Weaknesses in current ultrasonic pulse-echo technology include:contact heads limit measurement speed; need liquid couplant; and,beams launched through the rail top can miss internal defects hidden under horizontal shelling.A system based on non-contact ultrasonic testing is under development at UC San Diego under a Federal Railroad Administration R&D grant and with the technical support of ENSCO,Inc.This system uses a pulsed laser to excite guided waves traveling along the rail and an array of air-coupled sensors to detect these waves.Wave energy propagates equally in either direction from the impact point.Presence of cracks or other natural boundaries between the two sensors will cause the observed wave intensity to differ.This difference is used to determine the presence and approximate size of defects.Field tests in 2006 showed promising results.Further developments include the deployment of the system on a high-speed track inspection vehicle.
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