Second-order cone programming with probabilistic regularization for robust adaptive beamforming.

Probabilistic regularization (PR) is introduced to make superdirective array beamforming robust against sensor characteristic mismatches. The objective is to enlarge the directivity while ensuring robustness with high probability. The PR problem is solved via the second-order cone programming where the regularization parameter is chosen through a statistical analysis of the system perturbations, based on Monte Carlo simulations. Experiments are carried out on a miniaturized 3 × 3 uniform rectangular array without calibration. The results show that for this particular array, the PR method is robust to sensor mismatches and achieves a higher level of directivity compared with other robust adaptive beamforming approaches.

An upper bound for the directivity index of superdirective acoustic vector sensor arrays.

Approximate analytical expressions of the white noise gain (WNG) for two superdirective acoustic vector sensor arrays are provided, which disclose the strong dependence of the tradeoff between the WNG and the directivity index (DI) on the highest order of the modes for the pattern synthesis. The considered arrays are a uniform linear array and a uniform circular array. A condition on the WNG that ensures a high array gain in the two-dimensional homogeneous and isotropic noise field is deduced. Using this condition, an upper bound on the highest order of the modes for the pattern synthesis can be derived, and hence the maximum DI can be determined. The presented results are not strictly limited to the two array geometries considered herein, and can be extended to other superdirective acoustic array designs.

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

This paper proposes a mode domain beamforming method for a 3 × 3 uniform rectangular array of two-dimensional (2D) acoustic vector sensors with inter-sensor spacing much smaller than the wavelengths in the working frequency band. The acoustic modes are extracted from the particle velocity observations in light of the source-sink pictures of the Taylor's series multipoles [Wikswo and Swinney, J. Appl. Phys. 56(11), 3039-3049 (1984)]. Then, similar to other mode domain methods, the modes are synthesized to obtain the desired beam pattern. The proposed method is limited to the cases where five is the maximum order of the modes for pattern synthesis, meaning that the directivity index in the 2D isotropic noise case can reach up to 10.4 dB. The proposed method has been validated by field experiments.

A method for acoustic parameter measurement of viscoelastic material.

A method for acoustic parameters measurement of viscoelastic material, using the directivity pattern of scattering field of spherical sample made by that material, had been presented. Aluminum spheres had been used for verification of the accuracy of this method, and the measurement results of a kind of rubber had been given. It shows that this method can be used to measure parameters of viscoelastic material in sufficient wide frequency range.