Near field modulated backscatter for in vivo biotelemetry

Fully implantable wireless biotelemetry devices have traditionally used active VHF/UHF transmitters or load modulation at HF frequencies. HF systems tend to be bandwidth-limited due to low frequency magnetic induction, while active VHF/UHF transmitters generally consume a significant amount of power in DC bias current. We show in this paper that UHF near-field backscatter can be used to achieve higher data rates at lower implant power budgets. We present experimental path loss measurements in a saline proxy system using a segmented loop antenna designed for UHF near-field operation. We present experimental results from a modulated backscatter test circuit at bit rates of up to 30 Mbps and penetration depths of up to 6 cm. The main communication element, an RF switch, consumes about 164 μA at 3 V while operating at a data rate of 30 Mbps, which is equivalent to approximately 16.4 pJ/bit.