Sound attenuation in ducts using locally resonant periodic flush mounted flexible silicon aerogel patches

Abstract

In recent years, low frequency noise has become an important factor especially in the Aircraft, HVAC, and Automotive industries. In order to reduce this low frequency noise, noise attenuation by the classical Helmholtz resonators has size limitations due to the large wavelengths. Promising noise reductions, with flush mounted Silicon Aerogel patches, can be obtained implementing attenuation due to local resonance and that too without any size constraints. The objective of the current paper is to introduce locally resonant Silicon Aerogel patches flush mounted to an acoustic duct walls aiming at creating frequency stop bands at the low frequency zone (below 500 Hz). Green’s Function is used under the framework of interface response theory to predict the degree of attenuation of the local resonant patches. Realistic techniques for expanding the stop bandwidth have been introduced and difference between the Bragg scattering and the locally resonant mechanism was demonstrated using mathematical models. The effect of the arrays of patches on the effective dynamic density and bulk modulus has also been investigated. It is also shown that the numbers and periodicity of these local resonators also plays role in determining the depth and width of the acoustic band gap.