A Flexible Ultrasound Transducer with Tunable Focusing for Non-Invasive Brain Stimulation

Transcranial focused ultrasound (tFUS) is promising for non-invasive brain stimulation, due to its millimeter-level spatial resolution and centimeter-level penetration depth. To stimulate various regions within the human brain, including cortical and subcortical structures, it is necessary to adjust the focal depth of a single-element focused ultrasound transducer. Common approaches involve the utilization of an acoustic lens, altering the curvature of transducer surface, or controlling the distance between the transducer and the scalp using either a water bag or a gel pad. However, such methods require multiple interchanges of lenses, transducers, or bags/pads, rendering them impractical for clinical applications. In this paper, we introduce a novel ultrasound stimulation device comprising a flexible ultrasound transducer and a precise movable plunger to enable focus tunability. The focused effect was simulated through finite element analysis, while the adjustability of focal depth was gauged by controlling interface curvature of the flexible transducer, as measured with hydrophone. This novel apparatus has the potential to enhance ease of use of tFUS and efficiency of its clinical applications.