Acoustic Power Transfer Using Self-Focused Transducers for Miniaturized Implantable Neurostimulators

An emerging neurostimulation therapy utilizes electroceuticals to treat numerous neurological disorders. With the aim to discover novel clinical applications of neural stimulation, device miniaturization has been a key challenge for successful clinical translation of implantable stimulators. The battery size has been a limiting factor in further miniaturization, so wireless power transfer without the use of an implanted battery has gained interest. Among various power transfer techniques, acoustic power transfer (APT) provides substantial benefits for powering implantable devices due to its proven safety and efficiency for human body penetration. In this study, we proposed an APT-based neurostimulator with an integrated self-focused 3.6 MHz acoustic transducer and a receiver circuit composed of a power management module and pulse generator. The size of the entire device was 8 mm $\times$ 8 mm $\times8.6$ mm, which is small enough to be implanted with a small incision. A focused beam generated by an external transmitter was received by another focused beam from a receiver transducer, and this optimized pair of transducers with a receiver circuit generated 1.5 V, 1.3 ms pulse trains, which successfully transmitted stimulation pulses. We adopted a 1–3 composite with a piezolayer to implement a curved aperture, which enabled less-attenuated, focused, and matched beams for maximization of power transfer efficiency. We evaluated APT performance through rigorous bench-top and phantom tests and demonstrated the feasibility of stimulation through an in vivo experiment of sciatic nerve stimulation using a rat model.