The problem of low vibration energy collection efficiency in the environment is the focus of the current piezoelectric power generation technology. In order to improve the collection efficiency of vibration energy in the environment, a key technology of piezoelectric power generation is studied, which can collect the vibration energy of multiple directions in the environment. Firstly, the mathematical model of piezoelectric cantilever beam is established by using the basic theory of piezoelectric power generation technology, and the vibration mechanics analysis of the piezoelectric cantilever beam is carried out. Then, the finite element simulation of the piezoelectric cantilever beam is carried out by using ANSYS, and the natural frequency is consistent with the ambient vibration/environment frequency; finally, multi-directional piezoelectric power generation device is made, and the theoretical analysis and experimental test are carried out. The experimental results show that the key technology of multidirectional vibration piezoelectric power generation can effectively improve the collection efficiency of vibration energy in the environment.
Micro-electromechanical systems have been widely used in field animal GPS tracking monitoring, embedded systems, health monitoring, national defense security application systems and environmental monitoring, etc. [
With the continuous development of energy harvesting technology, piezoelectric power generation technology has become the focus of research in the field of Micro-electromechanical (MEMS) power supply [
Through investigation, the piezoelectric power generation technology is based on direct piezoelectric effect, excluding the reverse piezoelectric effect [
In this paper, the multi-directional vibration piezoelectric power generation technology is a multi-directional vibration piezoelectric power generation device, the structure design is as follows: A multidirectional piezoelectric generator is composed of five identical piezoelectric cantilever structures with a mass block, a support body and a fixed base. Five identical piezoelectric cantilever beams are equally fixed on the support like a fan; the geometry model is shown in
The direction of vibration in the environment is changeable, and the direction selectivity of the unidirectional power generation device is stronger. In this paper, the key technology of multidirectional vibration piezoelectric power generation breaks the traditional one way of collecting vibration, the vibration energy in the environment is collected from multiple directions. When the vibration direction changes, the cantilever beam in the corresponding direction generates vibration to collect the vibration energy in the environment. Therefore, as long as the optimization device is able to produce resonance, the multi-directional vibration piezoelectric power generation key technology can achieve the highest efficiency.
The mathematical model of piezoelectric cantilever beam is established based on the power generation theory of piezoelectric power generation technology. In the mathematical modeling of the piezoelectric cantilever, one piezoelectric cantilever is selected as the research object.
When the piezoelectric cantilever generator structure is forced to vibrate, the
vibration mechanics and open circuit voltage analysis are carried out. The piezoelectric cantilever power structure can be used with spring damping system as shown in
In the above vibration model, k c a represents the equivalent stiffness of the piezoelectric cantilever, the equivalent damping is expressed by C c a , and the m c a is the lumped mass of the system. The relative displacement between mass and support is expressed by y c a , o u , Displacement of vibration source is expressed by y c a , i n . The theoretical model of piezoelectric cantilever beam is as follows [
m c a y ¨ c a , o u + C c a y ˙ c a , o u + k c a y c a , o u = − m c a y ¨ c a , i n (1)
The vibration is analyzed; the absolute displacement of mass is y c a , o u + y c a , i n , under the excitation of vibration source, the inertial force generated by mass block can be expressed as
F c a = m c a ( y ¨ c a , o u + y ¨ c a , i n ) (2)
In the process of vibration of piezoelectric devices, the device converts mechanical energy into electrical energy. In this process, the open circuit voltage generated by the upper piezoelectric plate of the piezoelectric cantilever power generation structure is
V c a , 1 { − 1 4 x 1 e 31 b p , d a l p , d a F c a ( h p , d a + h m , d a ) ( 2 l a d , d a − l p , d a ) [ 1 3 x 1 E p , d a b p , d a h p , d a ( h p , d a 2 + 3 4 h m , d a 2 + 3 2 h m , d a ) + 1 ] } [ 1 12 x 1 2 e 31 2 E p , d a b p , d a 3 l p , d a h p , d a ( h p , d a 2 + 3 4 h m , d a 2 + 3 2 h m , d a h p , d a ) ( h p , d a + h m , d a ) 2 + 1 2 x 1 e 31 2 b p , d a 2 l p , d a ( h p , d a + h m , d a ) 2 + ε 33 l p , d a b p , d a 1 h p , d a ] (3)
where: x 1 = E p , d a b p , d a ( 2 3 h m , d a 3 h p , d a + h m , d a h p , d a 2 ) + 1 12 E m , d a b m , d a h m , d a 3 ; b p , d a , h p , d a
The width and thickness of the elastic substrate, respectively; l m , d a , l m e , d a The
The width and thickness of the piezoelectric plate, respectively; b m , d a , h m , d a length of the elastic substrate, the distance from the free end of the piezoelectric cantilever beam to the mass center of the mass block; l a d , d a and l m , d a is the sum of l m e , d a ; ε 33 Dielectric constant of piezoelectric material; e 3 , 1 The intensity of electric field in piezoelectric layer on cantilever beam; E m , d a , E p , d a The elastic modulus of the elastic substrate and the piezoelectric ceramic plate, respectively.
Similarly, the open circuit voltage produced by the lower lamination of the cantilever beam in the electromechanical conversion process V c a , 3 = − V c a , 1 .
Finite element simulation software ANSYS multi-physics coupling analysis module can do a good simulation of piezoelectric coupling field, to achieve mechanical energy and electrical coupling analysis. In the analysis of piezoelectric ceramic plates by ANSYS, the influence of the size of the elastic substrate and the parameters of the mass block on the output voltage and frequency of the piezoelectric cantilever beam is optimized.
