A Comparison of Vector-Sensing and Scalar-Sensing Linear Arrays.

Abstract : Some of the features which are unique to beamforming a linear array of vector sensors, not present with scalar-sensing elements (such as conventional pressure sensors), are described in this report. Vector sensors measure acoustic particle motion, for example acoustic particle velocity, in a given direction and these vectors have complex-valued components which are proportional to the amplitude and phase of a propagating acoustic field. Three types of vector sensors are considered; a uniaxial vector sensor which measures acoustic particle velocity along a single axis, a biaxial vector sensor measuring velocity in two orthogonal directions, and a triaxial sensor which measures all three orthogonal components of the velocity vector. Comparisons are made between the performance (in terms of received element and array sensitivity, array directivity, and signal gain with array curvature) of arrays comprised of each type of vector sensor, to arrays comprised of pressure sensors only. The comparisons have also evaluated two boundary conditions, perfectly baffled sensors and sensors in the free field. It is shown that a single triaxial vector sensor may be steered, in both azimuth and elevation, to any planewave arrival direction. A single pressure sensor provides no directivity in the free field. A comparison of array directivity indicates (for optimal real-valued amplitude shading coefficients) that triaxial and biaxial vector sensors can provide 5 dB of directivity gain over that obtained from an identical array of pressure sensors. The gain varies with the direction the array is steered to. Similarly, multiaxis vector sensors improve a conformal array's signal gain for all array steerings.