A piezoelectric energy harvesting device embedded inside an air spring

Abstract

The present invention discloses a piezoelectric energy harvesting device embedded inside an air spring, belonging to the field of vibration energy recovery. A piezoelectric energy harvesting device embedded inside an air spring includes an energy harvesting device, and the energy harvesting device includes a first tuned mass block, a first piezoelectric sheet, a flexible diaphragm, a diaphragm holder, a tubular flexible diaphragm, a second tuned mass block, a second piezoelectric sheet, bolts and gaskets. Based on the additional air chamber built-in air spring, the present invention proposes a piezoelectric energy harvesting device embedded inside an air spring; based on the equivalent mechanical model of the piezoelectric energy harvesting device, a mathematical model of the output voltage is established; a method for optimizing the piezoelectric energy harvesting device is proposed to achieve maximum power generation under environmental constraint conditions. Compared with the prior art, the present invention has the advantages of simple structure, compact installation, high energy conversion efficiency and strong applicability.

Description

Technical Field

[0001] The present invention belongs to the field of vibration energy recovery, and particularly relates to a piezoelectric energy harvesting device embedded inside an air spring. Background Art

[0002] Air springs have the advantages of low natural vibration frequency, adjustable stiffness, controllable damping, good noise reduction and vibration absorption ability, and long service life, and have gradually replaced traditional helical springs in some high-end vehicles. The main body of the air spring is made of rubber material, and air leakage will occur after long-term use. However, due to the high sealing requirement of the air spring, it is impractical to supply power to the internal air spring safety monitoring device through external circuits. At present, people can only roughly judge the safety status of the air spring through the usage time and driving experience, and cannot give an early warning of the occurrence of air spring damage in a timely manner.

[0003] Chinese patents ZL200810022475.5 and ZL201110121853.7 utilize piezoelectric materials to collect the energy of the vibration of the air spring, but the installation of the piezoelectric sheets cannot convert the air pressure change in the air spring into electrical energy, and the self-power supply of the air spring safety monitoring device cannot be achieved. Summary of the Invention

[0004] Based on the above background art, in order to supply power to the internal air spring safety monitoring device, the present invention proposes a piezoelectric energy harvesting device embedded inside an air spring. Based on the additional air chamber internal air spring, a piezoelectric energy harvesting device embedded inside an air spring is proposed; based on the equivalent mechanical model of the piezoelectric energy harvesting device, a mathematical model of the output voltage is established, and an optimization method is proposed to ensure a large output voltage at a low cost. Compared with the prior art, the present invention has the advantages of simple structure, compact installation, high energy conversion efficiency and strong applicability.

[0005] The present invention is implemented by adopting the following technical scheme: a piezoelectric energy feeding device embedded in an air spring, comprising an energy feeding device, the energy feeding device comprising a tuning mass block 1, a piezoelectric sheet 1, a flexible diaphragm, a diaphragm frame, a tubular flexible diaphragm, a tuning mass block 2, a piezoelectric sheet 2, bolts and a sealing gasket; the bottom surface of the tubular flexible diaphragm and the top surface of the annular platform on the lower cover of the air spring are fixedly connected by a sealing gasket and bolts, the piezoelectric sheet 2 is symmetrically attached to the tubular flexible diaphragm, and the tuning mass block 2 is attached to the piezoelectric sheet 2 symmetrically, so as to change the resonance of the piezoelectric sheet 2 frequency, capturing more energy; the middle of the diaphragm frame is fixedly connected to the upper end of the middle tube body of the lower cover, the lower side of the edge of the diaphragm frame is fixedly connected to the top surface of the tubular flexible diaphragm by bolts, the upper side of the edge of the diaphragm frame is fixed to the flexible diaphragm, the piezoelectric sheet is attached to the flexible diaphragm, the tuning mass is attached to the piezoelectric sheet, the lower cover, the sealing gasket, the tubular flexible diaphragm, the diaphragm frame, and the flexible diaphragm are sealed and connected to form an additional air chamber; a damping hole is also provided on the annular platform of the lower cover, and the main air chamber and the additional air chamber of the air spring are exchanged with gas through the damping hole on the lower cover. Due to the small diameter of the damping hole, the gas will bring a certain damping force when flowing through the damping hole, which can alleviate the impact. During the driving process of the vehicle, relative displacement will occur between the upper plate and the lower cover. Due to the damping force generated by the damping hole, a pressure difference will be generated between the main air chamber and the additional air chamber. The pressure forces the flexible diaphragm and the tubular flexible diaphragm in the energy feeding device to deform and generate reciprocating vibration. The piezoelectric sheet 1 and the piezoelectric sheet 2 attached to the flexible diaphragm and the tubular flexible diaphragm are bent and pulled under the action of the flexible diaphragm, converting the mechanical energy of the flexible diaphragm into electrical energy. The piezoelectric sheet 1 and the piezoelectric sheet 2 are connected to the circuit module of the air spring safety monitoring device to supply power to the air spring safety monitoring device.

