Extraction of the direct scattering of a sphere in a vortex beam: Theory and experiment

The suppression of direct forward scattering is challenging for object detection in the underwater environment under the incidence of quasi-planar waves. In this work, we study the lateral spatial phase of forward acoustic scattering in a vortex beam from a sphere. By subtracting a stable incident contribution, the forward scattering is extracted from the total field with good agreement between our experimental measurements and numerical simulations. A cross correlation method of the spatial phase is proposed, and results show a linear dependence of the phase singularity shift versus the sphere's offset to the beam axis, which may be potential for the underwater target detection and positioning by using the spatial phase information as the degree of freedom.