Adaptive Beamforming for Wireless Powering of a Network of Ultrasonic Implants

Networks of implantable medical devices (IMDs) capable of operating deep in the body are crucial for many novel diagnostic and therapeutic applications. Ultrasound (US) power and data transfer has shown promise for minimally invasive, deeply implantable devices wherein an external portable base station is used to power, coordinate, and communicate with IMD networks. Efficient US power transfer requires focused radiation on the IMD receiver, but current US arrays may have unwanted side lobes due to large transducer pitch with focusing being especially challenging when the application requires simultaneous powering of only a subset of IMDs while avoiding other IMDs in the network. In this work, we devise an adaptive beamforming approach, implemented using a least mean squares (LMS) algorithm, that allows for precise control over both the peak and null regions in the transmitted US beam. We demonstrate successful beamforming with multiple peaks at desired angles and transmit frequencies. In conjunction, we also show significant nulling (>40 dB) in regions where implants should not be activated.