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This paper reports a novel method for detecting ethylene by using KMn04/polyimide composite thin-films as the analyte-sensitive layer in a capacitive MEMS ethylene sensor which requires zero-DC power for reliable operation. The technique utilizes a MEMS parallel-plate capacitor with the thin-film as a dielectric layer. Exposure of ethylene to the KMnO 4 molecules embedded within the polyimide matrix results in oxidation of ethylene into CO 2 and H 2 0, which induces swelling of the thin-film and also changes its dielectric-constant. This leads to a change in device capacitance. Preliminary results indicate a nearly reversible linear decrease of sensor capacitance of ~1 - 14 pF when exposed to ethylene concentrations ranging from 130 - 1000 ppm, yielding a normalized capacitance sensitivity of ~3.74×10−6/ppm. Selectivity tests revealed a favorable response towards ethylene compared to gases such as hexanal, indole, pentane, acetone, and IPA.

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.

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.

This paper reports the design and implementation of a wake-up gas sensor node, including both a low-power sensor and a wake-up electrical circuit that was particularly capable of utilizing the “on/off” characteristic of a previously reported nano-gap sensor to produce the needed output electrical power for alerting operations (e.g. LED lighting) under power budgets. The designed circuit, as predicted by a SPICE model, consumed 3.7mW of power for its “on” operation at an applied voltage of 1V, while only consuming ∼970nW during its “off” operation. The measured power for both operations enabled an average power consumption of $155.1\mu\mathrm{W}$ and depicted the wake-up functionality of the integrated gas sensor node for longterm battery-supported deployment. The integrated sensor node successfully demonstrated the lighting of an LED as an alarm signal, when exposed to a threshold concentration of 550 ppm of 1,5-diaminopentane gas.

This paper reports the successful demonstration of modulating the threshold point in gas concentrations at which a gas sensor turns “on/of” for wake-up operation by adjusting the tunneling areas of a nano-gap in the previously reported ultra-low-power gas sensor. The nano-gap area of the sensor determines the total binding sites and thus the total amounts of “on” tunneling-current at a given concentration. Since the total current amounts trigger wake-up, their increase per given concentration could enable a lower minimum detectable wake-up concentration. Experimental results confirmed that the increase in the nano-gap area from 6.5 to $62.5\ \mu \mathrm{m}^{2}$ by 861.5% enabled the reduction in the required wake-up gas concentrations from 250.0 to 50.0 ppm by 80.0%, showing an exponential decay trend. Such a reduction in the wakeup threshold allows the previously-reported sensor to achieve the required wake-up range of 200.0 ppm for early detection of diamine gases for health safety, while indicating the design feasibility to enable various wake-up concentrations for adjustable operation.

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 detection of gas molecules with an identical functional group, but in different lengths due to varying numbers of CH 2 backbone units, by utilizing a nano-gap gas sensor. Significance of such a gas sensor lies on its ability to distinguish molecular lengths by down to 0.15nm in this testing. The fabricated nano-gap sensor, after being functionalized by a specific linker on the surface, successfully captured all three target gas molecules of 2-CH 2 -diamine (0.3nm), 3-CH 2 -diamine (0.45nm) and 5-CH 2 -diamine (0.75nm). The capture of each target molecules demonstrated significant differences in both resistance and capacitances, resulting in successful identification of 2-CH 2 -diamine (0.3nm), 3-CH 2 -diamine (0.45nm) and 5-CH 2 -diamine (0.75nm) by producing different on/off resistance ratios of 105, 2905 and 3832 and capacitance changes of 4.45pF, 16.21pF and 26.64pF, indicating the capability of identifying multiple gas molecules in different lengths despite identical functional groups.

This paper reports the development of a nano-gap vapor sensor that is capable of detecting an airborne target in a repeatable manner in near-zero static power consumption. The nano-gap sensor employed a matching gap distance of 5.8 nm to the lengths of both linkers and targets for selectivity. The nano-gap sensor was fabricated based on deposition and removal of a thin sacrificial layer via atomic-layer-deposition (ALD), and then coated with newly-synthesized linkers. The fabricated vapor sensor demonstrated the detection of a target gas (1, 5-Diaminopentane) or Cadaverine in a concentration of

Among the various form of renewable energy technologies Solar photovoltaic technology is perhaps the most used one to generate electricity especially in the rural area of all over the world. The purpose of this paper is to analyze the potentiality and cost effectiveness of using solar irrigation system in Bangladesh. In Bangladesh, the introduction of solar water pumps, which are manufactured using locally available technologies, will not only shorten the gap between demand and production of electricity immensely and help poor and marginal farmers increase their yield but also bring down their agricultural production costs substantially in the next 20 years. Existing projects in this sector are noted. Some limitations and remedies are discussed. The resulting cost-benefit analysis shows a great economic advantage for solar irrigation system over using traditional grid electricity driven pump irrigation system.