CN102710168A - Low-frequency multidirectional vibration energy recovery device - Google Patents

Abstract

The invention discloses a low-frequency multi-directional vibration energy recovery device, which includes a mass block and an outer frame, the mass block is located in the outer frame, the mass block is connected with the outer frame through a folded elastic beam, and a piezoelectric sheet is arranged on the folded elastic beam The four sides of the mass block are provided with folding elastic beams with the same folding method, and the folding method of the folding elastic beams is to fold layer by layer from outside to inside and the folding length decreases layer by layer. The device can be applied to the recovery of low-frequency vibration energy in various large mechanical bases or vibrating elements, automobile engines, mixers, washing machines and various microstructures. It can provide power for various portable devices, wireless sensors and micro-electro-mechanical systems.

Description

A low-frequency multi-directional vibration energy recovery device

technical field

The invention belongs to the technical field of resonance energy recovery devices, and relates to a low-frequency multi-directional vibration energy recovery device.

Background technique

Energy recovery refers to the process of obtaining external energy and converting it into usable electrical energy. In the past decade, with the rapid development of portable devices, wireless sensors, and microelectromechanical systems (MEMS), materials and structures with energy recovery capabilities have received extensive attention and research. For these devices that need to be self-powered, energy recovery from the vibration of the surrounding environment is undoubtedly the most convenient and potential way. At present, countries such as the United States, Japan, the Netherlands, and the United Kingdom have begun research on clean, reliable, and cheap micro-energy devices, and have begun to develop micro-energy devices based on piezoelectric principles to provide energy for these systems.

At present, there are three main methods of research on vibration energy recovery technology: electrostatic, electromagnetic and piezoelectric. Among them, piezoelectric energy recovery devices have been a research hotspot in the past ten years, because piezoelectric materials can It directly converts external vibration energy into usable electrical energy, and has a simple structure and is easy to integrate into the system.

The piezoelectric energy recovery device mainly utilizes the piezoelectric effect of the piezoelectric material, that is, the piezoelectric material deforms under the action of an external force and generates an electric charge, converting mechanical energy into electrical energy. When resonant, the piezoelectric material has the largest deformation, which can produce a considerable energy output. A large number of scholars have studied this aspect. At present, the main forms are: piezoelectric cantilever beam structure, piezoelectric disc structure, cymbal piezoelectric structure, piezoelectric helical structure, etc. Different configurations of piezoelectric energy recovery devices include: single-layer and double-layer piezoelectric cantilever beams, push-pull direct pressure structures, diaphragm structures, tubular and radial structures, and cymbal piezoelectric structures. By adjusting the size of the structure to change its natural frequency to match the frequency of environmental vibrations. Generally, a mass block with a larger mass is added at the end of the structure to reduce the resonance frequency of the structure.

As early as 1996, British scientists Williams and Yates proposed the scheme of "embedding piezoelectric ceramics in a vibration environment for energy harvesting". The self-powered device generates 1 μW of power at a vibration frequency of 70 Hz and 0.1 mW of power at 330 Hz. This experiment shows that piezoelectric ceramics, as a medium for converting mechanical energy into electrical energy, need to improve the energy conversion efficiency in the low frequency range.

Although in the following ten years, people have designed various structures to recover mechanical vibration energy, in order to obtain some valuable applications. But most of the current design principles of these devices still rely on an oversimplified physical model. For example, referring to the widely used single-degree-of-freedom "spring-mass" system model, by changing the material and structural geometric parameters, the energy recovery device is tuned to a specific resonance frequency in order to obtain greater energy conversion efficiency. However, the application of this simple single-degree-of-freedom "mass-spring" system or cantilever beam structure for research and testing has great limitations, and it is far from practical engineering applications. Because in practice, the energy of environmental vibration is not distributed on a single frequency, but has a certain bandwidth. The frequency distribution of most vibration sources is between 50 and 250 Hz.

Recently, research on broadband and frequency-tunable vibration energy recovery devices has also received more and more attention. The passive energy harvesting device designed by Shahruz et al. is composed of multiple cantilever beams with different natural frequencies connected to a common base. By properly selecting the length and end mass of each cantilever beam, the device can be made to resonate over a wide frequency range. Marinkovic et al. also proposed a broadband piezoelectric energy recovery structure. However, both such structures significantly increase the size and cost of the device, which is not conducive to the miniaturization of the structure.

