Broadband sound absorption by lattices of microperforated cylindrical shells

Abstract

Absorption of broadband noise by sonic crystals consisting of microperforated cylindrical shells is proposed and experimentally demonstrated. The theoretical study has been performed in the framework of multiple scattering method, where a model for the T matrix of the microperforated shells has been developed. It has been predicted an extraordinary broadband sound absorption that is explained in terms of the multiple scattering phenomena occurring at the surfaces of the absorptive units—the microperforated panels. Our proposal has been supported by experiments performed on a structure consisting of 3 rows of cylindrical shells 3 meters height.

Anomalous sound absorption in lattices of cylindrical perforated shells

“…These scattering units are obtained by rolling up perforated plates whose parameters (thickness, radius of the perforations, and perforation ratio) will determine the absorptive properties of the SC structure based on them. Thus, when the radius of the perforations is extremely small, viscosity effects inside the micro-pores lead to broadband attenuation spectra 6 as occurs for the case of flat panels. 11 However, if the perforation radius is of the order of hundreds of microns or more, the flat panels become acoustically transparent even for relatively low perforation ratios.…”

“…The last effect was applied to obtain acoustically transparent cylindrical shells which were used as containers of granular absorbers. 5 Though lattices of microperforated cylindrical shells have been comprehensively studied due to their application as broadband noise absorbers, 6 no attention has been paid for the case of cylindrical shells whose perforation radii are too high to produce significant losses.…”

“…However, in the last years, 2D SCs consisting of cylinders fabricated with lossy materials are deserving attention due to their potential application as acoustic barrier for broadband noise. [5][6][7][8][9][10] The attention is paid here to 2D lattices of cylindrical perforated shells at normal incidence. These scattering units are obtained by rolling up perforated plates whose parameters (thickness, radius of the perforations, and perforation ratio) will determine the absorptive properties of the SC structure based on them.…”

“…For an impinging plane wave with wavevector k 0 and a given angle of incidence, the reflectance R and transmittance T of a SC slab can be easily obtained using the formulas described elsewhere. 3,6 The resulting total absorption A is then obtained by assuming energy conservation, i.e., A ¼ 1 À R À T .…”

Air transparent soundproof window

“…Soundproofing using the high absorbing characteristics of MPP was demonstrated by Garcia-Chocano et al 6,7 They used a specially designed array of cylindrical columns or sonic crystals using MPP, and their principle is based on multiple scattering phenomena at the surfaces of absorptive units. Those layered structures could have the visibility limit, and thus are suitable for acoustic barriers rather than windows.…”