Bistable magnetic levitation electromagnetic vibration energy harvesting device

Abstract

The application discloses a kind of bistable magnetic levitation electromagnetic vibration energy harvesting device, and simultaneously gives the calculation method of suspension magnet potential function.The device structure is: three sleeves are installed from top to bottom on the outside of magnetic levitation pipe, the top sleeve is fixed with first annular magnet;The middle sleeve is fixed with copper coil;The bottom sleeve is fixed with second annular magnet.Cylindrical magnet is placed in magnetic levitation pipe, and has two static stable points.When the system is excited by external vibration, the suspension magnet moves axially inside the magnetic levitation pipe, and the coil cuts the magnetic induction lines to generate current through the polarity of the magnet.The application only needs to set the size of three magnets, and the distance between the two fixed annular magnets can realize the bistable magnetic levitation structure with consistent potential well depth on both sides.For the application of electromagnetic vibration energy harvester under wideband excitation, a new technical method is provided, which reduces the size of multi-stable vibration energy harvester and is beneficial to the improvement of energy harvesting effect.

Description

Technical Field

[0001] This invention belongs to the field of electromechanical technology, and specifically relates to an energy harvesting device that collects vibration energy and converts it into electrical energy. Background Technology

[0002] Wireless sensor and microelectronic component technologies have received widespread attention and development in recent years. However, the traditional chemical battery power supply strategy has shown significant drawbacks in the application of such devices, including short battery life, the need for periodic charging, and environmental pollution. An ideal solution is to directly harvest the vibration energy widely present in the environment for power generation. Vibration energy harvesting methods are mainly divided into piezoelectric, triboelectric, and electromagnetic types. Among them, electromagnetic energy harvesting devices have a large output current and high power, and have always attracted researchers' attention, especially the magnetic levitation electromagnetic vibration energy harvesting technology based on the interaction between magnets. The properties of magnets can ensure its long-term operation, and the electromechanical coupling unit between the coil and the magnet has low production and maintenance costs. How to further improve the energy harvesting performance of the system while ensuring structural simplicity is the key to designing a magnetic levitation electromagnetic vibration energy harvesting device.

[0003] Traditional magnetically levitated electromagnetic vibration energy harvesting devices typically consist of two fixed magnets and one suspended magnet. This type of structure exhibits monostable behavior, meaning the suspended magnet has only a single statically stable position. Although the nonlinear characteristics of magnetism can improve the output performance of the energy harvesting device to some extent near the resonant frequency, the operating bandwidth of this monostable structure remains relatively narrow. Further broadening the system's operating bandwidth and enabling its application to vibration excitation at different frequencies has become a focus of recent technological research.

[0004] To address the aforementioned issues, researchers have proposed combining multistable structures with traditional three-magnet magnetic levitation structures to create multistable magnetic levitation structures, thereby improving the broadband operation capability of energy harvesting. For example, uniformly mounting four additional magnets on the outside of a traditional three-magnet magnetic levitation structure can achieve a bistable structure. Furthermore, introducing more additional magnets can further achieve tristable and even tetrastable states. The advantage of multistable structures lies in the fact that the levitation magnets can transition between different potential wells. Compared to traditional monostable structures, the complex nonlinear characteristics introduced by multistable structures can effectively broaden the system's operating bandwidth.

[0005] Current multistable magnetic levitation structures often require the introduction of additional magnets, which not only increases the size of the device but also makes the parameter design more complex. Furthermore, in the optimized design of multistable structures, the gravity of the levitation magnets is often neglected. The presence of gravity causes asymmetry in the potential energy function and varying depths of the potential well; these phenomena have been confirmed by researchers to degrade the output performance of energy harvesting devices. Against this technical background, this invention proposes a magnetically levitation electromagnetic vibration energy harvesting device that achieves a bistable structure using only three magnets. Summary of the Invention

[0006] To overcome the technical deficiencies of magnetic levitation electromagnetic vibration energy harvesting devices, the purpose of this invention is to propose a three-magnet bistable magnetic levitation electromagnetic vibration energy harvesting device and its potential energy function calculation method.

