCB bottom plate 4 are encapsulated by epoxy resin. The piezoelectric resonator is arranged in the cavity surrounded by the upper cover plate 1, the upper frame 2, the lower frame 3 and the PCB bottom plate 4; the piezoelectric resonator includes a piezoelectric cantilever beam and a mass block 7; taking Figure 1Taking the orientation shown as an example, the left end of the piezoelectric cantilever beam is fixedly supported between the upper frame 2 and the lower frame 3. A flexible lead-out electrode 5 is connected to the fixed end of the piezoelectric cantilever beam. One end of the lead-out electrode 5 is led out between the upper frame 2 and the lower frame 3. Flexible lead-out electrodes 5 are padded between the piezoelectric cantilever beam and the upper frame 2 and between the piezoelectric cantilever beam and the lower frame 3; an electrode lead groove for embedding the lead-out electrode is provided on the upper frame 2. The mass block 7 is arranged at the free end of the piezoelectric cantilever beam ( Figure 1 the right end of the piezoelectric cantilever beam shown). The mass block 7 includes two identical L-shaped mass blocks arranged symmetrically up and down. The horizontal plane of the vertical side on the right side of the L-shaped mass block is directly bonded to the substrate layer at the free end of the piezoelectric cantilever beam (that is, only the substrate layer is provided for the part of the piezoelectric cantilever beam located inside the mass block 7, and the piezoelectric layer and the electrode layer are not provided, and the ends of the piezoelectric layer and the electrode layer are located inside the bottom edge of the mass block 7). The horizontal side of the L-shaped mass block is parallel to the piezoelectric cantilever beam and faces the fixed end of the piezoelectric cantilever beam. The two L-shaped mass blocks together form a U-shaped mass block 7; the present invention uses the L-shaped mass block to improve the piezoelectric output power and reliability, uses the rectangular limiter to prevent overload and perform collision frequency broadening at the same time, and uses magnetic coupling to adjust the resonant frequency. The bonding length between the L-shaped mass block and the piezoelectric cantilever beam is short, which does not weaken the effective length of the piezoelectric cantilever beam. The piezoelectric layer is thick and the power density is high.

[0040] See Figure 3 and Figure 2 , the piezoelectric cantilever beam includes a upper piezoelectric layer, a substrate layer 9 and a lower piezoelectric layer arranged in sequence. The surface of the substrate layer 9 is connected between the upper piezoelectric layer and the lower piezoelectric layer; the polarization directions of the upper piezoelectric layer and the lower piezoelectric layer are opposite; electrode layers 10 are provided on the surfaces of the upper piezoelectric layer and the lower piezoelectric layer, and both are connected with lead-out electrodes 5. The substrate layer 9 is a copper substrate layer. The surface of the substrate layer 9 is connected to the upper piezoelectric layer and the lower piezoelectric layer through a conductive epoxy resin layer 11; the electrode layer is a silver electrode layer 5. See Figure 1 and Figure 5 , a threaded hole is provided at the right frame of the encapsulation housing. The adjustable bolt 14 is screwed into this threaded hole. The head of the adjustable bolt 14 is located outside the encapsulation housing, and the screw part of the adjustable bolt 14 extends into the interior of the encapsulation housing. The permanent magnet is a circular neodymium iron boron permanent magnet. The first circular neodymium iron boron permanent magnet is bonded to the middle of the right end face of the whole mass block 7. The second circular neodymium iron boron permanent magnet is bonded to the end face of the screw part of the adjustable bolt 14. The first permanent magnet and the end face of the mass block 7, and the second permanent magnet and the end face of the adjustable bolt 14 are both bonded with ergo5800 glue. The limiter 12 includes two rectangular limiters. The end face of the left side of the first limiter is bonded to the inner surface of the left side of the upper frame 2. The end face of the upper side of the first limiter is bonded to the inner surface of the left side of the upper cover plate 1. The end face of the left side of the second limiter is bonded to the inner surface of the left side of the lower frame 3. The end face of the bottom of the second limiter is bonded to the inner surface of the PCB bottom plate 4.

