Six-stable piezoelectric vibration energy harvester and method for determining the number of stable states thereof

Abstract

The application discloses a six-stable-state piezoelectric vibration energy collector, which comprises a base, a cantilever beam, ring magnets, rectangular magnets, MFC piezoelectric sheets and wires. The six-stable-state design of the collector is realized by finely adjusting the equivalent stiffness of the piezoelectric beam, the size and magnetization intensity of the magnets, and the spatial layout of the magnets. When the base is subjected to external excitation in the vertical direction, the MFC piezoelectric sheet on the cantilever beam is subjected to extrusion to generate a voltage difference, and the vibration energy is effectively converted into electric energy. The traditional six-stable-state system needs at least six magnets, and the application only needs to configure four magnets to realize the six-stable-state characteristics. The application not only greatly simplifies the design, simulation and installation process of the multi-stable-state collector, but also brings a new breakthrough to the piezoelectric energy collection technology; and the application also provides a scientific method for determining the stable-state number of the collector, lays a solid theoretical foundation for the manufacture and application of the collector, and has a wide application potential.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy collection, and particularly relates to a nonlinear six-stable device for collecting vibration energy by using the positive piezoelectric effect of piezoelectric materials and converting the vibration energy into electric energy. BACKGROUND

[0002] In recent years, the rapid development of Internet of Things technology has promoted the popularity of low-power wireless sensor networks and portable electronic devices. However, continuous power supply is an essential element for the normal operation of these devices, and the limitations of traditional batteries, such as limited endurance and potential environmental hazards, have become increasingly apparent. Specifically, batteries need to be frequently charged or replaced after the battery power is depleted, and improper disposal of old batteries can pose a serious threat to the ecological environment. Therefore, it is particularly important to develop a new type of energy supply method that is both environmentally friendly and sustainable. As a result, energy harvesting technology has emerged, which can capture energy from various renewable energy sources such as light, heat, wind, rain, and vibration, and efficiently convert it into electrical energy, thereby providing power for sensors and electronic devices. This technology not only applies to extreme or special environments such as deep sea exploration, desert monitoring, bridge structure health monitoring, nuclear facilities, and volcano activity monitoring, but also meets the urgent needs of environmental protection due to its green and pollution-free characteristics. It is particularly worth mentioning that vibration energy is ubiquitous in daily life and industrial production, such as the vibration generated by the operation of mechanical equipment, the movement of vehicles, and human activity, which provides a rich source of energy for vibration energy harvesters. Therefore, vibration energy harvesting technology has attracted widespread attention and in-depth research from many researchers due to its wide application potential and unique advantages.

[0003] Vibration energy harvesters are mainly divided into four categories: electrostatic, electromagnetic, triboelectric, and piezoelectric, according to their operating mechanisms. Among them, piezoelectric harvesters have strong nonlinearity, wide operating frequency band, and high electromechanical conversion efficiency due to the positive piezoelectric effect of piezoelectric materials, which has brought new solutions to the problem of continuous power supply for micro-electronic devices and has become the focus of research in recent years. Piezoelectric harvesters can be further divided into linear and nonlinear categories according to their structural characteristics. Linear design performs well near its natural frequency, but the working bandwidth is limited, making it suitable for narrow-band excitation environments with relatively stable frequencies. However, in practical applications, the frequency of the vibration source is often complex and variable. In contrast, nonlinear design significantly improves the working efficiency of the harvester under complex excitation by widening the operating bandwidth. Nonlinear design is often achieved by using the special force field between magnets, and can be further divided into bistable, tristable, and quad-stable systems according to the number of stable points. Under certain conditions, increasing the number of stable points can expand the distance between the two stable points, allowing the system to move a larger amplitude under the same excitation, thereby enhancing the power generation performance.

[0004] Traditional multi-stable piezoelectric systems often rely on the magnetic force between rectangular or cylindrical magnets to build. Specifically, the bistable system is configured with at least two magnets, the tristable system needs at least three, and so on, until the six-stable system needs at least six magnets. This rule shows that with each additional stable point, the system needs to add an extra magnet. The increase in the number of magnets not only makes the structural parameters of the system more complex, but also increases the difficulty of system dynamics analysis and structural optimization, and further enhances the challenge of prototype installation and debugging. Therefore, in the existing research on multi-stable piezoelectric vibration energy harvesters based on magnetic interaction, the design and implementation of six-stable systems, as well as the corresponding stable number determination method, are still in the blank field and need to be explored. SUMMARY

[0005] In view of the technical limitations of traditional multi-stable piezoelectric vibration energy harvesters and the fact that the research on six-stable systems is still in the blank field, the purpose of the present invention is to propose an innovative six-stable piezoelectric vibration energy harvester and to propose a corresponding stable number determination method. The unique feature of this harvester is that only four magnets are needed to achieve the technical innovation of six-stable.

