ELECTROMAGNETIC ACOUSTIC TRANSDUCERS

摘要

An electromagnetic acoustic transducer (1) for generating ultrasound waves in an electrically conducting sample (2) comprises magnetic means (7) for producing a static magnetic field, and a coil (5) through which brief current pulses are passed to create a dynamic magnetic field, the interaction between the fields and the sample (2) generating ultrasound waves. The current pulses are produced by an input circuit (11), and their characteristics are arranged so that the frequency content of the ultrasound generated is broadband. Output pulses produced as a result of the input pulses are then also brief (substantially the same duration as the input pulses) so that accurate measurement of the interval between one output pulse and the next is relatively easy. The transducer can therefore be used to measure accurately the thickness of very thin samples, and to detect near surface defects. The generating transducer (1) may also be used for detection of the output pulses, or a similar but separate detecting transducer (1') may be used.