Noise control by sonic crystal barriers made of recycled materials

Abstract

A systematic study of noise barriers based on sonic crystals made of cylinders that use recycled materials like absorbing component is reported here. The barriers consist of only three rows of perforated metal shells filled with rubber crumb. Measurements of reflectance and transmittance by these barriers are reported. Their attenuation properties result from a combination of sound absorption by the rubber crumb and reflection by the periodic distribution of scatterers. It is concluded that the porous cylinders can be used as building blocks whose physical parameters can be optimized in order to design efficient barriers adapted to different noisy environments.

Optimum control of broadband noise by arrays of cylindrical units made of a recycled material

“…Figure 5 shows the R i coefficients measured and calculated for models T (bold circles) and T ef f (bold triangles). According to the absorptive properties of rubber crumb, the responses of attenuation obtained increase as frequency does [22]. As previously discussed, this barrier employs absorption as the main attenuation phenomenon while reflectance plays a minor role.…”

“…A detailed theoretical and experimental work about the application of this model within the multiple scattering method has been recently reported in Ref. [22]. Multiple scattering method works with coherent waves with well defined wave fronts, making difficult to model the diffuse sound field required by the ISO10140 norm [17].…”

Anomalous sound absorption in lattices of cylindrical perforated shells

“…These parameters correspond to those employed in Ref. 5 and will be used from now on. 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.…”

“…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.…”