[0041] Referring to Figure 1 , in the inclined surface amplitude-limiting and frequency-adjustable piezoelectric cantilever micro-vibration energy harvester of the present invention, the upper cover plate 1, the upper frame 2 and the lower frame 3 are all processed by laser using polymethyl methacrylate (PMMA). The upper frame 2 needs to be engraved with electrode lead grooves to facilitate the arrangement of the lead-out electrode 5, and the final packaging structure is bonded with epoxy resin. The piezoelectric layer 8 is made by the PZT powder sintering process. Silver electrode layers are respectively coated on the upper and lower surfaces of the piezoelectric layer 8, and then it is bonded to the middle copper substrate layer 9 at a low temperature through the epoxy resin layer 11, and this epoxy resin layer 11 can conduct electricity. The polarization directions of the upper and lower piezoelectric layers 8 are opposite, and the copper substrate layer 9 and the upper and lower piezoelectric layers 8 form a series structure, and the series connection can increase the piezoelectric voltage.

[0042] The working process of the inclined surface amplitude-limiting and frequency-adjustable piezoelectric cantilever micro-vibration energy harvester of the present invention includes: when the loading environmental vibration occurs, the PCB bottom plate 4 is subjected to vibration excitation, and the packaging shell of the whole device is in the same situation as the environmental vibration. The piezoelectric bimorph cantilever beam (that is, the piezoelectric cantilever beam adopts a piezoelectric bimorph) clamped by the upper frame 2 and the lower frame 3 generates forced vibration. This power generation method is based on the d31 power generation mode of piezoelectric materials, that is, axial tensile and compressive stresses are generated on the upper and lower piezoelectric layers of the piezoelectric cantilever beam during vibration, so as to generate an alternating voltage output on the surface electrode layer. The first limiter and the upper cover plate 1 form two limiting points, and the second limiter and the PCB bottom plate 4 form two limiting points. After the additional mass block 7 at the free end of the piezoelectric cantilever beam collides with the first limiting point, the collision energy can be converted into the bending moment at the free end of the cantilever beam, making the stress distribution at the free end more uniform, improving the structural electromechanical coupling coefficient, and only contacting the second limiting point when the bending moment is large enough. Compared with the traditional single-point amplitude limiting, the two limiting points form an inclined surface amplitude-limiting structure, which can prevent the piezoelectric beam from being overloaded in an S shape under large excitation in the traditional frame plane amplitude limiting. By rotating the adjustable bolt 14 to change the distance between the first and second permanent magnets to adjust the resonant frequency of the resonator to match the environmental vibration frequency, good output characteristics can be obtained.

[0043] In the inclined-plane amplitude-limiting and frequency-tunable piezoelectric cantilever micro-vibration energy harvester of the present invention, a threaded hole is provided at the right-side frame. The adjustable bolt 14 is rotatably inserted into this threaded hole. The permanent magnet 13 is a circular neodymium-iron-boron permanent magnet. The first circular neodymium-iron-boron permanent magnet is bonded to the end face of the mass block 7, and the second circular neodymium-iron-boron permanent magnet is bonded to the end face of the adjustable bolt 14. By rotating the adjustable bolt to control the distance between the permanent magnets 13, the axial force of the piezoelectric cantilever can be adjusted, thereby changing the stiffness of the piezoelectric cantilever, and further adjusting the resonant frequency of the resonator. The amplitude limiter 12 includes two rectangular amplitude limiters. The first amplitude limiter and the upper cover plate 1 form two amplitude-limiting points, and the second amplitude limiter and the PCB bottom plate 4 form two amplitude-limiting points. After the additional mass block at the free end of the piezoelectric cantilever collides with the first amplitude-limiting point, the collision energy can be converted into the bending moment at the free end of the cantilever, making the stress distribution at the free end more uniform, improving the structural electromechanical coupling coefficient, and only contacting the second amplitude-limiting point when the bending moment is large enough. Compared with the traditional single-point amplitude limiting, the two amplitude-limiting points form an inclined-plane amplitude-limiting structure, which can prevent the piezoelectric beam from being overloaded in an S shape under large excitation in the traditional frame plane limiting. The comprehensive frequency broadening of magnetic coupling and collision is easier to control the potential energy curve to achieve bistable frequency broadening with a low potential barrier. The frequency broadening based on tuning can obtain a wider resonant frequency band.

