Compact resonant systems for perfect and broadband sound absorption in wide waveguides in transmission problems

Abstract

This work deals with wave absorption in reciprocal asymmetric scattering problem by addressing the acoustic problem of compact absorbers for perfect unidirectional absorption, flush mounted to the walls of wide ducts. These absorbers are composed of several side-by-side resonators that are usually of different geometry and thus detuned to yield an asymmetric acoustic response. A simple lumped-element model analysis is performed to link the dependence of the optimal resonators surface impedance, resonance frequency, and losses to the duct cross-sectional area and resonator spacing. This analysis unifies those of several specific configurations into a unique problem. In addition, the impact of the potential evanescent coupling between the resonators, which is usually neglected, is carefully studied. This coupling can have a strong impact especially on the behavior of compact absorbers lining wide ducts. To reduce the evanescent coupling, the resonators should be relatively small and therefore their resonances should be damped, and not arranged by order of increasing or decreasing resonant frequency. Finally, such an absorber is designed and optimized for perfect unidirectional absorption to prove the relevance of the analysis. The absorber is 30 cm long and 5 cm thick and covers a single side of a 14.8 × 15 cm2 rectangular duct. A mean absorption coefficient of 99% is obtained experimentally between 700 and 800 Hz.

Subwavelength Broadband Perfect Absorption for Unidimensional Open‐Duct Problems

“…[40,43] Note that, by using two resonators of the same type, the distance between them in the wave direction should be properly chosen to produce the other type of resonance. [40,44] Alternatively, a degenerate resonator [26,40] could be considered, which is realized by introducing a monopolar and a dipolar resonances at the same position along the wave propagation. The use of degenerate resonators generally results in spatially compact designs for perfect absorption, at the price of a more difficult design process since the evanescent coupling is usually significant.…”

Nearly Perfect Transmission of Lamé Modes in a Rectangular Beam with Part and Through-Thickness Vertical Cracks

“…The nearly perfect transmission phenomenon for electromagnetic and acoustic waves has been extensively researched [33][34][35][36][37][38], while analogous studies have seldom been reported in the field of ultrasonic guided wave based damage detection. In this paper, the interaction between the first Lamé mode and a part-through or through-thickness crack of various sizes is analyzed quantitatively.…”