[0006] The technical solution of the present invention covers the structural design of the harvester and the stable number determination method. Specifically, the six-stable piezoelectric vibration energy harvester is composed of a base, a cantilever beam, an MFC piezoelectric sheet, a wire, a rectangular magnet, and three ring magnets. The base adopts a "U" shape design, with the left and right side columns perpendicular to the base bottom surface. The left side column is fixed with the cantilever beam inside, and the right side column is fixed with the ring magnet inside. The free end of the cantilever beam is fixed with the rectangular magnet, and the upper surface of its root is installed with the MFC piezoelectric sheet, which outputs electrical signals through the wire. The combination of the cantilever beam and the MFC piezoelectric sheet is called a piezoelectric beam. By adjusting the equivalent stiffness of the piezoelectric beam, the geometric dimensions and magnetization intensity of the rectangular magnet and the ring magnet, the distance between the ring magnets, and the horizontal distance between the rectangular magnet and the ring magnet, the present invention successfully enables the energy harvester to achieve six-stable working state. This innovative design not only breaks through the bottleneck of traditional technology, but also opens up a new path for the research and application of six-stable piezoelectric vibration energy harvesters.

[0007] The working principle of the six-stable piezoelectric vibration energy harvester is that when the base is subjected to external excitation in the vertical direction, the piezoelectric beam will generate dynamic response of up-down vibration under the common driving of the force transmitted by the base and the interaction force between the magnet. This vibration process will cause the MFC piezoelectric sheet pasted at the root of the cantilever beam to be extruded. Due to the low symmetry of the crystal inside the MFC piezoelectric sheet, when the crystal is deformed under external force, the positive and negative ions inside the crystal cell will move relatively, resulting in that the positive and negative charge centers no longer coincide, thereby causing the macro polarization phenomenon of the crystal. The charge surface density of the crystal surface is equal to the projection value of the polarization intensity on the surface normal, so in the process of pressure deformation of the MFC piezoelectric sheet, the two end faces will respectively accumulate charges of different signs, that is, a voltage difference is generated. This mechanism enables the harvester to effectively convert vibration energy into electrical energy.

[0008] The core technology of the present application is that the cantilever beam free end is loaded with a rectangular magnet, and three ring magnets with the same parameters are arranged on the right side of the base, and the distance between two adjacent ring magnets is the same. Only four magnets are needed to realize the six-stable transition motion of the energy harvesting system.

[0009] Generally, increasing the number of stable points can effectively broaden the working bandwidth of the energy harvester, and thus improve the energy harvesting efficiency. Compared with the single-stable harvester which oscillates in a single potential well near the resonance frequency and has a narrow energy collection band, the multi-stable harvester can significantly expand the working bandwidth and improve the working efficiency in complex excitation environment. However, the traditional design needs to increase the number of magnets while increasing the number of stable points, which not only complicates the system structure parameters, but also increases the difficulty of dynamic analysis and structure optimization, and increases the challenge of prototype manufacturing and installation. The present application takes a different approach, and only four magnets are needed to achieve the technical characteristics of the six-stable harvester, which shows the wisdom of ingenious design.

[0010] Compared with the prior art, the present application has the following advantages: compared with the traditional six-stable structure which needs to be equipped with six magnets, the harvester of the present application is configured with only four magnets, and through the fine adjustment of the equivalent stiffness of the piezoelectric beam, the geometric size and magnetization intensity of the magnet, and the spatial layout of the magnet, the six-stable technical breakthrough is successfully achieved. The present application not only greatly simplifies the complexity of multi-stable harvester in structure design, dynamic simulation and analysis, installation and debugging, etc., opens up a new path for the innovative design of piezoelectric vibration energy harvester, but also puts forward a method for determining the number of stable states of the six-stable piezoelectric vibration energy harvester, which lays a solid theoretical foundation for the manufacturing and practical application of the harvester. BRIEF DESCRIPTION OF DRAWINGS

[0011] ATTACHMENT Figure 1 The structure of the present application is shown in the figure.

