Research On Low-Frequency Multi-Directional Piezoelectric Vibration Energy Harvesters

With the widespread application of various microelectronic devices,the supply technology of traditional chemical batteries has gradually fallen behind.Moreover,the disadvantages of large size,limited lifespan,frequent replacement requirements,and potential environmental issues of batteries are no longer the optimal solution for energy supply.Thus,the technology of collecting and utilizing energy from the surrounding environment,such as renewable energy sources like solar,wind,and thermal energy,has become a hot research topic among numerous scholars.Compared with solar,wind,thermal energy,and other forms of energy,the collection of vibrational energy from the environment has advantages such as low cost,ease of production,and stable acquisition channels,making it more suitable for microelectronic devices.However,traditional piezoelectric vibration energy harvesters have defects such as a high resonant frequency and a single energy collection direction.To solve these issues,this paper proposes two types of low-frequency,multi-directional piezoelectric vibration energy harvesters suitable for low-frequency environments.The main research contents of this paper are as follows:(1)The working principle of the piezoelectric vibration energy harvester is elaborated.The piezoelectric effect and equation,types of piezoelectric materials,performance parameters,and operating modes are introduced,laying a foundation for subsequent work.(2)A circular arc-shaped multi-directional piezoelectric vibration energy harvester is proposed.The theoretical derivation of the circular energy harvester is presented,and finite element simulations are conducted using COMSOL software to compare the circular and traditional rectangular harvesters in terms of vibration mode,stress distribution,resonant frequency,and multi-directional vibration energy collection capability.The results show that the circular harvester has a lower resonant frequency and better multi-directional vibration energy collection capability.Based on the single circular structure,a low-frequency multi-directional piezoelectric vibration energy harvester composed of two layers of circular arc beam structures stacked on top of each other is designed.After simulations and experimental testing of the different structures formed by the relative positions of the upper and lower circular arc beams,the optimal structure is found to have a first-order resonant frequency of 12 Hz and an output power of 43.01 μW with a 153 kΩ load.(3)To further improve the collection efficiency of vibration energy in different directions,an Lshaped piezoelectric vibration energy harvester is proposed.Finite element analysis is conducted to determine the vibration mode distribution,stress distribution,and resonant frequency of the L-shaped harvester.It is found that the resonant frequency of the L-shaped harvester is further reduced compared with the circular harvester,while it has more efficient vibration energy collection capability in the Z-direction.To combine the advantages of the circular arc-shaped and L-shaped harvesters,a low-frequency multi-directional L-shaped piezoelectric vibration energy harvester composed of a lower circular arc-shaped harvester and an upper L-shaped harvester is proposed.Finite element analysis is conducted for the different structures formed by the relative positions of the upper and lower layers,and the vibration mode,stress distribution,resonant frequency,and open circuit voltage of each structure are obtained.The optimal structure is obtained by testing and the optimal structure has a first-order resonant frequency of 11 Hz and an output power of 57.1 μW with a 201 kΩ load.