Acoustic scattering by nonmetallic and metallic cubes in the elastic resonance regime: Experimental measurements and combined finite element/boundary element modeling

Abstract

The acoustic backscattering behavior of both nonmetallic (glass) and metallic (steel) cubes has been investigated over a wide frequency range where elastic resonances are important in determining the acoustic response of the cubes. A laboratory system incorporating a parametric array was used to make measurements between 20 and 200 kHz using cubes of side (l) 20 mm, and a combined finite element/boundary element code was used to numerically model scattering by the cubes. The frequency range covered corresponds to ka values up to 10, where a=l(3/4π)1/3 is a characteristic dimension of the cube. Results are presented for three scattering geometries involving incidence on to a face, an edge, and a corner. The backscattered form function differs greatly for the different geometries and is seen to depart significantly from that of a rigid cube when ka>5 due to the elastic resonances of the cube. The resonance contributions are clearly seen when the rigid background is subtracted from the elastic predictions.