Joonsung Bae

The Signal Transmission Mechanism on the Surface of Human Body for Body Channel Communication

The signal transmission mechanism on the surface of the human body is studied for the application to body channel communication (BCC). From Maxwells equations, the complete equation of electrical field on the human body is developed to obtain a general BCC model. The mechanism of BCC consists of three parts according to the operating frequencies and channel distances: the quasi-static near-field coupling part, the reactive induction-field radiation part, and the surface wave far-field propagation part. The general BCC model by means of the near-field and far-field approximation is developed to be valid in the frequency range from 100 kHz to 100 MHz and distance up to 1.3 m based on the measurements of the body channel characteristics. Finally, path loss characteristics of BCC are formulated for the design of BCC systems and many potential applications.

EFFECTS OF LITHIUM CONTENT ON THE ELECTROCHEMICAL LITHIUM INTERCALATION REACTION INTO LINIO2 AND LICOO2 ELECTRODES

Abstract The electrochemical lithium intercalation reaction into LiNiO 2 and LiCoO 2 electrodes in 1 M LiClO 4 —propylene carbonate solution is investigated as a function of lithium content in the oxide electrodes by using X-ray diffractometry (XRD), electrochemical impedance spectroscopy (EIS), and a galvanostatic intermittent titration technique (GITT). Li 1-δ NiO 2 shows a greater loss in capacity during the first intermittent discharge, as well as a higher resistance for the electrochemical intercalation reaction, in comparison with Li 1-δ CoO 2 . This is attributed to a partial cation mixing in Li 1-δ NiO 2 which is substantiated by XRD studies. The electrochemical impedance spectra of the Li 1-δ NiO 2 electrode reveals that the magnitude of the intermediate frequency arc that is associated with the absorption reaction decreases with increasing lithium content, (1 — δ), in the range from 0.5 to 0.7. By contrast, Li 1-δ CoO 2 exhibits the reverse behaviour.—The component diffusivities of lithium ions display a nearly constant value, in the order of 10 −11 cm 2 s −1 , for both electrodes at room temperature, irrespective of the value of (1 — δ) over the range 0.5–0.7. It is suggested that lithium-ion diffusion through both the layered oxides is affected by the number of empty sites within the lithium-ion layer, and not by the lattice parameter.

A 0.24-nJ/b Wireless Body-Area-Network Transceiver With Scalable Double-FSK Modulation

An energy-efficient wireless body-area-network (WBAN) transceiver is implemented in 0.18-μm CMOS technology with 1-V supply voltage. For the low energy consumption, the body channel communication (BCC) PHY is utilized with the theoretical results of Maxwells equation analysis behind the BCC. Based on the channel analysis, the resonance matching (RM) and contact impedance sensing (CIS) techniques are proposed to enhance the quality of the body channel. A double-FSK modulation scheme is adopted with high scalability to fulfill the IEEE 802.15.6 Task Group specifications. In addition, a low-power double-FSK transceiver is implemented by five circuit techniques: 1) a reconfigurable LNA with CIS; 2) a current-reuse wideband demodulator; 3) a divider-based local oscillator (LO) generation with duty-cycle correction in the receiver; 4) a reconfigurable driver with RM; and 5) a divider-based digital double-FSK modulator in the transmitter. As a result, fully WBAN compatible receiver and transmitter consume 2.4 and 2 mW, respectively, at a data rate of 10 Mb/s, corresponding to energy consumption of 0.24 nJ per received bit and 0.2 nJ per transmitted bit.

A 10.8 mW Body Channel Communication/MICS Dual-Band Transceiver for a Unified Body Sensor Network Controller

An energy-efficient dual-band transceiver for unified body sensor network is presented. The transceiver provides 30-70 MHz body channel communication (BCC) and 402-405 MHz medical implant communication service (MICS). For low energy consumption, the BCC and MICS band circuits in the receiver operate concurrently with their front-ends shared. As a result, up to 30% energy saving is achieved. The dual-band front-end circuits consist of a cascaded LC tank LNA and a current-recycling concurrent-down conversion mixer. The proposed LNA provides > 16 dB gains both in the BCC and MICS bands and suppresses interferences coupled through the human body by more than 10 dB. For BCC robustness, a variable adaptive frequency hopping is applied. The transceiver fabricated with 0.18 ¿m CMOS is fully compatible with the FCC regulations for MICS and consumes 10.8 mW and 4.9 mW in its RX and TX modes, respectively. The adjacent channel rejections are measured at > 30 dB in the dual-bands.

A 60 kb/s–10 Mb/s Adaptive Frequency Hopping Transceiver for Interference-Resilient Body Channel Communication

An interference-resilient 60 kb/s-10 Mb/s body channel transceiver using the human body as a signal transmission medium is designed for multimedia and medical data transaction in body-area network. The body antenna effect which interferes with signals in the human body channel is examined. The body-induced interferences degrade the SIR of the signal to -22 dB in the worst case. In order to overcome the body antenna effect, a 4-channel adaptive frequency hopping scheme using the 30-120 MHz band is introduced to the body channel transceiver. A direct-switching modulator using dual frequency synthesizers and a DLL-based demodulator are proposed for 10 Mb/s FSK and the 4.2 mus hopping time. The transceiver fabricated with 0.18 mum CMOS withstands -28 dB SIR and its operating distance is over 1.8 m with - 25 dB SIR. Its energy consumption is 0.37 nJ/b with -65 dBm sensitivity.

