ACOUSTIC WAVE MEASUREMENTS AT ELEVATED TEMPERATURE USING A PULSED LASER GENERATOR AND AN ELECTROMAGNETIC ACOUSTIC TRANSDUCER DETECTOR

A wide bandwidth non-contacting ultrasonic system is described For the measurements of acoustic wave velocities in metals at elevated temperatures. A Neodymium: Yttrium Aluminium Garnet (Nd:YAG) pulsed laser was used as the ultrasound generator and a water-cooled Electromagnetic Acoustic Transducer (EMAT) that is sensitive to radial motion in the plane of the sample surface, acts as the receiver. Various laser ultrasound generation mechanisms have been evaluated to obtain simultaneously both the longitudinal and shear wave signals. Measurements have been made on mild steel, a copper alloy and aluminium-silicon alloys to a maximum temperature of about 1100° C. The results obtained have demonstrated that the system can be used to make acoustic wave measurements not only at elevated temperature but also in the fully molten state.