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This paper reports the development of a wireless pressure sensing coil system by embedding a capacitive micro sensor onto a wire. The coil system, consisting of an inductor (coil itself) and multiple capacitors (sensors), formed a passive LC telemetry configuration for wireless sensing. The capacitive sensor, utilizing the movements of a liquid in a sealed chamber for hydraulic amplification, enabled high capacitance changes and amplified signal outputs. The capacitive sensor also produced digitized signal outputs as the liquid movement crossed a finite number of the interdigitated electrodes. Such characteristics were modeled and confirmed by establishing an equivalent fluidic circuit. The capacitive sensor was fabricated by grafting and polishing a copper wire piece on a silicon wafer, then performing standard microfabrication on the polished wire surface and filling a liquid into a sensor chamber. The fabricated pressure sensing coil system demonstrated a pressure sensitivity of 11.8 kHz/mmHg under a clinical pressure range of 0~206.9 mmHg in an ex vivo test with a water flowing tube, meeting the requirements for wireless detection of vessel restenosis. The sensitivity corresponded to the capacitance changes of 0.052 fF/mmHg and liquid displacement of $0.39~\mu \text{m}$ /mmHg. The fabricated coil system held a dimension of 2.5 mm in diameter and 7.2 mm in length in the form of a wound wire (copper, $260~\mu \text{m}$ in diameter). The embedded capacitive sensor consisted of a hydraulic chamber of $400\times 100\times 1 2\,\,\mu \text{m}^{3}$ and a microchannel of $500\times 20\times 1 2\,\,\mu \text{m}^{3}$ . [2020-0364]

Wearable eye tracking devices have broad uses in medicine, psychology, augmented & virtual reality and consumer market research. Most mobile eye trackers available today utilize infrared imaging of the pupil and corneal reflections with video cameras. This tracking method requires sophisticated real-time processing of video signals consuming substantial electrical power. This method is thus unsuitable for light weight wearables such as adaptive smart eyeglasses for correction of presbyopia. In this paper we present a low-profile, low-power (7.7 mJ/sample) digital eye tracker oculometer based on infrared sclera tracking. The system is implemented using eight, 24-bit infrared proximity sensors and synchronous infrared LEDs. The pupil location is determined from 32 reflected pulsed light measurements independent of ambient illumination. The digital oculometer is 3.1 mm thick and weighs ~3 g. The tracker mounts adjacent to the tunable lenses in the smart eyeglasses frame. The eye tracker showed a pointing error of 1.3 degrees rms over a vertical and horizontal range of 30 degrees when tested by an observer.

This paper reports the development of a high-sensitivity gas sensor and the demonstration of selectively detecting green leaf volatiles (GLV, here hexanal) released from damaged plant leaves. The developed sensor is a conductivity sensor that utilized a 5.2-nm gap as the key detection site between electrodes. The gap was coated with with customized molecular probes toward binding to hexanal. The fabricated sensor demonstrated the detection of a GLV, hexanal, from the collected gas samples from damaged plant leaves, sorghum. Gas samples were collected into a tedlar bag from a glass jar containing damaged sorghum leaves. When exposed to hexanal concentrations from 77.7 to 5181.3 ppm, it produced output signal changes in resistance by 1.64~4.45 times. The sensor response time was measured as 41.6 min at a hexanal concentration of 77.7 ppm.

