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Recent advances in audio-visual augmented reality (AR) and virtual reality (VR) demands 1) high speed (>10Mbps) data transfer among wearable devices around the human body with 2) low transceiver (TRX) power consumption for longer lifetime, especially as communication energy/b is often orders of magnitude higher than computation energy/switching. While WiFi can transmit compressed video (HD 30fps, compressed @6-12Mbps), it consumes 50-to-400mW power. Bluetooth, on the other hand, is not designed for video transfer. New mm-Wave links can support the required bandwidth but do not support ultra-low-power (<1mW). In recent years, Human-Body Communication (HBC) [1]–[6] has emerged as a promising low-power alternative to traditional wireless communication. However, previous implementations of HBC transmitters (Tx) suffer from a large plate-to-plate capacitance (C p , between signal electrode and local ground of the transmitter) which results in a power consumption of aC p V2f (Fig. 16.6.1) in voltage-mode (VM) HBC. The recently proposed Resonant HBC [6] tries to overcome this problem by resonating C p with a parallel inductor (L). However, the operating frequency is usually < a few 10's of MHz for low-power Electro-Quasistatic (EQS) operation, resulting in a large/bulky inductor. Moreover, the resonant LC p circuit has a large settling time (≈5Q 2 RC P , where R is the effective series resistance of the inductor) for EQS frequencies which will limit the maximum symbol rate to <1MSps for a 21MHz carrier (the IEEE 802.15.6 standard for HBC), making resonant HBC infeasible for> 10Mb/s applications. 

To solve the challenge of powering and communication in a brain implant with low end-end energy loss, we present Bi-Phasic Quasi-static Brain Communication (BP-QBC), achieving < 60dB worst-case channel loss, and ~41X lower power w.r.t. traditional Galvanic body channel communication (G-BCC) at a carrier frequency of 1MHz (~6X lower power than G-BCC at 10MHz) by blocking DC current paths through the brain tissue. An additional 16X improvement in net energy-efficiency (pJ/b) is achieved through compressive sensing (CS), allowing a scalable (6kbps-10Mbps) duty-cycled uplink (UL) from the implant to an external wearable, while reducing the active power consumption to 0.52μW at 10Mbps, i.e. within the range of harvested body-coupled power in the downlink (DL), with externally applied electric currents < 1/5th of ICNIRP safety limits. BP-QBC eliminates the need for sub-cranial interrogators, utilizing quasi-static electrical signals for end-to-end BCC, avoiding transduction losses. 

Applications like Connected Healthcare through physiological signal monitoring and Secure Authentication using wearable keys can benefit greatly from battery-less operation. Low power communication along with energy harvesting is critical to sustain such perpetual battery-less operation. Previous studies have used techniques such as Tribo-Electric, Piezo-Electric, RF energy harvesting for Body Area Network devices, but they are restricted to on-body node placements. Human body channel is known to be a promising alternative to wireless radio wave communication for low power operation [1-4], through Human Body Communication, as well as very recently as a medium for power transfer through body coupled power transfer [5]. However, channel length (L) dependency of the received power makes it inefficient for L>40cm. There have also been a few studies for low power communication through the human body, but none of them could provide sustainable battery-less operation. In this paper, we utilize Resonant Electro Quasi-Static Human Body Communication (Res-EQS HBC) with Maximum Resonance Power Tracking (MRPT) to enable channel length independent whole-body communication and powering (Fig.1). We design the first system to simultaneously transfer Power and Data between a HUB device and a wearable through the human body to enable battery-less operation. Measurement results show 240uW, 28uW and 5uW power transfer through the body in a MachineMachine (large devices with strong ground connection) Tabletop (small devices kept on a table, as in [5]) and Wearable-Wearable (small form factor battery operated devices) scenario respectively, independent of body channel length, while enabling communication with a power consumption of only 2.19uW. This enables >25x more power transfer with >100x more efficiency compared to [5] for Tabletop and 100cm Body distance by utilizing the benefits of EQS. The MRPT loop automatically tracks device and posture dependent resonance point changes to maximize power transfer in all cases. 

Applications such as secure authentication, remote health monitoring require secure, low power communication between devices around the body. Radio wave communication protocols, such as Bluetooth, suffer from the problem of signal leakage and high power requirement. Electro Quasistatic Human Body Communication (EQS-UBC) is the ideal alternative as it confines the signal within the body and also operates at order of magnitude lower power. In this paper, we design a secure HBC SoC node, which uses EQS-UBC for physical security and an AES-256 core for mathematical security. The SoC consumes 415nW power with an active power of 108nW for a data rate of 1kbps, sufficient for authentication and remote monitoring applications. This translates to 100x improvement in power consumption compared to state-of-the-art HBC implementations while providing physical security for the first time.