Receiver operating characteristic analysis of phase-sensitive and phase-insensitive ultrasonic detection in specimens with rough surfaces

We applied receiver operating characteristic (ROC) analysis to compare objectively and quantifiably the performance of phase-sensitive and phase-insensitive detection in the presence of surface roughness. To test detection methods, we measured signal loss in an isotropic specimen with a specially prepared rough surface in an immersion tank using a 10-MHz, 0.5-inch diameter, planar transmitting transducer and a pseudo-array receiver (a 1-mm diameter hydrophone scanned in a two-dimensional, 0.5-inch square grid). Signal loss was computed by determining the power spectrum transmitted through a region with surface roughness and compensating with the power spectrum transmitted through a region with smooth surfaces. We simulated an abnormality within our specimen as a 1 dB increase in signal loss. Results indicate that phase-insensitive detection can lead to significant, practical benefits for detecting material abnormalities that lie beneath rough surfaces.