Focalization of Acoustic Vortices Using Phased Array Systems

Acoustic vortices (AV) are helical wavefronts that exhibit a screw-type dislocation and a phase singularity along its principal axis of propagation, at which the pressure of the field is zero. AV can be generated using various methods among which stands out the use of phased array systems because they allow us to electronically control the acoustic beam by means of the application of a given delay law to the array elements. Little research has been reported regarding the focalization of AV to obtain a higher pressure distribution. In view of this, this work presents the study of different delay laws for generating and focusing AV. The analysis of the resultant geometry and pressure distribution of the focused beams is included. We demonstrate that it is possible to increase the pressure amplitude up to 3 times with respect to a non-focalized, at the focal distance. Experimental tests were carried out using a hexagonal multitransducer of 30 elements at 40 kHz. A good agreement between simulations and experimental results was obtained.