Ultrasonic signal enhancement of Rayleigh-wave electromagnetic acoustic transducers combining narrow magnet with uneven-distribution coil

The ultrasonic signal generated by a Rayleigh-wave electromagnetic acoustic transducer (EMAT) is typically weak comparing with the signals generated by piezoelectric transducers, limiting EMATs’ application in nondestructive testing and evaluation (NDT&E). Conventional design of Rayleigh-wave EMATs normally has a wide magnet to completely cover its meander-line coil, so that in-plane Lorentz force can be produced to generate Rayleigh waves. A novel design of Rayleigh-wave EMAT operating with Lorentz force mechanism is presented to improve the transduction efficiency of the transducer and thus increase the amplitude of the
ultrasonic signal. The magnet of the novel design of EMAT is narrower than the meander-line coil of the transducer and the coil has unevenly distributed conductors. The principle of this novel narrow-magnet uneven-distribution-coil (NMUDC) EMAT is analysed via three-dimensional simulations, showing that the NMUDC EMAT can generate Rayleigh waves more
efficiently by simultaneously utilising both horizontal and vertical magnetic fields produced by the magnet. Experimental measurement results demonstrate that the amplitude of the ultrasonic signal produced by NMUDC EMAT has been increased by 90%, compared to conventional EMAT designs operating in a pulse-echo configuration.