Effect of waveguide impedance on radiation in underwater acoustic leaky wave antennas

Abstract

Leaky wave antennas (LWAs) have been examined for decades as a way to steer electromagnetic waves as indexed by input frequency, enabling rapid video scanning of an environment with a simple compact device. Recently, an LWA device constructed of a rigid waveguide with open shunts was shown to produce a similar steering effect for acoustic waves in air [Naify et al., Appl. Phys Lett. 102, 203508 (2013)]. The shunts serve two purposes, to couple acoustic energy from the waveguide to the surrounding area, as well as control directionality of the radiated wave by changing the impedance, and thus modulating the phase speed of the waves in the waveguide. While this impedance contrast of the waveguide wall relative to that of the surrounding fluid is very large for an air background, when designing a structure for use in water the material of the waveguide can drastically change the directionality of the radiation profile. This study examines the effect of waveguide wall impedance on directionality of an acoustic LWA using both numerical and finite element methods. Three material impedance conditions are examined, including acoustically rigid, and two materials with finite impedance. [Work sponsored by the Office of Naval Research.]