We investigate the possibility of applying rectangular voltage pulses to the gate electrode of carbon nanotube field effect transistors (CNFETs) for NO2 detection. CNFET gate characteristics measured using pulsed gate voltages show a reduction of hysteresis by about 20% compared to measurements with linearly swept gate voltages. Moreover, an enhancement of the measurement range is observed in the pulsed regime. The characterized CNFET devices are based on individual single-walled carbon nanotubes (SWNTs), which act as the sensing elements

A sensing system for fractional exhaled nitric oxide (FeNO) measurement is presented, which is characterized by a compact setup and a cost potential to be made available for the patient at home. The sensing is based on the work function measurement of a phthalocyanine-type sensing material, which is shown to be sufficiently sensitive for NO(2) in the ppb range. The transducer used to measure the work function is a field effect transistor with a suspended gate electrode. Selectivity is given with respect to other breath components including typically metabolic by-products. The measurement system includes breath treatments in a simple setup, which essentially are dehumidification and a quantitative conversion of NO to NO(2) with a conversion rate of approx. 95%, using a disposable oxidation catalyst. The accomplishment of the correct exhalation maneuver and feeding of the suited portion of exhaled air to the sensor is provided by breath sampling means. The sensor is not gas consuming. This allows us to fill the measurement chamber once, instead of establishing a gas flow for the measurement. This feature simplifies the device architecture. In this paper, we report on sensor characteristics, system architecture and measurement with artificial breath-gas as well as with human breath with the device.

The pulsed polarization measurement technique using conventional thimble type lambda probes is suitable for low ppm NO_x detection in exhaust gas applications. To evaluate the underlying sensor mechanism, the unknown influence of the reference atmosphere on the NO sensing behavior is investigated in this study. Besides answering questions with respect to the underlying principle, this investigation can resolve the main question of whether a simplified sensor element without reference may be also suitable for NO sensing using the pulsed polarization measurement technique. With an adequate sensor setup, the reference atmosphere of the thimble type lambda probe is changed completely after a certain diffusion time. Thus, the sensor response regarding NO is compared with and without different gas atmospheres on both electrodes. It is shown that there is still a very good NO sensitivity even without reference air, although the NO response is reduced due to non-existing overlying mixed potential type voltage, which is otherwise caused by different atmospheres on both electrodes. Considering these results, we see an opportunity to simplify the standard NO_x sensor design by omitting the reference electrode.

This paper provides an update, how transient operation methods can improve the performance of gas sensors and sensor systems for specific applications. Even new applications can be enabled, if existing state-of-the-art sensors are operated in transient modes adapted to the needs of the application in mind. Several parameters are available for transient variation, depending on the particular sensing technology: Suspended Gate FET sensors deliver a simultaneous readout of work function and capacitive effects. By applying pulsed gate voltages these effects can be interpreted separately and used e.g. for compensation of humidity effects and improved selectivity. Modulation of the operating temperature of μ-machined metal oxide sensors is creating a type of virtual sensor array. In this case, the dynamic behavior of adsorption and desorption at changing temperature levels delivers a fingerprint for application relevant gas mixtures. The pulsed application of charge voltage on standard exhaust lambda probes and the recording of the related discharge characteristic over time provide an exhaust NOx sensor based on a standard sensor setup. The charging creates a misbalance in oxygen-related surface species not available under continuous operation conditions. The related discharge characteristic is strongly influenced by the interaction of these oxygen species with NOx

The pulsed polarization measurement technique applied on sensor devices based on yttria stabilized zirconia (YSZ) with porous platinum electrodes enables the detection of low ppm concentrations of NOx in exhaust gas applications with a simple device. Pulsed polarization is based on alternating voltage pulses with intermediate pauses for self discharging. The discharge characteristics after polarization depends strongly on NOx content in the low ppm range. Due to faster discharging in NOx containing atmospheres compared to base gas, the voltage difference between the discharge curves can act as a concentration dependent parameter. Sensor probes for usage in exhaust gas conditions have been built. The feasibility of NOx sensing in diesel exhaust gas by use of a planar cost-effective YSZ sensor element is evaluated in detail in comparison to commercial NOx exhaust sensors and referenced with gas analysis equipment.