Six-steady-state piezoelectric vibration energy collector and steady-state number determination method thereof

Abstract

The invention discloses a six-stable-state piezoelectric vibration energy collector which comprises a base, a cantilever beam, an annular magnet, a rectangular magnet, an MFC piezoelectric plate and a wire. Six-steady-state design of the collector is realized by finely adjusting the equivalent stiffness of the piezoelectric beams, the size and magnetization intensity of the magnets and the spatial layout between the magnets. When the base is subjected to external excitation in the vertical direction, the MFC piezoelectric patches on the cantilever beams are extruded to generate voltage difference, and vibration energy is effectively converted into electric energy. A traditional six-stable-state system at least needs six magnets, and the six-stable-state characteristic can be achieved only by configuring four magnets. According to the invention, the design, simulation and installation processes of the multistable collector are greatly simplified, and a new breakthrough is brought to the piezoelectric energy collection technology; the invention further provides a scientific method for determining the steady state number of the collector, a solid theoretical foundation is laid for manufacturing and application of the collector, and wide application potential is shown.

Description

Technical Field

[0001] The present invention belongs to new energy collection technology, and specifically relates to a nonlinear hexastable device which utilizes the positive piezoelectric effect of piezoelectric materials to collect vibration energy and convert it into electrical energy. Background Art

[0002] In recent years, the rapid progress of Internet of Things technology has promoted the popularization of low-energy wireless sensor networks and portable electronic devices. However, continuous power supply is an indispensable element for the normal operation of these devices, and the limitations of traditional batteries are increasingly prominent due to their limited endurance and potential environmental risks. Specifically, after the battery is exhausted, it needs to be frequently charged or replaced, and improper disposal of waste batteries will pose a serious threat to the ecological environment. In view of this, it is particularly important to develop a new energy supply method that is both environmentally friendly and sustainable. As a result, energy harvesting technology came into being. It can capture energy from a variety of renewable energy sources such as light energy, heat energy, wind energy, rain energy and vibration energy, and efficiently convert it into electrical energy to power sensors and electronic devices. This technology is not only suitable for extreme or special environments such as deep-sea exploration, desert monitoring, bridge structure health monitoring, nuclear facilities and volcanic activity monitoring, but also its green and pollution-free characteristics meet the urgent needs of current environmental protection. 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 driving of vehicles and human activities, which provide a rich source of energy for vibration energy harvesters. Therefore, vibration energy harvesting technology has attracted extensive attention and in-depth research from many scientific researchers due to its wide application potential and unique advantages.

[0003] Based on the operating mechanism, vibration energy harvesters are mainly divided into four categories: electrostatic, electromagnetic, triboelectric and piezoelectric. Among them, piezoelectric harvesters, relying on the positive piezoelectric effect of piezoelectric materials, have the characteristics of strong nonlinearity, wide working frequency band and high electromechanical conversion efficiency, which has brought new solutions to the problem of continuous power supply of microelectronic devices and has become the research focus in recent years. Piezoelectric harvesters can be divided into two categories: linear and nonlinear according to their structural characteristics. Linear design mainly performs well near its natural frequency, but the working bandwidth is limited, which is suitable for narrow-band excitation environments with relatively stable frequencies. However, the frequency of vibration sources in practical applications is often complex and changeable. In contrast, nonlinear design significantly improves the working efficiency of the harvester under complex excitation by broadening the working bandwidth. Nonlinear design is often realized by using special force fields between magnets. According to the number of stable points, it can be further subdivided into bistable, tristable, quadstable and other systems. Under certain conditions, increasing the number of stable points can expand the distance between the two stable points, so that the system can achieve a larger range of movement under the same excitation, thereby enhancing the power generation efficiency.

[0004] Traditional multi-stable piezoelectric systems often rely on the magnetic force between rectangular or cylindrical magnets to construct. Specifically, a bistable system is configured with at least two magnets, a tristable system requires at least three magnets, and so on, until a hexastable system requires at least six magnets. This rule indicates that for each additional stable state point, an extra magnet is needed for the system. The increasing number of magnets not only makes the structural parameters of the system more complex but also exacerbates the difficulty of system dynamics analysis and structural optimization, further increasing the challenge of prototype installation and debugging. Therefore, in the existing research on magnetically actuated multi-stable piezoelectric vibration energy harvesters, the design and implementation of hexastable systems, as well as the corresponding methods for determining the number of stable states, still remain blank areas to be explored. Summary of the Invention

[0005] Aiming at the technical limitations of traditional multi-stable piezoelectric vibration energy harvesters and considering that the research on hexastable systems is still blank, the purpose of this invention is to propose an innovative hexastable piezoelectric vibration energy harvester and a corresponding method for determining the number of stable states. The uniqueness of this harvester lies in the technological innovation that only four magnets are required to achieve hexastability.