For these traditional piezoelectric energy recovery devices, to meet the low-frequency and wide-band requirements of environmental vibration energy recovery, it is necessary to increase the size and cost of the structure, which is difficult to apply to self-powered microsystems. What's more: These traditional piezoelectric energy recovery devices only work on vibrations in one direction, and don't have any electrical energy output for vibrations in other directions.

Phononic crystal is a new type of functional material with periodic structure, which has attracted great attention at home and abroad due to its good vibration and filtering properties. Phononic crystals can use the basic characteristics of waves (such as scattering and interference) and the local resonance characteristics of structures to form complete forbidden bands in certain frequency bands, preventing waves in these frequency bands from propagating in all directions in the structure. Therefore, phononic crystals are divided into two types: Bragg scattering phononic crystals and local resonance phononic crystals. For Bragg scattering phononic crystals, a high-Q resonant cavity or waveguide can be formed in the structure by properly introducing point defects or line defects. This characteristic makes it suitable for various devices and devices potential advantages.

In the past two years, the use of phononic crystals to recover environmental vibration energy has also attracted people's attention and research. But there are three big disadvantages: first, the structure is huge. If the resonant frequency of such a structure is to reach the low frequency stage of 50-250 Hz, one cycle of the structure needs to reach more than 0.7 meters, which is far from practical application; Single frequency, for the determined phononic crystal structure, the introduced defects can only resonate at a single frequency to form a resonant cavity; the third is the design difficulty, for resonance at one frequency, it is necessary to design a piezoelectric sheet with the same resonant frequency match it. For the multifunctional energy recovery device, the cantilever beam structure is still used, and its resonance frequency is difficult to lower to a low frequency due to structural limitations.

Liu Zhengyou first proposed the concept of local resonance phononic crystals in Science in 2000, and obtained a low-frequency band gap by using a smaller-sized structure. They wrapped lead balls in silicon rubber and arranged them in an epoxy resin matrix according to a simple cubic lattice, and carried out corresponding experiments. Both theory and experiments have confirmed that this structure with a unit characteristic length of 2 cm has a low-frequency band gap of about 400 Hz, which is two orders of magnitude lower than the first band gap frequency of the Bragg scattering phononic crystal of the same size. The biggest advantage of this structure is its low-frequency characteristics, but it is still far from practical application. The disadvantage of this device is that the piezoelectric material is difficult to implant into the soft rubber coating. Even if the new piezoelectric material is used as the coating, the efficiency of energy recovery is very low due to the limitation of the vibration amount in the solid.

To sum up, for the recovery of low-frequency vibration energy distributed in the 50-250Hz frequency band in the environment, the existing recovery devices either cannot meet the low-frequency requirements of environmental vibration energy recovery; or can meet the low-frequency requirements but have a large structure that is not conducive to the device or the device is only effective for a single frequency or a narrow frequency band; or it does not have a multi-directional recovery function; or there is a certain degree of difficulty in design, or the recovery efficiency is low.

Contents of the invention

The problem solved by the present invention is to provide a low-frequency multi-directional vibration energy recovery device. Energy recovery from low-frequency vibrations in a microstructure.

The present invention is achieved through the following technical solutions:

A low-frequency multi-directional vibration energy recovery device, including a mass block and an outer frame, the mass block is located in the outer frame, the mass block is connected to the outer frame through a folded elastic beam, and a piezoelectric sheet is arranged on the folded elastic beam; the mass block Folding elastic beams with the same folding method are arranged on all sides, and the folding method of the folding elastic beams is to fold layer by layer from outside to inside, and the folding length decreases layer by layer.

Both the mass block and the outer frame are square, the mass block is located in the center of the outer frame, each side of the mass block is connected to one side of the outer frame through a folded elastic beam, and the folded elastic beam is folded layer by layer from outside to inside Conical.

The effective stiffness of the folded elastic beam is adjusted by the thickness and folding times of the folded elastic beam; the resonance frequency and resonance bandgap of the energy recovery device are adjusted by the material of the mass block and the folded elastic beam.

The piezoelectric sheet is a piezoelectric ceramic sheet, which is pasted on the surface of the folded elastic beam where the strain is the largest.