[0006] Among them, the number of piezoelectric sheets one and two and the mass of tuning mass blocks one and two can be changed.

[0007] The above-mentioned piezoelectric energy feeding device is embedded in the air spring, and the buffer block is fixedly installed on the upper plate and the rubber airbag. When the movement between the vehicle body and the axle is violent and the gap is too small, the upper plate is prevented from directly hitting the lower cover, thereby protecting the energy feeding device.

[0008] In the above-mentioned piezoelectric energy feeding device embedded in the air spring, in the equivalent mechanical model of the piezoelectric energy feeding device embedded in the air spring, the deformation of the flexible diaphragm and the tubular flexible diaphragm is small during the operation of the air spring. Therefore, the influence of the flexible diaphragm and the tubular flexible diaphragm on the volume of the additional air chamber during the deformation process is ignored. It can be considered that the stiffness and damping of the flexible diaphragm and the tubular flexible diaphragm do not affect each other during the deformation process.

[0009] The output voltage of the piezoelectric energy feeding device embedded in the air spring and the piezoelectric piece 1 attached to the flexible diaphragm is expressed as:

[0010]

[0011]

[0012] z r = z3 - z1

[0013] K m = n1·K p1 + K FD

[0014] Wherein, M1 is the mass of the first tuned mass block, z3 is the displacement of the first tuned mass block, z1 is the displacement of the lower cover, C m is the damping of the flexible diaphragm after attaching the first piezoelectric sheet, K m is the bending stiffness of the flexible diaphragm after attaching the first piezoelectric sheet, n1 is the number of the first piezoelectric sheets, K p1 is the bending stiffness of the first piezoelectric sheet, K FD is the bending stiffness of the flexible diaphragm, V T is the voltage generated by the first piezoelectric sheet, R L is the load resistance, C p1 is the clamping capacitance of the first piezoelectric sheet, l p is the free length of the first piezoelectric sheet, α is the electromechanical coupling coefficient of the inverse piezoelectric effect, is the current generated by the first piezoelectric sheet due to bending, is the current generated by the first piezoelectric sheet under the traction of the flexible diaphragm.

[0015] For the above piezoelectric energy harvesting device embedded inside the air spring, the output voltage of the second piezoelectric sheet pasted on the tubular flexible diaphragm is expressed as:

[0016]

[0017]

[0018] K n = n2·K p2 + K FC

[0019] Wherein, M2 is the mass of the second tuned mass block, z4 is the displacement of the second tuned mass block, C n is the damping of the tubular flexible diaphragm after attaching the second piezoelectric sheet, K n is the bending stiffness of the tubular flexible diaphragm after attaching the second piezoelectric sheet, n2 is the number of the second piezoelectric sheets, K p2 is the bending stiffness of the second piezoelectric sheet, K FC is the bending stiffness of the tubular flexible diaphragm, V C is the voltage generated by the second piezoelectric sheet, λ is the relationship between the forces on the tubular flexible diaphragm and the flexible diaphragm, R L is the load resistance, Cp2 is the clamping capacitance of piezoelectric sheet 2, l m is the free length of piezoelectric sheet 2, is the current generated by the bending of piezoelectric sheet 2, is the current generated by the traction of the tubular flexible diaphragm of piezoelectric sheet 2.

