A broadband electromagnetic UT system

An ultrasonic testing system based on contactless electromagnetic acoustic (e.m.a.) transduction has been developed by which broadband ultrasonic pulses are excited. This system overcomes disadvantages of usual e.m.a.transducers with meanderlike coil configuration, namely the excitation of narrowband pulses and the symmetrical radiation pattern. By dividing up a meanderlike coil into single elements and time delay is given by the distance of the elements and the phase velocity of the wave propagating along the surface, the ultrasonic pulse radiated in one preferred direction becomes broadband by constructive interference. The signals radiated in the opposite dircetion do no more interfere. Its amplitude is samaller than that of the other direction, so that the transducer becomes unidirectional. This technique can be applied of the excitation of all dispersionless waves (bulk waves and guided waves).