[0006] The technical solution of this invention covers the structural design of the harvester and the method for determining the number of stable states. Specifically, the hexastable piezoelectric vibration energy harvester consists of a base, a cantilever beam, an MFC piezoelectric sheet, a wire, a rectangular magnet, and three annular magnets. The base is designed in a "U" shape, with the left and right side columns perpendicular to the base bottom surface. The cantilever beam is fixed inside the left column, and the annular magnet is fixed inside the right column. The free end of the cantilever beam is fixed with the rectangular magnet, and the MFC piezoelectric sheet is installed on the upper surface of its root. The piezoelectric sheet outputs an electrical signal through the wire. The combination of the cantilever beam and the MFC piezoelectric sheet is called the piezoelectric beam. By adjusting the equivalent stiffness of the piezoelectric beam, the geometric dimensions and magnetization intensities of the rectangular magnet and the annular magnets, the spacing between the annular magnets, and the horizontal distance between the rectangular magnet and the annular magnets, this invention successfully enables the energy harvester to reach a hexastable working state. This innovative design not only breaks through the bottleneck of traditional technologies but also opens up a new path for the research and application of hexastable piezoelectric vibration energy harvesters.

[0007] The working principle of the hexastable piezoelectric vibration energy harvester is: when the base is subjected to external excitation in the vertical direction, the piezoelectric beam will produce a dynamic response of up and down vibration under the joint drive of the force transmitted by the base and the interaction force between the magnets. This vibration process will cause the MFC piezoelectric sheet attached to the root of the cantilever beam to be squeezed. Due to the low symmetry of the crystal inside the MFC piezoelectric sheet, when it is deformed by external force, the positive and negative ions inside the unit cell will undergo relative displacement, resulting in the positive and negative charge centers no longer coinciding, thereby inducing the macroscopic polarization phenomenon of the crystal. The surface charge density on the crystal surface is exactly equal to the projection value of the polarization intensity on the surface normal. Therefore, during the process of the MFC piezoelectric sheet being compressed and deformed, its two end faces will accumulate charges of opposite signs, that is, a voltage difference will be generated. This mechanism enables the harvester to effectively convert vibration energy into electrical energy.

[0008] The key to the core technology of the present invention is that a rectangular magnet is mounted on the free end of the cantilever beam, and three annular magnets with the same parameters are arranged on the right column of the base, and the distance between two adjacent rings is the same; only four magnets are needed to realize the six stable-state 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, thereby improving its energy collection efficiency. Compared with a monostable harvester that only oscillates in a single potential well near the resonant frequency and has a narrow energy collection band, a multistable harvester can significantly expand the working bandwidth and improve the working efficiency in a complex excitation environment. However, while traditional designs increase the number of stable points, they also need to increase the number of magnets, which not only complicates the system structure parameters, but also increases the difficulty of dynamic analysis and structural optimization, and increases the challenge of prototype manufacturing and installation. The present invention takes a different approach and achieves the technical characteristics of a six-stable harvester with only four magnets, demonstrating ingenious design wisdom.

[0010] Compared with the prior art, the beneficial effect of the present invention is that compared with the traditional six-stable structure that needs to be equipped with six magnets, the collector of the present invention has successfully achieved a technical breakthrough of six stable states by simplifying the configuration to four magnets, and combining 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 present invention not only greatly simplifies the complexity of the multi-stable collector in terms of structural design, dynamic simulation and analysis, installation and debugging, and opens up a new path for the innovative design of piezoelectric vibration energy harvesters, but also proposes a method for determining the number of stable states of a six-stable piezoelectric vibration energy harvester, laying a solid theoretical foundation for the manufacture and practical application of the collector. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Attached Figure 1 It is a structural schematic diagram of the present invention.

