Sound insulation performance of membrane-type acoustic metamaterial based on defect state structure

Although conventional Membrane-type Acoustic Metamaterial(MAM) has good sound insulation performance in low frequency bands, the sound insulation performance in middle and high frequency bands is not as good as conventional sound insulation materials with the same quality. This problem still persists by using the double-layer MAM structures. To solve this problem, the defect state is introduced into the double-layer MAM structure. Although the ideal periodic structure is destroyed, the sound insulation performance will also change greatly, and it has a strong creativity. In this paper, the sound insulation performance of MAM with defect states is studied. Firstly, the theoretical model of sound insulation of double-layer membrane-type acoustic metamaterial with eccentric composite mass block (MAMEM) structure is calculated by using modal superposition method and transfer matrix method. Secondly, the influence of different defect locations on the sound insulation of membrane-type acoustic metamaterial with eccentric composite mass block(MAMECM) structure is discussed. The results show that the sound insulation peaks of the angular defect structure appear at 300 Hz, 320 Hz, 1040 Hz and 1410 Hz. The average sound insulation in the whole study frequency band of the angular defect structure is 4.23 dB higher than the non-defect structure. In addition, the experiment verifies the accuracy of the results. Thirdly, based on genetic algorithm, the area enclosed by the sound translation loss (STL) curve of the double-layer MAMECM structure above the mass law curve is taken as the optimization target to optimize the structure topology. The results show that the optimal structure not only has good sound insulation performance in the low frequency band, but also reaches the sound insulation peak at 1230 Hz, 1300 Hz, 1430 Hz and 1450 Hz. Besides, the optimal structure heaviness is reduced by 12%.