[0012] ATTACHMENT Figure 2For cantilever beam in bending, the magnet magnetization current and the system main size diagram.

[0013] Attached Figure 3 For piezoelectric beam equivalent stiffness change on the system potential energy.

[0014] Attached Figure 4 For ring magnet thickness change on the system potential energy.

[0015] Attached Figure 5 For ring magnet outer radius change on the system potential energy.

[0016] Attached Figure 6 For ring magnet inner radius change on the system potential energy.

[0017] Attached Figure 7 For rectangular magnet thickness change on the system potential energy.

[0018] Attached Figure 8 For rectangular magnet width change on the system potential energy.

[0019] Attached Figure 9 For rectangular magnet length change on the system potential energy.

[0020] Attached Figure 10 For two adjacent ring magnet spacing change on the system potential energy.

[0021] Attached Figure 11 For trapezoidal magnet and ring magnet surface horizontal distance change on the system potential energy.

[0022] Attached Figure 12 For ring magnet magnetization intensity on the system potential energy.

[0023] Attached Figure 13 For trapezoidal magnet magnetization intensity on the system potential energy. DETAILED DESCRIPTION

[0024] The technical solutions of the present application will be further described below in combination with the drawings and by examples. It should be noted that although the drawings of the specification describe the examples, the embodiment is only illustrative and not limited. The materials and size parameters of each component can be changed without departing from the purpose of the present application and the scope protected by the claims, which are all within the protection scope of the present application.

[0025] The technical solutions include six stable piezoelectric vibration energy harvester and the determination method of the number of stable state of the harvester.

[0026] The six-stable piezoelectric vibration energy harvester has the structure that the base 1 is in the shape of a "N" and the left and right vertical columns are perpendicular to the base bottom surface. The left vertical column is fixed with a cantilever beam 2 inside, and the right vertical column is fixed with three annular magnets 3-1, 3-2 and 3-3 of the same parameters inside. The free end of the cantilever beam is fixed with a rectangular magnet 4, and the root upper surface thereof is fixed with an MFC piezoelectric sheet 5, and the piezoelectric sheet outputs an electric signal through a wire 6. In the initial state, the annular magnets are opposite to the N-pole of the rectangular magnet, and the distance between two adjacent annular magnets is the same. The energy harvester is in the six-stable state by adjusting the equivalent stiffness of the piezoelectric beam, the geometric size and magnetization intensity of the magnet and the spatial layout of the magnet.

[0027] The number of stable states, i.e. the six-stable state, of the six-stable piezoelectric vibration energy harvester is determined by the following calculation process:

[0028] (1) The magnetic induction intensity B(x, y, z) of the three annular magnets at any position P(x, y, z) in space is calculated by means of the basic principle of electromagnetism, i.e. the Biot-Savart law:

[0029]

[0030]

[0031]

[0032] In the formula, B B1o (x, y, z), B B1i (x, y, z) respectively represent the magnetic induction intensity of the magnetization current on the outer and inner surfaces of the annular magnet 3-1 at any position in space; similarly, B B2o (x, y, z), B B2i (x, y, z) and B B3o (x, y, z), B B3i (x, y, z) respectively correspond to the magnetic induction intensity of the magnetization current on the outer and inner surfaces of the annular magnets 3-2 and 3-3 at any position in space; μ0 is the magnetic permeability of vacuum, μ0 = 4π × 10 -7 H / m (Henry / m); M B1 , M B2 , M B3 are the magnetization intensities of the annular magnets 3-1, 3-2 and 3-3, respectively, with the unit of A / m (Ampere / m); t B1 , t B2 , t B3 are the thicknesses of the annular magnets 3-1, 3-2 and 3-3, respectively, with the unit of m (meter); φ B1o , φ B2o , φ B3o are the outer diameters of the annular magnets 3-1, 3-2 and 3-3, respectively, with the unit of m.B1i , φ B2i , φ B3i are the inner diameters of the ring magnets 3-1, 3-2, 3-3, respectively, with the unit of m; d e is the distance between two adjacent ring magnets, with the unit of m; l is the thickness integral variable; θ is the angle integral variable; i, j, k are the unit vectors in x, y, z directions; B i (x, y, z), B j (x, y, z), B k (x, y, z) represent the magnetic induction intensity components of the three ring magnets in x, y, z directions at any point P(x, y, z) in space, respectively, with the unit of T (Tesla).