[0007] The technical solution of the present invention consists of three parts: a three-magnet bistable magnetic levitation electromagnetic vibration energy harvesting device, a method for calculating the potential energy function in a three-magnet bistable magnetic levitation structure, and a method for optimizing the design of magnet dimensions.

[0008] A bistable magnetic levitation electromagnetic vibration energy harvesting device includes a magnetic levitation tube, sleeves, coils, and magnets. Its key feature is that three sleeves are installed from top to bottom on the outside of the magnetic levitation tube: a first annular magnet is fixed to the top sleeve; a copper coil is fixed to the middle sleeve; and a second annular magnet is fixed to the bottom sleeve. A cylindrical magnet is placed inside the magnetic levitation tube. By setting the polarity of the magnet and the characteristic dimensions of the annular magnet, the cylindrical magnet can be levitated inside the magnetic levitation tube, achieving two static stable points.

[0009] One of the main technical features of this invention is that by changing the fixed positions of the top sleeve and the bottom sleeve, the distance between the first and second annular magnets can be changed, thereby obtaining a bistable magnetic levitation structure with different nonlinear characteristics.

[0010] The potential energy function in a bistable magnetic levitation electromagnetic vibration energy harvesting device is calculated using the following steps:

[0011] (1) Taking the axial magnetic force between the second ring magnet and the cylindrical levitation magnet as an example, first calculate the axial force between the equivalent magnetic charge surface at the upper end of the second ring magnet and the equivalent magnetic charge surface at the lower end of the cylindrical levitation magnet:

[0012]

[0013] (2) Calculate the axial magnetic force between the second ring magnet and the cylindrical magnet, which is the superposition of the interaction forces between the equivalent magnetic charge end faces of the two magnets. The expression for the magnetic force between the two magnets is:

[0014] F mag =F(M a M b r a R a R b d ab +h a )-F(M a M b r a R a R b d ab +h a +h b )-F(M a M b r a R a R b d ab )+F(M a M b r a R a R b d ab +h D (2)

[0015] (3) Calculate the resultant force exerted on the cylindrical levitation magnet by the first and second annular magnets, assuming the positions of the two annular magnets are fixed and the distance between them is d. Establish a coordinate system with point Z as the origin. Let the position of the center of the cylindrical levitation magnet be z. Then the distances between the cylindrical levitation magnet and the first and second annular magnets are respectively... The net force exerted on the cylindrical magnet by the ring magnet is:

[0016]

[0017]

[0018] (4) Calculate the potential energy in the bistable magnetic levitation electromagnetic vibration energy harvesting device. Considering the weight of the cylindrical levitation magnet itself and the magnetic force exerted by the fixed ring magnets at both ends, the potential energy function can be expressed as:

[0019] V = W1 + W2 = ∫m b gdz-∫F mag dz (4)

[0020] In the bistable magnetic levitation electromagnetic vibration energy harvesting device, the (optimal) size of the ring magnet is determined by the following calculation steps: (1) Substitute the initially set size parameters of the cylindrical magnet and the first and second ring magnets, as well as the distance between the two ring magnets, into formulas (1) to (4) to obtain the initial bistable potential energy function.

[0021] (2) Prioritize the optimization design of the first and second annular magnets, taking the first annular magnet as an example. Based on the potential well depths on both sides of the initial bistable potential energy function curve, change the inner radius and height of the annular magnets respectively and calculate the corresponding potential energy functions.

[0022] (3) When the potential well depths on the upper and lower sides of the bistable structure are equal, the inter-well transition capability of the suspending magnet can reach the optimal level, corresponding to the optimal output performance.

[0023] (4) If changing the parameters of the first and second ring magnets cannot meet the conditions in step (3), the parameters of the cylindrical levitation magnet need to be redesigned and steps (1) to (3) are repeated to finally obtain the ring magnet size parameters that match the size of the levitation magnet.

