The Design of Acoustic Radar Baffles

C. J. Werkhoven Physics Department, University of Auckland, Auckland, New Zealand

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S. G. Bradley Physics Department, University of Auckland, Auckland, New Zealand

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Abstract

Compact acoustic antenna arrays, commonly used for profiling urban atmospheres, usually require acoustic baffles to minimize reflections from hard objects and to limit the impact of the 2–6-kHz signals on inhabitants. To facilitate optimum compact design, the authors show how to find the velocity potential or intensity for a wide range of baffle illuminations and baffle shapes immersed in a homogeneous atmosphere. Results are presented for baffle configurations in terms of wavenumber k = 2π/λ.

Baffle height needs to be about 40k−1, and baffle sides should not be so close to the speaker array as to cut the main beam. This is particularly important for steered beams, when sloping baffle sides are recommended. Square plan baffles are advantageous for arrays of regular columns and rows of speakers. A triangular fringe baffle top edge (thnadner) will also reduce sidelobes by about 18 dB if their width is about a wavelength and their height more than 10k−1. The basic baffles design criteria suggested are not extremely frequency-dependent, so practical implementation should be straightforward.

Corresponding author address: Dr. S. G. Bradley, Physics Dept., University of Auckland, Private Bag 92019, Auckland, New Zealand.

Abstract

Compact acoustic antenna arrays, commonly used for profiling urban atmospheres, usually require acoustic baffles to minimize reflections from hard objects and to limit the impact of the 2–6-kHz signals on inhabitants. To facilitate optimum compact design, the authors show how to find the velocity potential or intensity for a wide range of baffle illuminations and baffle shapes immersed in a homogeneous atmosphere. Results are presented for baffle configurations in terms of wavenumber k = 2π/λ.

Baffle height needs to be about 40k−1, and baffle sides should not be so close to the speaker array as to cut the main beam. This is particularly important for steered beams, when sloping baffle sides are recommended. Square plan baffles are advantageous for arrays of regular columns and rows of speakers. A triangular fringe baffle top edge (thnadner) will also reduce sidelobes by about 18 dB if their width is about a wavelength and their height more than 10k−1. The basic baffles design criteria suggested are not extremely frequency-dependent, so practical implementation should be straightforward.

Corresponding author address: Dr. S. G. Bradley, Physics Dept., University of Auckland, Private Bag 92019, Auckland, New Zealand.

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