A 3-coil simultaneous power and uplink data transmission inductive link for battery-less implantable devices

Traditional 2-coil inductive link, for battery-less medical implantable devices, could hardly be used for the simultaneous wireless power and data transmission when the coupling is ultra-weak, since the strong power carrier could overwhelm the uplink signal and saturate the receiver. We thus proposed a 3-coil inductive link to transmit power and downlink data, as well as uplink data from the in-body device to the out-body part simultaneously. That is to add one extra out-body coil for the uplink receiving to minimize the power interference to the uplink signal by balanced canceling interference magnetic field. The inbody coil is still shared by the wireless power transfer (WPT) and the uplink communication. Two carriers (i.e. 2 MHz power carrier and 500 kHz uplink data carrier) are used for the WPT and the communication separately. Through optimizing the relative position of the two out-body coils and the circuit parameters, we achieved satisfied signal quality and sufficient efficiency of WPT. The prototype of this link sent −10 dBm power carrying 10 kbps uplink data rate under 10 mW power carrier interference with much relaxed −23 dB signal-to-interference ratio (SIR). This SIR was 67 dB higher than that of the 2-coil solution in our previous work. At the same time, the uplink caused less than 14% relative drop of the WPT efficiency compared with the pure WPT link without the uplink circuits.