Conference Paper

A Handheld Microdischarge Spectroscopy System for High-Speed Chemical Analysis of Gaseous and Liquid Samples

Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, USA
DOI: 10.1109/MEMSYS.2006.1627859 Conference: Micro Electro Mechanical Systems, 2006. MEMS 2006 Istanbul. 19th IEEE International Conference on
Source: IEEE Xplore


This paper presents a handheld microsystem that uses discharge spectroscopy to analyze chemicals both in vapor and liquid phases. The system employs a battery-operated circuit and interface for generating the microdischarge and performing the analysis. It uses swappable liquid and gas discharge microchips, which interface to the common platform. A pump and inert carrier gases are not utilized. The system can generate one or a series of single shot microdischarges per chemical analysis. Synchronized emission spectroscopy is used to optimize sampling. The liquid discharge microchip has an active area of 1 mm x 1 mm and a discharge gap of 50 µ m. It employs a porous cathode which for introduction of the liquid into the microplasma. This results in a reliable system that can detect 2 ppm of Cr sample without preconcentration. The gas discharge microchip uses the discharge between two metal electrodes. It has a discharge gap of 50 µ m and and an active area of 500 µ m x 500 µ m. The sensor detects 13 ppm of acetone vapor in air.

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    • "These techniques are often used in chemical laboratories as analyzers, also they have been used in instruments for air pollutant measurements [8]. Small sized OES based sensor for exhaust emission has been reported [9] and another handheld micro system to analyze chemicals both in vapor and liquid phases using discharge spectroscopy was presented in [10]. The first optical gas sensors were based on the absorption spectrum difference measurement like the infrared IR gas detectors which have been in use for long time ago, they have long life time with greater stability over time. "
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    ABSTRACT: This paper proposes a new method for gas concentration measurement. The method relies on the principle of plasma emissions of gases under high voltage. We proposed a method that uses digital image processing to model the color mixing of the emissions of the gases. The application of the inverse model allows us to get the percentages of each gas in a mixture of up to four gases knowing already the color of emission of the whole mixture and the color of emission of each gas alone. Our proposed sensor has the advantages of high selectivity where it is not limited to a certain number of gases and is considered to be a good candidate for miniaturization.
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    • "An optical fiber directly opposite the microplasma, outside the quartz lid, couples the emitted light to a spectrometer (USB2000 from Ocean Optics Corp.). Pulsed discharges have significant afterglow periods, and integrating both the afterglow and initial discharge emissions improves the signal to noise ratio [6]. The recorded spectra are examined to determine the unknown gas composition, based on the characteristic line spectra produced by individual gases. "
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    ABSTRACT: A system for gas phase chemical detection in harsh environments has been developed that utilizes three microplasma-based devices: pressure sensor, gas purifier, and optical emission sensor. The devices all utilize microplasmas between thin-film electrodes and occupy a combined active area of 10.5 mm<sup>2</sup>. They are fabricated on glass chips and enclosed in a 0.33 cm<sup>3</sup> ceramic package. The optical emission sensor operates by fractionating and exciting gas species for chemical spectral detection. The pressure sensor measures the change in microplasma current distribution with pressure, and achieves a sensitivity of 9800 ppm/Torr at 200degC. The gas-purifying microscale sputter ion pump purifies the environment by selectively removing nitrogen and oxygen, and achieves a 56.5times reduction in nitrogen concentration relative to helium. This purification enhances the ability to detect trace amounts of gases. As a validation of this system, a spectral enhancement of 8times at 200degC for carbon line emission intensity relative to nitrogen has been demonstrated.
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    ABSTRACT: Micro-scale electrical discharges can be useful in both manufacturing contexts and sensing modalities. With regard to manufacturing, they provide structural and material diversity: microplasmas ignited between thin film metal patterns permit localized etching and deposition, whereas micro-arcs permit stainless steel and other bulk metals. Micro-electrodischarge machining has been used for the lithography-compatible fabrication of "smart stents" that are integrated with pressure sensors. It has also been used to embed sensors at the tip of biopsy needles. With regard to sensing modalities, spectroscopic detection of chemicals in both gas and liquid phase has been explored. For example, discharge spectroscopy has been used to detect inorganic contaminants such as lead and chrome in water. The converse application has also been reported: salts dissolved in aqueous sample are used to tune the emission spectrum, which is subsequently filtered and used as an inexpensive UV source for the fluorescent detection of biochemicals. Gas-phase discharges are used for radiation sensing by Geiger counters and related micromachined devices. It has been shown that the RF emissions associated with these discharges are in the UWB spectrum, and can be detected by common AM/FM radios, creating some interesting opportunities for wireless networking
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