Time-domain flaw imaging system

Abstract

Ultrasonic Non Destructive Evaluation of materials is a useful tool for flaw detection and characterization. A typical ultrasonic imaging system may consist of a single transducer or an array of sensors working in a B-scan mode. This mode operates by transmitting a pulse of train of pulses from several locations and detecting the echoes coming from in-homogeneities. The reflected energy can be represented as a map of ultrasonic reflectivity. A time-delay beamformer has been successfully used to reconstruct the image, and localize the in-homogeneities within the scanned medium, by time shifting the signals, and summing them up. This process enables to locate regions at which signals are added constructively. It is however, a time consuming process and requires $\lambda/2$ distance of motor steps or inter-element distance between array elements. An algorithm based on time-domain envelope beamformer is presented here. This algorithm is able to diminish the number of computational operations without losing relevant information about the location of in-homogeneities. A comparison between classical and envelope beam-formers is presented when applied to sets of simulated signals. Lateral and longitudinal resolutions are also computed when two targets are within the scanned medium.