Both the height of the mass block and the height of the folded elastic beam can be adjusted.

The piezoelectric sheet is pasted on the horizontal surface and the vertical surface of the folded elastic beam.

The outer frame includes a plurality of mass blocks, and a mass block is connected to a folded elastic beam to form a unit, and each mass block is located at the center of a unit, and the folded elastic beams of all units are folded in the same way; adjacent The units are connected in series through folded elastic beams, and the folded elastic beams adjacent to the outer frame are connected with the outer frame.

The masses of the plurality of mass blocks are the same or different, and the thickness and width of the folded elastic beams are the same or different.

There are four or more mass blocks.

Compared with the prior art, the present invention has the following beneficial technical effects:

The low-frequency multi-directional vibration energy recovery device provided by the present invention firstly solves the low-frequency multi-directional problem through the folding design of the mass block and the folded elastic beam. According to the localization effect of the local resonance structure, when the vibration propagates in the structure in the form of waves, due to the coupling effect of the resonance unit and the matrix traveling wave, the vibration energy is continuously confined by the resonance unit, and the potential energy and mass of the elastic layer The kinetic energy of the blocks is transformed into each other. Implanting the piezoelectric material into the elastic layer with large deformation can continuously convert the energy confined in the resonant structure of the unit into electrical energy output. Moreover, this design has two advantages: first, the effective stiffness of the folded elastic beam can be effectively adjusted through the thickness of the beam and the number of folds; second, the structure of the folded elastic beam is convenient for the attachment and placement of piezoelectric materials. The sheet is attached to the surface of the elastic beam where the strain is the largest, which solves the problem that the cladding layer of the traditional local resonance structure is difficult to implant piezoelectric materials.

Further, through the design of the mass block and the height of the folding elastic beam, the omni-directional problem is solved, and the piezoelectric sheet should be attached to the horizontal surface and the vertical surface of the elastic folding beam, no matter the vibration is incident from any angle, the elastic folding Beams will be deformed, and devices will output electrical energy.

Furthermore, the problem of broadband is solved by connecting multiple units in series. Specifically, four mass blocks can be placed in the middle of a square frame four times the original size, and a mass block and the folded elastic beam connected to it form a resonance unit, each mass is located at the center of a resonant unit. When the materials and structural dimensions of the four resonance units are the same, the energy recovery device with four-core fractal structure has more than 30 resonance frequencies in the range below 250Hz, and the lowest resonance frequency reaches 12Hz. . This greatly improves the low-frequency and broadband characteristics of the energy recovery device. If each unit adopts mass blocks of different masses, elastic beams of different widths or folding times, the energy recovery device will have more resonance frequencies in the low frequency range.

Based on the above design, the present invention has the following technical effects:

More than 30 resonant frequencies are located in the low-frequency range below 250Hz, and the lowest resonant frequency reaches 12Hz, which meets the requirements of broadband;

It has more than 30 resonant frequencies below 250Hz, has broadband characteristics, and has high recovery efficiency;

The side length of the unit structure of the device can be less than 5cm, meeting the miniaturization requirements of the structure;

The two-dimensional structure has omni-directional recovery function in two-dimensional space, and the three-dimensional structure has omni-directional recovery function in three-dimensional space, which meets the multi-directional requirements of vibration in the environment;

The design is simple, easy to process and manufacture.

According to the above characteristics, it can be applied to the recovery of low-frequency vibration energy in various large mechanical bases or vibration components, automobile engines, mixers, washing machines and various microstructures. It can provide power for various portable devices, wireless sensors and MEMS.

Description of drawings

Fig. 1 is a two-dimensional structural schematic diagram of an energy recovery device; wherein, 1 is a mass block, 2 is an elastic folding beam, and 3 is an outer frame;

Figure 2 is a diagram of the energy band structure of the resonant frequency in each two-dimensional direction; where, the ΓX, ΓY, and ΓM directions are the horizontal, vertical, and diagonal directions along the structure; the a and b energy bands in the figure are two at 55 Hz A resonant flat band; c band is the 119Hz resonant band; d is the 222Hz resonant band; e, f are the 225Hz resonant band; g is the 230Hz resonant band.

