Lift-off performance of electromagnetic acoustic transducers (EMATs) for surface acoustic wave generation

Electromagnetic acoustic transducers (EMATs) have a behaviour that depends on the distance between transducer and surface of material under test, namely lift-off. Rayleigh waves generated by EMATs suffer from waveform distortion as lift-off is increased. This paper describes this numerically experimentally, focusing spatial distribution induced currents hence ultrasound pulses. verified experimentally using an EMAT consisting magnet single 1.5 mm wide linear coil, showing decrease in peak frequency for wideband wave order 100 kHz/mm with The when array configuration (equivalent to meander-coil, where current through neighbouring coils opposite directions) then described. Coil spacing shown affect behaviour, model predicting well behaviour. behaviours physically spaced those which are pulsed time delays give effective separation be equivalent all but smallest separations; unless very small separations required high signal, spread coil counteracts benefits reducing dipole effect. Good performance variation hard achieve at frequency, must considered if particular operation required.