A new electromagnetic acoustic transducer (EMAT) design for operation on rail

•New design of EMAT, with a useful single-shot SNR over a large 10 mm liftoff range.•It achieves better lift-off performance than conventional rigid EMAT designs.•The EMAT coil skims over the sample surface, whilst the magnet is kept safely back.•EMAT pairs mounted to a moving train can detect defects during a scan of a rail.

Electromagnetic acoustic transducers (EMATs) can emit and receive ultrasound on a conducting sample without contact, but are usually kept within 3 mm lift-off from the sample surface, to achieve a sufficient signal-to-noise ratio (SNR). There are scenarios under which EMATs must scan a sample at high speed, with the EMAT-sample separation varying by more than the standard lift-off range, such as for detection of gauge corner cracks in rail. A new EMAT has been designed that allows the low weight and flexible EMAT coil to skim over the sample surface, while the heavier and bulkier magnet behind the coil has a lift-off that can vary over 10 mm whilst still achieving a reasonable SNR. In experiments conducted with the EMATs mounted on a train, scanning a rail, they were demonstrated as being sufficiently robust, with an SNR sufficient for defect detection.