Compensated High-Bandwidth Laser Ultrasonic Detector Based on Photo-Induced Emf in GaAs

Mitchell, P.
Dunning, G.
McCahon, S.
Klein, M.
O'Meara, T.
Pepper, D.
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The trend toward intelligent manufacturing has produced an increase in the need for sensors which can nondestructively evaluate components and processes in real-time. One commonly used nondestructive approach is ultrasonic inspection. The most common method for generating and sensing ultrasound in materials makes use of contacting piezoelectric transducers. A gel or water interface is often used to match the acoustic impedance between the sensor and part. This constraint can impose limitations on their applicability for some types of in-process industrial control or inspection, specifically, inspection of moving parts at elevated temperatures or in vacuum. While noncontact receivers have been made using capacitance or magnetic induction, often their spacing to the workpiece must be maintained within a close tolerance. The lack of a substantial standoff distance for these sensors also reduces their usefulness in some industrial inspection and process control applications. Specifically, contacting schemes and close proximity sensors are not well suited for conditions such as extreme vibrations and fast moving parts with irregular surfaces. Furthermore, it may be more cost effective, from the users perspective, to use a long standoff, remote sensing system which could be applied to a wide range of materials including metals, semiconductors and composites.