Fig. 3 is a schematic diagram of a three-dimensional structure of an energy recovery device; wherein, 1 is a mass block, 2 is an elastic folding beam, and 3 is an outer frame;

Figure 4 is a schematic diagram of the multi-unit series structure of the energy recovery device; please adjust the reference number 1 in the drawings to be a quality block, 2 to be an elastic folding beam, and 3 to be an outer frame;

Fig. 5 is the energy band structure diagram of the resonant frequency of the energy recovery device in various directions; the directions of ΓX, ΓY and ΓM are the horizontal, vertical and diagonal directions along the structure.

Detailed ways

The present invention will be further described in detail below in conjunction with specific embodiments and drawings, which are explanations of the present invention rather than limitations.

The low-frequency multi-directional vibration energy recovery device provided is firstly a low-frequency multi-directional multi-resonance solution:

According to the local resonance mechanism, under the excitation of external elastic waves, the resonant unit resonates and interacts with the low-frequency traveling waves in the matrix, thereby inhibiting its propagation and resulting in the generation of a band gap. The position and width of the bandgap can be adjusted by the structure of the phononic crystal (such as triangular, tetragonal, etc.), size (such as lattice constant), composition (such as two-component, three-component), material and filling rate, and It has nothing to do with the arrangement of the resonant units. Liu Zhengyou and others analyzed the displacement distribution of the original cell of the local resonant phononic crystal at the resonant frequency, and pointed out that: at the lower resonant frequency, the core ball vibrates with a larger amplitude, driving the cladding layer to move; Resonant frequency, the vibration is confined in the cladding layer, and the displacement of the core ball is very small. In both cases, the place of greatest deformation is in the cladding. Such a local resonance structure can be simplified as a negative effective mass system. The core ball is equivalent to the mass m, the cladding layer provides elasticity K (hereinafter referred to as the elastic layer), and the matrix is equivalent to the external mass M. Regardless of whether the frequency of the external excitation is in the bandgap, they will move in phase or in antiphase. As long as there is relative motion between M and m, the spring K connecting them will deform and store and release elastic potential energy continuously. When the frequency of the external excitation is near the low-frequency resonance frequency, the mass vibrates with the maximum amplitude, and the spring will produce the maximum deformation. The kinetic energy of the mass block and the elastic potential energy of the spring are mutually transformed, and the energy cannot be transmitted forward, which is the localization effect of the local resonance structure on the energy. The more resonance frequencies the structure has in the low frequency range and the higher the quality factor, the stronger the localization effect.

According to the localization effect of the local resonance structure, when the vibration propagates in the structure in the form of waves, due to the coupling effect of the resonance unit and the matrix traveling wave, the vibration energy is continuously confined by the resonance unit, and the potential energy and mass of the elastic layer The kinetic energy of the blocks is transformed into each other. According to the displacement distribution in the local resonance structure, as long as the piezoelectric material is implanted into the elastic layer with large deformation, the energy confined in the unit resonance structure can be continuously converted into electrical energy output.

On the basis of the traditional local resonance structure, the present invention uses four groups of folded elastic beams as elastic elements to design an energy recovery structure, as shown in Figure 1:

A low-frequency multi-directional vibration energy recovery device, comprising a mass block 1 and an outer frame 3, the mass block 1 is located at the center of the outer frame 3, the mass block 1 is connected to the outer frame 3 through a folded elastic beam 2, and the folded elastic beam 2 is provided with There are piezoelectric sheets; the four sides of the mass block 1 are provided with folding elastic beams 2 in the same folding manner, and the folding elastic beams 2 are folded layer by layer from outside to inside and the folding length decreases layer by layer.

Specifically, the mass block 1 and the outer frame 3 are square, and each side of the mass block 1 is connected to one side of the outer frame 3 through a folded elastic beam 2, and the folded elastic beam 2 is folded layer by layer from outside to inside Conical.

This design has three advantages: First, the folded elastic beam structure facilitates the attachment and placement of piezoelectric materials, and the piezoelectric sheet (piezoelectric ceramic sheet) is attached to the surface of the elastic beam where the strain is the largest, which solves the problem of traditional local resonance. The cladding layer of the structure is difficult to implant piezoelectric materials; second, the vibration energy is distributed on the folded elastic beams with a smaller area, which is more conducive to centralized recovery; third, the effective stiffness of the folded elastic beams can be improved by the folded elastic beams The thickness and the number of folds can be effectively adjusted, and the resonance frequency of the structure can be effectively reduced by changing the structural parameters of the folded elastic beam.