[0012] Attached Figure 2The diagram shows the magnetizing current and main dimensions of the system when the cantilever beam is bent.

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

[0014] Attached Figure 4 This is the effect of the thickness change of the ring magnet on the potential energy of the system.

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

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

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

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

[0019] Attached Fig. 9 is the effect of the change in the length of the rectangular magnet on the potential energy of the system.

[0020] Attached Fig.10 This is the effect of the distance change between two adjacent ring magnets on the potential energy of the system.

[0021] Attached Fig.11 This is the effect of the change in the horizontal distance between the surfaces of the rectangular magnet and the ring magnet on the potential energy of the system.

[0022] Attached Fig.12 is the influence of the magnetization intensity of the ring magnet on the potential energy of the system.

[0023] Attached Fig.13 This is the influence of the magnetization intensity of the pitch magnet on the potential energy of the system. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further described below with reference to the accompanying drawings and examples. It should be noted that although the embodiments are described in the drawings of the specification, the implementation is only illustrative and not restrictive. Without departing from the scope of protection of the present invention and the claims, the materials and dimensional parameters of each component can also be changed, which are all within the scope of protection of the present invention.

[0025] The technical solution includes a six-stable piezoelectric vibration energy harvester and a method for determining the number of stable states of the harvester.

[0026] Six - stable piezoelectric vibration energy harvester, its structure is as follows: The shape of the base 1 is "U", and the left and right side columns are perpendicular to the bottom surface of the base. The cantilever beam 2 is fixed inside the left - hand column, and three annular magnets 3 - 1, 3 - 2, 3 - 3 with the same parameters are fixed inside the right - hand column. The rectangular magnet 4 is fixed at the free end of the cantilever beam, and the MFC piezoelectric sheet 5 is fixed on the upper surface of its root. The piezoelectric sheet outputs an electrical signal through the wire 6. In the initial state, the annular magnets are opposite to the rectangular magnet with the N - pole; the distances between two adjacent annular magnets are the same. By adjusting the equivalent stiffness of the piezoelectric beam, the geometric dimensions and magnetization intensity of the magnets, and the spatial layout of the magnets, the energy harvester is in a six - stable state.

[0027] The number of stable states of the six - stable piezoelectric vibration energy harvester, that is, the six - stable state, is determined through the following calculation process:

[0028] (1) By means of the Biot - Savart law, a basic principle of electromagnetism, calculate the magnetic induction intensity B(x, y, z) at any position P(x, y, z) in space by the three annular magnets:

[0029]

[0030]

[0031]

[0032] In the formula, B B1o (x, y, z), B B1i (x, y, z) respectively represent the magnetic induction intensities of the magnetization currents 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 intensities of the magnetization currents 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);

[0033] M B1 , M B2 , M B3 are the magnetization intensities of the annular magnets 3 - 1, 3 - 2, 3 - 3 respectively, and their unit is A / m (Ampere / m); t B1 , t B2 , t B3 are the thicknesses of the annular magnets 3 - 1, 3 - 2, 3 - 3 respectively, and their unit is m (meter); φ B1o , φ B2o , φ B3oare the outer diameters of the annular magnets 3-1, 3-2, and 3-3, respectively, and the unit is m; φ B1i ,φ B2i ,φ B3i are the inner diameters of the annular magnets 3-1, 3-2, and 3-3, respectively, and the unit is m; d e is the distance between two adjacent ring magnets, and its unit is m; l is the thickness integral variable; θ is the angle integral variable; i, j, k are the unit vectors in the x, y, and z directions; in order to fully describe the magnetic field in space, B i (x,y,z),B j (x,y,z),B k (x, y, z) represent the components of the magnetic induction intensity of the three ring magnets in the x, y, and z directions at any point P (x, y, z) in space, and their units are all T (Tesla).

[0034] (2) Based on the magnetizing current theory, the nonlinear magnetic force F in the vertical direction between the rectangular magnet and the three annular magnets is calculated by the following formula: i :

[0035]

[0036] Where M A is the magnetization intensity of the rectangular magnet 4, and its unit is A / m; t A 、w A , l A are the thickness, width and length of the rectangular magnet 4, respectively, and the unit is m; α is the deflection angle of the rectangular magnet when the cantilever beam is bent; t B (t B =t B1 =t B2 =t B3 ) and l b are the thickness of the annular magnet and the length of the cantilever beam, respectively, in m; d is the initial surface horizontal distance between the rectangular magnet and the annular magnet, in m; F i The unit is N (Newton).

