CN101908836A - Miniature Vibrating Wind Turbine with Mass - Google Patents

Abstract

The miniature vibrating wind power generator with mass block proposed by the present invention is made of substrate, vibrating beam/membrane and mass block supported by the vibrating beam/membrane, wherein vibrating beam/membrane and mass block constitute the vibration of generator In part, the vibrating beam/membrane contains a piezoelectric layer with electrodes on both its upper and lower surfaces. The vibrating beam/membrane can be a cantilever beam, a beam fixed at both ends, a plurality of beams fixed at one end or a membrane fixed at the periphery. The generator uses the microstructure vibration caused by the wind load to convert the environmental wind energy into the vibration energy of the microstructure, and further uses the piezoelectric effect to convert the vibration energy of the microstructure into electrical energy to realize the power supply to the load or the energy storage. The introduced mass block reduces the natural frequency of the vibrating part of the generator and reduces the critical wind speed for normal application of the generator. The generator is convenient to adopt silicon micromachining technology for batch processing, has low cost, and is especially suitable for supplying power to wireless sensor network nodes and the like.

Description

Miniature Vibrating Wind Turbine with Mass

technical field

The invention belongs to the field of micro-electro-mechanical systems (MEMS), in particular to MEMS micro-energy (Power MEMS) technology for converting wind energy into electric energy.

Background technique

The development of integrated circuits and MEMS technology has made it possible to construct wireless sensor networks with tens of thousands of nodes. Due to the shortcomings of traditional batteries, such as large size, limited life, and need to be replaced, their application in wireless sensor networks is limited. limit. The micro-energy that converts environmental energy (such as vibration energy, thermal energy, solar energy, etc.) One of the most effective ways to solve energy problems. Based on the wind-induced vibration mechanism, the MEMS micro-vibration wind turbine uses the microstructure vibration caused by wind load to convert the environmental wind energy into the microstructure vibration energy, and further uses the electromagnetic effect, piezoelectric effect or electrostatic effect to convert the microstructure vibration energy into electrical energy. Realize the power supply to the load or energy storage, which has many advantages such as simple structure and no rotating parts, and has broad application prospects in wireless sensor networks such as environmental monitoring and building health monitoring.

The electric energy output by the micro-vibrating wind turbine needs to be rectified and stored by the power management circuit before it can supply power to the load. The power management circuit itself also needs to consume part of the electric energy. When the output power of the generator is too low, the generated Most of the electric energy is consumed by the power management circuit, which is difficult to be utilized by the application object. The output power of the micro-vibrating wind turbine is determined by the amplitude of the vibration part of the generator, and the amplitude directly depends on the size of the ambient wind speed. According to the characteristics of wind load, the wind load imposed by the wind on the structure includes two parts: static wind load and dynamic wind load. The frequency of dynamic wind load increases with the increase of wind speed. When the ambient wind speed reaches a certain value (critical wind speed) When the frequency of the dynamic wind load is close to or reaches the natural frequency of the vibrating part of the micro-vibrating wind turbine, the vibrating part of the generator will vibrate strongly, making its amplitude above a certain value (critical amplitude), and the generator can be used normally (that is, supplying normal power to the application object). The invention patent "Mini Wind Power Generator Based on Wind-Induced Vibration Mechanism and Piezoelectric Effect" (application number: 200910104106.5) applied by Chongqing University proposes a micro wind power generator structure based on a vibrating beam/membrane structure with a piezoelectric layer, but Since the generator structure does not contain mass and has a high natural frequency, it can only be used normally in environments with high wind speeds (such as on the surface of aircraft, high-speed trains, etc.), which greatly limits its application range. Wireless sensor networks have broad application prospects in the fields of large-scale building health monitoring, homeland security monitoring, and atmospheric monitoring. In these application environments, the wind speed is not large (below 15m/s) most of the time. Mechanism micro-wind generators are used in these medium and low wind speed environments, and the wind speed at which the generators work normally must be reduced. The present invention proposes a new structure of micro-wind generators based on wind-induced vibration mechanisms that can work normally at lower wind speeds.

