Metamaterial-based micro-perforated panels (MMPPs) were proposed by adding local resonators (LRs) upon one face of a conventional flexible micro-perforated panel (FMPP). Mass-cantilever resonant structures are adopted as LRs here, and they are separated on a sub-wavelength scale. Through theoretical and numerical analyzing, MMPPs are proved able to enhance sound absorption in the stop bands caused by local resonances. Specifically, the theoretical model is developed based on effective medium method, as the distance between the LRs is much smaller than the structural wavelength in the host panel (i.e. FMPP) in the considered frequency range. The full-size simulation model is conducted by utilizing the commercial software COMSOL, considering all the multi-physical couplings among the fluid and solid domains. Good agreement is achieved between the theoretical predictions and the simulation results, for both the FMPPs and MMPPs. Physically, the theoretical and numerical models reveal that the sound absorption enhancement mechanism stems from the resulted additional phase shift, and the enlarged divergence between the average velocity of the air particles inside the perforations and that of the panel attached with LRs. The proposed MMPPs possess great potential in noise reduction industry.
