Optimizing acoustic metasurface within their propagation environment

This article compares several design strategies for an acoustic metasurface intended to maximize insertion loss at a target frequency in a semi-open configuration involving a wall, a source, and a receiver. The first strategy, commonly used in acoustic metamaterial design, focuses on maximizing an intrinsic acoustic property of the metasurface, such as the omnidirectional absorption coefficient. The second strategy aims to account for the geometry of the problem by optimizing the reflection coefficient to achieve destructive interference while the last strategy directly optimizes insertion loss by embedding the metasurface within the complete propagation environment, thus accounting for geometry-dependent interference and scattering effects. The problem is addressed analytically with the Transfer Matrix Method (TMM) and numerically using a frequency domain finite element model coupled with a differential evolution optimization algorithm. The metasurface considered consists of a parallel slit-type Helmholtz resonator array. For a target frequency of 500 Hz, the insertion-loss-optimized configuration achieves an insertion loss approximately 4.2 dB higher than that obtained through absorption-based optimization. Interestingly, the configuration that maximizes insertion loss exhibits a lower absorption coefficient at the target frequency than the absorption-optimized design. These results show that maximizing absorption, although widely pursued in acoustic metamaterial research, does not necessarily lead to optimal system-level performance in semi-open configurations. The findings highlight the importance of evaluating metasurfaces within their full acoustic propagation environment when the objective is to maximize global acoustic metrics such as insertion loss.