Double defects in trampoline effect and Helmholtz coupled acoustic metamaterial for broadband piezoelectric energy harvesting

An acoustic metamaterial with double defects is proposed to widen bandwidth and improve energy collection. Defects can limit elastic waves to achieve energy localization. The introduction of defects in acoustical supermaterials can improve energy localization and amplify the effect, but single defects are easily limited by narrow bandwidth. Therefore, the bandwidth is broadened by adding double defects to the acoustic supermaterial. At the same time, the existence of double defect can influence the coupling effect of each other to a certain extent, which is helpful to the improvement of energy recovery. In order to further enhance the local resonance at the defect location, the trampoline effect and Helmholtz resonator are used to further enhance the energy recovery. Using finite element method (FEM) simulations, the comparison results show the double defect enhances energy recovery and broadens bandwidth of energy collection compared with single defect, and the maximum voltage output is about 0.86 V under the effective sound pressure of 100 dB.