Design and Simulation of PDMS and PMMA Based Touch Mode Capacitive Pressure Sensor: A Comparative Study

Aims: In this research work, a design method and a comparative of a touch mode capacitive pressure sensor (TMCPS) using poly-dimethyl-siloxane (PDMS) and poly-methyl methacrylate (PMMA) is the done. A novel method is proposed to linear the output characteristics of the sensor because planer type capacitive sensors are non-linear.

Study Design: This method uses a mechanical coupler to convert the deflection of the diaphragm into a linear displacement that helps to linear the output characteristics. The mathematical model of the sensor is designed and simulated the 3D model to validate the mathematically calculated values.

Place and Duration of Study: This study is done in the Department of Electronics and Communication Engineering, Rajiv Gandhi University, Arunachal Pradesh at COMSOL Simulation Laboratory during 2021 to 2023.

Methodology: The mechanical and electrostatic components of the sensor are represented mathematically model in two separate parts. For this study, a square diaphragm was used since it exhibits greater deflection than circular or rectangular diaphragms. In order to validate the model equation, a 3D model of a sensor is created in the COMSOL Multiphysics simulator and simulated. For the pressure range of 0.1 [MPa] to 10.1 [MPa], the identical 3D model of the sensor construction with a square diaphragm thickness of 20 µm is simulated for PDMS and PMMA. The different elements influencing the sensor's sensitivity are discovered, and the effects of the materials PDMS and PMMA on the output characteristic are discussed.

Results: The simulated and calculated sensitivity of the sensors based on PDMS are 0.03685 [fF/MPa] and 0.03467 [fF/MPa] respectively. And the simulated and calculated sensitivity of the sensors based on PMMA are 0.03929 [fF/MPa] and 0.03748 [fF/MPa] respectively. It is observed that the PDMS based TMCPS has more sensitivity then the PMMA based TMCPS.

Conclusion: The PMMA based TMCPS has higher sensitivity than the PDMS based TMCPS. The various parameters that affect the sensitivity of the sensor are diaphragm shape, size, Poisson’s ratio and Young’s modulus, area covered by the dielectric material, dielectric constant of the polymers dielectric and surface are of the electrode plate.

Future Scope: Future research for TMCPS can be conducted using composite polymer dielectric materials and new polymer dielectric materials to improve the sensitivity. One can optimize the sensor using different tools as the mathematical model is developed.