Scattering by an array of perforated cylinders with a porous core

Abstract

In this work multiple scattering by an array of perforated cylindrical shells with a porous core has been investigated. A semi-analytical model to predict scattering from such cylindrical units is presented in the context of the multiple scattering theory (MST), and validated against laboratory experiments. The suggested semi-analytical multiple scattering model uses an impedance expression to include the perforated shell in the scattering coefficients, which is a compact way to describe a composite scatterer in MST. Calculation results of a small array are shown to be in excellent agreement with measured data. Predictions and data show that perforated cylinders with empty cavities exhibit a strong and narrow insertion loss peak at resonance, though simultaneously suffer from amplification below resonance. By adding porous material in the core of the scatterer adverse effects below the resonance peak were suppressed. In addition, it was found that the reduction peak broadens, though at a cost of a reduced peak amplitude. Finally, it has been shown that adding porous material in a perforated shell will introduce partial absorption of the incoming field, which can be optimized by adjusting the perforation ratio of the shell.

Boundary element solution for periodic acoustic problems

“…The insertion loss in the shadow zone of the barrier obtained using the periodic BEM technique is compared with results from the 2D FE model and with the data from Ref. [26]. Close agreement in the results for all models can be observed.…”

“…The centre frequency of the band gap generated by the periodic structure can be Comparison of insertion loss obtained using the semi-analytical method from Ref. [26], the 2D FE model and the 3D PBEM for a 2 Â 3 square lattice sonic crystal barrier. approximately predicted by Bragg's law and is given by…”

“…The insertion loss for a sonic crystal barrier comprising three rows of two cylinders obtained using a 2D semi-analytical method by van der Aa and Forssén [26] was used as the reference solution. A 2D finite element (FE) model of the same sonic crystal barrier in a square lattice was also developed using the commercial software COMSOL Multiphysics (v5.0).…”

“…Their results revealed that rigid hollow and solid cylinders produce similar sound transmission. van der Aa and Forssén [26] carried out a laboratory experiment to analyse multiple scattering by an array of perforated cylindrical shells with a porous core. They identified that adding porous material in the core of a perforated cylinder introduces partial absorption of the incoming field, which can be optimised by adjusting the perforation ratio of the shell.…”

Anomalous sound absorption in lattices of cylindrical perforated shells

“…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.…”