A Low Energy Injection-Locked FSK Transceiver With Frequency-to-Amplitude Conversion for Body Sensor Applications

An energy-efficient 920 MHz FSK transceiver for wireless body sensor network (BSN) applications is implemented in 0.18 μm CMOS technology with 0.7 V supply. A transceiver architecture based on injection-locked frequency divider (ILFD) is proposed for the low energy consumption. In the receiver, the ILFD in the signal path converts the received FSK signal to amplitude-modulated signal which is applied to the next envelope detector. In the transmitter, the ILFD is used as digitally-controlled oscillator (DCO) which directly modulates the FSK signal with digital data. The DCO replaces the frequency synthesizer to eliminate the crystal oscillator (XO), which leads to reduce power consumption and cost. The transceiver can detect whether injection locking occurs or not, and calibrates the frequency drift of DCO over temperature variation thanks to ILFD based architecture. The receiver and transmitter consume 420 μW and 700 μW , respectively, at - 10 dBm output power with a data rate of 5 Mb/s, corresponding to energy consumption of 84 pJ per received bit and 140 pJ per transmitted bit.

The ac impedance study of electrochemical lithium intercalation into porous vanadium oxide electrode

Abstract The electrochemical lithium intercalation into vanadium oxide in LiClO4 propylene carbonate solution has been investigated by using electrochemical impedance spectroscopy as a function of lithium content. Impedance spectra measured in the lithium content range investigated (δ = 0–0.8 in LiδV2O5) consist of a high frequency depressed arc and a low frequency straight line. The high frequency arc is attributed to the charge transfer reaction at the vanadium oxide/electrolyte interface and the low frequency line is associated with the diffusion of lithium ion through single vanadium oxide phase or with the movement of the boundary separating two phases. The chemical and component diffusivities of lithium ion in vanadium oxide were determined from the low frequency line combined with coulometric titration curve. The variation of the chemical and component diffusivities with lithium content has been discussed in relation to the coulombic interaction between the intercalated lithium ion and the oxide lattice.

A 3.9 mW 25-Electrode Reconfigured Sensor for Wearable Cardiac Monitoring System

A low power highly sensitive Thoracic Impedance Variance (TIV) and Electrocardiogram (ECG) monitoring SoC is designed and implemented into a poultice-like plaster sensor for wearable cardiac monitoring. 0.1 Ω TIV detection is possible with a sensitivity of 3.17 V/Ω and SNR > 40 dB. This is achieved with the help of a high quality (Q-factor > 30) balanced sinusoidal current source and low noise reconfigurable readout electronics. A cm-range 13.56 MHz fabric inductor coupling is adopted to start/stop the SoC remotely. Moreover, a 5% duty-cycled Body Channel Communication (BCC) is exploited for 0.2 nJ/b 1 Mbps energy efficient external data communication. The proposed SoC occupies 5 mm × 5 mm including pads in a standard 0.18 μm 1P6M CMOS technology. It dissipates a peak power of 3.9 mW when operating in body channel receiver mode, and consumes 2.4 mW when operating in TIV and ECG detection mode. The SoC is integrated on a 15 cm × 15 cm fabric circuit board together with a flexible battery to form a compact wearable sensor. With 25 adhesive screen-printed fabric electrodes, detection of TIV and ECG at 16 different sites of the heart is possible, allowing optimal detection sites to be configured to accommodate different user dependencies.

A Planar MICS Band Antenna Combined With a Body Channel Communication Electrode for Body Sensor Network

A 2.5 times 1.8 cm2 medical implant communication service band antenna is combined with an electrode for body channel communication. The proposed design enables a body sensor network controller to communicate with health-care devices located on and inside a patients body. The spiral microstrip antenna with its radiating body and ground plane placed side-by-side has the thickness of 2 mm and can be attached to human skin conveniently. The propagation loss of the body channel is measured when the proposed antenna is used as the skin interface for BCC in the 10-70-MHz band, and the results are compared with the cases of Ag/AgCl and circular dry electrodes. The equivalent-circuit model of the antenna as the electrode is also derived from the measured impedance characteristics. The LC resonance structure to drive the on-body antenna with its capacitance increased due to the skin contact reduces the power consumption of the TX buffer by >50%. TheS 11-parameter of the on-body antenna, its radiation pattern, and the signal loss inside the human body are investigated.

A low energy injection-locked FSK transceiver with frequency-to-amplitude conversion for body sensor applications

An energy-efficient 915MHz FSK transceiver for wireless body sensor network (BSN) applications is implemented in 0.18um CMOS technology with 0.7V supply. A transceiver architecture based on injection-locked frequency divider (ILFD) is proposed for the low energy consumption. In the receiver, through the ILFD in the signal path, the received FSK signal is converted to amplitude-modulated signal which is applied to the following envelope detector. In the transmitter, the ILFD is used as digitally-controlled oscillator (DCO) which replaces the frequency synthesizer to eliminate the crystal oscillator (XO). The receiver and transmitter consume 420uW and 700uW, respectively, at −10dBm output power with a data rate of 5Mb/s, corresponding to energy consumption of 84pJ per received bit and 140pJ per transmitted bit.