[0037] (3) Based on the relationship between work and energy, the potential energy V of the system can be calculated by the following formula:

[0038]

[0039] In the formula, K eq is the equivalent stiffness of the piezoelectric beam, with the unit of N / m (Newton / meter); the unit of V is J (joule).

[0040] With the help of MATLAB software, equations (1) to (11) are numerically analyzed to depict the potential energy images of the system under different structural parameter configurations. By observing and analyzing these potential energy images, the key system parameters required to achieve the six stable states can be accurately identified.

[0041] As an embodiment of the six-stable system (just a name), it can be set that the size of the ring magnet 3-1 is φ B1o 20mm×φ B1i 15 mm×t B1 3 mm, magnetization intensity M B1 7.5×10 5 A / m; the parameters of the ring magnets 3-2 and 3-3 are the same as those of the ring magnet 3-1; the size of the rectangular magnet is l A 15 mm×w A 15 mm×t A 3mm, magnetization intensity M A 9.5×10 5 A / m; equivalent stiffness K of piezoelectric beam eq is 12N / m; the distance d between two adjacent ring magnets e is 29mm; in the initial state, the surface horizontal distance d between the annular magnet and the rectangular magnet is 3mm; the cantilever beam length l b It is 100mm.

[0042] Attached Figure 3 It is shown that by adjusting the equivalent stiffness K of the piezoelectric beam while keeping all other parameters constant eq The curve of the potential energy of the system when the load reaches 4N / m, 8N / m, 12N / m, and 16N / m. The valley point of the potential energy curve in the figure marks the steady-state point of the system, that is, the lowest position of the energy in the stable range.

[0043] Attached Figure 4 To ensure that other parameters remain unchanged, change the thickness of the ring magnet t B Potential energy image of the system when the diameter reaches 1mm, 3mm, 5mm and 7mm.

[0044] Attached Figure 5 To ensure that the other parameters mentioned above remain unchanged, the outer radius r of the ring magnet is set o Potential energy image of the system when the diameter is 8mm, 10mm, 12mm and 14mm.

[0045] Attached Figure 6 To ensure that the other parameters mentioned above remain unchanged, the inner radius r of the ring magnet is set i Potential energy image of the system when the diameter is 3.5mm, 5.5mm, 7.5mm and 9.5mm.

[0046] Attached Figure 7 To ensure that the other parameters mentioned above remain unchanged, set the thickness of the rectangular magnet t A Potential energy image of the system when the diameter is 1mm, 3mm, 5mm and 7mm.

[0047] Attached Figure 8 To ensure that the other parameters mentioned above remain unchanged, set the width w of the rectangular magnet A Potential energy image of the system when the diameter is 5mm, 10mm, 15mm and 20mm.

[0048] Attached Fig. 9 To ensure that the other parameters mentioned above remain unchanged, set the length of the rectangular magnet l A Potential energy image of the system when the diameter is 5mm, 10mm, 15mm and 20mm.

[0049] Attached Fig.10 To ensure that the other parameters mentioned above remain unchanged, the distance d between two adjacent ring magnets is set e Potential energy image of the system when the diameter is 25mm, 29mm, 33mm and 37mm.

[0050] Attached Fig.11 To ensure that the other parameters mentioned above remain unchanged, the potential energy image of the system is set when the initial surface horizontal distance d between the annular magnet and the rectangular magnet is 3mm, 7mm, 11mm, and 15mm.

[0051] Attached Fig.12 To ensure that the other parameters mentioned above remain unchanged, set the magnetization intensity M of the rectangular magnet 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 A / m, the potential energy image of the system.

[0052] Attached Fig.13 To ensure that the other parameters mentioned above remain 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 A / m, the potential energy image of the system.

[0053] By observing the Figure 3 To Attachment Fig.13It can be clearly understood that the stable state of the system is affected by many factors, including the equivalent stiffness of the piezoelectric beam, the geometric dimensions and magnetization intensity of the annular magnet and the rectangular magnet, the distance between two adjacent annular magnets, and the horizontal distance between the annular magnet and the rectangular magnet.

