Design and analysis of an acoustic random spherical volumetric array

Rigelsford, Jonathan Michael

Engineering design and manufacture
September 2001

Thesis or dissertation

© 2001 Jonathan Michael Rigelsford. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

Acoustic arrays have been widely studied and can be used for a variety of applications. Existing acoustic array systems have mainly utilised linear and planar geometries. Such geometries have limited scan angles and can suffer from beam broadening and large grating lobes.

This thesis presents a new acoustic array topology, the random spherical volumetric array. The system developed consists of 64 omni-directional microphones arranged at pseudo random locations within a spherical volume. The spherical array geometry provides the potential for full elevation and azimuth scan coverage. The projected aperture of a spherical array is direction independent, with the beamwidth and gain of the direction response being constant for all scan angles. The non-periodic element arrangement eliminates the possibility of large grating lobes and results in an array pattern with an average sidelobe level that is inversely proportional to the number of array elements. These properties enable wide-angle beam steering over a very large frequency bandwidth.

The potential of acoustic volumetric arrays is examined and the results of theoretical and experimental investigations are presented. Holographic techniques have been implemented on the experimental system to produce images of sound sources and of reflections in the test environment. The concept of a synthetic volumetric array is introduced in which original synthetic aperture and multiple frequency techniques can be successfully used to reduce the average sidelobe level of the random spherical volumetric array.

Initially, the acoustic random spherical volumetric array was envisaged as an inexpensive test-bed for microwave and radar system algorithm development. Since that time it has been found that application areas for the random spherical volumetric array also include covert surveillance operations, acoustic imaging and auditorium characterisation. Development of the system could allow security forces to monitor large crowds and riot situations; help in the detection of sniper location; and assist designers to build better auditoriums by highlighting areas of high reflection and reverberation.

Department of Engineering, Design and Manufacture, The University of Hull
Tennant, Alan
Sponsor (Organisation)
Engineering and Physical Sciences Research Council
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