C. Maury and T. Bravo
16ème Congrès Français d’Acoustique
Del 11 al 15 de abril de 2022, Marseille, France.
Acoustic optimization of micro-perforated absorbers is generally achieved by maximizing the total energy dissipated over a frequency band. However, there is a low frequency limit, determined by the principle of causality, below which a broadband absorber will dissipate little energy. In this study, an integral causal relationship is derived in the case of a single-layer micro-perforated resonator (MPR) under normal incidence. It shows that the ultimate broadband performance of the absorber is quantified by the reflected intensity in logarithmic scale integrated over all the positive wavelengths and is upper bounded by the cavity depth. A sensitivity study led to the proposal of a causal optimization criterion in order to obtain the MPR constitutive parameters which provide the broadest possible performance while ensuring total absorption at the MPR Helmholtz resonance. This criterion maximizes the directional gradient of the total intensity with respect to the MPR parameters and is readily implemented using a quadrature method and a global optimization solver. It is an alternative to maximizing the total absorption with the advantage of ensuring a critical coupling condition at resonance. This criterion has been extended to the case of general incidence and to a serial arrangement of MPRs. Impedance tube measurements validated the approach, but also showed its limitations for thin elastic structu
