Wireless powering and the study of RF propagation through ocular tissue for development of implantable sensors

This paper evaluates RF powering techniques, and corresponding propagation through tissue, to supply wireless-energy for miniature implantable devices used to monitor physical-conditions in real-time. To improve efficiencies an impulsive powering technique is used with short duty-cycle high instantaneous-power-bursts, which biases the rectifier in its nonlinear regime while maintaining low average input-powers. The RF rectifier consists of a modified two-stage voltage multiplier which produces the necessary turn-on voltage for standard low-power CMOS systems while supplying the required current levels. The rectifier, fabricated on the TI 130 nm CMOS process, measures 215 μm × 265 μm, and is integrated with an antenna to quantify wireless performance of the power transfer. In-vivo studies performed on New Zealand white rabbits demonstrate the ability of implanted CMOS RF rectifiers to produce 1 V across a 27 kΩ load at a distance of 5 cm with a transmit-power of just over 1.5 W. Using a pulsed-powering technique, the circuit generates just under 0.9 V output with an average transmit-power of 300 mW. The effects of implantation on the propagation of RF powering waves are quantified and demonstrated to be surmountable, allowing for the ability to supply a low-power wireless sensor through a miniature rectifier IC.