An acoustical helicoidal wave transducer with applications for the alignment of ultrasonic and underwater systems

Abstract

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 wavefront 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. The screw dislocation in the transducer beam is along the beam axis and 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. The helicoidal wave is also shown to possess axial angular momentum. A related transducer was summarized previously [J. Acoust. Soc. Am. 103, 2971 (1998)] and is also discussed here for the purposes of comparison.

Airborne ultrasonic vortex generation using flexible ferroelectrets

“…This type of beam exhibits many of the special characteristics of a helicoidal wave. Because of this, and considering their rather simple mathematical description, they are commonly used to synthesize acoustical vortices [7], [18].…”

“…In the acoustic context, AV can occur either in the linear or nonlinear regime [7], [8]. Considering that several researchers have found analogies between the structure of screw dislocations and vortices in fluids and quantum mechanics, the AV has been proposed as a tool for the experimental study of their optical, fluidic, and quantum counterparts.…”

“…This can be attributed, in part, to the need for complex instrumentation to generate a helical wavefront. Thus far, different methods for AV generation have been proposed, namely, direct generation from a specially shaped source [7], [12], the optoacoustic technique [13], mode conversion from wave plane to AV [9], or use of a phased array system [11].…”

A One-Sided View of Acoustic Traps

“…Looking at the phase diagram [ Fig. 1(c)], its variation from −π to π around the beam axis is characteristic of a vortex of topological charge equal to 1 [39][40][41]. The wave front describes a single helix with a pitch equal to λ and is left handed.…”

“…Field synthesis.-These peculiar wave fields have been successfully generated in acoustics [39][40][41] and applied to investigate the transfer of orbital angular momentum to matter [42][43][44][45][46]. In Fig.…”