Contents of the invention

The purpose of the present invention is to propose a micro vibratory wind generator structure to reduce the critical wind speed of the normal application of the micro vibratory wind generator.

In order to achieve the above-mentioned purpose of the invention, the present invention takes the following technical solutions:

The miniature vibrating wind power generator with mass blocks adds one or more mass blocks to the vibrating part of the micro vibrating wind power generator. The generator is composed of a substrate, a vibrating beam/membrane and a mass supported by the vibrating beam/membrane, wherein the vibrating beam/membrane and the mass constitute the vibrating part of the generator. The vibrating beam/membrane of the miniature vibrating wind power generator with a mass can be a cantilever beam, a beam fixed at both ends, a plurality of beams fixed at one end or a membrane fixed at the periphery. The mass block is fixed on the movable part of the vibrating beam/membrane with a large amplitude (such as the free end of the cantilever beam, near the center of the beam fixed at both ends, near the interconnection point of multiple single-end fixed beams, or the boundary fixed support membrane Near the center of the upper surface or the small surface, or both the upper surface and the small surface of the movable part. The vibrating beam/membrane includes a piezoelectric layer, and electrodes are arranged on the upper and lower surfaces of the piezoelectric layer. The generator uses the vibration of the vibrating beam/membrane caused by the wind load to convert the ambient wind energy into the vibration energy of the vibrating beam/membrane. The vibration of the vibrating beam/membrane will cause the alternating change of the piezoelectric layer stress on it. Due to the piezoelectric effect , a potential difference will be generated on the upper and lower surfaces of the piezoelectric layer, and the power supply to the load or energy storage can be realized by using the potential difference.

The wind generator adds a mass block to the movable part of the vibrating beam/membrane, which reduces the natural frequency of the vibrating part of the generator. The reduction of the natural frequency makes the vibrating part of the generator vibrate strongly under the action of lower wind speed. Therefore, the introduction of the mass block will effectively reduce the critical wind speed of the normal application of the micro-wind generator based on the wind-induced vibration mechanism.

The present invention has the following characteristics:

1. The mass block introduced in the present invention will reduce the natural vibration frequency of the vibrating part of the micro vibrating wind power generator, so that the vibrating part of the generator will vibrate strongly under the action of lower wind speed.

2. The vibrating beam/membrane of the miniature vibrating wind power generator with a mass block proposed by the present invention can be a cantilever beam, a beam fixed at both ends, a plurality of beams fixed at one end or a membrane fixed at the periphery.

3, the miniature vibrating type wind power generator with mass block that the present invention proposes, its mass block is positioned at the larger movable part of the amplitude of vibration beam/membrane (as the free end of cantilever beam, the vicinity of the center of the fixed support beam at both ends, Near the connection point of multiple single-end fixed-supported beams, or near the center of the boundary fixed-supported membrane) on the upper or lower surface, or simultaneously fixed on the upper and lower surfaces of the movable part of the vibrating beam/membrane with a large amplitude.

4. The vibrating beam/membrane of the miniature vibrating wind power generator with mass proposed by the present invention includes a piezoelectric layer, and electrodes are arranged on the upper and lower surfaces of the piezoelectric layer.

5. The structure of the above miniature vibrating wind power generator with mass block is simple, it is convenient to adopt silicon micromachining technology for batch processing, and the cost is low.

Description of drawings

Figure 1 is a schematic diagram of silicon dioxide grown on an SOI substrate

Figure 2 is a schematic diagram of etching single crystal silicon on an SOI substrate

Figure 3 is a schematic diagram of thermally oxidized silica

Figure 4 is a schematic diagram of a metal electrode prepared by a lift-off process

Figure 5 is a schematic diagram of the prepared piezoelectric film

Figure 6 is a schematic diagram of a metal electrode prepared by a lift-off process

Figure 7 is a schematic diagram of the photoresist coated on the back of the SOI substrate

Fig. 8 is a schematic diagram of a micro vibrating wind generator with a mass block on one side after release

