Advanced Film-Type Acoustic Reflector Inspired by Helmholtz Resonator

Abstract

Sound waves propagate in a manner in which energy is transmitted by adjacent molecules in the medium. These adjacent molecules exhibit inherent sound wave characteristics, such as height and wavelength, depending on the sound frequency. The Helmholtz resonator, one of the well-known acoustic elements, comprises a neck and a cavity, and features a resonance at a specific frequency related to structural dimensions. The acoustic characteristics of the Helmholtz resonator can be explained by a lumped spring-mass system in mechanical engineering; the resonant frequency can be calculated with the same analysis. The Helmholtz resonator is widely used as an acoustic filter as it can re-radiate sound waves with the opposite phase and significantly attenuate the original sound wave in the resonance frequency range. In this study, we fabricated a Helmholtz resonator-inspired film-type acoustic absorber (FAA), comprising a microscale resonator array made with polydimethylsiloxane (PDMS). Through acoustic attenuation experiments, the FAA revealed that the novel attenuation values reached up to 36.3 dB mm-1. Additionally, a continuous fabrication of the FAA was achieved via a custom-built roll-type equipment.