[0024] The working principle of this three-magnet bistable magnetic levitation electromagnetic vibration energy harvesting device is as follows: Ring magnets are fixed at both ends of the magnetic levitation tube. A cylindrical magnet, under the combined force of the two ring magnets, maintains levitation within the tube and has two static stable points. When the system is subjected to external vibration excitation, the cylindrical magnet vibrates axially within the magnetic levitation tube. The cylindrical magnet and the coil winding fixed to the outside of the tube generate relative motion; that is, the coil cuts magnetic field lines to generate current, and the system converts vibration energy into electrical energy. When the excitation signal meets certain conditions, the cylindrical magnet overcomes the potential barrier to achieve inter-well transition vibration. This nonlinear phenomenon enables the harvesting of vibration energy over a wide frequency range.

[0025] The features and beneficial effects of this invention are as follows: Compared with conventional magnetic levitation electromagnetic vibration energy harvesting devices, this bistable magnetic levitation electromagnetic vibration energy harvesting device can achieve a bistable structure with consistent potential well depths on both sides using only three appropriately sized magnets without increasing the number of magnets. This bistable structure avoids the increase in device size caused by introducing additional magnets, facilitating miniaturization through transposition. Furthermore, it simplifies the complexity of system design and dynamic calculations, providing a new technical method for designing multistable structures. In addition, the bistable nature of the structure enables the system to exhibit rich nonlinear dynamic phenomena such as inter-well transitions and potential well escape, which helps improve the energy harvesting capability of the device over a wide frequency band. Attached Figure Description

[0026] Appendix Figure 1 This is a schematic diagram illustrating the principle and structure of the device of the present invention.

[0027] Appendix Figure 2 This is the system potential energy function graph for different values ​​of the height of the first ring magnet.

[0028] Appendix Figure 3This is the system potential energy function diagram when the inner radius of the first ring magnet takes different values.

[0029] Appendix Figure 4 It is a curve showing the change in the depth of the potential wells on both sides of the bistable structure with the height and inner radius of the first annular magnet.

[0030] Appendix Figure 5 This refers to the output power of the device when the distance between the first and second annular magnets in this embodiment of the invention is 43mm. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that although the embodiments are described in the accompanying drawings, these embodiments are merely illustrative and not restrictive. The materials and dimensional parameters of the components can be changed without departing from the spirit and scope of the claims, and these changes are all within the scope of protection of the present invention.

[0032] The technical solution includes a three-magnet bistable magnetic levitation electromagnetic vibration energy harvesting device, a method for calculating the potential energy function in the three-magnet bistable magnetic levitation structure, and a method for optimizing the magnet dimensions. The key technology of this invention is that ring magnets are fixed at both the upper and lower ends of the magnetic levitation tube. By arranging the polarities of the magnets, a third cylindrical magnet is suspended within the magnetic levitation tube, possessing two statically stable points. By optimizing the dimensional parameters of the ring magnets, the potential well depths on both sides of the bistable structure are made consistent in the vertical direction, which facilitates the transition motion of the cylindrical magnet between the two potential wells. Therefore, the energy harvesting device can adapt to broadband vibration excitation.

[0033] Combined with appendix Figure 1 The structure of the bistable magnetic levitation electromagnetic vibration energy harvesting device is as follows: Three sleeves are installed from top to bottom on the outside of the magnetic levitation tube 1. The top sleeve 2-1 is fixed with a first annular magnet 4-1; the middle sleeve 2-2 is fixed with a copper coil 3; and the bottom sleeve 2-3 is fixed with a second annular magnet 4-3. A cylindrical magnet 4-2 is placed inside the magnetic levitation tube. By setting the polarity of the magnet and the characteristic dimensions of the annular magnet, the cylindrical magnet can be levitated inside the magnetic levitation tube and has two static stable points.

[0034] The north pole of the second ring magnet is opposite to the south pole of the cylindrical magnet, and the south pole of the top ring magnet is opposite to the north pole of the cylindrical magnet. Three sleeves act as fasteners to fix the two ring magnets and a coil winding to the magnetic levitation tube. The shape of the sleeves should match the parts being connected.

[0035] By changing the fixed positions of the top sleeve and the bottom sleeve, the distance between the first and second annular magnets can be changed, thereby obtaining a bistable magnetic levitation structure with different nonlinear characteristics.

[0036] An intermediate sleeve with a fixed copper coil is installed on the magnetic levitation tube, forming a bistable magnetic levitation electromagnetic vibration energy harvesting device together with the bistable magnetic levitation structure.

