Quasi-perfect absorption of broadband low-frequency sound in a two-port system based on a micro-perforated panel resonator

In this study, micro-perforated panel (MPP) resonators are designed to exhibit quasi-perfect absorption in a two-port system. Compared to a one-port system in which near-unity absorption can be achieved by attenuating the reflected wave, the absorption coefficient of a single resonator is limited to 0.5 due to the symmetry of the system in a two-port system. By coupling multiple resonators, near-zero transmission and reflection can be achieved simultaneously, leading to near-unity absorption over the broadband frequency range. Here, the optimal distribution of MPP resonators is obtained with the use of the quality factors, so that the intrinsic loss and leakage rate out of the resonator are collectively balanced in a broadband target frequency. The particular geometric parameters for single-leaf MPP resonators are then determined through the proposed design method. The acoustic properties are evaluated by numerical simulations and experiments, demonstrating that the designed MPP-based absorber exhibits quasi-perfect absorption and that the surface impedance of the realized absorber is well-matched with that of the surrounding medium in the target low-frequency band. (C) 2021 Elsevier Ltd. All rights reserved.