Research On Low-density Acoustic Energy Harvesting Method Based On Helmholtz Cavity And Acoustic Metamaterial

As a clean and renewable energy source,sound energy can be used to provide energy for low-power miniaturized devices.However,due to the low power density and wide frequency range of sound itself,there are still some difficulties in converting it into usable energy.Therefore,this paper focuses on the problems of low sound energy density and narrow acquisition frequency in the acoustic energy harvesting technology.Through the design of multi-frequency tunable energy gathering amplification structure and electromechanical conversion device,the sound energy is converted into electric energy.The main research contents include:A cylindrical-square cavity finite element simulation model is established,and the accuracy of the simulation model is verified by the Helmholtz resonant cavity sound pressure amplification theory.An electromechanical conversion device is arranged at the end of the cavity with the maximum sound pressure amplification effect to construct a resonant cavity acoustic energy harvester.A multi-physics finite element simulation model is established for the resonant cavity acoustic energy harvester,and the influence of different masses on the backplane of the cavity on the voltage and frequency is compared and analyzed.An acoustic energy collection device based on Helmholtz resonant cavity is built,and the voltage output effect under the same cavity size is analyzed experimentally.The characteristics of acoustic energy amplification of local resonance metamaterials and Bragg metamaterials are compared and analyzed,and a research plan for low-frequency energy harvesting by using local acoustic metamaterials' small size and large wavelength control characteristics is determined.Based on the theory of energy band structure,a solution model of the unit cell energy band curve is established,and the band gap and eigenmodes of the local resonance metamaterial are obtained.The analysis of the band gap structure shows that: The mutual coupling between the cylindrical resonator and the plate is the key to opening the band gap.The change law of the unit cell band gap under different parameters is theoretically analyzed.By introducing defect state into the metamaterial plate to achieve energy concentration at the defect,an acoustic energy harvester based on the acoustic metamaterial plate is constructed.The band structure of the defect state is calculated by the supercell method,the displacement mode and the sound pressure distribution under different defect states are compared and analyzed,and the metamaterial plate structure with the best energy accumulation amplification effect is optimized.A multifrequency acoustic energy harvester is established by combining the defected acoustic metamaterial plate and the Helmholtz cavity.The acoustic energy harvesting characteristics of the coupled structure are simulated and analyzed.The simulation results show that: The coupled acoustic energy harvester can not only collect the sound source at the cavity resonance frequency of 413 Hz,but also collect the sound energy at the frequency of the defect mode about 1003 Hz.A frequency-tunable metamaterial acoustic energy harvester is designed to compare and analyze the band gap change under different external forces and the influence of different defect resonance bodies on the defect state and local amplification,and obtain the tunable defect state frequency and voltage output relationship.The results show that the defect state frequency close to the lower edge of the band gap has greater local amplification and voltage output,when the external resistance value is 10M?,the maximum output voltage is 1.14 V.It is verified through experiments that the acoustic energy harvester with acoustic metamaterial has larger voltage output.