Superdirective line arrays can provide a significant array gain from a structure that is relatively small in terms of acoustic wavelengths. However, system imperfections, electronic noise and acoustic scatter from the array structure can degrade their performance. An acoustic calibration of a six-element line array, 0.8 m in length, has been performed over the frequency range 1 to 4 kHz in order to investigate the performance of a real array. The data is used to identify the angular variation of the hydrophone outputs and the phase difference between hydrophone pairs. These angular responses are analyzed in terms of a modal series in order to quantify the variations and help identify the source of perturbations. The effects of imperfections are also investigated by synthesising superdirective arrays of order 1 to 5 and monitoring how the array gain varies for both deterministic signals and ambient acoustic noise. These results are compared with theoretical predictions. Further evidence of the variation in performance is gained by comparing the output of different implementations of lower order arrays, synthesized from subsets of the full array. The results indicate the influences that the array structure may have on the performance of the array.
Acoustical Society of America Journal
- Pub Date:
- October 2003