Low power respiration monitoring using wearable 3D knitted helical coils.

We demonstrate a novel low power inductive wearable plethysmography system. This consists of ultra-sensitive 3D knitted helical coils integrated in a garment and an oscillator circuit with high quality factor. The low power oscillator is built using two cross coupled FET pairs with low capacitance drawing only 95 μA during operation and with a response time smaller than 10 μs . The sensor system is linear, with negligible hysteresis. The best compromise in sensitivity and power consumption is obtained with a 3D knitted helical coil using jersey knit with elastic yarn, a lower knitting needle size than recommended for the yarn and minimizing both the number of stitches per winding as well as the stitches containing metal. A sensitivity of 2.7 kHz per mm change in circumference with a power consumption of 6.85 mW per 30 ms measurement time is reported. This system can be used for long term breathing monitoring using a garment indistinguishable from everyday clothing

Magnetic coupling with 3D knitted helical coils

Continuous power supply for wearable electronics can be facilitated using wireless power transfer (WPT). We use a 3D knitted helical coil as the receiver coil in the wrist or the waist of a garment. This 3D knitted helical coil is a novel approach to integrate coils in garments that maintains full flexibility of the garment. Measurements and simulations of coil-coil coupling give compelling evidence of the feasibility of this approach for wearable WTP. The coupling factor between a closely wound and knitted coil is found to be ~0.25 and ~0.55 for adjacent coils for a knit in the border of a cuff and waist, respectively. Using a simple circuit, we demonstrate a 30% efficiency between a closely wound transmitter coil worn on the wrist and a 3D knitted helical receiver coil integrated in the cuff of a garment at 6 mm distance

Knitted coils as breathing sensors

A new implementation of a wearable respiratory inductive plethysmography garment is obtained by knitting a 250 μm thin insulted Cu wire simultaneously with yarn in the round. This was used to integrate a knitted coil in the body of a baby romper suit. During simulated breathing the diameter of knitted coil changes by stretching the knit circularly, causing a variation of the self-inductance of the coil. Coils with 5 rows of integrated metal wire with different stitch types and patterns were investigated to determine their influence on inductance, series resistance and sensitivity. We observed that knit styles that reduce the resistance of the coil, such as lace and jacquard also reduce the inductance and flexibility of the garment. Jacquard with three colours and one metal wire for each colour, gave the highest coil quality factor but also the poorest flexibility. We found that 1/1 rib stitch has the highest self-inductance for all yarn types. Its sensitivity of 0.5 – 0.6 μH/cm is similar to stockinette stitch except when elastic viscose yarn is used. Coils in stockinette stitch and elastic viscose yarn have the highest sensitivity of 0.84 μH/cm. No hysteresis in self-inductance was observed for circumference variations between 44 and 53 cm of the body of the baby romper in 1/1 rib stitch due to the elasticity of knitted garments

Cyclic voltammetry peaks due to deep level traps in Si nanowire array electroes

When metal-assisted chemical etching (MACE) is used to increase the effective surface area of Si electrodes for electrochemical capacitors, it is often found that the cyclic voltammetry characteristics contain anodic and cathodic peaks. We link these peaks to the charging-discharging dynamics of deep level traps within the nanowire system. The trap levels are associated with the use of Ag in the MACE process that can leave minute amounts of Ag residue within the nanowire system to interact with the H2O layer surrounding the nanowires in a room temperature ionic liquid. The influence of the traps can be removed by shifting the Fermi level away from the trap levels via spin-on doping. These results in lower capacitance values but improved charge-discharge cycling behavior. Low-frequency noise measurements proof the presence or absence of these deep level traps

Average drift mobility and apparent sheet-electron density profiles in strained-Si-SiGe buried-channel depletion-mode n-MOSFETs

Published versio

SiGe HMOSFET monolithic inverting current mirror

Accepted versio

Analogue micropower FET techniques review

A detailed introduction to published analogue circuit design techniques using Si and Si/SiGe FET devices for very low-power applications is presented in this review. The topics discussed include sub-threshold operation in FET devices, micro-current mirrors and cascode techniques, voltage level-shifting and class-AB operation, the bulk-drive approach, the floating-gate method, micropower transconductance-capacitance and log-domain filters and strained-channel FET technologies

SiGe HMODFET "KAIST" micropower model and amplifier realization

Published versio

Monolithic large-signal transimpedance amplifier for use in multi-gigabit, short-range optoelectronic interconnect applications

Published versio

Characterization of Knitted Coils for e-Textiles

Inductor coils are integrated in many wearable garments for EM wave screening, heating and health monitoring. This paper presents a critical evaluation of the inductor characteristics of circular weft knitted coils for applications in etextiles. Inductors are knitted using circular needles with thin insulated metal wire and yarn knitted together. The resulting helical coils are characterized as a function of number of turns, coil diameter, needle size and insulated metal wire material. The results are compared to wound coils. Simulations of the knitted and wound coils show close agreement with the experimental results and confirm a higher inductance for the knits compared to the wound coils with the same pitch between turns. The parasitic coil capacitance is higher in the knit due to the vertical legs of the stitches, absent in wound coils. Knits with thin Cu and Litz wires result in flexible and wearable textile coils