Magnetically Balanced Power and Data Telemetry for mm-scale Neural Implants

Millimeter-sized implants for neural interface have been of great interest in the neuroengineering field due to their minimal invasiveness and great potential as an alternative to conventional bulky neural interfacing systems. However, their size poses great challenges not only on wireless power transmission, but also on uplink (implant to outside) data communication. One of most feasible data communication methods is load-shift keying based on the backscattering principle utilizing the existing inductive power link. This method consumes minimal power inherently, but its achievable modulation index is infinitesimal so that it is greatly challenging to detect the transmitted data on the outside. In this paper, we explore new schemes using a separate data reception coil that is magnetically balanced with the power coil. Due to its minimal crosstalk between the power transmission coil and data coil, a much higher data modulation index can be achieved. In addition to circular coils, we also present elliptical magnetic-balanced coil structures. According to finite element model stimulations with a realistic brain tissue model in Ansys HFSS and time domain simulation in Cadence, up to 15 × improvement in data modulation index can be achieved compared to conventional methods.