Sensing Catalytic Converters and Filters at Work Using Radio Frequencies

The state of catalysts and filters plays a key role in automotive exhaust gas aftertreatment. The soot or ash loading of particulate filters (GPF or DPF), the oxygen loading of three-way catalysts (TWC), the amount of stored ammonia in SCR catalysts, or the NOx loading degree in NOx storage catalysts (NSC) are important parameters. Today, they are determined indirectly based on models that are calibrated by gas or pressure sensors in the exhaust pipe. This contribution overviews a novel approach that determines directly the state of the devices by a radio frequency based technique. For that purpose, the housing of the devices serves as a cavity resonator. As “sensing” element, one or two simple antennas are mounted in the catalyst canning. This contactless-obtained information correlates very well with the catalyst or filter state.