We report the electrical detection of captured gases through measurement of the quantum tunneling characteristics of gas-mediated molecular junctions formed across nanogaps. The gas-sensing nanogap device consists of a pair of vertically stacked gold electrodes separated by an insulating 6 nm spacer (~1.5 nm of sputtered α-Si and ~4.5 nm ALD SiO2), which is notched ~10 nm into the stack between the gold electrodes. The exposed gold surface is functionalized with a self-assembled monolayer (SAM) of conjugated thiol linker molecules. When the device is exposed to a target gas (1,5-diaminopentane), the SAM layer electrostatically captures the target gas molecules, forming a molecular bridge across the nanogap. The gas capture lowers the barrier potential for electron tunneling across the notched edge region, from ~5 eV to ~0.9 eV and establishes additional conducting paths for charge transport between the gold electrodes, leading to a substantial decrease in junction resistance. We demonstrated an output resistance change of >108 times upon exposure to 80 ppm diamine target gas as well as ultralow standby power consumption of

The paper reports the fabrication and testing results of a graphene-based thermal conductivity detector (TCD) by taking advantages of ultra low mass, large surface area and high thermal conductivity of a multilayer graphene (MLG) for low power gas detection. The fabricated TCD consists of a transferred and thus suspended MLG across a micro channel where target gases flow through. The sophisticated transfer process was successfully performed to construct a relatively large free-standing MLG membrane with a footprint of 75x3,600 um2. The fabricated TCD, when connected to a micro gas chromatography (μGC) column, demonstrated the chromatographic detection of pentane, hexane and heptane gases with a limit of detection (LOD) of 4760 ppm of pentane, while consuming only 26 mW.

We report a novel concept and testing results of utilizing a pressure sensor as an in-situ gas sensor for a micro gas chromatography system. The pressure sensor utilized a phenomenon that instant viscosity variation by an injection of gas molecules into a background gas stream caused instant pressure transient thus making it feasible to the in-situ monitor gas molecules using a pressure sensor during gas chromatography operation. Such a concept of viscosity-to-pressure conversion was experimentally proven and implemented. The implemented pressure sensors at multiple locations successfully monitored the progress of gas molecules in separation in four serially connected micro columns. This pressure sensor based chromatogram generated 125.5 Pa of pressure for $0.5\ \mu\mathrm{L}$ of hexane sample and showed a separation of hexane and heptane mixture with plate numbers of 93.68 and 244.69 respectively and with a separation distance and resolution of 30.5 and 2.4 respectively. The separation distance and resolution were 0.86 and 1.45 times to that of in FID separation, indicating no significant pressure sensor influences on separation.

This paper reports a new proof-of-concept gas sensor based on statistical behavior of multiple gas molecules. The reported gas sensor, consisting of a tiny gap, provides on/off switching behavior as it captures the target gas molecules. The key innovation lies in the fact that such an off/off switching becomes statistically-reliable when multiple gaps and molecules are utilized. Such a statistics-based gas sensor was demonstrated by fabricating multiple nano-gap arrays, coating the gaps with specific chemistry linkers, and monitoring the reliability of the performance as well as other variables. The fabricated sensors in $1\mathrm{x}1,\ 5\mathrm{x}5$ and $9\mathrm{x}9$ arrays showed statistics-based trends of (1) increasing decisiveness (sharper on/off slopes vs. concentrations), (2) decreasing failures (increasing repeatability) and (3) lower off-switching speed. The fabricated sensors also resulted in (4) ultra-low power of $ due to normally-off operation.

This paper reports the establishment of a theoretical model of a bubble chromatography system, based on our previous experimental results [1], to investigate into characteristics and limitations in the gas-to-bubble conversion. The established model (i) utilized the gas loss mechanism into a bubble volume equation, and (ii) successfully described the phenomena of reduction in bubble diameters when a target gas was injected in comparison to those of a carrier gas. The established bubble volume model successfully predicted the volume of a single gas bubble that matched with the experimental measurements by considering 40.45% volumetric loss of input gases into liquid during bubble formation as confirmed by two experiments: quantitative analysis of CO 2 and pentane in liquid. The established bubble chromatogram model successfully predicted the volume of a binary gas mixture bubble with experimental data, by considering two different volumetric losses (50% and 40%) for a binary mixture of pentane target and helium carrier gas.

