A Systematic Study of Wireless Link Frequency Selection Strategies for Miniaturized Backscattering Neural Implants

In this article, we present a systematic analysis on the frequency selection scheme of wireless link, toward miniaturized backscattering neural implants. A novel frequency selection scheme is proposed that takes more comprehensive consideration of frequency-dependent design constraints, including the power transfer efficiency (PTE) of the coils, the limitations of human electromagnetic exposure, the RF-to-dc conversion efficiency, and the power budget of a backscattering circuit. Frequency-dependent design constraints of brain implants are critically investigated first. Two representative application scenarios are then analyzed accordingly, including implants at the upper limb peripheral nervous system (PNS) and spinal cord. It is concluded that an upper limit of the wireless link operating frequency exists for miniaturized backscattering implants. For the application of cortical interfaces, the feasibility of the scheme was verified through prototyping and measurements at representative frequencies.