A two-stage multi-directional vibration energy harvesting device and its design method

Abstract

This invention discloses a two-stage multi-directional vibration energy harvesting device and its design method. The device includes a chassis with a magnet holder welded to its center for fixing a ring magnet. A number of long and short cantilever beams are alternately arranged at equal intervals around the ring magnet. A pointed magnet block at the same height as the ring magnet is welded to the tail end of each short cantilever beam, and a piezoelectric plate for energy conversion is located at the bottom end of each long cantilever beam. The multi-directional two-stage piezoelectric energy harvesting device of this invention collects vibration energy from various directions through eight equally spaced ring-shaped cantilever beams and piezoelectric plates. The long and short cantilever beams are designed with different natural frequencies based on the environmental excitation frequency, thus widening the system's operating frequency band. Simultaneously, the ring magnet and the pointed magnet blocks on the cantilever beams attract each other, and the introduction of nonlinear magnetic force gives each beam a wider operating frequency band, thereby further improving the energy conversion efficiency of the entire system.

Description

Technical Field

[0001] This invention belongs to the field of piezoelectric vibration energy harvesting technology, and relates to a multi-directional two-stage piezoelectric energy harvesting device and design method with high energy conversion rate. Background Technology

[0002] With social development and technological advancements, microelectromechanical systems (MEMS), portable smart wearable devices, and wireless communication technologies have experienced rapid growth. Wireless sensor networks are widely used in civilian, military, medical, and industrial production. Currently, most miniature wireless sensing devices rely on chemical batteries for power. These batteries require regular maintenance or replacement and pose environmental pollution problems, failing to meet the power supply needs of devices operating in special environments. Therefore, researching and developing sustainable and environmentally friendly new power sources to replace traditional chemical batteries has become a widely recognized research direction and hot topic.

[0003] The natural environment contains abundant energy sources, such as vibration energy, wind energy, tidal energy, solar energy, thermoelectric energy, hydroelectric energy, noise energy, geothermal energy, and radio frequency radiation energy. Among these, solar energy has a high energy density and is easy to harvest. However, using solar power to power wireless sensing devices installed indoors or in shady locations still faces many challenges. Wind energy is a low-cost clean energy source, but its harvesting requires favorable geographical conditions, which limits its effectiveness. Vibration energy, as the most widely distributed energy source in the natural environment, has attracted much attention from scholars due to its high energy density, wide distribution, and independence from weather conditions. The technology of converting ubiquitous vibration energy in the environment into electrical energy to power low-power electronic devices is called vibration energy harvesting technology.

[0004] Vibration energy harvesters have attracted much attention in recent years as a highly efficient and clean energy harvesting technology. They utilize the piezoelectric properties of piezoelectric materials to convert environmental vibration energy into electrical energy, powering wireless sensors or low-power components. However, existing vibration energy harvesters generally suffer from several problems, such as narrow operating bandwidth, difficulty in exciting operating modes, and a single direction of vibration energy harvesting. If the vibration frequency in the environment deviates slightly from the resonant frequency of the piezoelectric energy harvester, or if the vibration direction deviates slightly from the designed vibration direction of the harvester structure, the energy harvesting efficiency and output power will drop significantly. Therefore, designing new, more efficient, multi-directional, wideband piezoelectric vibration energy harvesting devices remains a hot topic.

[0005] It should be noted that this section is intended to provide background or context for the embodiments of the invention set forth in the claims. The description herein does not constitute an admission that it is prior art simply because it is included in this section. Summary of the Invention

[0006] The purpose of this invention is to provide a two-stage multi-directional vibration energy harvesting device, which improves upon the problems of narrow operating frequency band, difficulty in excitation, and single collection direction of ordinary cantilever beam energy harvesting devices. This device adopts a two-stage cantilever beam ring array structure, which enables the energy harvester to not only have a wider operating frequency band, but also to achieve multi-directional energy harvesting, thereby significantly improving the energy harvesting efficiency of the device.

[0007] This invention is achieved through the following technical solution:

[0008] A two-stage multi-directional vibration energy harvesting device includes a chassis, a magnet holder for fixing a ring magnet welded to the center of the chassis, and a number of long cantilever beams and short cantilever beams alternately around the ring magnet at equal intervals; a pointed magnet block at the same height as the ring magnet is welded to the tail end of each short cantilever beam, and a piezoelectric plate for energy conversion is located at the bottom end of the long cantilever beam.