This paper reports the first time wireless performance of the previously reported pressure sensing stent [1–2]. Previously we reported only optical and electrically-tethered measurement [1]. This paper reports the first time wireless measurement data with improved fabrication control. Specifically, this paper reports (1) the accurate control of evaporation to define the filling distance (54μm) of a hydraulic liquid (glycerol) in a microchannel (Fig.2b) and (2) wireless measurement of fluid flow pressure in a tube by utilizing the fabricated pressure-sensing stent (Fig.4). The liquid amount, which was encapsulated to enable the hydraulic amplification ratio, was controlled with accuracy of ±10.51% by the newly modified method. The new method resulted in liquid-filling efficiency as low as 10.88μm/min via controlled evaporation at 900C, 0.32Torr. The fabricated wireless pressure sensing stent demonstrated successful sensing of surrounding fluid pressure between 0 and 260mmHg, in a resolution of 5.42fF/mmHg over a distance of 2cm and at power consumption of 165μW/cm2, in connection to an external capacitor of 30fF. The center frequency was measured as 79.668MHz.

This paper reports both the novel configuration and the operation principle of a pressure sensing stent (medical mesh tube) that (1) completely incorporates a micro pressure sensor into the stent wire structure and (2) achieves 75 times amplification in output signals of capacitive sensing via micro-scale hydraulic movement. A fabrication method was developed for wafer-level manufacture of the ‘on-wire’ pressure sensors, by grafting and processing multiple wires onto a silicon wafer. The fabricated pressure sensor on a stent successfully (1) detected the full cardiovascular pressure range of 60∼260mmHg with a resolution of 0.24µm/mmHg; (2) produced 114fF of capacitive signal outputs, which is x75 times amplified compared to conventional measurement without hydraulic mechanism; and (3) demonstrated a frequency-based-sensing resolution of 0.4 kHz/mmHg at a resonance of 13.89MHz. The fabricated on-wire sensor held a tiny footprint of 8000×100µm2, engraved on a 260µm-diameter copper wire, still enabling measureable outputs.

We report a new proof-of-concept bubble-based gas sensor for a gas chromatography system, which utilizes the unique relationship between the diameters of the produced bubbles with the gas types and mixture ratios as a sensing element. The bubble-based gas sensor consists of gas and liquid channels as well as a nozzle to produce gas bubbles through a micro-structure. It utilizes custom-developed software and an optical camera to statistically analyze the diameters of the produced bubbles in flow. The fabricated gas sensor showed that five types of gases (CO2, He, H2, N2, and CH4) produced (1) unique volumes of 0.44, 0.74, 1.03, 1.28, and 1.42 nL (0%, 68%, 134%, 191%, and 223% higher than that of CO2) and (2) characteristic linear expansion coefficients (slope) of 1.38, 2.93, 3.45, 5.06, and 5.44 nL/(kPa (μL s(-1))(-1)). The gas sensor also demonstrated that (3) different gas mixture ratios of CO2 : N2 (100 : 0, 80 : 20, 50 : 50, 20 : 80 and 0 : 100) generated characteristic bubble diameters of 48.95, 77.99, 71.00, 78.53 and 99.50 μm, resulting in a linear coefficient of 10.26 μm (μL s(-1))(-1). It (4) successfully identified an injection (0.01 μL) of pentane (C5) into a continuous carrier gas stream of helium (He) by monitoring bubble diameters and creating a chromatogram and demonstrated (5) the output stability within only 5.60% variation in 67 tests over a month.

This paper reports a new class of a gas sensor that utilizes the variation in bubble sizes when different gases are introduced into a liquid flow to identify gas types. The fabricated device enabled the detection of pentane (3μL) by producing the average bubble size of 130μm3, which showed size reduction by 2.4μm (1.7%) from the background bubble sizes (132.4μm) of nitrogen. The measurement also showed a preliminary correlation between the injection volume and the bubble size: increase in the injection volume of pentane from 3μL to 5μL (66.7% increases) resulted in the bubble size reduction from 1.7% to 2.1% (24% decreases) and the time span increase from 5s to 10s (100% increases).