Real-time analysis signal processor for ultrasonic nondestructive testing

Abstract

Hilbert transform processors were developed to improve flaw detection in parts by sensing the rate of total energy arrival. Analytic signal processing is used to improve pulse resolution. A real-time analytic processor was built using single-sideband (SBB) AM techniques. An upper sideband processor using the filter method to maximize signal bandwidth and in which the lower sideband aliases was built. This processor has a transducer bandwidth of 0.5 to 20 MHz and can resolve echoes 90-ns apart. The spurious products of practical mixers and amplifiers make the aliased approach impractical due to high noise and distortion. By using a bandpass filter after the mixer, distortion is reduced. A processor built with a lower sideband filter method yielded the lowest distortion and noise. The lower sideband processor has a bandwidth of 2 to 42 MHz and can resolve echoes 60-ns apart. With a single-cycle tone-burst processor input, ringing in the IF filter causes temporal asymmetry of the output pulse, while ringing in the detector filter causes ringing in the output pulse. Performance is expected to improve through the design of optimized filters. The ringing is less with ultrasonic echoes, because they do not start and stop as abruptly as a tone burst.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>