Non-contact ultrasonic characterization of defects using EMATs

We have developed a non-contact ultrasonic technique for detecting and gauging the depth Of Surface and subsurface defects in metals. A low-frequency broadband Rayleigh-wave pulse is generated and detected by two electro-magnetic acoustic transducers (EMATs) held at a standoff of LIP to 5 mm, with laser generation and detection also possible. This technique has applications for online testing such as rail track inspection, where faster speeds than will conventional contact ultrasonic techniques should be possible. We describe experiments gauging the position and depth of cracks by measuring the change in signal amplitude and frequency Content with the EMATs oil either side of the defect.. or by looking for all enhancement of the signal close to tire defect.