Particle velocity gradient based acoustic mode beamforming for short linear vector sensor arrays

Abstract

In this paper, a subtractive beamforming algorithm for short linear arrays of two-dimensional particle velocity sensors is described. The proposed method extracts the highly directional acoustic modes from the spatial gradients of the particle velocity field measured at closely spaced sensors along the array. The number of sensors in the array limits the highest order of modes that can be extracted. Theoretical analysis and numerical simulations indicate that the acoustic mode beamformer achieves directivity comparable to the maximum directivity that can be obtained with differential microphone arrays of equivalent aperture. When compared to conventional delay-and-sum beamformers for pressure sensor arrays, the proposed method achieves comparable directivity with 70%-85% shorter apertures. Moreover, the proposed method has additional capabilities such as high front-back (port-starboard) discrimination, frequency and steer direction independent response, and robustness to correlated ambient noise. Small inter-sensor spacing that results in very compact apertures makes the proposed beamformer suitable for space constrained applications such as hearing aids and short towed arrays for autonomous underwater platforms.

Low-frequency beamforming for a miniaturized aperture three-by-three uniform rectangular array of acoustic vector sensors

“…If a different steering vector bðuÞ is used, the beam pattern changes; see Ref. 25, for example. However, since the pattern synthesis is analogous to the ULA case, in this paper, we will focus on how to estimate the mode components bð/Þ for the 3 Â 3 2D-AVS URA.…”

“…The mode amplification step handles the imbalanced amplitudes of the mode components, at the cost of a sharp increase in the uncorrelated noise power. For comparison purposes, the WNG of Gur's subtractive beamformer for the ULA of 2D AVS 25 is also illustrated in Fig. 5.…”

“…A superdirective beamformer has also been proposed for the short uniform linear array (ULA) of 2D AVS. 25 Unlike most superdirective ULAs that only comprise the pressure sensors, the main response axis of this superdirective ULA of 2D AVS can be freely steered to any direction in the 2D space.…”

“…This paper introduces a superdirective mode domain beamformer for a 3 Â 3 uniform rectangular array (URA) of 2D AVS with miniaturized aperture. Similar to Gur's ULA, 25 the proposed beamformer design is also based on the finite differences of the particle velocity measurements for the extraction of the acoustic modes. The differential coefficients are obtained in light of the source-sink pictures of the Taylor's series dipole, quadrupole, and multipoles of higher orders.…”

Unidirectional acoustic probe based on the particle velocity gradient

“…After the Microflown sensor was introduced, its reduced dimensions and high similarity between sensor elements enabled the creation of complex configurations to achieve highly directional probes. [9][10][11] Free-field and pressure microphones have a sensitivity response which is not dependent upon the direction of arrival of the incident sound, i.e., they have an omnidirectional directivity pattern. By contrast, acoustic particle velocity sensors (also called Microflown sensors) have a frequency-independent figure eight directivity.…”