Fundamental constraints on the performance of broadband ultrasonic matching structures and absorbers

Abstract

Recent fundamental results concerning the ultimate performance of electromagnetic absorbers were adapted and extrapolated to the field of sound waves. It was possible to deduce some appropriate figures of merit indicating whether a particular structure was close to the best possible matching properties. These figures of merit had simple expressions and were easy to compute in practical cases. Numerical examples illustrated that conventional state-of-the-art matching structures had an overall efficiency of approximately 50% of the fundamental limit. However, if the bandwidth at -6 dB was retained as a benchmark, the achieved bandwidth would be, at most, 12% of the fundamental limit associated with the same mass for the matching structure. Consequently, both encouragement for future improvements and accurate estimates of the surface mass required to obtain certain desired broadband properties could be provided. The results presented here can be used to investigate the broadband sound absorption and to benchmark passive and active noise control systems.

Design optimization of embedded ultrasonic transducers for concrete structures assessment

“…It is briefly presented in Appendix A. Nevertheless, the design of piezoelectric transducers is still often determined by optimizing the acoustic impedance matching between the piezoelectric material and the tested material [32][33][34][35].…”

PID-like active control strategy for electroacoustic resonators to design tunable single-degree-of-freedom sound absorbers

“…To overcome such issue, active sound absorbers have received a surge of interest, since they can be constructed in limited space while providing tunable acoustic properties. Moreover, it is well known that for any passive, linear and timeinvariant system, the bandwidth and the absorption efficiency are mutually constrained [4,5,6]. Active treatments can violate the passivity of materials, thereby leading to efficient sound absorption in a wider frequency range.…”

Subwavelength broadband sound absorber based on a composite metasurface

“…Moreover, due to the sharp absorptive peak of individual unit cell, the absorptance of the combined system is bound to emerge low-efficiency absorption valleys at some extent. Recently, based on causality principle [23][24][25] , optimal sound absorber 20 showing highly efficient absorption at full frequency above the low-frequency cutoff frequency (with a thickness of /10 ) have been proposed. The ingenuity of the strategy is letting the system simultaneously dissipates the propagated and evanescent sound wave components to approach near-unity absorption.…”