Wireless power transmission and energy harvesting techniques could be used to power and operate devices in, on and around the human body. However, near-field power transmission approaches are limited by distance, and the efficiency of far-field radiofrequency methods is limited by the body shadowing effect. Here, we show that the body-coupling characteristics of electromagnetic waves—which are either artificially introduced or present in the immediate surroundings—can be used to enable a power transmission and energy harvesting method that offers power to locations all around the body. The body-coupled power transmission exhibits a path loss 30- to 70-dB lower than far-field radiofrequency transmission in the presence of body shadowing. The system can recover 2 µW at the head from an ~1.2-mW transmitter placed 160 cm away at the ankle. In the absence of an active power transmitter, we demonstrate placement-independent scavenging of ambient electromagnetic waves coupled onto the human body, resulting in a power recovery of ~2.2 µW from electromagnetic waves of up to −10-dBm on the body. Electromagnetic waves, which are either artificially introduced or present in the immediate surroundings, can couple to the surface of the human body, creating a power transmission and energy harvesting method that can be used to provide sustainable power to wearable devices all around the body.

Body-coupled power transmission and energy harvesting

Flexible electronics are compatible with film substrates that are soft and stretchable, resulting in conformal integration with human body. Integrated with various sensors and communication ICs, wearable flexible electronics are able to effectively track human vital signs without affecting the body activities. Such a wearable flexible system contains a sensor, a front-end amplifier (FEA), an analog-to-digital converter (ADC), a micro-controller unit (MCU), a radio, a power management unit (PMU), where the radio is the design bottleneck due to its high power consumption. Different from conventional wireless communications, body channel communication (BCC) uses the human body surface as the signal transmission medium resulting in less signal loss and low power consumption. However, there are some design challenges in BCC, including body channel model, backward loss, variable contact impedance, stringent spectral mask, crystalless design, body antenna effect, etc. In this paper, we conduct a survey on BCC transceiver, and analyze its potential role and challenges in wearable flexible electronics.

The Role and Challenges of Body Channel Communication in Wearable Flexible Electronics

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.

/pdf/body-area-powering-with-human-body-coupled-power-2xkzvmrhhr.pdf

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

As the number of body area electronics increases, the power source is becoming a major bottleneck. Using a battery for each node is bulky and inconvenient due to the need of frequent battery replacement/recharging. Conventional harvesting methods are largely placement confined and thus unable to sustain multiple nodes of heterogeneous placements simultaneously [1], [2]. For simultaneous power delivery to multiple nodes on body, [3] utilizes the near-field inductive link for power delivery to sensor nodes placed on the eTextiles shirt and thus exhibits placement constraints, whereas the far-field RF transfer based [4] suffers from antenna pattern distortion and body shadowing effect (RF energy blocked by human body), leaving sensor nodes under such effect practically uncovered due to the 20~40 dB more channel degradation [5]. Such placement-induced nonidealities, along with distance/environment induced impedance variations and voltage/power degradations, challenges the powering system design for wider body coverage. This paper presents the full-body coverage “body-coupled power delivery” and the placement-independent “body-coupled ambient energy harvesting” ICs, achieved by the Bulk Adaptation Rectifier (BAR) and the Detuned Impedance Booster (DIB), with the power sustainability supported by the Dual Mode Buck-Boost Converter (DM-BBC).

34.5 Human-Body-Coupled Power-Delivery and Ambient-Energy-Harvesting ICs for a Full-Body-Area Power Sustainability

In this paper, the feasibility of the intra-body power transfer is verified and an area-efficient rectifier with threshold voltage cancellation for intra-body power transfer is proposed. Through the measurement, the optimum power transmission frequency is determined as 1 MHz. Since the transmission voltage gain is sufficiently high (about 0.3) and nearly constant over a wide range of the load resistance, the intra-body power transfer works well even with the nonlinear and varying input impedance of the rectifier that is placed right after the receiving electrode. The proposed area-efficient rectifier cancels the threshold voltage by using a diode-connected device with a dynamically biased current source. It achieves a considerably smaller area of 65 μm × 30 μm than the area consumed by other designs reported previously. The overall power conversion efficiency (PCE) and voltage conversion ratio (VCR) are also improved. It achieves 84.4% of PCE and 85.6% of VCR with 1-V input voltage and 40-kΩ load.

