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Development of MOF-Coated Electrostatic Mems Resonators for Gas and Chemical Sensing Applications
Hemid, Mohamed Mahmoud
Hemid, Mohamed Mahmoud
Description
A Master of Science thesis in Mechatronics Engineering by Mohamed Mahmoud Hemid entitled, “Development of MOF-Coated Electrostatic Mems Resonators for Gas and Chemical Sensing Applications”, submitted in April 2024. Thesis advisor is Dr. Mehdi Ghommem and thesis co-advisor is Dr. Rana Sabouni. Soft copy is available (Thesis, Completion Certificate, Approval Signatures, and AUS Archives Consent Form).
Abstract
In this work, we investigate the potential use of electrostatic MEMS resonators for gas and chemical sensing. We study the characterization of two different MEMS devices for CO₂ detection and characterization of aqueous media. The CO₂ MEMS sensor, which will be referred to as the gas sensor, is coated with a metal organic framework (MOF), namely ZIF-8, which demonstrated high sensitivity and selectivity to CO₂ gas. Both resonant MEMS devices are electrically actuated via a fixed electrode while investigating their dynamic response near resonance. In the case of the gas sensor, the exposure to CO₂ result in an added mass to the vibrating microstructure due to the adsorption of CO₂ via the active layer of MOF. This results in changes in its motion characteristics which are exploited to detect the presence of CO₂ and evaluate its concentration. The MEMS chemical sensor is tested in different aqueous environments. The detection mechanism is based on the electrical resonance of the MEMS device. Still, the electrical resonance is influenced by the mechanical motion of the sensor and varies based on the liquid properties. Finite element models for the MEMS sensors were developed and verified against experimental data. These models were used to identify the mode shapes, their associated natural frequencies, and the pull-in voltage. We use the motion-induced current method to analyse the response of the MEMS sensors. This method relies on a transduction mechanism that converts the motion of the resonator to a current signal. The third harmonic of the current is directly related to the motion of the resonator. The experimental results demonstrated the capability of the proposed gas sensor to detect CO₂. Indeed, the electrical measurements captured the nonlinear features associated with the motions of the gas sensor when subjected to CO₂ with varying concentrations. We showed effective deployment of frequency and amplitude changes in peak output current as detectors for the presence of CO₂ and quantifiers of its concentration. Moreover, we showed evidence of the potential of the motion-induced current method to characterise different liquids by tracking the electrical resonance.