[0020] For the above piezoelectric energy harvesting device embedded inside an air spring, an optimization method for the piezoelectric energy harvesting device is proposed. A cost function is defined, and the tuned mass M and the number of piezoelectric units n are selected as the design variables for optimization to achieve maximum power generation under environmental constraints;

[0021] The cost function of piezoelectric sheet 1 is expressed as:

[0022] f(M1, n1) = q p V tot -q s n1S p1

[0023]

[0024] where q p and q s are the weight coefficients, is the experimentally measured voltage of piezoelectric sheet 1, and S p1 is the cost of a set of piezoelectric sheet 1 transducers;

[0025] The cost function of piezoelectric sheet 2 is expressed as:

[0026] f(M2, n2) = q l V tob -q z n2S p2

[0027]

[0028] where q l and q z are the weight coefficients, is the experimentally measured voltage of piezoelectric sheet 2, and S p2 is the cost of a set of piezoelectric sheet 2 transducers;

[0029] In the present invention, the selection range of n1 is 1 ≤ n1 ≤ 8, and the selection range of M1 is 0 ≤ M1 ≤ 0.5 kg; since piezoelectric sheet 2 is symmetrically distributed, the value of n2 is a multiple of 2, and the selection range is 2 ≤ n2 ≤ 32, and the selection range of M2 is 0 ≤ M2 ≤ 0.25 kg.

[0030] Advantages of the present invention:

[0031] 1. A piezoelectric energy harvesting device embedded inside an air spring according to the present invention is an improvement and addition based on the existing air spring with an additional air chamber built-in, and does not require additional installation space.

[0032] 2. During vehicle driving, under the repeated action of the air pressure difference on both sides of the diaphragm, the diaphragm will generate reciprocating vibrations, and the piezoelectric sheets attached to the diaphragm can preferably convert the mechanical energy of the diaphragm vibrations into electrical energy.

[0033] 3. Based on the equivalent mechanical model of the piezoelectric energy harvesting device, a mathematical model of the output voltage is established, and an optimization method for the piezoelectric energy harvesting device is proposed. The cost function is defined to achieve maximum power generation under environmental constraints. The tuned mass and the number of piezoelectric units are selected as the optimized design variables, providing an important reference for the modeling and optimization of similar piezoelectric energy harvesting devices embedded in air springs. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings forming a part of this application are used to provide a further understanding of this application. The schematic embodiments and descriptions thereof of this application are used to explain this application and do not constitute an improper limitation to this application.

[0035] Figure 1 It is a schematic diagram of the overall structure of the air spring.

[0036] Figure 2 It is a schematic diagram of the structure of the piezoelectric energy harvesting device.

[0037] Figure 3 It is a schematic diagram of the deformation of the piezoelectric sheet.

[0038] Figure 4 It is a schematic diagram of the equivalent mechanical model of the air spring.

[0039] Figure 5 It is a flow chart of the optimized design of the piezoelectric energy harvesting device.

[0040] Description of the marks in the figures:

[0041] 1 - upper plate, 2 - rubber airbag, 3 - buffer block, 4 - energy harvesting device, 5 - lower cover, 6 - damping hole, 41 - first tuned mass block, 42 - first piezoelectric sheet, 43 - flexible diaphragm, 44 - diaphragm bracket, 45 - tubular flexible diaphragm, 46 - second tuned mass block, 47 - second piezoelectric sheet, 48 - bolt, 49 - gasket. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] It should be noted that the following detailed descriptions are all illustrative and are intended to provide further explanations for this application. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs.

[0043] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings:

[0044] Combination Figure 1 The schematic diagram of the overall structure of the air spring introduces a piezoelectric energy feeding device embedded in the air spring of the present invention. The piezoelectric energy feeding device that can be used for the air spring includes an energy feeding device 4, which includes a tuning mass block 1 41, a piezoelectric sheet 1 42, a flexible diaphragm 43, a diaphragm frame 44, a tubular flexible diaphragm 45, a tuning mass block 2 46, a piezoelectric sheet 2 47, a bolt 48, and a sealing gasket 49.

[0045] The air spring comprises an upper plate 1, a rubber airbag 2, a buffer block 3 and a lower cover 5; the lower cover 5 is a cylindrical structure, with an annular platform on its bottom plate, and an intermediate tube body is also arranged in the middle of the bottom plate.

[0046] The upper plate 1 has an air inlet connected to the isobaric valve; the lower cover 5 has an air outlet connected to the pressure reducing valve. Without specific instructions, the isobaric valve and the pressure reducing valve are assumed to be closed.

[0047] like Figure 1 , 2 As shown, the upper plate 1 is fixedly connected to the vehicle body, the lower cover 5 is fixedly connected to the axle, and the rubber airbag 2 is sealedly connected to the upper plate 1 and the lower cover 5 to form a main air chamber.

