Low-frequency acoustic scattering by a cube: Experimental measurements and theoretical predictions

Abstract

The acoustic backscattering from a submerged metal (iron) cube has been investigated as a function of frequency and angle of incidence in the low-frequency regime ka<5, where k is the acoustic wave number and a is a characteristic dimension of the cube. The experimental measurements were made in the laboratory using a parametric array as an acoustic source at frequencies between 8 and 120 kHz and a cube of side length 20 mm. The backscattered field is expressed as a dimensionless “form function” and normalized in terms of the average projected cross-sectional area of the cube. The scattered field is seen to vary considerably with the orientation of the cube. The scattering behavior of a rigid cube is modeled numerically using a boundary element code. The results for a cube are compared with calculations of the form function for an elastic sphere. When averaged over cube orientations the form function has characteristics reminiscent of a spherical scatterer, suggesting the propagation of creeping waves.