Thesis defense of Bernard Bobby NGOUNE - December 21st, 2023

Bernard-Bobby NGOUNE will defend his thesis on December 21st, 2023 at 10:00 am, (amphi JP. DOM – IMS Laboratory) on the subject : “Selective sensing of exhaust gas using printed radiofrequency sensors”.
The impact of air pollution on the society, environment and human health has increased drastically in the recent years mostly due to the increase industrialisation and transportation.
Several gases contribute to this effect namely NO 2 , SO2 , O3 and CO2 . Microwave gas sensorsoffer promising avenues for air quality monitoring, due to their cost effectiveness, low energyconsumption, robustness, and high frequency facilitating wireless communication. This research delves into the design, simulation, fabrication and characterisation of a dual-channel microstrip interdigitated sensor fabricated on a flexible Kapton substrate, enhanced by several synthesized polymers (EB-PEI, HBPEI Silane, LPEI-COPh, and LPEI-CH2 Ph) derived from commercially available polyethyleneimine for accurate gas monitoring. The synthesized sensitive materials were characterised morphologically using SEM and AFM. Revealing the pronounced roughness and porous nature of HBPEI Silane as opposed to the smoother surfaces of the other polymers. Electrical characterisation of the fabricated sensors corroborated the simulation results.
In rigorous controlled laboratory settings, the sensors underwent characterization. Initial tests for atmospheric interferences, humidity (RH) and temperature, indicated pronounced RH sensitivity for COM HBPEI and EB PEI, while LPEI-COPh and LPEI-CH2 -Ph displayed minimal sensitivity. However, LPEI-COPh showed higher sensitivity to temperature as compared to RH. Relative to literature benchmarks, COM HBPEI and EB-PEI demonstrated consistent selectivity for RH with limited temperature and the other environmental parameter influence. Interestingly, the sensors demonstrated CO2 sensitivity solely at 0% RH, with HBPEI Silane emerging as particularly more sensitive, attributed to its rough surface fostering enhanced molecular interactions. However, the response to other gases, including NO2 , SO2 , CO, and O3 , remained subdued under targeted ranges. Field tests were carried out over different periods (summer 2021, summer 2022 and winter 2023). Results corroborated laboratory findings, especially the dominant RH sensitivity of EB-PEI and COM HBPEI. Introducing the HBPEI Silane 1:0.5 sensor response to calibration models incorporating known environmental parameters such as RH, temperature, and NO2 improved ozone prediction, highlighting the sensor’s secondary ozone sensitivity. This secondary sensitivity and the crucial role of priorNO2 knowledge for accurate ozone prediction, was reinforced during the sensor array winter 2023 deployment. Moreover, utilizing the COM HBPEI-based sensor and LPEI-COPh, known for their respective RH and temperature sensitivity, proved advantageous for ozone prediction over direct usage of RH and temperature data. An analysis of the winter 2023 dataset solidified these findings. The primary limitation during outdoor testing arose from the brief deployment durations, leading to cross correlations among environmental variables, thereby complicating the distinction of individual gas sensitivities. For future endeavours, extended deployments spanning several months are recommended. Furthermore, the exploration of novel sensitive materials, especially those based on conducting polymers and metal oxides, for a more expanded sensor array facilitating the discrimination of gaseous species and reduction of atmospheric interferences. Measurement over a wider frequency range might yield deeper insights. The development of cost-effective wireless sensor instrumentation remains an essential in the future.