In-plane and out-of-plane particle velocity measurement using electromagnetic acoustical transducers

Abstract

The electromagnetic acoustic transducer (EMAT) is a particle velocity sensor. EMATs can be used to preferentially measure particle velocities in a particular direction (such as in-plane or out-of-plane) by arranging a static magnetic field perpendicular to the vector plane constructed by the wire direction and the specific direction of interest without interfering with the incident ultrasonic field. A receiving EMAT model is given for both infinite and finite sized magnets and ultrasonic waves, explaining the influence of EMAT size, ultrasonic wave size on induced coil voltage and the sensitivity to liftoff. Rayleigh waves and Lamb waves are measured using in-plane and out-of-plane EMATs, and are validated by comparison to the theoretical predictions. More specifically predicted and measured phase and amplitude measurements for Rayleigh and Lamb waves are compared.