Fig. 9 is a schematic diagram of a released single-sided micro-generator containing multiple piezoelectric layers with mass blocks

Figure 10 is a schematic diagram of a typical structure of a micro-vibrating wind turbine with mass blocks on both the front and back sides

Figure 11 is a schematic diagram of a typical structure of a micro-vibrating wind turbine with mass blocks on one side

Figure 12 is a schematic diagram of the typical structure of a miniature vibrating wind turbine with mass blocks on both the front and back sides

Figure 13 is a schematic diagram of a typical structure of a micro vibrating wind turbine with a mass block on one side

Figure 14 is a schematic diagram of a typical structure of a miniature vibrating wind turbine with mass blocks on both the front and back sides

Figure 15 is a six schematic diagram of a typical structure of a miniature vibrating wind turbine with a mass block on one side

Detailed ways

The present invention will be further described below by taking a micro-vibrating wind power generator based on the principle of piezoelectric conversion as an example, combined with theoretical analysis, examples and experimental results.

The vibration part of the micro wind generator based on wind-induced vibration can be simplified as a single-degree-of-freedom system composed of a spring-mass block. According to the vibration theory, the natural frequency of the generator is

$\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; K</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the above formula, K is the equivalent stiffness, which is determined by the material, thickness, length, width and boundary conditions of the vibrating beam/membrane. In the above formula, m is the equivalent mass: when there is no mass block, m is mainly determined by the mass of the vibrating beam/membrane and the mode shape corresponding to the natural frequency. Since the vibrating beam/membrane is small in size, m is very small, and the corresponding natural frequency The frequency is very high; when the mass block is added at the position where the vibrating beam/membrane has a large amplitude (such as the free end of the cantilever beam, near the midpoint of the beam fixed at both ends, etc.), since the mass block is large in size, its mass is also large, at this time m Compared with the situation without a mass block, it will be increased by tens to tens of thousands of times, so the introduction of this mass block will effectively reduce the natural frequency of the generator.

According to the wind-induced vibration mechanism of the structure, when the frequency of the dynamic wind load is close to or reaches the natural frequency of the micro wind turbine, the vibrating beam/membrane structure and mass block of the generator will vibrate strongly. The main part of dynamic wind load is caused by vortex shedding, and the frequency of vortex shedding is

为斯脱罗哈数(Strouhal数)，D是结构垂直于来流方向平面上的特征尺寸，U是风速。由上式可见，漩涡脱落的频率随着风速U的提高而提高。由于当旋涡脱落的频率接近或达到微型风力发电机振动部分的固有频率时，发电机的复合梁/膜和质量块才产生强烈振动，因此在迎风尺寸不变的情况下，振动部分的固有频率更高的发电机只有在更高的风速下才能产生强烈的振动，才能正常应用。本发明引入的质量块可以有效降低基于风致振动的微型风力发电机的固有频率，所以可以有效降低发电机正常工作的风速。In the formula

is the Strouhal number, D is the characteristic dimension of the structure on the plane perpendicular to the incoming flow direction, and U is the wind speed. It can be seen from the above formula that the frequency of vortex shedding increases with the increase of wind speed U. When the frequency of vortex shedding is close to or reaches the natural frequency of the vibrating part of the micro wind turbine, the composite beam/membrane and mass block of the generator will vibrate strongly. Taller generators can only be used normally if they generate strong vibrations at higher wind speeds. The mass block introduced in the invention can effectively reduce the natural frequency of the micro-wind generator based on wind-induced vibration, so it can effectively reduce the wind speed at which the generator works normally.

