Reconfigurable liquid-based acoustic lens for controlling the focal depth of focused ultrasound

Focused ultrasound (FUS) enables noninvasive treatment.Conventional FUS transducers with fixed geometries lack depth control, whereas dynamic focusing with multi-element phased arrays requires complex electronics that limit scalability.This study introduces a reconfigurable, liquid-based acoustic lens that attaches to a single-element planar ultrasound transducer to provide tunable focal-depth control.The lens consisted of a deformable low-density polyethylene membrane filled with perfluorooctyl bromide (PFOB), a biocompatible liquid with matching acoustic impedance and low reflectivity, and was coupled to a 500-kHz transducer.Adjusting the internal PFOB volume changed the lens curvature and acoustic wavefront, thereby controlling focal depth.Acoustic pressure fields were mapped under three conditions: no lens, 2 mL PFOB, and 3 mL PFOB.Cross-sectional analysis showed volume-dependent plano-convex lens deformation, with central heights of approximately 3.6 mm and 4.7 mm at 2 mL and 3 mL, respectively.Acoustic field maps showed that increasing the PFOB volume shortened the focal depth from 52 mm without a lens to 37 mm and 26 mm, with improved focal localization.Numerical simulations closely reproduced the experimental pressure maps.These findings demonstrate controllable focusing with a reconfigurable, liquid-based acoustic lens in a compact, single-element FUS system.