Investigations into acoustic dipole helical wave generation.

Abstract

Acoustic waves that transmit phase information spatially have recently been applied to navigation and communications systems. This paper will describe a helical wave, a type of wave that transmits phase information across a section of the plane linearly about the azimuth. The wave will be described from the ground up. First, a circular baffled transducer pressure field will be derived. Next, the field generated using two crossed circular transducers will be derived and approximations given for the far field. The general expression for the acoustic field from this arrangement is derived in the far field utilizing a paraxial ray approximation for ideal sources but applied to the more complex conceptualization of the monopole source being given by the circular piston source. In addition, the work presented was investigated numerically in comparison to a different approximation made in the field dependence on monopole separation of the two sources making up the dipole. Next, numerical examination of two crossed dipoles is examined with visualizations of the pressure and discussion of transients created when the direction of spiral changes. Finally, there is a discussion for the detection and estimation of helical waves and potential uses.