Experimental performance analysis of a superdirective line array

Abstract

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.

Robust high-order superdirectivity of circular sensor arrays

“…Equations (19) and (20) indicate that the SFs and DFs will be zero at frequencies where J m ðka sin h 0 Þ ¼ 0. It is inferred that for the synthesis of a desired beampattern which requires an apparent contribution of a specific eigenbeam near a zero frequency, the amplification will be very large and the final result will be non-robust.…”

“…(3) New superdirectivity models have been established. The differential model 20,21 and Taylor series framework (vector sensor technology) [22][23][24][25] provide different analytical solutions of superdirectivity, but they make approximations only to a certain degree and are thus considered insufficiently accurate.…”

A general superdirectivity model for arbitrary sensor arrays

“…Linear arrays for superdirectivity have been extensively investigated [11,24,[32][33][34][35][36]. An endfire linear array has been proven to possess the highest superdirectivity for a given number of sensors, and its DI approaches 20logN (dB) when the inter-sensor spacing becomes infinitely small [2,23], where N is the number of sensors.…”

Acoustic backscatter measurements from littoral seabeds at shallow grazing angles at 4 and 8 kHz

“…To address this concern, the singlehydrophone data were compared to the same returns processed using a fifth-order superdirective ͑SD͒ array. 25 The beam pattern of the fifth-order SD array is such that, relative to the on-axis response, the received sensitivity is Ϫ6 dB at 30°off-axis, and Ϫ10 dB at 35°off-axis. If significant energy was scattered/reflected by the frame, then it would show up in the single-hydrophone data but would be rejected by the superdirective processing.…”