Modeling and FEM simulation of love wave SAW-based Dichloromethane gas sensor

Dichloromethane (DCM) or methyl chloride is a volatile organic compounds (VOC) infamous for its carcinogenic properties. The gas mainly used in industrial solvents is found to cause lung and liver cancers in animal experiments, whereas they are proven to cause cancers of the brain, liver, and a few types of blood cancers including Non-Hodgkin’s lymphoma in humans. The deteriorative effects are found to exposure as low as 200 ppm for a few continuous hours, whereas exposure above 1000 ppm is found to cause cancers in mammals. Among the various techniques available today for the detection of gases in atmospheric air the SAW (Surface Acoustic Wave) sensors are highly accurate. SAW offers higher sensitivity, simplicity of fabrication, rapid response time, room temperature operation, and/or the possibility of wireless operation at low costs.

In this paper, FEM design and analysis of the Surface Acoustic Wave technology based on love waves was used for detecting volatile organic gases. The 3D gas sensor was composed of interdigitated transducers modeled on a piezoelectric substrate and covered by a guiding layer of SiO₂, and on top of that was a film of polyisobutylene (PIB) that served as the sensing layer. The material used for the piezoelectric substrate was 64⁰YZ-cut Lithium Niobate (LiNbO₃) for love wave generation, and the lightweight electrodes were made of Aluminium (Al). Analytical simulations were conducted using COMSOL Multiphysics 6.0 software based on the Finite Element Method (FEM).

The impact of mass loading on the sensing layer was utilized to detect volatile organic gases. The resonant frequency of the SAW device was determined, and simulations were performed by exposing the sensor to dichloromethane gas at concentrations ranging from 0 to 1000 ppm. This work also described the analysis of various parameters of the SAW sensor such as the quality factor, coupling coefficient, equivalent circuit components, S parameter, and admittance. The simulation result exhibited a linear frequency shift of the sensor with dichloromethane gas concentration and explained the behavior of the sensor through its equivalent circuit.