SYNCHRONIZED TRIGGERING FOR ULTRASONIC TRANSIENT DETECTION USING OPTICAL-FIBER INTERFEROMETERS AND APPLICATION TO THE MEASUREMENT OF BROAD-BAND LAMB WAVE-DISPERSION CHARACTERISTICS

A method of synchronous acoustic source triggering is described for th e detection of ultrasound using an optical fibre interferometer. The c omparative noise immunity was higher than that for a comparable homody ne detection technique. The system was used in conjunction with an opt ical fibre Michelson interferometer to record spark-gap-source-generat ed ultrasonic Lamb waves propagating in aluminium and carbon fibre com posite plates. A two-dimensional fast Fourier transform approach enabl ed the broadband Lamb wave dispersion characteristics of aluminium to be measured.