# Design and Structure of a Non-Coaxial Multi-Focal Composite Fresnel Acoustic Lens for Synergistic Ultrasound Stimulation of Multiple Brain Regions

## TL;DR

A new acoustic lens design enables focused ultrasound to stimulate multiple brain regions simultaneously, overcoming skull-related limitations.

## Contribution

A novel non-coaxial multi-focal composite Fresnel lens design for synergistic multi-region brain stimulation using TcFUS.

## Key findings

- The OFL and ASFL lenses successfully generated four non-coaxial foci from a planar ultrasound wave.
- Significant differences in focal morphology and intensity between OFL and ASFL were observed.
- Lens parameters significantly influence focal pressure distribution, guiding optimization of multi-target TcFUS.

## Abstract

Transcranial focused ultrasound (TcFUS) neuromodulation is hindered by skull-induced acoustic limitations. To enable synergistic multi-region brain stimulation, we designed non-coaxial multi-focal composite Fresnel acoustic lenses, including an overlapping Fresnel lens (OFL) and an alternating-segmented Fresnel lens (ASFL). These lenses convert planar ultrasound into multiple foci. Based on Fresnel theory, acoustic fields were analyzed via simulations and experiments, validating the generation of four non-coaxial foci (10/30 mm focal lengths) from a 1 MHz planar wave using both OFL and ASFL. The influence of lens parameters on focal pressure distribution was investigated, and morphology was quantified using a linear least-squares method. Significant differences in focal morphology and intensity between OFL and ASFL provide crucial guidance for optimizing multi-target TcFUS strategies.