A GAS SENSOR SYSTEM WITH DIELECTRIC AND MASS SENSORS

A basic principle of gas sensors is that under the influence of gases a sensitive layer changes its properties, which are measured by a transducer. Normally, a sensor operates only with one specific property of the sensitive material, e.g., the permittivity. This paper proposes a sensor system that uses the measurement of different physical properties (permittivity, mass, refractivity, etc.) of one sensitive material by various transducers to improve the characteristics (e.g., selectivity, stability) of the whole system. The design concept of such a sensor system is given in the first Section. In this paper the SO2 adsorption of a particular sensitive material is measured with a dielectric sensor (interdigital capacitor, IDC) and a mass sensor (10 MHz bulk wave oscillator, BAW). The two adsorption isotherms show significant differences. The dielectric-adsorption isotherm reaches its saturation point at a lower SO2 concentration than the mass-adsorption isotherm. This effect can be used to determine the saturation point exactly and to avoid the ambiguity of a single sensor signal in a sensor system.