Radio-frequency-based high-temperature nitrogen oxide sensor for dosimeter-type detection of NOx in the ppb range for continuous air quality monitoring

• Applicant: Professor Dr.-Ing. Ralf Moos
• Subject Area: Microsystems ; Synthesis and Properties of Functional Materials ; Measurement Systems
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 465563965

The overall project goal is a self-heated high-temperature radio-frequency sensor platform (HT-RF-platform) for dosimeter-like detection of lowest NO and NO2 concentrations for air quality monitoring. The underlying accumulation principle with simultaneous electrical readout is based on the load-dependent dielectric properties at several GHz of a NOx-storing film. At the end of the project, a working demonstrator of a RF NOx dosimeter is available, which consists of a HT-RF-sensor platform coated with a NOx storage material. In further work, an application of the sensor platform for other sensitive layers and analytes or as a material characterization tool is envisaged.Divided into three thematic complexes, the following scientific questions are to be addressed:1. Development and construction of a self-heated HT RF sensor platform with qualification of substrate materials and resonator structures for high-temperature GHz measurements.- Which substrate materials are suitable for RF investigations up to 600 °C?- What coplanar waveguide arrangement enhances sensor sensitivity?- How should the heater structure and substrate geometry be dimensioned for homogeneous temperature of the sensitive layer and minimal heat transport to the connection pads?- How can interferences from the backside heater structure be minimized?2. Evaluation of the suitability of barium-containing NOx storage materials for dielectric NOx dosimetry by RF analysis in NO or NO2 atmospheres depending on temperature.- How do the dielectric properties of barium-containing NOx storage materials change during NOx loading? Which measurands are suitable as sensor signals?- Which material compositions are suitable for RF monitoring of air quality? - How large is the temperature-dependent linear measuring range? Can daily mean signals without regeneration interval and peak values be determined with sufficient accuracy?- What influence does the loading of the oxygen storage material part have on the measured variables?- What are the cross-sensitivities and can they be eliminated?- When should the thermal regeneration of the sensor be initiated?3. Correlation of dielectric properties with chemical processes during NOx adsorption and desorption by combined operando RF-DRIFT spectroscopy.- Is operando DRIFT analysis of self-heated sensor platforms possible? - How do dielectric properties (HF) correlate with NOx loading (DRIFTS)?- Which NOx sorption sites can be identified depending on the dosed species and the operating temperature? What is the influence of nitrite and nitrate formation?- How do measured variables and chemical composition of the NOx reservoir correlate?- Is the linear measurement range limited by electrical or chemical processes?- Which temperature-time profile is permanently suitable for thermal regeneration?

• DFG Programme: Research Grants