The resonant frequency of the energy recovery device and the resonant bandgap of the structure can be adjusted by changing the material and side length of the central mass block, and changing the material, thickness and folding times of the folded elastic beam. Specifically provide the following designs:

The mass block is square, and the material is metallic lead (lead: ρ _lead = 11600kg/m ³ , E _lead = 40.8GPa, μ _lead = 14.9GPa);

The material of the folded elastic beam is plexiglass (ρ _plexiglass =1142kg/m ³ , E _plexiglass =2.0GPa, μ _plexiglass =0.72GPa); the structural dimensions are: the side length of the folded elastic beam a=22mm, the mass block The side length b=12mm; the thickness of the folded elastic beam h=0.3mm, and the equal interval t=1mm after the elastic beam is folded three times.

The resonant frequency of this energy recovery device is calculated when the vibration is input from all directions. The structure is shown in Figure 2 (also the energy band structure of the phononic crystal). From the energy band structure in the figure, It can be seen that the energy recovery device has lower resonance frequency and band gap in all directions. In the ΓM direction (that is, the diagonal incidence along the structure), there are 7 relatively flat resonance bands at 55Hz (two modes), 119Hz, 222Hz (two modes), 225Hz and 230Hz respectively, and they are all located at In the range of 50~250Hz. In the ΓX and ΓY directions (that is, incident perpendicular to the boundary of the structure), the resonance frequencies of the two modes are basically consistent with the ΓM direction, except that the resonance frequencies of the two modes change greatly with the change of the incident wavelength. For the XM and YM regions in the figure, as the incident direction of the wave is gradually deflected from the ΓX or ΓY direction to the ΓM direction, the resonance frequency of the energy recovery device remains basically unchanged. This shows that the energy recovery device has the characteristics of low frequency and multi-resonance in two dimensions and all directions, and each resonance frequency is within the range of 50-250 Hz.

The piezoelectric ceramic sheet is pasted on the side of each elastic folding beam where the strain is the largest. When the structure resonates at the above-mentioned resonance frequencies, the elastic beam will drive the piezoelectric sheet to undergo a large deformation, thereby outputting more electric energy.

On the basis of the above, provide omni-directional solutions:

With the above structure, the device is effective regardless of the direction from which the vibration propagates to the place where the energy recovery device is installed, within the two-dimensional plane. But in three dimensions, if vibrations are input into the structure perpendicular to the plane of the paper, the structure will not be able to output electricity. Therefore, a three-dimensional omnidirectional energy recovery device is designed, as shown in Figure 3: on the basis of the two-dimensional design, the design of the height of the mass block 1 and the folded elastic beam 2 is added. At this time, piezoelectric sheets should be pasted on both the horizontal surface and the vertical surface of the elastic folded beam 2, no matter the vibration is incident from any angle, the elastic folded beam 2 will be deformed, and the device can output electric energy.

Going a step further, providing broadband solutions:

As shown in Figure 4, on the basis of the two-dimensional structure, four mass blocks 1 can be placed in the middle of a square outer frame 3 four times the original size, and a folded elastic beam connected with a mass block 1 2 form a unit, each mass block 1 is located in the center of a unit, and the folded elastic beams 2 of all units are folded in the same way; adjacent units are connected in series through the folded elastic beams 2, and the elastic folds of the adjacent mass blocks are connected The beam 2 is no longer connected to the outer frame, and other elastic folded beams 2 are connected to the outer frame 3, so that multiple energy blocks 1 constitute multiple resonance units.

In order to make the energy recovery device have a denser resonance frequency in the range of 50-250 Hz, a four-core fractal structure is specifically adopted, and its structural unit is shown in Figure 4. Each mass resonance unit has its own resonance frequency, and every two mass blocks can form a resonance unit to increase a low-frequency resonance frequency, and the same is true for every three or four mass blocks. When the materials and structural dimensions of the four resonance units are the same, the resonance frequency of the energy recovery device is calculated in all directions, as shown in Figure 5. It can be seen from the figure that this four-core fractal structure operates at 250Hz In the following low-frequency range, there are many resonance flat bands in all directions (corresponding to the resonance frequency of the structure in this direction). These resonance frequencies only change in the ΓX and ΓY directions, and basically remain unchanged in other directions.

