Micro arc-plasma hybrids for detection of vapors at atmospheric pressure

Chemical sensors based on microdischarges - both arcs and plasmas $provide rapid and simultaneous detection of vapors by using their characteristic emission spectra in the plasma glow. Generally, D.C, microplasmas operate in vacuum while arcs exist at higher pressures. Arcs are driven by high transient currents and exhibit wider spectral distribution than plasmas, which are driven by steady currents that are smaller in magnitude. In this paper we report the controlled combination of these discharges and the combined use in ambient air to detect low concentrations of organic vapors. It is found that as the discharge gap is scaled to <75 mum, it becomes possible for a microplasma to exist at 1 atm. With appropriate powering circuitry, an arc can also exist under the same conditions. The relative strengths of the arc and plasma components can be controlled by the adjusting the value of a single resistor. The emission spectra of combined discharges have the spectral characteristics of both arc and plasma spectra. The utility of such a system to vapor sensing is demonstrated by detecting 17 ppm of acetone in air ambient with a 65 ms detection time, and without any pre-concentration. This is accomplished using pulses that consume 60 mJ/discharge, on a device that has an active area of 300 mum times 300 mum