[0009] The multi-directional dual-stage piezoelectric energy harvesting device of this invention collects vibration energy from various directions through eight cantilever beams and piezoelectric plates arranged in a ring at equal intervals. Based on the environmental excitation frequency, long and short cantilever beams with different natural frequencies are designed, thus widening the system's operating frequency band. Simultaneously, the ring magnet and the pointed magnet blocks on the short cantilever beams attract each other, and the introduction of nonlinear magnetic force gives each beam a wider operating frequency band, thereby further improving the energy conversion efficiency of the entire system.

[0010] Furthermore, the chassis and magnet mounting bracket are made of metal materials such as aluminum or copper.

[0011] Furthermore, four long cantilever beams and four short cantilever beams are alternately welded around the annular permanent magnet at equal intervals, and the material is elastic metal material such as spring steel.

[0012] Furthermore, the long cantilever beam and the short cantilever beam have similar secondary vibration structures, and their natural frequencies can be designed to be consistent with the external vibration excitation frequency.

[0013] Furthermore, the piezoelectric element is made of polyvinylidene fluoride.

[0014] Furthermore, both the ring magnet and the pointed magnet block are neodymium iron boron permanent magnets.

[0015] The principle is to convert the vibrations on the eight cantilever beams into electrical energy on piezoelectric plates, which is then collected by a harvesting circuit. During operation, the natural frequencies of the long and short cantilever beams are designed according to environmental excitation, corresponding to the first two natural frequencies of the attached structure, thus significantly improving energy harvesting efficiency. The long and short cantilever beams are alternately and evenly spaced around the ring magnet, giving the device multiple energy harvesting directions. The nonlinear magnetic interaction between the pointed magnets on the long cantilever beams and the ring magnet widens the operating frequency band of the cantilever beams.

[0016] Compared with ordinary cantilever beam piezoelectric energy harvesting devices, this device can avoid problems such as difficulty in excitation during operation, single harvesting direction, and narrow operating frequency band. By specifically designing the natural frequency of the beam, it can maximize the harvesting of multi-directional vibration energy under certain vibration environments.

[0017] The main structural design steps of the above-mentioned two-stage multi-directional vibration energy harvesting device are as follows:

[0018] S1: Determine the energy capture frequencies: Analyze the vibration energy capture object and determine the vibration energy concentration frequencies f1 and f2 of the energy capture object.

[0019] S2: Design of a single secondary piezoelectric energy harvesting beam structure:

[0020] (1) Establish the structural parameters calibration of the double-stage cantilever beam: The length of the long cantilever beam is denoted as L1, the length of the short cantilever beam as L2, the equivalent mass of the long cantilever beam as m1, the equivalent mass of the short cantilever beam as m2, and the displacement of the long cantilever beam as y. 1 The displacement of the short cantilever beam is y0, k1 is the stiffness of the main beam, k2 is the stiffness of the secondary beam, and F m This indicates the magnetic force between the pointed magnet block 3 and the ring magnet 2.

[0021] (2) Electromagnetic force calculation: After both the long and short cantilever beams are equivalent to a concentrated mass spring system, the magnetic force F m It can be represented as:

[0022]

[0023] Where y1 is the displacement of the long cantilever beam 5, y0 is the displacement of the short cantilever beam, and a and b are magnetic parameters.

[0024] (3) Determine the mass matrix: The mass matrix of a double-stage cantilever beam can be defined as:

[0025]

[0026] (4) Determine the stiffness matrix: The linear stiffnesses of the long cantilever beam and the short cantilever beam are represented by k1 and k2, respectively. Then the stiffness matrix of the lumped model is expressed as:

[0027]

[0028] Using the stiffness matrix modeling method for discontinuous structures, the stiffness matrix of a double-stage cantilever beam can be transformed into:

[0029]

[0030] Where E is Young's modulus, β is the ratio of the length of the main beam L1 to the length of the secondary beam L2, I1 is the internal moment of the main beam cross-section, and I2 is the internal moment of the secondary beam cross-section.

