4.1.3 Electromagnetic acoustic testing (EMAT)

EMAT, as a kind of excitation and detection technique of propagating ultrasonic wave, can provide detection of defects located in subsurface area of railhead. Thus, a promising method appears to be electromagnetic-acoustic method which is realised by EMAT transducers. Both transverse and longitudinal cracks in railhead can be detected by using EMATs, as shown in Figure 4 [59]. University of Warwick and University of Birmingham [60] developed a railway surface-detect inspection technique based on EMAT equipped with two EMAT converters, one for emitting surface Rayleigh waves and the other for receiving surface propagating Rayleigh waves. It is found that this technique can improve the inspection rate of horizontal and vertical defects on the railheads, compared with piezoelectric transducers. University of Warwick [61] designed a lab-based laser-EMAT system to investigate the ultrasonic surface wave's generation, propagation and interaction on the railhead with a Michelson interferometer measuring the out-of-plane displacement. The Rayleigh-like wave generated by EMAT can flood the whole curve makes it capable to detect the gauge corner cracking.
