Ultrasonic measurements of defects in metals using cepstral processing

We consider the problem of measuring the size of a spherical inclusion in a host metal. Ultrasound is directed at the test piece, and the echo returns are detected. Among other components, the received signal contains two echoes of the incident pulse, whose time separation is a measure of the diameter of the inclusion, or defect. A modified version of cepstral processing is used to determine this time separation. Simulated data are generated using a certain scattering model, and processed with good results. Sample test pieces were also constructed, and data collected and processed. The resulting measured defect diameters agreed with the true diameters.