[0031] (5) The motion control equations for the double-stage cantilever beam are:

[0032]

[0033] α is the electromechanical coupling coefficient, C S V represents the clamping capacitance of the piezoelectric element, and V represents the voltage across the piezoelectric element.

[0034] (6) Solving the equations of motion: By analyzing the equations, the length of the long cantilever beam can be obtained.

[0035] The length of the short cantilever beam and the weight of the mass block.

[0036] S3: Calculate the voltage of the energy capture system.

[0037] The total system voltage is:

[0038]

[0039] S4: Vibration natural frequency test of long and short cantilever beams of the energy harvesting system, calibration of the structure's natural frequency, and ensuring true energy harvesting efficiency.

[0040] At this point, the design of the multi-directional double-layer vibration energy revival device is complete.

[0041] The advantages of this invention are:

[0042] 1. This invention has great application prospects. Vibration energy is everywhere, and developing vibration energy harvesting devices, an environmentally friendly technology, is a promising option.

[0043] 2. Compared with ordinary cantilever beams, the two-stage cantilever beam in this invention has a lower natural frequency. Furthermore, by adjusting the beam length and the mass of the tip magnet, a natural frequency that matches the environmental excitation can be designed more easily, thereby improving the energy capture efficiency.

[0044] 3. In this invention, the cantilever beams are evenly spaced around the annular magnet, which can collect vibration energy from multiple directions and improve the efficiency of vibration energy collection.

[0045] 4. The interaction between the tip magnet and the ring magnet of the cantilever beam in this invention broadens the operating frequency band of the cantilever beam, making it easier to collect vibration energy.

[0046] 5. The present invention has a compact structure and low manufacturing cost. Compared with traditional chemical battery power supply, it has the advantages of being environmentally friendly and pollution-free, and can meet the structural requirements of miniaturization and integration of MEMS power supply devices. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of a two-stage multi-directional vibration energy harvesting device.

[0048] Figure 2 This is a cross-sectional view of a two-stage multi-directional vibration energy harvesting device.

[0049] Figure 3 This is a top view of a two-stage multi-directional vibration energy harvesting device.

[0050] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures. The reference numerals have the following meanings: 1 for magnet holder, 2 for ring magnet, 3 for pointed magnet block, 4 for long cantilever beam, 5 for short cantilever beam, 6 for piezoelectric sheet, and 7 for chassis. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0052] A two-stage multi-directional vibration energy harvesting device includes a chassis 7, which is circular and has a magnet fixing frame 1 for fixing a ring magnet 2 welded to its center. Four long cantilever beams 4 and four long cantilever beams 5 are alternately and equally spaced around the ring magnet 2.

[0053] A pointed magnet block 3, at the same height as the ring magnet 2, is welded to the tail end of each short cantilever beam, and a piezoelectric sheet 6 for energy conversion is located at the bottom end of the long cantilever beam 5.

[0054] The multi-directional dual-stage piezoelectric energy harvesting device of this invention collects vibration energy from various directions through eight cantilever beams and piezoelectric plates 6 arranged in a ring at equal intervals. Based on the environmental excitation frequency, long and short cantilever beams with different natural frequencies are designed, thus widening the system's operating frequency band. Simultaneously, the ring magnet 2 and the pointed magnet blocks 3 on the cantilever beams are arranged with like poles attracting each other. The introduction of nonlinear magnetic force further enhances the operating frequency band of each beam, thereby improving the overall energy conversion efficiency of the system.

[0055] As shown in the attached diagram, four long cantilever beams and four short cantilever beams are equidistantly distributed around the ring magnet 2. Therefore, the piezoelectric plates on the eight cantilever beams can collect vibrational energy from all directions. To maximize energy conversion efficiency, the cantilever beams must be installed at the same height as the central ring magnet, ensuring the pointed magnets on each beam are at the same height. Furthermore, since the vibrational energy of the structure in the environment is mainly concentrated at its first two natural frequencies, the natural frequencies of the long and short cantilever beams can be designed to match the first two natural frequencies of the load structure. This ensures that our energy harvester is more easily excited, resulting in a higher energy conversion rate.

