From Springer description: "We present the design considerations of an autonomous wireless sensor and discuss the fabrication and testing of the various components including the energy harvester, the active sensing devices and the power management and sensor interface circuits. A common materials platform, namely, nanowires, enables us to fabricate state-of-the-art components at reduced volume and show chemical sensing within the available energy budget. We demonstrate a photovoltaic mini-module made of silicon nanowire solar cells, each of 0.5 mm2 area, which delivers a power of 260 μW and an open circuit voltage of 2 V at one sun illumination. Using nanowire platforms two sensing applications are presented. Combining functionalised suspended Si nanowires with a novel microfluidic fluid delivery system, fully integrated microfluidic–sensor devices are examined as sensors for streptavidin and pH, whereas, using a microchip modified with Pd nanowires provides a power efficient and fast early hydrogen gas detection method. Finally, an ultra-low power, efficient solar energy harvesting and sensing microsystem augmented with a 6 mAh rechargeable battery allows for less than 20 μW power consumption and 425 h sensor operation even without energy harvesting."
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From Science direct: One of the nanowires was covered with a 2-Hydroxyethyl methacrylate based compound to prevent hydrogen from reaching the wire. The compound was dried by a UV source and tested in chamber for comparison with previous measurements. The results shows that temperature effects can be reduced by a digital signal processing algorithm without measuring temperature near or at the substrate. With this method no additional temperature probes are necessary making this solution a candidate for ultra low power wireless applications.
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Author supplied from the article: Abstract A temperature compensated hydrogen sensor was designed and made capable of detecting H2 within a broad range of 100–10.000 ppm while compensating instantaneously for large (±25 °C) temperature variations. Two related operational constraints have been simultaneously addressed: (1) Selective, and sensitive detection under large temperature changes, (2) Fast warning at low and increasing H2 levels. Accurate measurements of hydrogen concentrations were enabled by matching relevant time-constants. This was achieved with a microchip having two temperature coupled palladium nanowires. One of the H2 sensitive Pd nanowires was directly exposed to hydrogen, whilst the other nanowire was used as a temperature sensor and as a reference. A drop forging technique was used to passivate the second Pd wire against H2 sensing. Temperature effects could be substantially reduced with a digital signal processing algorithm. Measurements were done in a test chamber, enabling the hydrogen concentration to be controlled over short and long periods. An early response for H2 sensing is attainable in the order of 600 milliseconds and an accurate value for the absolute hydrogen concentration can be obtained within 15 s.
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In this project, Photons in Focus, researchers from The Hague University of Applied Sciences will work together with the company Photosynthetic to fabricate high-quality microlenses that will optimally focus light onto microscopic light detectors. Specifically, the microlenses will be designed to focus light onto superconducting nanowire single-photon detectors (SNSPDs) from the company Single Quantum. SNSPDs are cryogenic single-photon detectors with photon detection efficiencies up to 99% and timing resolutions down to 15 picosecond. Recently, Single Quantum has been developing arrays of SNSPDs for free-space biomedical imaging and deep space communications. The photon detection efficiency of these arrays is suboptimal, because 15-20% of the light falls onto nonsensitive areas. In Photons in Focus, fabrication of two types of microstructures will be explored for optimally focusing light onto these SNSPDs and improving the photon detection efficiency. First, 3-dimensional microlenses will be created at Photosynthetic using their method of dual-wavelength volumetric microlithography. Second, phase-reversal Fresnel zone plates will be fabricated using standard 2-dimensional photolithography at The Hague University of Applied Sciences. Both types of microstructures will be tested for their focusing properties and potential optical losses, and their ability to enhance to photon detection efficiency of SNSPDs in cryogenic conditions.