[0044] Referring to Figure 7 , the mass block 7 includes two L-shaped mass blocks. Each L-shaped mass block is divided along the dotted line (the extended plane of the inner side of the first side of the first L-shaped mass block) as shown. The L-shaped mass block is divided into two large and small rectangular mass blocks up and down. The part above the dotted line is denoted as the large mass block C, and the part below the dotted line is denoted as the small mass block D. By optimizing the sizes of the two large and small rectangular mass blocks, the centroid of the entire piezoelectric resonator is located at point B, and point B is also the position point of the small mass block (i.e., the projection line of the left side of the small mass block D on the neutral layer of the substrate layer 9), avoiding the situation where the centroid of the piezoelectric resonator is not at point B, which may cause the charge polarities in the partial regions on the left and right sides of the centroid of the piezoelectric resonator to be opposite, reducing the output energy. Figure 7

[0045] Figure 7 Referring to Figure 7 , the mass block 7 includes two L-shaped mass blocks. Each of the two L-shaped mass blocks contains a large rectangular mass block. Considering the two large rectangular mass blocks as a whole, A is the centroid of this whole. When the centroid of the entire piezoelectric resonator is located at point B, the distance l between A and B AB The length l of the small mass block sm , height t sm and the length l of the large mass block bm , height l sm satisfy the functional relationship:

[0046]

[0047] According to the above functional relationship, by optimizing the bonding length, the effective length of the piezoelectric cantilever beam can be ensured, the resonance frequency can be reduced, and it is easier to achieve a collision with the limiting point by optimizing the length of the large rectangular mass block, avoiding the situation of excessive stress in the piezoelectric layer caused by using a traditional large-length rectangular mass block to achieve a collision with the limiting point, and at the same time, the overall volume of the piezoelectric resonator can be reduced.

[0048] Furthermore, the upper piezoelectric layer and the lower piezoelectric layer are PZT piezoelectric layers, and the substrate layer 9 is a copper substrate layer; a copper-based PZT bulk piezoelectric bimorph is used. The PZT bulk material sintered by powder has good densification, mature process, and high electromechanical coupling coefficient of the material. The copper substrate ensures the toughness of the piezoelectric cantilever beam. The thickness of the piezoelectric bimorph can ensure a large additional mass block.

[0049] Referring to Figure 2 and Figure 3 , in this embodiment, the dimensions of each component are shown in Table 1:

[0050] Table 1

[0051] Symbol Parameters Value <![CDATA[l c > Length of piezoelectric cantilever beam 14 mm <![CDATA[w c > Width of piezoelectric cantilever beam 10 mm <![CDATA[t p > Thickness of piezoelectric layer 0.2 mm <![CDATA[t s > Thickness of substrate 0.1 mm <![CDATA[t bm > Thickness of large mass block 2 mm <![CDATA[t sm > Thickness of small mass block 0.5 mm <![CDATA[l bm > Length of large mass block 12 mm <![CDATA[l sm > Length of small mass block 5 mm <![CDATA[l e1 > Electrode length 1 2 mm <![CDATA[l e2 > Electrode length 2 4 mm <![CDATA[t b > Thickness of bonding layer 0.1 mm

[0052] Referring to Figure 6 , under the excitation of 1g acceleration, the output voltage of this embodiment can be increased by about 40% when setting the inclined plane limit compared with the single-point limit.

[0053] The above is only one implementation manner of the present invention, not all or the only implementation manner. Any equivalent transformation of the technical solution of the present invention adopted by those of ordinary skill in the art by reading the specification of the present invention is covered by the claims of the present invention.