[0054] Attach Figure 3 For a specific example, when the equivalent stiffness K of the piezoelectric beam is eq When set to 4N / m and 16N / m respectively, the system only exhibits four steady-state points. Therefore, to realize a system embodiment with six steady-state points, all the above parameters must be adjusted comprehensively and finely. This includes adjusting the equivalent stiffness of the piezoelectric beam to an appropriate range, optimizing the geometric dimensions of the annular magnet and the rectangular magnet, adjusting the magnetization intensity, and precisely controlling the spacing between two adjacent annular magnets and the horizontal distance between them and the rectangular magnet, so as to work together on the system to ensure that it reaches the expected stable state.

Claims

1. A hexastable piezoelectric vibration energy harvester, comprising a base, a cantilever beam, three annular magnets, a rectangular magnet, an MFC piezoelectric sheet and a conductor, characterized in that: The shape of the base (1) is "凵", and the left and right side columns are perpendicular to the bottom surface of the base. The cantilever beam (2) is fixed inside the left side column of the base, and the ring magnets (3-1), (3-2), and (3-3) are fixed inside the right side column. The free end of the cantilever beam is fixed with a rectangular magnet (4), and the upper surface of its root is fixed with an MFC piezoelectric sheet (5), and the piezoelectric sheet outputs an electrical signal through a wire (6). The parameters of the three ring magnets are the same; in the initial state, the ring magnets are opposite to the N pole of the rectangular magnet. By adjusting the equivalent stiffness of the piezoelectric beam, the geometric dimensions and magnetization intensities of the rectangular magnet and the ring magnets, the spacing between the ring magnets, and the horizontal distance between the rectangular magnet and the ring magnets, the energy harvester is in a six-stable state.

2. The hexastable piezoelectric vibration energy harvester according to claim 1 is characterized in that: The magnetic induction intensity B(x, y, z) at any position P(x, y, z) in space of the three ring magnets is determined by the following formula In the formula, B B1o (x,y,z),B B1i (x, y, z) represent the magnetic induction intensity of the magnetizing 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) correspond to the magnetic induction intensity of the magnetizing 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; M B1 、M B2 、M B3 are the magnetization intensities of the annular magnets (3-1), (3-2), and (3-3) respectively; t B1 ,t B2 ,t B3 are the thicknesses of the annular magnets (3-1), (3-2), and (3-3) respectively; φ B1o ,φ B2o ,φ B3o are the outer diameters of the annular magnets (3-1), (3-2), and (3-3); φ B1i ,φ B2i ,φ B3i are the inner diameters of the annular magnets (3-1), (3-2), and (3-3); d e is the distance between two adjacent annular magnets; l is the thickness integral variable; θ is the angle integral variable; i, j, k are unit vectors in the x, y, z directions; B i (x,y,z),B j (x,y,z),B k (x, y, z) represent the components of the magnetic induction intensity of the three ring magnets in the x, y, and z directions at any point P (x, y, z) in space.

3. The hexastable piezoelectric vibration energy harvester according to claim 1 is characterized in that: The nonlinear magnetic force F between the rectangular magnet and the three ring magnets in the vertical direction i Determined by the following formula Where M A is the magnetization intensity of the rectangular magnet (4); t A 、w A , l A 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 are the thickness of the annular magnet and the length of the cantilever beam respectively; d is the initial surface horizontal distance between the rectangular magnet and the annular magnet.

4. The hexastable piezoelectric vibration energy harvester according to claim 1 is characterized in that: The system potential energy V and the number of system steady states are determined by the following formula In the formula, K eq is the equivalent stiffness of the piezoelectric beam.

5. The hexastable piezoelectric vibration energy harvester according to claim 1 is characterized in that: When the energy harvester is in the six-stable state, the sizes of the annular magnets (3-1), (3-2), and (3-3) are all φ B1o 20 mm×φ B1i 15 mm×t B1 3 mm, and the magnetization intensity is 7.5×10 5 A / m; rectangular magnet (4) size is l A 15mm×w A 15 mm×t A 3 mm, magnetization intensity M A 9.5×10 5 A / m; equivalent stiffness K of piezoelectric beam eq is 12N / m; the distance d between two adjacent ring magnets e is 29 mm; in the initial state, the surface horizontal distance d between the annular magnet and the rectangular magnet is 3 mm; the length of the cantilever beam (2) is l b It is 100mm.

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