[0037] The top and bottom magnets are both ring-shaped, while the levitation magnet is cylindrical.

[0038] The potential energy function in a bistable magnetic levitation electromagnetic vibration energy harvesting device is calculated using the following steps:

[0039] (1) Taking the axial magnetic force between the second ring magnet and the cylindrical levitation magnet as an example, first calculate the axial force between the equivalent magnetic charge surface at the upper end of the second ring magnet and the equivalent magnetic charge surface at the lower end of the cylindrical levitation magnet:

[0040]

[0041] Where r a R a These are the inner and outer radii of the bottom ring magnet, R. b It is the radius of the cylindrical levitation magnet, d ab It is the distance between the equivalent magnetic charge surface at the upper end of the bottom ring magnet and the equivalent magnetic charge surface at the lower end of the cylindrical levitation magnet, μ0, M. a M b These represent the vacuum permeability, the magnetization of the second ring magnet, and the magnetization of the cylindrical levitation magnet, respectively.

[0042] (2) Calculate the axial magnetic force between the second ring magnet and the cylindrical magnet. By superimposing the interaction forces between the equivalent magnetic charge end faces of the second ring magnet and the cylindrical magnet, the expression for the magnetic force between the two magnets is:

[0043] F mag =F(M a M b r a R a R b d ab +h a )-F(M a M b r a R a R b d ab +h a +h b )-F(M a M b r a R a R b dab )+F(M a M b r a R a R b d ab +h b (2)

[0044] Where h a h b These are the heights of the bottom ring magnet and the cylindrical levitation magnet, respectively.

[0045] (3) Calculate the resultant force exerted on the cylindrical levitation magnet by the first and second annular magnets. Assume the positions of the two annular magnets are fixed and the distance between them is d. Establish a coordinate system with point z as the origin. Let z be the position of the center of the cylindrical levitation magnet. Then the distances between the cylindrical levitation magnet and the first and second annular magnets are respectively... The net force exerted on the cylindrical magnet by the ring magnet is:

[0046]

[0047]

[0048] Where r c R c h c These are the inner radius, outer radius, and height of the top ring magnet, M. c It is the magnetization intensity of the first ring magnet.

[0049] (4) Calculate the potential energy in the structure of the bistable magnetic levitation electromagnetic vibration energy harvesting device. Considering the gravity of the cylindrical levitation magnet itself and the magnetic force exerted by the first and second fixed ring magnets, the potential energy function can be expressed as:

[0050] V = W1 + W2 = ∫m b gdz-∫F mag dz (4)

[0051] Where m b Let g represent the mass of the cylindrical levitation magnet, and g be the acceleration due to gravity.

[0052] In a bistable magnetic levitation electromagnetic vibration energy harvesting device, the optimal size of the annular magnet is determined by the following calculation steps:

[0053] (1) Substitute the initially set size parameters of the cylindrical magnet and the first and second annular magnets, as well as the distance between the two annular magnets, into formulas (1) to (4) to obtain the initial bistable potential energy function.

[0054] (2) Prioritize the design of the first and second ring magnets. Taking the first ring magnet as an example, based on the depth of the potential wells on both sides of the initial bistable potential energy function, change the inner radius and height of the first and second ring magnets respectively and calculate the corresponding potential energy functions.

[0055] (3) When the potential well depths on both sides of the bistable structure are equal, the inter-well transition capability of the levitated magnet reaches its optimum, corresponding to the optimal output performance. (Appendix) Figure 2 This represents the bistable potential energy function for different values ​​of the height of the first annular magnet; the greater the height, the deeper the potential well on the right. (See attached diagram.) Figure 3 Let be the bistable potential energy function corresponding to different values ​​of the inner radius of the first ring magnet; the larger the inner radius, the deeper the potential well on the right. According to... Figure 2 , Figure 3 The influence of the size of the first annular magnet on the potential well depth on both sides of the bistable structure is investigated, and an appropriate size is selected to satisfy the condition that the potential well depths on both sides are consistent.

[0056] (4) If changing the parameters of the first and second ring magnets cannot meet the conditions in step (3), the parameters of the cylindrical levitation magnet need to be redesigned and steps (1) to (3) are repeated to finally obtain the optimal ring magnet size parameters that match the size of the levitation magnet.