[0048] The buffer block 3 is fixedly mounted on the upper plate 1 and the rubber airbag 2 . When the vehicle body and the axle move violently and the gap is too small, the upper plate 1 is prevented from directly hitting the lower cover 5 , thereby protecting the energy feedback device 4 .

[0049] The energy feeding device 4 is located as a whole in the cylindrical structure of the lower cover 5. The tubular flexible diaphragm 45, the sealing gasket 49, and the annular platform on the lower cover 5 are fixedly connected by bolts 48. The piezoelectric sheet 47 is symmetrically attached to the tubular flexible diaphragm 45, and the tuning mass block 46 is attached to the piezoelectric sheet 47 symmetrically, which is used to change the resonance frequency of the piezoelectric sheet 47 and capture more energy. The upper end of the middle tube body of the lower cover 5 is splined, and the middle part of the diaphragm frame 44 is fixedly connected to the spline on the middle tube body of the lower cover 5 through a retaining ring. The lower side of the edge of the diaphragm frame 44 is fixedly connected to the top surface of the tubular flexible diaphragm 45 by bolts 48, and the lower side of the edge of the diaphragm frame 44 is fixedly connected to the flexible diaphragm 43. The piezoelectric sheet 42 is attached to the flexible diaphragm 43, and the tuning mass block 41 is attached to the piezoelectric sheet 42. The lower cover 5, the sealing gasket 49, the tubular flexible diaphragm 45, the diaphragm frame 44, and the flexible diaphragm 43 are sealed and connected to form an additional air chamber.

[0050] like Figure 2 , 3As shown in the figure, gas exchange between the main air chamber and the additional air chamber is carried out through the damping hole 6 on the lower cover 5. Since the diameter of the damping hole is small, a certain damping force will be generated when the gas flows through the damping hole, which can mitigate the impact. During the vehicle driving process, relative displacement will occur between the upper plate 1 and the lower cover 5. Due to the damping force generated by the damping hole, a pressure difference will be generated between the main air chamber and the additional air chamber, and the pressure forces the flexible diaphragm 43 and the tubular flexible diaphragm 45 in the energy harvesting device 4 to deform. The piezoelectric sheet 1-42 and the piezoelectric sheet 2-47 pasted on the flexible diaphragm 43 and the tubular flexible diaphragm 45 undergo bending and traction deformation, generating electrical energy.

[0051] As Figure 4 shown, the equivalent mechanical model of the piezoelectric energy harvesting device that can be used for an air spring is as Figure 3 shown. During the operation of the air spring, the deformation of the flexible diaphragm 43 and the tubular flexible diaphragm 45 is small. Therefore, the influence of the flexible diaphragm 43 and the tubular flexible diaphragm 45 on the volume of the additional air chamber during the deformation process can be ignored, and it can be assumed that during the deformation process of the flexible diaphragm 43 and the tubular flexible diaphragm 45, their stiffness and damping do not affect each other.

[0052] The output voltage of the piezoelectric sheet 1-42 pasted on the flexible diaphragm 43 is expressed as:

[0053]

[0054]

[0055] z r = z3 - z1

[0056] K m = n1·K p1 + K FD

[0057]

[0058] Among them, M1 is the mass of the tuning mass 1-41, z3 is the displacement of the tuning mass 1-41, z1 is the displacement of the lower cover 5, C m is the damping of the flexible diaphragm 43 after pasting the piezoelectric sheet 1-42, K m is the bending stiffness of the flexible diaphragm 43 after pasting the piezoelectric sheet 1-42, n1 is the number of piezoelectric sheets 1-42, K p1 is the bending stiffness of the piezoelectric sheet 1-42, K FD is the bending stiffness of the flexible diaphragm 43, V T is the voltage generated by the piezoelectric sheet 1-42, F1 is the pressure received by the flexible diaphragm 43, R L is the load resistance, C p1 is the clamping capacitance of the piezoelectric sheet 1-42, l pis the free length of piezoelectric sheet 1-42, and α is the electromechanical coupling coefficient of the inverse piezoelectric effect. is the current generated by piezoelectric sheet 1-42 due to bending. is the current generated by piezoelectric sheet 1-42 due to traction.

