Recent Advancements in Helmholtz Resonator Based Low-Frequency Acoustic Absorbers: A Critical Review

Helmholtz resonator (HR) is an elementary resonating structure predominantly used for acoustic wave manipulation. The sound absorption capabilities of HR are well examined and widely accepted, and it has extensive applications in engineering acoustics. Perhaps, low-frequency sound mitigation is a major technological challenge wherein, HR based absorbers play a pivotal role. In this review, the recent advancements in various HR based sound absorbers are considered in general and low-frequency absorbers in particular for a detailed comparison and critical evaluation. Since the majority of the reported investigations have numerical predictions to corroborate the experimental findings, a detailed review of analytical and computational methods is necessary. Initially, finite element computations of a conventional HR are performed to assess the efficacy of trusted simulation techniques such as thermo-viscous, narrow-region and poro-acoustics models. Then, the structural aspects and noise absorption characteristics of various alterations of conventional HR configurations are critically examined using an analytical approach. Thereafter, a detailed appraisal of the low frequency sound attenuation properties of different HR combinations such as arrays of resonators, hybrid models, and acoustic metamaterials is performed. Moreover, a non-dimensional performance parameter is introduced for uniform comparison among available absorbers and to identify suitable candidates for efficient low-frequency acoustic attenuation. Finally, different optimization approaches including forward and inverse design strategies for selecting appropriate sub-wavelength HR designs for targeted low-frequency noise mitigation are also provided. The development of effective strategies for the creation of HR structures amenable to the real-life industrial environment that provide low-frequency acoustic attenuation is discussed as a future direction.