G. Noetzel

Odours and flavours identified with hybrid modular sensor systems

Abstract Hybrid sensor systems contain different types of chemical sensors whereby each type (transducer principle) contains an array of individual sensors. This leads to a large flexibility in the choice of transducers and sensor materials with the general aim of optimising the analytical performance of the total system. This concept makes it possible to optimise the quantitative analysis of mixtures of known gases as it will be demonstrated for mixtures of volatile organic compounds (VOCs). Alternatively this makes it possible to optimise the system for characterising odours and flavours. This will be demonstrated for different plastic as well as textile materials used in car industries and for different products of food industries, i.e. coffees, tobaccos, whiskeys, and olive oils. In our modular sensor systems we used arrays of different semiconductor gas sensors (based on metal oxides), of polymer coated quartz microbalance (QMB) sensors, of calorimetric sensors and of electrochemical sensors, with an option to add metal oxide semiconductor field effect transistor (MOSFET) sensors. These arrays are arranged as separate components in a modular sensor system ‘MOSES’. For the qualitative discrimination of different odour samples a headspace-autosampler was added and transient sensor signals were monitored. The use of different transducer principles is shown to be essential for an unequivocal identification of odours and flavours.

Performances of Mass-Sensitive Devices for Gas Sensing: Thickness Shear Mode and Surface Acoustic Wave Transducers

In this work we investigated different thickness shear mode resonators (TSMRs) with fundamental frequencies of 10 and 30 MHz and surface acoustic wave devices with fundamental frequencies of 80 and 433 MHz. Four aspects were of primary interest in this comparison:  noise levels and signal-to-noise ratios (S/N), influence of the polymer film thickness, influence of temperature on the transducer signal before and after coating, and minimum threshold values for monitoring different volatile organic compounds in the environment. We limited our investigations to a temperature range between 298 and 308 K, with 303 K the routine measuring temperature. Analyte concentrations (n-octane, tetrachloroethene) were chosen from the minimum detection limit up to 5000 μg/L. The temperature was found to strongly affect the performance of all the devices. The sorption of the analyte vapors into the polymeric films was demonstrated to be transducer-independent (identical partition coefficients for all the devices). The 30 MHz TSMRs showed very satisfying results in terms of S/N and limits of detection.

Capacitive sensors in CMOS technology with polymer coating

Abstract In this paper we report the fabrication of a new integrated capacitive chemical sensor by industrial CMOS technology, followed by a single maskless polymer-coating step. An on-chip sigma-delta modulator measures the difference between the sensing and reference capacitors, performs offset and gain calibration and provides a digital output signal. Experimental data have been obtained in a series of measurements, in which several transducers covered with different polymer films (poly-etherurethane, PUT, polycyanopropylmethylsiloxane, PCM, ethylcellulose, EC, and polyepichlorohydrine, PECH) are exposed to various organic gases at different concentrations. The sensor signals show a clear linearity and low hysteresis for both polar and non-polar gases, thus confirming the feasibility of smart capacitive chemical sensors in IC technology.

Development of Modular Ozone Sensor System for application in practical use

Abstract A computerized Modular Ozone Sensor System (MOSS) for evaluating the sensitivity and reliability of different sensor/transducer combinations is presented. The system consists of a compact and portable apparatus that can be used to compare various sensors. The sensor types bench-marked using MOSS are electrochemical cells, various semiconducting gas sensors based on metal oxides (In2O3, SnO2), and Thickness Shear Mode Resonator (TSMR) sensors, which were mounted on separate modules. The gas mixtures containing known amounts of ozone were analyzed using this modular array of different sensors. All electronic sensor modules, including standardized connections are home-built and optimized as a part of this investigation. Computerized data acquisition and evaluation was performed using a standard hardware and an analysis software developed during this work. In order to test the setup, a set of different sensors was employed. Their sensitivity to ozone and their cross-sensitivity to other gases in ambient condition and to humidity were evaluated. Sensors, based on indium oxides, performed best in detecting ozone. They had the largest sensor sensitivity as well as the smallest cross-sensitivities.

Polymer Coated Capacitive Microintegrated Gas Sensor

Detection of volatile organic compounds (VOCs) is important for various environmental and industrial applications such as alarm devices for pollution or building control purposes. The feasibility of smart capacitive chemical micro sensors in CMOS technology has already been assessed [I]. The objective of the current investigation was to elabo rate an analytical model for the gas/polymer interaction and to compare FEM simulations and measurements. In order to develop a model for the interactions between VOCs and the polymer layers, systematic measurementsof various parameters affecting the sensing layer were carried out. The efforts were concentrated on commercially avail able polyetherurethane (PUT, Thermedics Inc., USA), as the sensitive layer.

Comparison Of Mass-sensitive Devices For Gas Sensing: Bulk Acoustic Wave (baw)- And Surface Acoustic Wave (saw) Transducers

In this work we investigated comparatively different BAW devices with fundamental frequencies of 10 and 30 MHz and SAW devices with fundamental frequencies of 80 and 433 MHz. Three aspects were of primary interest in this comparison: influence of temperature on the transducer signal before and after coating, 0 maximum achievable frequency shift by coating and 0 minimum threshold value to monitor different volatile organics (VOCs) in the environment. In view of future practical applications, we limited our investigations to a temperature range between 298 and 308 K with 303 K as routine measuring temperature. For the same reason analyte concentrations were chosen from the detection limit up to 1000 ppm.