Transcranial focusing of ultrasonic vortices by acoustic holograms

Abstract

[EN] Acoustic vortex beams have great potential for contactless particle manipulation and torque-based biomedical applications. However, when focusing acoustic waves through aberration layers such as the human skull at ultrasonic frequencies results in strong phase aberrations which prevent the generation of sharp acoustic images. In the case of a wavefront containing phase dislocations, skull aberrations inhibit the focusing of acoustic vortex beams inside the cranial cavity. In this work, we demonstrate that phase-conjugated acoustic holograms can encode time-reversed fields simultaneously allowing the compensation of the aberrations of the skull and the generation of a focused vortex inside an ex-vivo human skull. The method is applied for single-element geometrically focused sources and results in a very simple and compact ultrasonic system. This work will pave the road to design low-cost particle trapping applications, clot manipulation, torque exertion in the brain and acoustic-radiation-force based biomedical applications.