Laser/EMAT Measurement Systems for Ultrasound B-scan Imaging

摘要

A laser/EMAT ultrasonic sensor for time-of-flight analysis of laser-generated shear and longitudinal-shear mode-converted waves provided an effective method for monitoring the thickness of metal plates. A Q-switched Nd: YAG laser provided optical pulses delivered via an optical fibre and focused to a line source by a cylindrical lens onto the material surface. Transient acoustic waves propagated through the material, were reflected from the far surface and detected upon their return by an EMAT sensitive to in-plane motion. B-scans generated as the sensor head moved along the material's surface formed a 2D intensity profile, making changes in the plate thickness easy to visualize.