Impedance spectroscopy in the frequency range 100 Hz to 10 kHz has been applied to the Inter-Digitated Electrode (IDE) structure that is conventionally operated as a resistive sensor for the measurement of Particulate Matter (PM). The measurement of both the in-phase (resistive) and out-of-phase (capacitive) components of the impedance over this frequency range provides more data on PM as compared to DC resistance measurement only. Experimental validation confirms a more gradual change in capacitance with soot buildup as compared to the sudden reduction of resistance with dendrite formation. The effect of an additional vertical electric field for an increased capacitive sensitivity due to stimulated soot buildup has been experimentally investigated using the electrically conductive flow housing of the IDE structure as an additional suspended electrode.

Exhaust gas measurement in the harsh environment of the tailpipe of a combustion engine by optical techniques is a highly robust technique, provided that optical access is maintained in the presence of particulate matter (PM). The considerations are presented for the systematic design of membranes with integrated heaters in SiC-on-Si technology for generating a well-defined lateral temperature profile with peak temperatures above 600 °C. Periodically raising the temperature of the membranes to such a level is demonstrated to keep the surface transparent by oxidation of soot deposits. This paper is about continuous heating of the membrane to a temperature slightly higher than that of the exhaust gas. At such temperatures thermophoretic repulsion of PM allows allows long-term optical measurement in the exhaust without the thermo-mechanical loading by repetitive thermal cycling.