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A capacitive soot sensor was built up on basis of a known resistive device by covering the electrode area with a thin but dense alumina layer manufactured by the aerosol-deposition-method (ADM). Deposited soot cannot short-circuit the electrodes but leads to an increasing capacitance of the sensor. Experiments were conducted in real exhaust. Increasing soot concentrations lead to a more fast and sharp increase of the capacitance and the blind time of the sensor decreased to almost zero. The performance of such sensors could be enhanced when a voltage is applied at the electrodes during soot collection.

A solid-state potentiometric CO 2 sensor of the type CO 2 , O 2 , Au, Li 2 CO 3 -BaCO 3 | Nasicon | Na 2 Ti 6 O 13 -TiO 2 , Au, O 2 , CO 2 was fully manufactured in planar thick-film technology. On the rear side of the sensor substrate an integrated heater is applied. Thus, it is possible to operate the sensor as a stand-alone device. On the one hand, based on the special meander structure of the heater, a homogeneous temperature distribution on the sensor side can be obtained. And on the other hand, it is possible to operate the sensor with the ideal working temperature of 525 °C. At this temperature, the sensor signal follows the theoretical considerations and responds to the Nernst equation. That way, it is possible to use the sensor in different applications, for example to detect the CO 2 concentration of human breathing air or to monitor the air quality in closed rooms.

Soot sensors are required for on-board diagnostics (OBD) of automotive diesel particulate filters (DPF) to detect filter failures. If installed upstream of a DPF, the “engine-out” soot emissions can be determined by conductometric soot sensors. For that purpose, conductometric soot sensors were characterized in a diesel engine under varying operation conditions. Sensor data and soot analytics (SMPS) agree well. However, the orientation of the sensor electrodes with respect to the exhaust flow direction significantly affects the sensor signal.