Distributed Mode Absorbers (DMAs) are resonant panel absorbers, in which plates are mounted in front of a closed volume of air. The idea is to absorb sound at several modal frequencies. This broadens the usable frequency range compared to conventional membrane absorbers, which are generally limited to one resonance frequency. The front panels of DMAs previously had uniform thicknesses. In this study, the modal behaviours of the DMAs having non-uniform panel thickness were investigated. Therefore, several thickness patterns for the front panels were considered and examined.
Numerical models were developed by using an approach that combines boundary element (BE) and finite element (FE) methods. Besides, an experimental study was conducted in an anechoic chamber to validate the numerical results by comparing the vibration response of the DMAs subjected to acoustic excitation. The results show that using multi-thickness panels can provide better distributed mode characteristics by including more resonance frequencies. These frequencies can be used for broadband noise absorption in the low frequency range.