[0057] As a specific example:

[0058] As a specific embodiment: the magnetic levitation tube is made of polytetrafluoroethylene (PTFE) and has the following dimensions: inner radius 6mm, outer radius 8mm, and length 60mm. The second ring magnet is made of Nd₂Fe₂. 14 B, with dimensions of: inner radius 8.5mm, outer radius 12mm, and height 1.5mm. The first ring magnet is made of Nd2Fe. 14 B, with dimensions of: inner radius 9.1mm, outer radius 12mm, and height 3mm. The cylindrical levitation magnet is made of Nd2Fe. 14 B, dimensions: radius 6mm, height 18mm. The copper coil is made of copper, with a total of 2000 turns. The dimensions of the copper coil winding are: inner radius 9mm, outer radius 12mm, height 20mm, and internal resistance 200Ω.

[0059] In the bistable magnetic levitation structure, the distance between the first and second annular magnets is set to 43mm.

[0060] Appendix Figure 4 The curves show the changes in the depth of the potential wells on both sides as a function of the height and inner radius of the first annular magnet. It is found that when the magnet height is 3 mm and the inner radius is 9.1 mm, the depths of the potential wells on both sides of the bistable structure are equal, which is the optimal magnet size parameter.

[0061] In this embodiment, the two ends of the bistable magnetic levitation electromagnetic vibration energy harvesting device are not sealed, and the smoothness of the inner wall of the magnetic levitation tube is not treated (no lubricant, friction agent or other substances are added).

[0062] In this embodiment, a 200Ω resistor is connected externally to the coil winding to detect the output power of the device. (See attached image) Figure 5 The figures show the output power curves of the device under different excitation conditions when the magnet spacing is 43 mm. The results show that this bistable magnetic levitation electromagnetic vibration energy harvesting device exhibits significant nonlinear characteristics. The output power of the device increases substantially when the levitation magnets can perform large-amplitude inter-well transitions. Under an acceleration excitation intensity of 0.5 g, the device can output a large power in the frequency range of 6.25-9.5 Hz, enabling it to harvest vibration energy over a wide frequency band.

[0063] In this embodiment, the device has a volume of 27 cm³. 3 The experimentally obtained maximum normalized power density of the device is 1040 W / (m²). 3 g 2 It has a good ability to harvest vibration energy.

Claims

1. A bistable magnetic levitation electromagnetic vibration energy harvesting device, comprising: The magnetic levitation tube, sleeves, coils, and magnets are characterized in that: three sleeves are installed from top to bottom on the outside of the magnetic levitation tube (1); the top sleeve (2-1) is fixed with a first annular magnet (4-1); the middle sleeve (2-2) is fixed with a copper coil (3); the bottom sleeve (2-3) is fixed with a second annular magnet (4-3); and a cylindrical magnet (4-2) is placed inside the magnetic levitation tube. By setting the polarity of the magnet and the characteristic dimensions of the annular magnet, the cylindrical magnet can be suspended inside the magnetic levitation tube and has two static stable points. The magnetic levitation tube is made of polytetrafluoroethylene and has the following dimensions: inner radius 6mm, outer radius 8mm, and length 60mm. The second ring magnet is made of Nd2Fe. 14 B, with dimensions of: inner radius 8.5mm, outer radius 12mm, and height 1.5mm; The first ring magnet is made of Nd2Fe. 14 B, with dimensions of: inner radius 9.1mm, outer radius 12mm, and height 3mm; The cylindrical levitation magnet is made of Nd2Fe. 14 B, dimensions: radius 6mm, height 18mm; The copper coil is made of copper, and the copper coil winding has a total of 2000 turns. The dimensions of the copper coil winding are: inner radius 9mm, outer radius 12mm, and height 20mm. In the bistable magnetic levitation electromagnetic vibration energy harvesting device, the distance between the first and second annular magnets is 43mm.

2. The bistable magnetic levitation electromagnetic vibration energy harvesting device according to claim 1, characterized in that: By changing the fixed positions of the top sleeve and the bottom sleeve, the distance between the first and second annular magnets can be changed, thereby obtaining a bistable magnetic levitation structure with different nonlinear characteristics.