[0033] (2) Based on the magnetization current theory, the nonlinear magnetic force F i in the vertical direction between the rectangular magnet and the three ring magnets is calculated by the following formula:

[0034]

[0035] In the formula, M A is the magnetization intensity of the rectangular magnet 4, with the unit of A / m; t A , w A , l A are the thickness, width, and length of the rectangular magnet 4, respectively, with the unit of m; α is the deflection angle of the rectangular magnet when the cantilever beam bends; t B (t B =t B1 =t B2 =t B3 ) and l b are the thickness of the ring magnet and the length of the cantilever beam, respectively, with the unit of m; d is the initial surface horizontal distance between the rectangular magnet and the ring magnet, with the unit of m; F i has the unit of N (Newton).

[0036] (3) According to the relationship between work and energy, the system potential energy V

[0037]

[0038] In the formula, K eq is the equivalent stiffness of the piezoelectric beam, with the unit of N / m (Newton / meter); V has the unit of J (Joule).

[0039] With the help of MATLAB software, numerical analysis is carried out on formulas (1)~(11), and then the potential energy images of the system under different structural parameter configurations are drawn. By observing and analyzing these potential energy images, the key system parameters required to achieve the six-stable state can be accurately identified.

[0040] As an example of the six-stable system (just a name), the following parameters can be set: the annular magnet 3-1 has a size of φ B1o 20mm x φ B1i 15mm x t B1 3mm, the magnetization M B1 is 7.5 x 10 5 A / m; the annular magnets 3-2 and 3-3 have the same parameters as the annular magnet 3-1; the rectangular magnet has a size of l A 15mm x w A 15mm x t A 3mm, the magnetization M A is 9.5 x 10 5 A / m; the equivalent stiffness K eq of the piezoelectric beam is 12 N / m; the distance d e between two adjacent annular magnets is 29 mm; the surface horizontal distance d b between the annular magnet and the rectangular magnet in the initial state is 3 mm; the length l eq of the cantilever beam is 100 mm.

[0041] The Figure 3 graph of the change of the potential energy of the system is shown when the equivalent stiffness K eq of the piezoelectric beam is adjusted to 4 N / m, 8 N / m, 12 N / m, 16 N / m while keeping all other parameters constant. The lowest point of the potential energy curve in the graph marks the stable point of the system, i.e., the lowest position of the energy in the stable interval.

[0042] The Figure 4 graph of the potential energy of the system is shown when the thickness t B of the annular magnet is changed to 1 mm, 3 mm, 5 mm, 7 mm while keeping all other parameters constant.

[0043] The Figure 5 graph of the potential energy of the system is shown when the outer radius R of the annular magnet is set to 8 mm, 10 mm, 12 mm, 14 mm while keeping all other parameters constant.

[0044] The Figure 6 graph of the potential energy of the system is shown when the inner radius r of the annular magnet is set to 3.5 mm, 5.5 mm, 7.5 mm, 9.5 mm while keeping all other parameters constant.

[0045] The Figure 7 graph of the potential energy of the system is shown when the thickness t A of the rectangular magnet is set to 1 mm, 3 mm, 5 mm, 7 mm while keeping all other parameters constant.

[0046] Appendix Figure 8 To keep the other parameters unchanged, set the width w of the rectangular magnet. A Potential energy images of the system at 5mm, 10mm, 15mm, and 20mm.

[0047] Appendix Figure 9 To keep the other parameters unchanged, the length l of the rectangular magnet is set. A Potential energy images of the system at 5mm, 10mm, 15mm, and 20mm.

[0048] Appendix Figure 10 To keep the other parameters unchanged, the distance d between two adjacent ring magnets is set. e Potential energy images of the system at 25mm, 29mm, 33mm, and 37mm.

[0049] Appendix Figure 11 To keep the other parameters unchanged, the potential energy images of the system were obtained when the initial horizontal distance d between the ring magnet and the rectangular magnet was set to 3mm, 7mm, 11mm, and 15mm.

[0050] Appendix Figure 12 To keep the other parameters unchanged, the magnetization intensity M of the rectangular magnet is set. B1 (M B1 =M B2 =M B3 ) is 5.5×10 5 A / m, 7.5×10 5 A / m, 9.5×10 5 A / m, 1.15×10 6 Potential energy diagram of the system at A / m.

[0051] Appendix Figure 13 To keep the other parameters unchanged, the magnetization intensity M of the ring magnet is set. A 5.5×10 5 A / m, 7.5×10 5 A / m, 9.5×10 5 A / m, 1.15×10 6 Potential energy diagram of the system at A / m.