The four-core fractal structure energy recovery device has more than 30 resonance frequencies in the range below 250Hz, and the lowest resonance frequency reaches 12Hz. This greatly improves the low-frequency and broadband characteristics of the energy recovery device. If each unit uses mass blocks of different masses, elastic beams of different widths or folding times, the energy recovery device will have more resonance frequencies in the low frequency range, thereby realizing the broadband function of the energy recovery device.

According to the resonance frequencies of the energy recovery device shown in Figure 5 in various directions, it can be seen that the technical effects achieved by the present invention are:

① More than 30 resonant frequencies are located in the low frequency range below 250Hz, and the lowest resonant frequency reaches 12Hz, which meets the requirements;

②It has more than 30 resonant frequencies below 250Hz, has broadband characteristics, and has high recovery efficiency;

③The side length of the unit structure of the device is less than 5cm, meeting the miniaturization requirements of the structure;

④The two-dimensional structure has omni-directional recovery function in two-dimensional space, and the three-dimensional structure has omni-directional recovery function in three-dimensional space, which meets the multi-directional requirements of vibration in the environment;

⑤The design is simple, easy to process and manufacture.

According to the above-mentioned characteristics of the energy recovery device, it can be applied to low-frequency vibration energy recovery in various large mechanical bases or vibrating elements, automobile engines, mixers, washing machines and various microstructures. It can provide power for various portable devices, wireless sensors and MEMS.

Claims (9)

1. multi-direction vibrational energy retracting device of low frequency; It is characterized in that; Comprise mass (1) and outside framework (3); Mass (1) is positioned within the outside framework (3), and mass (1) is connected with outside framework (3) through folding spring beam (2), and folding spring beam (2) is provided with piezoelectric patches; Be equipped with the identical folding spring beam (2) of folding mode around the mass (1), the folding mode of folding spring beam (2) is that ecto-entad successively folds and folded length successively successively decreases.

2. the multi-direction vibrational energy retracting device of low frequency as claimed in claim 1; It is characterized in that; Described mass (1) and outside framework (3) are square; Mass (1) is positioned at the center of outside framework (3), on each limit of mass (1) all through a folding spring beam (2) with outside framework (3) one side be connected, folding spring beam (2) ecto-entad is successively folding tapered.

3. the multi-direction vibrational energy retracting device of low frequency as claimed in claim 1 is characterized in that, the effective rigidity of described folding spring beam (3) is regulated by the thickness and the folding times of folding spring beam; The resonance frequency of energy recycle device and LOCALLY RESONANT ELASTIC WAVE are regulated by the material of mass (1) and the material of folding spring beam (3).

4. the multi-direction vibrational energy retracting device of low frequency as claimed in claim 1 is characterized in that described piezoelectric patches is a piezoelectric ceramic piece, is attached to the surface of folding spring beam (2) strain maximum.

5. the multi-direction vibrational energy retracting device of low frequency as claimed in claim 1 is characterized in that, the height of the height of described mass (1) and folding spring beam (2) is all adjustable.

6. the multi-direction vibrational energy retracting device of low frequency as claimed in claim 1 is characterized in that described piezoelectric patches is attached on the horizontal surface and vertical surface of folding spring beam (2).

7. the multi-direction vibrational energy retracting device of low frequency as claimed in claim 1; It is characterized in that; Comprise a plurality of masses (1) in the outside framework (3); The coupled folding spring beam (2) that connects of a mass (1) constitutes a unit, and each mass (1) is positioned at the center of a unit, and the folding mode of the folding spring beam (2) of all unit is identical; Adjacent unit interconnects through folding spring beam and connects, and the folding spring beam (2) adjacent with outside framework (3) is connected with outside framework (3).

8. the multi-direction vibrational energy retracting device of low frequency as claimed in claim 7 is characterized in that, described a plurality of masses (1) identical in quality or different, and thickness, the width of folding spring beam (2) are identical or different.

9. the multi-direction vibrational energy retracting device of low frequency as claimed in claim 7 is characterized in that described mass (1) is four.

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