Development of stackable subwavelength sound absorber based on coiled-up system

Abstract

A subwavelength structure absorber is developed and demonstrated. Unlike other subwavelength systems, we use several coiled-up resonator systems combined in a stack way. Such a system is proposed to cover acceptable absorption coefficient as well as obtain relatively wider absorption bandwidth. Moreover, it is expected that such a system offers a great tunability and configurable system in absorption to meet targeted frequency and bandwidth. The theoretical prediction is derived for such a system, while experimental works are provided to validate the concept. It is found that the proposed approach can offer a resonance absorption tuning framework in which the total length of the resonator channel is adjusted by adding or reducing the number of resonator units while the cross-section is kept the same for all elements involved. Meanwhile, absorption bandwidth extension can be obtained by combining two or more resonator units with different cross-sections and channel lengths. All these features have been confirmed by the experimental results. Compared to the conventional resonance-based absorbers, the proposed structure can be 94 % thinner for single absorption peak and 66 % thinner for the case of three absorption peaks that forms a broadband absorption characteristic.