Claims

1. A sloped amplitude-limited and frequency-adjustable piezoelectric cantilever micro vibration energy harvester, characterized in that, It includes a piezoelectric resonator, a packaging shell, and a PCB bottom plate (4). The piezoelectric resonator is disposed within the packaging shell, and the packaging shell is disposed on the PCB bottom plate (4). The piezoelectric resonator includes a piezoelectric cantilever beam and a mass block (7). One end of the piezoelectric cantilever beam is fixedly supported on the packaging shell, the other end of the piezoelectric cantilever beam is a free end, the overall shape of the mass block (7) is a U shape, and the free end of the piezoelectric cantilever beam is connected to the middle part of the inner side of the bottom edge of the mass block (7). Limiters (12) are provided on both the upper and lower sides of the mass block (7) in the inner cavity of the packaging shell. The limiter (12) is located on the side of the mass block (7) close to the fixed end of the piezoelectric cantilever beam, and the limiter (12) is used to limit one end of the mass block (7) close to the fixed end of the piezoelectric cantilever beam. The packaging shell can limit the end of the mass block (7) far from the fixed end of the piezoelectric cantilever beam. A first permanent magnet is provided on the outer side of the bottom edge of the mass block (7). A second permanent magnet is provided in the inner cavity of the packaging shell at a position opposite to the first permanent magnet. The packaging shell and the second permanent magnet are connected through an adjustment mechanism, and the adjustment mechanism is used to adjust the distance between the second permanent magnet and the first permanent magnet. The mass block (7) includes a first L-shaped mass block and a second L-shaped mass block that are symmetrically arranged. Both the first L-shaped mass block and the second L-shaped mass block include a first side and a second side that are perpendicularly connected. The first side of the first L-shaped mass block, the first side of the second L-shaped mass block, and the piezoelectric cantilever beam are parallel to each other. The second side of the first L-shaped mass block and the second side of the second L-shaped mass block are connected and form a U-shaped structure as a whole for the mass block (7). The free end of the piezoelectric cantilever beam is inserted between the interfaces where the second sides of the first L-shaped mass block and the second L-shaped mass block are connected. Among them, the second sides of the first L-shaped mass block and the second L-shaped mass block are connected to the substrate layer of the free end of the piezoelectric cantilever beam. The first L-shaped mass block divides the first L-shaped mass block into a rectangular large mass block (C) and a rectangular small mass block (D) along the inner side surface of the first side and its extension surface. The centroid of the whole mass block (7) is located at the intersection of the surface of the small mass block (D) close to the fixed end of the piezoelectric cantilever beam and the neutral layer of the substrate layer of the free end of the piezoelectric cantilever beam. The centroids of the large mass blocks of the first L-shaped mass block and the second L-shaped mass block as a whole are located on the neutral layer of the substrate layer of the piezoelectric cantilever beam and between the centroid of the whole mass block (7) and the fixed end of the piezoelectric cantilever beam. The centroid of the whole mass block (7) and the centroids of the large mass blocks of the first L-shaped mass block and the second L-shaped mass block as a whole satisfy the following relationship: Among them, is the length of the small mass block (D) along the length direction parallel to the piezoelectric cantilever beam, is the length of the large mass block (C) along the length direction parallel to the piezoelectric cantilever beam, is the distance between the centroid of the whole mass block (7) and the centroid of the large mass blocks of the first L-shaped mass block and the large mass blocks of the second L-shaped mass block as a whole, is the thickness of the large mass block (C) along the direction perpendicular to the piezoelectric cantilever beam, is the thickness of the small mass block (D) along the direction perpendicular to the piezoelectric cantilever beam.

2. The adjustable-frequency piezoelectric cantilever micro-vibration energy harvester with slope limiting according to claim 1, characterized in that, The adjustment mechanism uses an adjustable bolt (14). The adjustable bolt (14) is threadedly connected to the packaging shell. The nut of the adjustable bolt (14) is located outside the packaging shell, and the screw end of the adjustable bolt (14) extends into the interior of the packaging shell and is connected to the second permanent magnet.