[0059] The output voltage of piezoelectric sheet 2-47 pasted on the tubular flexible diaphragm 45 is expressed as:

[0060]

[0061]

[0062] K n = n2·K p2 +K FC

[0063] where M2 is the mass of tuning mass block 2-46, z4 is the displacement of tuning mass block 2-46, and C n is the damping of the tubular flexible diaphragm 45 after pasting piezoelectric sheet 2-46, and K n is the bending stiffness of the tubular flexible diaphragm 45 after pasting piezoelectric sheet 2-46, n2 is the number of piezoelectric sheets 2-47, and K p2 is the bending stiffness of piezoelectric sheet 2-47, and K FC is the bending stiffness of the tubular flexible diaphragm 45, F2 is the pressure on the tubular flexible diaphragm 45, V C is the voltage generated by piezoelectric sheet 2-47, λ is the relationship between the tubular flexible diaphragm and the force on the flexible diaphragm, R L is the load resistance, and C p2 is the clamping capacitance of piezoelectric sheet 2-47, l m is the free length of piezoelectric sheet 2-47. is the current generated by piezoelectric sheet 2-47 due to bending. is the current generated by piezoelectric sheet 2-47 due to traction.

[0064] As Figure 5 shown, a cost function is defined to ensure a large output voltage at a low cost.

[0065] The cost function of piezoelectric sheet 1-42 is expressed as:

[0066] f(M1, n1) = q p V tot -q s n1S p1

[0067]

[0068] where q p and q s are weight coefficients. It is the voltage measured in the experiment of piezoelectric sheet 1 - 42, S p1 It is the cost of a group of piezoelectric sheet 1 - 42 transducers.

[0069] The cost function of piezoelectric sheet 2 - 47 is expressed as:

[0070] f(M2, n2) = q l V tob -q z n2S p2

[0071]

[0072] Among them, q l and q z are weight coefficients, It is the voltage measured in the experiment of piezoelectric sheet 2 - 47, S p2 It is the cost of a group of piezoelectric sheet 2 - 47 transducers.

[0073] In the present invention, the selection range of n1 is 1 ≤ n1 ≤ 8, and the selection range of M1 is 0 ≤ M1 ≤ 0.5 kg; because the piezoelectric sheet 2 - 47 is symmetrically distributed, so the value of n2 is a multiple of 2, and the selection range is 2 ≤ n2 ≤ 32, and the selection range of M2 is 0 ≤ M2 ≤ 0.25 kg.

Claims

1. A piezoelectric energy harvesting device embedded inside an air spring, characterized in that: The energy feeding device (4) comprises a first tuning mass block (41), a first piezoelectric sheet (42), a flexible diaphragm (43), a diaphragm frame (44), a tubular flexible diaphragm (45), a second tuning mass block (46), a second piezoelectric sheet (47), bolts (48) and a sealing gasket (49); the bottom surface of the tubular flexible diaphragm (45) and the top surface of the annular platform on the lower cover (5) of the air spring are fixedly connected by the sealing gasket (49) and the bolts (48); the second piezoelectric sheet (47) is symmetrically attached to the tubular flexible diaphragm (45) from top to bottom; the second tuning mass block (46) is attached to the second piezoelectric sheet (47) symmetrically from top to bottom; the middle part of the diaphragm frame (44) and the middle part of the lower cover (5) are connected to each other. The upper end of the tube body is fixedly connected, the lower side of the edge of the diaphragm frame (44) is fixedly connected to the top surface of the tubular flexible diaphragm (45) by means of bolts (48), the upper side of the edge of the diaphragm frame (44) is fixed to the flexible diaphragm (43), the piezoelectric sheet (42) is attached to the flexible diaphragm (43), the tuning mass block (41) is attached to the piezoelectric sheet (42), the lower cover (5), the sealing gasket (49), the tubular flexible diaphragm (45), the diaphragm frame (44), and the flexible diaphragm (43) are sealed and connected to form an additional air chamber; a damping hole (6) is also provided on the annular platform of the lower cover (5), and gas exchange is performed between the main air chamber and the additional air chamber of the air spring through the damping hole (6) on the lower cover (5).

2. The piezoelectric energy harvesting device embedded inside an air spring according to claim 1, wherein: The buffer block (3) is fixedly mounted on the upper plate (1) and the rubber airbag (2). When the vehicle body and the axle move violently and the gap is too small, the upper plate (1) is prevented from directly hitting the lower cover (5), thereby protecting the energy feedback device (4).

