Research On Piezoelectric Vibro-acoustic Energy Harvesting Characteristics Based On Acoustic Metamaterial Defect State

As a clean energy source,acoustic energy is widely distributed in people’s daily life,and harvesting acoustic energy can suppress noise to a certain extent while powering low-power electronic devices.Acoustic metamaterials are designed by artificial subwavelength structure,destroy the periodicity of the perfect supercell structure of acoustic metamaterials,after the introduction of defects,defect bands will appear in their forbidden bands,and the sound waves at the frequency of defect bands can be localized at the defects of metamaterials,so the energy localization effect of the defect mode can be used to improve the efficiency of energy harvesting.In order to control the sound in a specific frequency band,improve the collection efficiency of the acoustic energy harvester and collect the acoustic energy in different frequency bands,three kinds of acoustic energy harvesters are designed in this paper.The main work of this paper is as follows:(1)An acoustic metamaterial with Helmholtz resonant cavity is designed,its energy band structure and transmission spectrum are analyzed by finite element,the band gap formation mechanism is analyzed by studying the band gap edge eigenmode,and the influence of structural parameters of Helmholtz resonant cavity on the energy band structure is studied.The results show that the subsidence frequency range in the energy band structure and transmission spectrum is the same:with the change of the inner neck(inner cavity)radius,inner neck(inner cavity)height,and cavity of the Helmholtz acoustic metamaterial,the onset frequency,cutoff frequency and bandwidth of the band gap tend to increase or decrease.Defects were introduced in the supercell structure of a 6 × 6 perfect acoustic metamaterial,and the energy harvesting characteristics of the acoustic energy harvester with specific structural parameters were analyzed using finite element analysis software,and the results showed that the energy was limited to the central defect at a defect frequency of 2605.6 Hz,and its maximum output power was 12 μW.(2)A mathematical relationship between the performance of acoustic energy harvesters based on acoustic metamaterials and their substrate thickness and resonator radius is found from the perspective of metamaterial piezoelectric dynamics.Multi-field coupled computational simulations and experimental studies of acoustic energy harvesting support the theoretical inference.The results show that the optimal substrate thickness is 0.3 mm and the optimal resonator radius is 6 mm,and the maximum peak power output of the substrate thickness of 0.3 mm is 195.52 μW,which is 6 times and 331 times that of the substrate thickness of 0.4 mm and 0.2 mm,respectively,under the optimal impedance and resonant frequency acoustic incidence.The maximum peak output power of the metamaterial energy harvester with a resonator radius of 6 mm is 32.28 μW,which is 1.46 and 1.89 times higher than that of the resonator radius of 5 mm and 4 mm,respectively.(3)A gradient-type dual piezoelectric acoustic energy harvester is designed to obtain higher acoustic energy harvesting efficiency and solve the single-band energy harvesting problem.A multi-physics field finite element simulation model is established to compare the energy harvesting effects of two different boundary conditions on the acoustic energy harvester in three frequency bands,and its sound pressure level,kinetic energy density,and vibration mode are analyzed by finite element analysis software.The energy harvesting characteristics of the acoustic energy harvester with two boundary conditions are analyzed by building a test bench to test the open circuit voltage sweep curve with frequency and the optimal resistance.The experimental results show that the maximum effective output power of the acoustic energy harvester with the boundary condition of a short-sided simple-branch third frequency band at the optimal resistance is 325.58 μW.