The miniature vibrating wind power generator with a mass block is composed of a substrate, a vibrating beam/membrane and a mass block supported by the vibrating beam/membrane, wherein the vibrating beam/membrane and the mass block constitute the vibrating part of the generator. Based on the micro-machining process, it is easy to manufacture a micro-vibrating wind-driven generator with a mass block. The micro-vibrating wind power generator with a mass block on one side can use monocrystalline silicon as the mass block, and a beam/membrane containing a piezoelectric layer as the vibrating beam/membrane. The piezoelectric layer on the vibrating beam/membrane is also realized by the generator. The structure of electromechanical conversion. The following is a typical process flow:

1. Select a double-sided polished SOI substrate as the substrate. The SOI substrate consists of a first monocrystalline silicon layer 1 with a thickness of about 450-500 μm, a first _SiO layer ₂ with a thickness of about 1 μm, and a thickness of about 1-500 μm. The second single crystal silicon layer 3 is composed of 20 μm, and the second _{SiO layer} of about 200nm is grown by thermal oxidation, coated with photoresist, photolithography, using the photoresist as a mask, and using BHF to etch the second SiO2 _layer O ₂ layer, remove photoresist, form _{SiO 2} layer pattern 4, as shown in Figure 1;

2. Using the _{SiO 2} layer pattern 4 as a mask, use inductively coupled plasma etching or KOH to etch the second single crystal silicon layer 3 that is not protected by the _{SiO 2} layer, and remove the second _{SiO 2} layer pattern 4 , to obtain the structure shown in Figure 2;

3. A third _SiO layer 5 of about 200 nm is thermally oxidized and grown on the second _single crystal silicon layer 3, as shown in FIG. 3 ;

4. A lower metal electrode (Ti/Pt) 6 of about 150 nm is grown on _the third _SiO layer 5 by stripping and sputtering, as shown in FIG. 4 ;

5. A lead zirconate titanate (PZT) piezoelectric film with a thickness of 1-10 μm is grown on the lower metal electrode (Ti/Pt) 6 by the sol-gel method, and the PZT film is patterned by reactive ion etching (RIE) , forming a piezoelectric layer pattern 7, as shown in Figure 5;

6. An upper metal electrode (Ti/Pt) 8 of about 150 nm is grown on the piezoelectric layer pattern 7 by the lift-off method and the sputtering method, as shown in FIG. 6 ;

7. Coating photoresist on the back side of the SOI substrate, photolithography, forming photoresist pattern 9, as shown in Figure 7;

8. Using photoresist as a mask, use inductively coupled plasma etching to etch the first single crystal silicon layer 1 from the back side of the SOI substrate, stop etching when reaching the first _SiO2 layer 2, and remove _the photoresist , use HF solution to remove _{SiO 2} , release the structure, that is, obtain the vibrating beam/membrane and single crystal silicon mass block containing the piezoelectric layer, as shown in Fig. 8 .

The vibrating beam/membrane of the micro-generator shown in Figure 8 only contains a PZT piezoelectric layer, and the piezoelectric layer can also use other piezoelectric materials, such as PVDF, ZnO, AlN, etc., and the growth of the piezoelectric layer can also be used Sputtering, MOCVD and other methods. In order to adjust the internal impedance of the micro-generator to match the impedance of the load, the vibrating beam/membrane of the micro-generator can use a beam/membrane containing multiple piezoelectric layers (as shown in Figure 9). The above miniature vibrating wind generator with mass blocks utilizes the piezoelectric effect of the piezoelectric layer on the beam/membrane to realize electromechanical conversion (that is, convert the vibration energy of the microstructure into electrical energy).

The micro-vibrating wind turbine with mass blocks can be realized in various structural forms, and the following are some typical structural forms:

As shown in FIG. 10 , a cantilever beam 11 fixed on a substrate 10 is used as a vibrating beam, and there are mass blocks 12 on the upper and lower surfaces of the free end of the cantilever beam.

As shown in FIG. 11 , the difference from FIG. 9 is that there is only a mass block 12 on one surface of the free end of the cantilever beam, such as only a mass block 12 on the lower surface.

As shown in Figure 12, the beam 11 fixed at both ends fixed on the substrate 10 is used as the vibrating beam, and there are mass blocks 12 on the upper and lower surfaces of the middle position of the beam at both ends, by changing the mass block The location can optimize the performance of the generator.

As shown in FIG. 13 , the difference from FIG. 11 is that there is a mass block 12 on the middle surface of the beam fixed at both ends, such as only the mass block 12 on the lower surface.

