Theoretical modelling of a planar piston field focussed by reflection

This work describes a full rigorous theoretical prediction of the field from a planar piston ultrasonic transducer that is focussed by reflection from an off-axis parabolic mirror. This configuration is of interest in that it produces very high quality images of surfaces and defects. An impulse response method is used with the surface of the mirror approximated to a fine grid of point scatterers to give an overall reflected response. The predictions of this model have been compared with those measured experimentally in air using an optics-grade parabolic mirror, at frequencies of up to 1MHz. Good correlation of theory and experiment is observed.