Acoustical helicoidal wave transducers with applications for the alignment of ultrasonic and underwater systems

A simple four-panel transducer capable of producing a beam with a screw-dislocation along its axis was constructed and evaluated. A screw-dislocation in a wave front is characterized by a phase dependence about the dislocation axis that varies as exp(−imφ), where m is an integer and φ is the angle about the axis. At the axis the phase is indeterminate and as a result there is a corresponding null in the pressure magnitude. To generate a wave front with these characteristics, a four-panel 3-1 composite piezoelectric transducer was driven with the appropriate phasing of the panels to create dislocation along the beam axis. As a result the beam does not possess cylindrical symmetry, however, the dislocation is found to exist in both the far and near fields of the transducer. This null then clearly indicates the axis of the beam at all distances and has the potential to be used as an aid in the alignment of objects in sonar experiments or other similar applications. A related transducer was summarized previously [J. Acoust. Soc. Am. 103, 2971 (1998)] and is also discussed here for the purposes of comparison. [Work supported by the Office of Naval Research.]