An Area-Efficient Rectifier with Threshold Voltage Cancellation for Intra-Body Power Transfer

A galvanically-coupled body-channel communication (GCBCC) transceiver (TRX) is proposed for bionic arms, offering robust communication and human-body safety. The GC-BCC mitigates the influence from the environmental changes and disturbances. A simple termination at the RX input widens the channel bandwidth (BW), enabling 100Mb/s communication. The implantable TX guarantees the user’s safety by employing a current-regulating channel driver, a charge-balancing scheme, and a biphasic waveform generated by bipolar RZ (BRZ) encoding. The TRX IC fabricated in 0.18 mm CMOS, achieves a low bit-error rate (BER) of 10-9 with excellent TX and RX energy efficiencies of 4.75pJ/b and 26.8pJ/b, respectively.

A 100Mb/s Galvanically-Coupled Body-Channel-Communication Transceiver with 4.75pJ/b TX and 26.8 pJ/b RX for Bionic Arms

This paper presents a fully differential implantable neural recording front-end IC for monitoring neural activities. Each analog front-end (AFE) consists of a low-noise amplifier (LNA), a variable gain amplifier (VGA), and a buffer. The output signal of the AFE is digitized through a successive approximation register analog-to-digital converter (SAR ADC). The LNA adopts the currentreuse technique to improve the current efficiency, achieving the power consumption as low as 0.95 μW. The implemented LNA has the gain of 40 dB, the lowpass cutoff frequency of 10 kHz, and the high-pass cutoff frequency of sub-1 Hz which is realized using the current-controlled pseudoresistor. The VGA controls the gain from 21.9 dB to 33.9 dB for efficient digitization while consuming the power of 0.35 μW. The buffer drives the capacitive DAC of the ADC and consumes the power of 3.28 μW. The fabricated AFE occupies the area of 0.11 ㎟/Channel and consumes 4.6 μW/Channel under 1-V supply voltage. Each channel achieves the input-referred noise of 2.88 μVrms, the NEF of 2.38, and the NEF²VDD of 5.67. The front-end IC is implemented in a standard 1P6M 0.18-mm CMOS process.

A 1-V 4.6-μW/channel Fully Differential Neural Recording Front-end IC with Current-controlled Pseudoresistor in 0.18-μm CMOS

This brief presents an input-data-jitter-tolerant injection-type clock and data recovery (CDR) circuit with a super-harmonic injection-locked ring oscillator (SH-ILRO). Unlike prior injection-type CDRs that utilize a power-hungry CML-type data injection path or for which the data rate is limited to the process-defined CMOS logic bandwidth, the proposed injection-type CDR achieves energy-efficient data edge injection. The proposed wide-bandwidth source follower-based edge detector extracts the input data edge energy efficiently. The proposed SH-ILRO enables quarter-rate injection-locking without high-speed injection selection logic. Fabricated in 65-nm CMOS, the prototype injection-type CDR consumes 19.08 mW at 12 Gb/s with 87-MHz jitter transfer bandwidth and more than 1.0 UIpp jitter tolerance at 20 MHz.

A 12 Gb/s 1.59 mW/Gb/s Input-Data-Jitter-Tolerant Injection-Type CDR With Super-Harmonic Injection-Locking in 65-nm CMOS

This paper presents a galvanic coupling communication (GCC) receiver for bionic arms. The detachability of the bionic arms results in various changes such as contact impedance variation and electrode misalignment. Its dynamic usage conditions may lead to contact with metallic objects. Moreover, the GCC has an inherent drawback of narrow channel bandwidth, which limits the communication speed. In this work, we demonstrate that the GCC can offer robust operation under varying channel conditions by using HFSS simulations. In addition, by applying a cascaded continuous-time linear equalizer, the proposed receiver widens the bandwidth from 1 MHz to 60 MHz. Implemented in 0.18-um CMOS process, a 30-Mbps GCC receiver operates successfully for bionic arms with robustness against channel condition variations while following body safety guidelines and consuming 650 uW.

Chongsoo Jung

Papers

An Area-Efficient Rectifier with Threshold Voltage Cancellation for Intra-Body Power Transfer

A 100Mb/s Galvanically-Coupled Body-Channel-Communication Transceiver with 4.75pJ/b TX and 26.8 pJ/b RX for Bionic Arms

A 1-V 4.6-μW/channel Fully Differential Neural Recording Front-end IC with Current-controlled Pseudoresistor in 0.18-μm CMOS

A 12 Gb/s 1.59 mW/Gb/s Input-Data-Jitter-Tolerant Injection-Type CDR With Super-Harmonic Injection-Locking in 65-nm CMOS

A 650-uW 30-Mbps Galvanic Coupling Communication Receiver for Bionic Arms