Unravelling electromechanical mechanism of mechanoreceptor inspired capacitive pressure sensor considering size effect

The rapid development of intelligent sensing technologies, including electronic skins, wearable devices and robots, has put forward an urgent demand for various tactile biomimetic sensors. However, the design of tactile sensors is mostly based on independent experimental research and lack theoretical guidance at present. In this work, drawing inspiration from human skin microstructure mechanoreceptors responsible for tactile sensation, we proposed a capacitive pressure sensor model featuring a biomimetic conformal microstructured electrode with a round-crown shape. Moreover, at the micrometer scale, size effect profoundly influences the mechanical behavior of sensing materials and microstructured devices. Firstly, we conducted in-depth research on the electromechanical behavior of conformal microstructured electrode pressure sensor, considering the size effect based on couple stress elasticity and Hertz contact theory. We validated the effectiveness of the model by comparing it with experimental and simulation results of human skin. Through numerical simulation, we further verified that the theoretical model of a single microstructured electrode can be utilized for calculating microstructured electrode arrays. Furthermore, our analysis reveals that the geometric morphology and material properties of the dielectric layer, the arrangement density of the microstructured electrode arrays, along with the radius of the round-crown shaped microstructured electrode are the dominant parameters influencing the electromechanical sensitivity through parameter analysis. Finally, we devised a high-k (high dielectric permittivity) polymer composites dielectric layer with a tunable Poisson's ratio structure, offering a feasible approach to achieving highly sensitive capacitive microstructure sensors. This theoretical model that takes into account the size effect in microstructured electrode contact problem provides theoretical insights that can guide the optimization design of high-performance tactile sensors. © 2024 Elsevier Ltd.