Bidirectional communications in wireless microstimulators based on electronic rectification of epidermically applied currents

Functional Electrical Stimulation (FES) has been used in order to restore muscle functions in patients suffering from neurological disorders. This therapeutic approach benefits from technological improvements that yield miniaturization. We previously have proposed and demonstrated an innovative electrical stimulation method in which wireless implants act as rectifiers of innocuous high frequency (HF) currents. These currents are conductively supplied to the tissues where the implants are located through external electrodes. Locally, the implants generate low frequency currents capable of stimulating excitable tissues. The method has the potential to enable unprecedented levels of miniaturization. The implant needs only two peripheral electrodes both for picking-up the HF current and for performing electrical stimulation. In addition, a tiny hybrid microcircuit, or a single integrated circuit, may integrate all the necessary electronic components. No bulky parts such as coils or batteries are required. We have demonstrated a number of circuit architectures for the implants with advanced capabilities such as digital addressability. In here, we demonstrate that the proposed method also allows bidirectional communications between the implants and the external system that powers and governs them, enabling proprioception-like sensing capabilities that may be crucial for closed-loop FES systems. We demonstrate a scheme based on amplitude modulation and Manchester encoding.