3. The bistable magnetic levitation electromagnetic vibration energy harvesting device according to claim 1, characterized in that: The intermediate sleeve with the fixed copper coil is installed on the magnetic levitation tube, forming a bistable magnetic levitation electromagnetic vibration energy harvesting device together with the bistable magnetic levitation structure.

4. The bistable magnetic levitation electromagnetic vibration energy harvesting device according to claim 1, characterized in that: The top and bottom magnets are both ring-shaped, while the levitation magnet is cylindrical.

5. A method for calculating the potential energy function in the bistable magnetic levitation electromagnetic vibration energy harvesting device according to claim 1, characterized in that: The potential energy function is determined by the following calculation steps: (1) Taking the axial magnetic force between the second ring magnet and the cylindrical levitation magnet as an example, first calculate the axial force between the equivalent magnetic charge surface at the upper end of the second ring magnet and the equivalent magnetic charge surface at the lower end of the cylindrical levitation magnet: （1） in , These are the inner and outer radii of the bottom ring magnet, respectively. It is the radius of the cylindrical levitation magnet. It is the distance between the equivalent magnetic charge surface at the upper end of the bottom ring magnet and the equivalent magnetic charge surface at the lower end of the cylindrical levitation magnet. , , These are the vacuum permeability, the magnetization of the second ring magnet, and the magnetization of the cylindrical levitation magnet, respectively. (2) Calculate the axial magnetic force between the second ring magnet and the cylindrical magnet. By superimposing the interaction forces between the equivalent magnetic charge end faces of the second ring magnet and the cylindrical magnet, the expression for the magnetic force between the two magnets is: （2） in , These are the heights of the bottom ring magnet and the cylindrical levitation magnet, respectively. (3) Calculate the resultant force exerted by the first and second annular magnets on the cylindrical levitation magnet, assuming that the positions of the two annular magnets are fixed and the distance between them is . Between two ring magnets Establish a coordinate system with point O as the origin, and let the center of the cylindrical levitation magnet be located at point I. The distances between the cylindrical levitation magnet and the first and second annular magnets are respectively , The net force exerted on the cylindrical magnet by the ring magnet is: （3） in , , These are the inner radius, outer radius, and height of the top ring magnet, respectively. It is the magnetization intensity of the first ring magnet; (4) Calculate the potential energy in the structure of the bistable magnetic levitation electromagnetic vibration energy harvesting device. Considering the gravity of the cylindrical levitation magnet itself and the magnetic force exerted by the first and second fixed ring magnets, the potential energy function can be expressed as: （4） in This indicates the mass of the cylindrical levitation magnet. This is the acceleration due to gravity.

6. The bistable magnetic levitation electromagnetic vibration energy harvesting device according to claim 1, and the method for calculating the potential energy function in the bistable magnetic levitation electromagnetic vibration energy harvesting device according to claim 5, characterized in that: In the bistable magnetic levitation electromagnetic vibration energy harvesting device, the size of the annular magnet is determined by the following calculation steps: (1) Substitute the initially set size parameters of the cylindrical magnet and the first and second annular magnets, as well as the distance between the two magnets, into formulas (1) to (4) to obtain the initial bistable potential energy function; (2) Prioritize the design of the first and second ring magnets. Taking the first ring magnet as an example, based on the depth of the potential wells on both sides of the initial bistable potential energy function, change the inner radius and height of the first and second ring magnets respectively and calculate the corresponding potential energy functions. (3) When the potential well depths on the upper and lower sides of the bistable structure are equal, the inter-well transition capability of the suspending magnet can reach the optimal level, corresponding to the optimal output performance. (4) If changing the parameters of the first and second ring magnets cannot meet the conditions in step (3), the parameters of the cylindrical levitation magnet need to be redesigned and steps (1) to (3) are repeated to finally obtain the ring magnet size parameters that match the size of the levitation magnet.

7. The bistable magnetic levitation electromagnetic vibration energy harvesting device according to claim 1, characterized in that: The two ends of the magnetic levitation tube are not sealed, and the smoothness of the inner wall of the magnetic levitation tube is not treated.

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