Other Methods for Transmitting and Receiving Ultrasound

Abstract

Besides piezoelectric, also other physical effects can be utilized for generating and receiving ultrasound. Although many of these produce weaker signals than obtainable by the piezoelectric effect, they nevertheless offer a number of advantages which in special cases make their application in the testing of materials useful. In the case of many of these effects the energy is transmitted by electrical or magnetic fields which in principle make mechanical contact with the test piece unnecessary. The conversion into or from acoustic energy takes place in the surface of the workpiece concerned. Compared with the piezoelectric oscillator, which is coupled to the workpiece, the surface of the work piece forms in the case of these “direct” methods a part of the acoustic transducer. The direct or dry methods thus require no coupling medium, so avoiding some of the difficulties analysed in the next paragraph.