3. A sloped amplitude-limited and frequency-adjustable piezoelectric cantilever micro-vibration energy harvester according to claim 1, characterized in that, The first permanent magnet is provided in the middle of the outer side of the bottom edge of the mass block (7).

4. A sloped amplitude-limiting and frequency-adjustable piezoelectric cantilever micro-vibration energy harvester according to claim 1, characterized in that, The piezoelectric cantilever beam comprises a upper piezoelectric layer, a substrate layer (9) and a lower piezoelectric layer which are arranged in sequence; the polarization directions of the upper piezoelectric layer and the lower piezoelectric layer are opposite, electrode layers (10) are arranged on the surfaces, and lead-out electrodes (5) are connected to both of them. The surface of the substrate layer (9) is connected to the upper piezoelectric layer and the lower piezoelectric layer through a conductive layer capable of conducting electricity.

5. A sloped amplitude-limited frequency-adjustable piezoelectric cantilever micro-vibration energy harvester according to claim 4, characterized in that, Both the upper piezoelectric layer and the lower piezoelectric layer adopt PZT piezoelectric layers (8), the substrate layer (9) adopts a copper substrate layer, and the surface of the substrate layer (9) is connected to the upper piezoelectric layer and the lower piezoelectric layer through an epoxy resin layer (11) capable of conducting electricity.

6. The micro-vibration energy harvester of a bevel-limited adjustable-frequency piezoelectric cantilever beam according to claim 1, characterized in that The encapsulation housing comprises an upper cover plate (1), an upper frame (2) and a lower frame (3). The lower end of the lower frame (3) is connected to the PCB bottom plate (4), the upper end of the lower frame (3) is connected to the lower end of the upper frame (2), and the upper end of the upper frame (2) is connected to the upper cover plate (1). The piezoelectric resonator is arranged in a cavity surrounded by the upper cover plate (1), the upper frame (2), the lower frame (3) and the PCB bottom plate (4); the fixed end of the piezoelectric cantilever beam is fixed between the upper frame (2) and the lower frame (3), and flexible lead-out electrodes (5) are padded between the piezoelectric cantilever beam and the upper frame (2) and between the piezoelectric cantilever beam and the lower frame (3).

7. A sloped amplitude-limiting and frequency-adjustable piezoelectric cantilever micro-vibration energy harvester according to claim 6, characterized in that An electrode lead slot for embedding the lead-out electrode (5) is formed on the upper frame 2, and the upper cover plate (1), the upper frame (2), the lower frame (3) and the PCB bottom plate (4) are encapsulated with epoxy resin; the end faces of the first permanent magnet and the mass block (7) and the second permanent magnet and the adjustable bolt (14) are bonded with ergo5800 glue.

8. A working method of a bevel-limited adjustable-frequency piezoelectric cantilever micro-vibration energy harvester according to any one of claims 1-7, characterized in that, It includes the following processes: When ambient vibration is applied, the PCB bottom plate (4) is subjected to vibration excitation, the piezoelectric cantilever beam generates forced vibration. After the mass block (7) collides with the limiter (12), the collision energy between the mass block (7) and the limiter (12) is converted into the bending moment at the free end of the piezoelectric cantilever beam. When the forced vibration of the piezoelectric cantilever beam continues to increase, the mass block (7) can still contact the encapsulation housing, and at this time, the encapsulation housing can limit the mass block (7). When it is necessary to make the resonance frequency of the inclined-plane limited-amplitude adjustable-frequency piezoelectric cantilever beam micro-vibration energy harvester match the ambient vibration frequency, adjust the adjustment mechanism to adjust the distance between the first permanent magnet and the second permanent magnet until the resonance frequency of the inclined-plane limited-amplitude adjustable-frequency piezoelectric cantilever beam micro-vibration energy harvester matches the ambient vibration frequency.

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