Non-contact inspection of rail surface and internal defects based on electromagnetic ultrasonic transducers

A non-contact ultrasonic rail integrity inspection technique is discussed in this work as an alternative to concurrent contact-type ultrasonic testing method using piezoelectric transducers, which have some disadvantages due to physical contact between transducers and rails. To this end, transducers which can produce and measure elastic waves in rails without any physical contact were suggested based on electromagnetic ultrasonic transducers. The transducers were designed to selectively produce ultrasonic bulk waves or surface waves according to excitation frequency; it is possible to detect internal and surface defects with same transducer. Simulations using finite element models were performed to determine transducer operating frequencies optimal to defect types. With a series of experiments, it was shown that the proposed method could detect rail internal damages without any physical contact. The effects of air gap between the transducer and a rail and the position of a receiving transducer on the signals were studied to check practical lift-off distance and scanning speed of the method. Non-contact examination of rail surface defects was also carried out using the same transducers only by changing the frequency of excitation current and showed successful results.