3. The piezoelectric energy harvesting device embedded inside an air spring according to claim 2, characterized in that: In the equivalent mechanical model of the piezoelectric energy feeding device embedded in the air spring, the deformation of the flexible diaphragm (43) and the tubular flexible diaphragm (45) is small during the operation of the air spring. Therefore, the influence of the flexible diaphragm (43) and the tubular flexible diaphragm (45) on the volume of the additional air chamber during the deformation process is ignored. It can be considered that the stiffness and damping of the flexible diaphragm (43) and the tubular flexible diaphragm (45) do not affect each other during the deformation process.

4. The piezoelectric energy harvesting device embedded inside the air spring according to claim 3, characterized in that: The output voltage of the piezoelectric sheet 1 (42) attached to the flexible diaphragm (43) is expressed as: Z r = Z3 - Z l K m = n1·K p1 + K FD Among them, M1 is the mass of the first tuned mass block (41), z3 is the displacement of the first tuned mass block (41), z1 is the displacement of the lower cover (5), C m is the damping of the flexible diaphragm (43) after attaching the first piezoelectric sheet (42), K m is the bending stiffness of the flexible diaphragm (43) after attaching the first piezoelectric sheet (42), n1 is the number of the first piezoelectric sheets (42), K p1 is the bending stiffness of the first piezoelectric sheet (42), K FD is the bending stiffness of the flexible diaphragm (43), V T is the voltage generated by the first piezoelectric sheet (42), R L is the load resistance, C p1 is the clamping capacitance of the first piezoelectric sheet (42), l p is the free length of the first piezoelectric sheet (42), α is the electromechanical coupling coefficient of the inverse piezoelectric effect, is the current generated by the first piezoelectric sheet (42) due to bending, is the current generated by the first piezoelectric sheet (42) under the traction of the flexible diaphragm.

5. The piezoelectric energy harvesting device embedded inside an air spring according to claim 4, characterized in that: The output voltage of the piezoelectric sheet 2 (47) attached to the tubular flexible diaphragm (45) is expressed as: K n = n2·K p2 + K FC Among them, M2 is the mass of the second tuned mass block (46), z4 is the displacement of the second tuned mass block (46), C n is the damping of the tubular flexible diaphragm (45) after attaching the second piezoelectric sheet (46), K n is the bending stiffness of the tubular flexible diaphragm (45) after attaching the second piezoelectric sheet (46), n2 is the number of the second piezoelectric sheets (47), K p2 is the bending stiffness of the second piezoelectric sheet (47), K FC is the bending stiffness of the tubular flexible diaphragm (45), V C is the voltage generated by the second piezoelectric sheet (47), λ is the relationship between the forces on the tubular flexible diaphragm (45) and the flexible diaphragm (43), R L is the load resistance, C p2 is the clamping capacitance of the second piezoelectric sheet (47), l m is the free length of the second piezoelectric sheet (47), is the current generated by the second piezoelectric sheet (47) due to bending, is the current generated by the second piezoelectric sheet (47) under the traction of the tubular flexible diaphragm (45).

6. The piezoelectric energy harvesting device embedded inside the air spring according to claim 5, wherein: An optimization method for piezoelectric energy feeding device is proposed. The cost function is defined and the tuning mass M and the number of piezoelectric units n are selected as the optimized design variables to maximize power generation under environmental constraints. The cost function of the piezoelectric film (42) is expressed as: f(M1, n1) = q p V tot -q s n1S p1 where q p and q s are weighting coefficients, is the experimentally measured voltage of piezoelectric sheet 1 (42), and S p1 is the cost of a set of piezoelectric sheet 1 (42) transducers; The cost function of piezoelectric film 2 (47) is expressed as: f(M2, n2) = q l V tob -q z n2S p2 Among them, q l and q z are weight coefficients, is the experimentally measured voltage of piezoelectric sheet two (47), and S p2 is the cost of a group of piezoelectric sheet two (47) transducers; In the present invention, the selection range of n1 is 1≤n1≤8, and the selection range of M1 is 0≤M1≤0.5kg; because the piezoelectric plate 2 (47) is symmetrically distributed, the value of n2 is a multiple of 2, and the selection range is 2≤n2≤32, and the selection range of M2 is 0≤M2≤0.25kg.

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