Ultrasonic Wireless Neural Recording and Stimulation Interfaces

Over the last decade, clinical implants have become smaller, increasingly wireless, more targeted for deep-tissue operation, and supportive of both neural recording and stimulation functions in a single implant. In this context, ultrasound has been explored as an attractive alternative to electromagnetic fields when coupling power to and communicating with implants. At its core, this new field is driven by the observation that the physics of ultrasonic (acoustic) waves make them attractive for coupling to very small implants (similar to mm(3)) deep in tissue (>5 cm). This chapter begins with an overview of this modality and its benefits. Subsequent sections provide an in-depth look at the state of the art in ultrasonic neural recording and stimulation systems and the associated engineering and physiological challenges, limiting the discussion to systems developed for central and peripheral nervous system applications. The chapter concludes with an overview of future research directions.