Acoustic emission measurement using a strain-insensitive fiber Bragg grating sensor under varying load conditions.

Acoustic emission (AE) during a pressure test of a carbon fiber-reinforced plastic tank was measured using a fiber Bragg grating (FBG) sensor and, for comparison, using a conventional piezoelectric sensor. The FBG-inscribed optical fiber was used not only as an optical transmission line but also as an ultrasonic transmission line. The FBG sensor showed resonant characteristics and could detect AE continuously during the test. AE detected with the FBG sensor exhibited a cumulative behavior similar to that detected with the piezoelectric sensor. The FBG sensor was demonstrated to have comparable AE detection capability to piezoelectric sensors.