[0052] By observing the appendix Figure 3 To be continued Figure 13 It can be clearly recognized that the stable state of the system is affected by a variety of factors, including the equivalent stiffness of the piezoelectric beam, the geometric dimensions and magnetization of the ring magnet and the rectangular magnet, the distance between two adjacent ring magnets, and the horizontal distance between the ring magnet and the rectangular magnet.

[0053] With attachmentFigure 3 To illustrate, when the equivalent stiffness K eq When the equivalent stiffness Kp of the piezoelectric beam is set to 4 N / m and 16 N / m respectively, the system only exhibits four steady states. Therefore, to realize a system embodiment with six steady states, a comprehensive and fine adjustment of all the above parameters is necessary. This includes adjusting the equivalent stiffness of the piezoelectric beam to an appropriate range, optimizing the geometric dimensions of the annular magnets and the rectangular magnet, adjusting the magnetization strength, and precisely controlling the distance between two adjacent annular magnets and the horizontal distance between them and the rectangular magnet, so as to jointly act on the system and ensure that it reaches the expected steady state.

Claims

1. A hexagonal steady-state piezoelectric vibration energy harvester, comprising a base, a cantilever beam, three ring magnets, a rectangular magnet, an MFC piezoelectric plate, and wires, characterized in that: The base (1) is in the shape of a "U", and the left and right vertical columns are perpendicular to the base bottom surface; the left vertical column inside is fixed with a cantilever beam (2), and the right vertical column inside is fixed with three annular magnets; the free end of the cantilever beam is fixed with a rectangular magnet (4), and the root upper surface is fixed with an MFC piezoelectric sheet (5), which outputs an electric signal through a wire (6); the three annular magnets have the same parameters, and in the initial state, the annular magnets are opposite to the N-pole of the rectangular magnet; by adjusting the equivalent stiffness of the piezoelectric beam, the geometric size and magnetization intensity of the rectangular magnet and the annular magnet, the spacing of the annular magnets, and the horizontal distance between the rectangular magnet and the annular magnet, the energy collector is in a six-stable state; the system potential energy V and the number of system stable states are determined by the following formula ， wherein, K eq is the equivalent stiffness of the piezoelectric beam, F i is the nonlinear magnetic force in the vertical direction between the rectangular magnet and the three annular magnets; when the energy harvester is in the six-stable state, the annular magnets (3-1), (3-2), and (3-3) have the same size of Ф B1o 20 mm´ Ф B1i 15 mm´ t B1 3 mm, and the magnetization is 7.5´10 5 A / m; the rectangular magnet (4) has the size of l A 15 mm´ w A 15 mm´ t A 3 mm, and the magnetization is M A 9.5´10 5 A / m; the equivalent stiffness of the piezoelectric beam is K eq 12 N / m; the distance between two adjacent annular magnets is d e 29 mm; the surface horizontal distance between the annular magnet (3-2) and the rectangular magnet (4) in the initial state is d 3 mm; the length of the cantilever beam (2) is l b 100 mm.

2. The hexa-stable piezoelectric vibration energy harvester of claim 1, wherein: The magnetic induction at any position in space P (x , y , z) of the three ring magnets B ( x , y , z ) is determined by the formula ， wherein B B1o x y z B B1i x y z B B2o x y z B B2i x y z B B3o x y z B B3i x y z μ 0 M B1 M B2 M B3 t B1 t B2 t B3 Ф B1o Ф B2o Ф B3o Ф B1i Ф B2i Ф B3i d e l θ ​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​is the angle integration variable; i , j , k are the unit vectors in x, y, z directions; B i ( x , y , z ), B j ( x , y , z ), B k ( x , y , z ) represent the magnetic induction components in x, y, z directions at arbitrary points P (x , y , z) in space for the three toroidal magnets, respectively.

3. The hexa-stable piezoelectric vibration energy harvester of claim 2, wherein: Nonlinear magnetic force in vertical direction between rectangular magnet and three ring magnets F i is determined by the formula wherein, M A H is the magnetization of the rectangular magnet (4); t A 、w A 、l A t, w, and l are the thickness, width, and length of the rectangular magnet (4), respectively; α is the deflection angle of the rectangular magnet when the cantilever beam (2) is bent; t B and l b t and l are the thickness of the ring magnet and the length of the cantilever beam, respectively; d is the initial surface level distance between the rectangular magnet and the ring magnet.

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