Calculation and measurement of scattering coefficients for surface-breaking cracks sonified by a focused array

A simulation of a focused beam of surface wave motion generated by a line a rray of surface wave transducers is used to calculate the field scattered b ack from a surface-breaking crack. The backscattered field is expressed in terms of a scattering coefficient, which is derived from the reciprocal ide ntity for elastodynamic states, and which is calculated numerically by usin g the Kirchhoff approximation. In an earlier work the validity of the focus ed beam simulation has been verified. In this paper, the theoretical result s for the backscattered field are compared with measurements for two crack sizes, one of which is used for calibration.