As shown in Figure 14, a plurality of beams 11 are used as vibrating beams, one end of these vibrating beams is fixed on the substrate 10, and the other ends are connected together. The location of the blocks can be optimized for generator performance.

As shown in FIG. 15 , the difference from FIG. 13 is that there is a mass block 12 only on one surface at a specific position of the vibrating beam, such as only a mass block 12 on the lower surface. The beam/membrane of the miniature vibrating wind power generator with a mass block can also be a circular, rectangular, polygonal or other shaped vibrating membrane with a part of the boundary fixed on the substrate. There is a mass, or there is a mass only on the upper or lower surface of the diaphragm.

The miniature vibrating wind power generator shown in FIG. 16 is fixed with a mass block on the upper surface of the circular membrane 11 whose periphery is fixed to the substrate 10 .

In order to further verify the effectiveness of wind-induced vibration-based micro-wind turbines with mass blocks in reducing the wind speed in normal application of micro-vibration wind turbines, experiments were carried out on the principle prototypes of micro-wind turbines without mass blocks and with mass blocks. Research. The prototype 1 of the typical structure 2 of the miniature vibrating wind power generator with a mass block on one side was produced by using the micro-assembly technology, as shown in Figure 11, and the prototype 2 of the generator structure without the mass block (the vibrating beam containing the piezoelectric layer was produced at the same time) The length of is the sum of the length of the vibrating beam and the length of the mass block of prototype 1). The upper and lower piezoelectric layers of the vibrating beam with a piezoelectric layer are PZT piezoelectric layers with a thickness of 139 μm. The polarization directions of the two piezoelectric layers are opposite. The intermediate metal is copper with a thickness of 102 μm. The piezoelectric composite beam The width is 6.4mm. The piezoelectric composite beam lengths of prototype 1 and prototype 2 are 19mm and 2.6mm respectively, and the mass block of prototype 1 is a tungsten block with a density of about 15000kg/m ³ , and its size is 7mm×6.02mm×5.08mm. Fix the two generator samples at the same position on the same aluminum sheet. Under the action of a wind speed of about 9m/s, the open circuit voltage of the micro vibrating wind turbine sample with a mass block is 2.2V. For 200kΩ and 300kΩ The maximum output power of the resistive load is 5.55μW and 5.58μW; the open circuit voltage of the micro vibrating wind turbine sample without mass is 0.733V, and the maximum output power of the resistive load of 200kΩ and 300kΩ is 1.18μW and 0.93μW respectively .

The above experiments show that the new structure proposed by the present invention can effectively reduce the normal working wind speed of the micro-wind generator based on the wind-induced vibration mechanism, and expand its application range.

Claims (3)

1. A miniature vibrating wind-driven generator with a mass block, which comprises a substrate and a vibrating beam/film, wherein the vibrating beam/film comprises a piezoelectric layer, and electrodes are provided on the upper and lower surfaces of the piezoelectric layer ; It is characterized in that: the generator also includes a mass block supported by the vibration beam/membrane, there is at least one mass block, and the mass block is fixed on the upper surface or the lower surface of the movable part of the vibration beam/membrane, Or be fixed on the upper and lower surfaces of the movable part of the vibrating beam/membrane at the same time. 2. the miniature vibrating type wind generator with mass block as claimed in claim 1, is characterized in that, described vibrating beam adopts cantilever beam, two-end fixed-support beam or many single-end fixed-support beams; A peripherally anchored membrane is used. 3. the miniature vibrating wind generator with mass block as claimed in claim 1 or 2, is characterized in that, described mass block is positioned at the upper surface or the lower surface of the larger movable part of the vibration beam/membrane, Or be fixed on the upper and lower surfaces of the movable part with larger amplitude of the vibrating beam/membrane at the same time; The movable part with a large amplitude refers to the free end of the cantilever beam, the vicinity of the center of the beam fixed at both ends, the vicinity of the connection point of multiple single-ended beams, or the center of the boundary fixed membrane.

Images