Investigation and analysis of silver interdigitated electrodes with natural rubber infused graphene for capacitive-based flexible pressure sensor

The development of flexible capacitive pressure sensors has recently drawn significant interest among researchers for emerging wearable electronic devices, monitoring applications, and smart systems. However, it still poses enormous difficulty to design capacitive sensors with excellent sensitivity. Few studies have reported the use of interdigitated electrodes (IDE) designs to improve the sensitivity of sensors. In our study, we selected graphene-infused natural rubber (NRG) as the sensing dielectric layer owing to its excellent cyclic pressure loading response as well as its high flexibility and conductivity. Here, we reported the impedance response of different graphene contents in natural rubber (NR) with the optimization of different geometrical parameters of IDEs. The electrical properties of silver IDEs are simulated using COMSOL Multiphysics. The impedance characteristics of NRG and its capability for detecting a wide variety of pressures and bending angles are analyzed using a Digilent Analog Discovery impedance analyzer. Understanding these properties and how they can be affected is vital in designing highly sensitive capacitive pressure sensors. Simulations were used to show the voltage potential, electrical field, and capacitance developed between the individual digits of the electrodes. The impedance analysis was helpful in computing the electrical conductivity of the NRG. The impedance analysis showed that the NRG sensing material improved in conductivity (≈0.006 S/m) and capacitance (≈0.30 pF) with a graphene loading of 5 wt.%. In this novel work, a capacitive-based pressure sensor incorporating unvulcanized NR and 5 wt.% graphene nanoplatelet as the sensing material was successfully fabricated with a sensor sensitivity of 0.004 kPa⁻¹ for the low-force detection region of 40 kPa.