[0056] In this invention, the interaction between the tip magnet 3 and the ring magnet 2 of the cantilever beam can broaden the working frequency band of the cantilever beam, making it easier to collect low-frequency vibration energy, which further broadens the energy conversion rate of the energy harvesting device.

[0057] This invention is a two-stage multi-directional vibration energy harvesting device. Compared with traditional cantilever beam piezoelectric harvesting devices, it has the advantages of multiple harvesting directions, compact structure, high energy conversion rate, and easier structure to be excited, thus enabling more efficient harvesting of vibration energy in the environment.

[0058] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A two-stage multi-directional vibration energy harvesting device, characterized in that, Includes a chassis (7), with a magnet fixing frame (1) for fixing the ring magnet (2) welded to the center of the chassis (7), and a number of long cantilever beams (4) and short cantilever beams (5) alternately surrounding the ring magnet (2) at equal intervals; the long cantilever beams (4) and short cantilever beams (5) constitute a secondary vibration structure, and each set of long and short axes can be set with two different natural frequencies; A pointed magnet block (3) at the same height as the ring magnet (2) is welded to the tail end of each short cantilever beam, and a piezoelectric sheet (6) for energy conversion is located at the bottom end of the long cantilever beam (4). The design steps of the two-stage multi-directional vibration energy harvesting device are as follows: S0: Determine the energy trapping frequency: Analyze the vibration energy trapping object and determine the concentrated frequency of the vibration energy of the energy trapping object. f 1 and f 2. S1: Design of a single secondary piezoelectric energy harvesting beam structure: (1) Establish the structural parameter calibration of the double-stage cantilever beam: The length of the long cantilever beam is defined as L1, the length of the short cantilever beam as L2, the equivalent mass of the long cantilever beam as m1, the equivalent mass of the short cantilever beam as m2, and the displacement of the long cantilever beam as y. 1 The displacement of the short cantilever beam is y0, k1 is the stiffness of the main beam, k2 is the stiffness of the secondary beam, and F m This indicates the magnetic force between the pointed magnet block (3) and the ring magnet (2); (2) Electromagnetic force calculation: After both the long and short cantilever beams are equivalent to a concentrated mass spring system, the magnetic force... F m Represented as: Where y1 is the displacement of the long cantilever beam, y0 is the displacement of the short cantilever beam, and a and b are magnetic parameters. (3) Determine the mass matrix: The mass matrix of a double-stage cantilever beam is defined as follows: (4) Determine the stiffness matrix: The linear stiffness of the long cantilever beam and the short cantilever beam are represented by k1 and k2 respectively. Then the stiffness matrix of the lumped model is expressed as: Using the stiffness matrix modeling method for discontinuous structures, the stiffness matrix of a double-stage cantilever beam can be transformed into: Where E is Young's modulus. The ratio of the main beam length L1 to the secondary beam length L2. The internal moment of the main beam cross section, The internal moment of the secondary beam cross section, (5) The motion control equations for the double-stage cantilever beam are: The electromechanical coupling coefficient is... This refers to the clamping capacitance of the piezoelectric element. Indicates the voltage of the piezoelectric element; (6) Solve the equation of motion: By analyzing the equation, the length of the long cantilever beam, the length of the short cantilever beam, and the weight of the mass block are obtained; S3: Calculate the voltage of the energy harvesting system; The total system voltage is: S4: Vibration natural frequency test of long cantilever beams and short cantilever beams of the energy harvesting system, calibration of the structure's natural frequency, and ensuring true energy harvesting efficiency; At this point, the design of the multi-directional double-layer vibration energy revival device is complete.

2. The dual-stage multi-directional vibration energy harvesting device as described in claim 1, characterized in that: The ring magnet (2) and the tip magnet block (3) are both neodymium iron boron permanent magnets. The magnets are arranged in a same-pole-attracting-each-pole configuration to amplify the amplitude of the secondary vibration structure.

3. The dual-stage multi-directional vibration energy harvesting device according to claim 1, characterized in that: The chassis (7) and magnet mounting bracket (1) are made of aluminum; the long cantilever beam (4) and short cantilever beam (5) are made of spring steel; and the piezoelectric sheet (6) is made of polyvinylidene fluoride.

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