SURFACE-BONDED AND EMBEDDED OPTICAL FIBERS AS ULTRASONIC SENSORS

The effectiveness of surface-bonded and embedded optical fibers for th e detection of ultrasonic Lamb waves in 2-3-mm-thick steel, carbon-fib er-reinforced plastic (CFRP) and glass-reinforced plastic (GRP) plates are compared. A novel integrating ultrasonic sensor was achieved usin g the signal arm of an actively stabilized 633-nm homodyne Mach-Zehnde r fiber interferometer which was either bonded directly to the plate s urface or spliced to single-mode fibers embedded within a composite pl ate during manufacture. An embedded fiber is shown to be about 20 time s more sensitive to Lamb wave motions than a surface-bonded fiber. How ever, the latter may be more practical. (C) 1996 Optical Society of Am erica