PZT (Lead zirconate Titanate) is used to make ultrasound transducers and other sensors and actuators, as well as high-value ceramic capacitors and FRAM chips. The PZT piezoelectric ceramics were used as the initial piezoelectric cantilever beam, its length, width and thickness were 30 mm, 15 mm and 0.2 mm, respectively. Beryllium bronze is used as material for metal elastic substrate. Its length, width and thickness are 45 mm, 15 mm and 0.2 mm, respectively. Using iron blocks (mass) of length, width and thickness of 12 mm, 15 mm and 5 mm, respectively. The finite element model of the piezoelectric cantilever beam is shown in
In order to obtain the relationship between the mass size parameter and the natural frequency of the piezoelectric cantilever, the thickness of the mass is set to 4 - 8 mm, and the other parameters are unchanged. Results as shown in
the one or two order natural frequency of the piezoelectric cantilever decreases with the increase of the thickness of the mass block, and the second order natural frequencies are below 100 Hz. Thus, the natural frequency of the piezoelectric cantilever can be easily adjusted by adjusting the size of the mass block.
In order to analyze the influence of the thickness of piezoelectric ceramic plates on the natural frequency and output voltage of piezoelectric cantilever, the thickness of piezoelectric ceramic is set to 0.1 - 0.8 mm, and the other parameters remain unchanged. The static force analysis and modal analysis of the piezoelectric cantilever beam are carried out at the free end (without mass) by applying the force of 0.3 N. The analysis results are shown in
The relation curves of synthesis
In order to analyze the effect of the metal elastic length on the natural frequency and output voltage of the piezoelectric cantilever, the length of the elastic substrate is set to 35 - 65 mm, and the other parameters remain unchanged. The static force analysis and modal analysis of the piezoelectric cantilever beam are carried out at the free end (without mass) by applying the force of 0.3 N. The analysis results are shown in
The analysis of the relation curve between synthesis
output voltage. Therefore, in the actual design, long elastic substrate should be chosen as far as possible but within the scope of the stress permit.
In order to analyze the influence of the thickness of the metal elastic substrate on the natural frequency and the output voltage of the piezoelectric cantilever, the thickness of the elastic substrate is set to 0.2 - 1 mm, and the other parameters remain unchanged. The static force analysis and modal analysis of the piezoelectric structure are carried out at the free end (without mass) by applying 0.3 N, and the analysis results are shown in
The relation curve between synthesis
energy collection circuit. The oscilloscope is mainly used to observe the voltage signal generated by the multi-directional vibration piezoelectric power generation device.
The energy collection circuit of a cantilever beam in a single direction is a standard energy collection circuit, the theoretical load voltage and load power are respectively
V 1 , c u = ω R V 1 , n C 1 ω R C 1 + π 2 (4)
P 1 , c u = ω 2 R ( V 1 , n C 1 ) 2 ( ω R C 1 + π 2 ) 2 (5)
The energy collecting circuit of the multidirectional vibration device is connected in parallel by five standard energy collecting circuits. The theoretical load voltage and the load power are respectively
V r , c u = ω R ( V 1 , n C 1 + V 2 , n C 2 + V 3 , n C 3 + V 4 , n C 4 + V 5 , n C 5 ) ω R ( C 1 + C 2 + C 3 + C 4 + C 5 ) + π 2 (6)
P r , c u = ω 2 R ( V 1 , n C 1 + V 2 , n C 2 + V 3 , n C 3 + V 4 , n C 4 + V 5 , n C 5 ) 2 [ ω R ( C 1 + C 2 + C 3 + C 4 + C 5 ) + π 2 ] 2 (7)
where: C 1 ~ C 5 and V 1 , n ~ V 5 , n , respectively, the equivalent capacitance and voltage of piezoelectric plates ,in different directions. Through comparison and analysis, we can get:
V r , c u > V 1 , c u (8)
P r , c u > P 1 , c u (9)
The theoretical load output is verified by applying different directions of excitation to the multidirectional piezoelectric device. When the 50 Hz vibration frequency is applied in the Z axis direction,
load resistance of the device, respectively. It can be seen from the diagram that the variation trend of theoretical curve and experimental curve is basically the same, it is proved that the output voltage and the load power of the multidirectional vibration piezoelectric generator are larger than that of the unidirectional piezoelectric generator.
cantilever beam with multiple directions in the piezoelectric device can largely eliminate the strong directional selectivity of the unidirectional piezoelectric generator, The vibration energy collection efficiency of the device reaches the highest level to adapt to the changeable vibration direction in the environment. Therefore, the multi directional vibration piezoelectric power generation device designed in this paper has higher energy collection efficiency than the traditional unidirectional piezoelectric generator.
The key technology of multidirectional vibration piezoelectric power generation is studied. The optimal model of piezoelectric power generation device is established by finite element simulation and analysis, the natural frequency of the device is consistent with the environmental frequency, which greatly improves the vibration energy collection efficiency of the piezoelectric device, and the energy collection in a plurality of directions breaks the limitation of the directional selectivity to the piezoelectric device. The problem of reducing the energy collection efficiency of unidirectional piezoelectric power generation devices due to the change of the vibration direction in the environment is eliminated. Finally, the feasibility and correctness of the design concept are proved through theoretical analysis and experimental comparison. The key technology of multidirectional vibration piezoelectric power generation can improve the energy collection efficiency of piezoelectric power generation device, and the technology is a green pollution-free technology, and has broad prospects for development.
Habib, A. and Ananta, A. (2018) Study on Fundamental Technology of Multi Directional Vibration Piezoelectric Power Generation. World Journal of Engineering and Technology, 6, 1-16. https://doi.org/10.4236/wjet.2018.61001