Distortion characterization for non-normal incidence in pulse-echo ultrasound

A technique for determining the spectral distortion of received echo signals due to angular misalignment between the transducer and plane specular targets is presented. Pulse-echo measurements carried out on stratified media, the interfaces of which have small angular deviations from normal incidence, suffer such spectral distortion due to phase-cancellation (diffraction) effects across the face of the transducer. The object of this investigation is to compute this distortion effect in the nearfield of an unfocused circular piston transducer for the case of an arbitrary angular misalignment of an infinite, planar reflecting surface. The spectral distortion produced is characterized over frequency, angular misalignment, transducer geometry, and distance to the reflector. Experimental verification of the results is presented for several misalignment angles and transducer geometries using pulse-echo measurements