A theoretical model of a flexible capacitive pressure sensor with microstructured electrodes for highly sensitive electronic skin

Abstract

Electronic skin (e-skin) has attracted much attention in smart wearables, prosthetics, and robotics. Capacitive-type pressure sensors are generally regarded as a good option for designing tactile sensing devices owing to their superior sensitivity in low-pressure regions, fast response time, and convenient manufacturing. Introducing microstructures on the electrode surface is an effective approach to achieve highly sensitive capacitive pressure sensors. In this work, an electromechanical model is proposed to build the relationship between capacitance change and compressive force. The present model can predict the sensitivity of the capacitive pressure sensor with microstructured electrodes, where each cellular microstructure is modeled using contact mechanics theory. It is the first time in the literature that, based on the Hertz theory framework, a rigorous electromechanical theory framework is established to model a flexible capacitive pressure sensor. In addition, the model can be extended to other microstructures, such as micro-pyramid, micro-pillar, and micro-dome array. The validation indicates that the analytical results agree well with the experimental data from our previous work and other literature. Moreover, the present model can effectively capture the sensitivity of the pressure sensor in the beginning range of small pressure. Sensitivity in this range is the most significant for the e-skin due to its robust linearity for a pressure sensor. Besides, we analyzed the compressive force–displacement relationship, the compressive force–contact radius relationship, and the influences of the geometrical and material parameters on the electromechanical coupling effect. The results show that the height and the Young’s modulus of the soft dielectric layer are regarded as the dominant influencing factors in the sensitivity of capacitive pressure sensors.