Search

A millimeter wave resonator used as a sample cell for spectroscopic oxygen measurement is presented. The rotational absorption spectrum of oxygen for normal pressure shows a significant peak at 60.6 GHz. The resonator is virtually increasing the absorption path by its quality factor. It is designed to operate at high order resonant modes to cover the wavelength range between 50 GHz and 75 GHz by multiple resonances with a peak density of approximately 1 GHz. Two different types of resonators have been considered, a Fabry-Perot resonator and a waveguide loop resonator. First resonator samples were coupled to a commercial VNA for transmission measurement. With the Fabry-Perot resonator different oxygen concentrations were measured, resulting in a decrease of peak amplitude and quality factor. For the full measurement system the concept envisages two integrated transceiver circuits directly coupling to the resonator. [ABSTRACT FROM AUTHOR]

Abstract: We report on novel kinds of miniaturized gas sensors whose operation is based on the principle of surface ionization (SI). In SI gas sensing adsorbed analyte species are ionized at a heated solid surface and the formed ions are extracted towards an oppositely charged collector electrode positioned a short distance from the emitting surface. Here, we show that SI sensors allow for a fast, sensitive and selective detection of illicit drugs in the presence of large concentrations of solvent water. [Copyright &y& Elsevier]

Abstract: Gas detection experiments were performed with individual tin dioxide (SnO2) nanowires specifically configured to observe surface ion (SI) emission response towards representative analyte species. These devices were found to work at much lower temperatures (T≈280°C) and bias voltages (V≈2V) than their micro-counterparts, thereby demonstrating the inherent potential of individual nanostructures in building functional nanodevices. The high selectivity of our miniaturized sensors emerges from the dissimilar sensing mechanisms of SI as compared to standard resistive (RES) type gas sensors. By employing this innovative detection principle (SI) together with conventional RES measurements, significantly improved selectivity can be attained with a single gas sensor device. Self-heating of the SnO2 nanowires moreover opens up a road towards ultra-low power consumption gas sensors. [Copyright &y& Elsevier]

Abstract: Gas sensing experiments have been performed on SnO2 thin films using a wide range of different analyte gases. In these experiments, the SnO2 layers were specifically configured to observe the familiar resistive (RES) gas response alongside with the novel surface ionisation (SI) response. It is shown that the RES and SI responses, in general, occur in dissimilar temperature ranges and that both follow very different selectivity criteria. Microscopically, both kinds of response proceed through analyte-specific sequences of adsorption, surface reaction, charge transfer and desorption steps. A generalisation of the Ahlers model , originally developed to account for the bell-shaped temperature variation of the RES response of thin film metal oxide layers, is shown to quantitatively account for the whole range of SI data. Fits to experimental SI response vs. temperature curves allow the total energy input into the surface ionisation process to be determined and insights into the ionisation mechanism to be gained. [Copyright &y& Elsevier]

Abstract: Microelectromechanical systems (MEMS) with integrated heaters, originally designed for the readout of the resistance of metal oxide (MOX) layers, were configured to observe surface ionisation (SI) gas signals. Interdigital platinum (Pt) electrodes on top of the dielectric membranes acted as ion emitting layers while flat-plate counter electrodes, positioned at a short distance above them, were used for the current readout. In this work, we show that this device configuration leads to SI responses orders of magnitude higher than those previously reported for thin-film, flat-plate devices and fully comparable to the performance of parallel-nanowire devices (PNDs). The high ionisation efficiency of our MEMS devices, which are suitable for large-scale production and further integration steps, is attributed to the electric field enhancement that takes place at the sharp edges of the Pt electrodes. [Copyright &y& Elsevier]