LOW-FREQUENCY ACOUSTIC SCATTERING BY A CUBE - EXPERIMENTAL MEASUREMENTS AND THEORETICAL PREDICTIONS

The acoustic backscattering from a submerged metal (iron) cube has bee n investigated as a function of frequency and angle of incidence in th e low-frequency regime ka<5, where k is the acoustic wave number and a is a characteristic dimension of the cube. The experimental measureme nts were made in the laboratory using a parametric array as an acousti c source at frequencies between 8 and 120 kHz and a cube of side lengt h 20 mm. The backscattered field is expressed as a dimensionless ''for m function'' and normalized in terms of the average projected cross-se ctional area of the cube. The scattered field is seen to vary consider ably with the orientation of the cube. The scattering behavior of a ri gid cube is modeled numerically using a boundary element code. The res ults for a cube are compared with calculations of the form function fo r an elastic sphere. When averaged over cube orientations the form fun ction has characteristics reminiscent of a spherical scatterer, sugges ting the propagation of creeping waves. (C) 1997 Acoustical Society of America.