Human body and head characteristics as a communication medium for Body Area Network

An Intra-Body Power Transfer System With 1-mW Power Delivered to the Load and 3.3-V DC Output at 160-cm of on-Body Distance

This paper presents an intra-body power transfer (IBPT) system that can deliver power greater than 1 mW across an on-body distance of 160 cm. A system simulation model is built for the characterization of the channel and optimization of the power transfer. Our system analysis and experimental validation demonstrate that 1 MHz is an optimal carrier frequency for IBPT in terms of power delivered to the load (PDL) and power efficiency (PE). Prototype TX and RX boards were built, and an IC was fabricated in a 180-nm CMOS process for the RX. The proposed RX IC consists of a voltage doubler (VD) and a charge pump (CP) to obtain a sufficiently high voltage conversion ratio (VCR). Among various rectifier topologies, the VD is the optimal topology for the power receiver front-end because the parasitic ground coupling capacitances, which inevitably exist in the IBPT system, act as an inherent input-coupling capacitance for the VD. The implemented VD utilizes a dynamic V_TH compensation (DVC) for its diode components. Compared to the conventional static V_TH compensation (SVC), DVC in the VD reduces the reverse leakage current of the diode, thus maximizing the power conversion efficiency (PCE) and VCR. In addition, the PDL is enhanced by inserting an inductor on the TX board. It reduces the backward-path impedance without increasing the RX volume, boosting the PDL by up to 9.9 times compared to the PDL without the inductor insertion. The proposed IBPT system delivers up to 178.8 μW of power at 11.7% of maximum power efficiency with 3.3-V DC output voltage and even 1.385 mW of power with the inductor insertion, supporting various biomedical wearable sensors, such as ECG sensor modules.

Body-Area Powering With Human Body-Coupled Power Transmission and Energy Harvesting ICs

This paper presents the body-coupled power transmission and ambient energy harvesting ICs. The ICs utilize human body-coupling to deliver power to the entire body, and at the same time, harvest energy from ambient EM waves coupled through the body. The ICs improve the recovered power level by adapting to the varying skin-electrode interface parasitic impedance at both the TX and RX. To maximize the power output from the TX, the dynamic impedance matching is performed amidst environment-induced variations. At the RX, the Detuned Impedance Booster (DIB) and the Bulk Adaptation Rectifier (BAR) are proposed to improve the power recovery and extend the power coverage further. In order to ensure the maximum power extraction despite the loading variations, the Dual-Mode Buck-Boost Converter (DM-BBC) is proposed. The ICs fabricated in 40 nm 1P8M CMOS recover up to 100 μW from the body-coupled power transmission and 2.5 μW from the ambient body-coupled energy harvesting. The ICs achieve the full-body area power delivery, with the power harvested from the ambiance via the body-coupling mechanism independent of placements on the body. Both approaches show power sustainability for wearable electronics all around the human body.