Flexible Capacitive Pressure Sensor Based on Laser–Induced Graphene and Polydimethylsiloxane Foam

Flexible pressure sensors have been extensively employed in a range of fields, such as electronic skin (E–skin), humanoid robots, and personal health care. Laser–induced graphene (LIG) is an ideal active material to produce flexible sensors due to its advantages of one–step fabrication, excellent mechanical performance, and high conductivity. This paper presents a flexible capacitive pressure sensor (FCPS) consisting of LIG and polydimethylsiloxane (PDMS) foam. LIG can be fabricated by using a laser to directly write on polyimide (PI) film. By transferring the LIG to a porous PDMS foam, the FCPS acquired a plate–foam–plate integrated structure and it had high sensitivity ( $\sim 0.026\,\textit {kPa}^{-1}$ in $15\sim 40\,\textit {kPa}$ ) and a fast response time ( $\sim 120\,\textit {ms}$ ). In dynamic testing, the FCPS exhibited a stable ( $\delta _{r}=\sim 1.785$ %) and low–hysteresis ( ${h}=\sim 9.762$ %) response to pressure. Furthermore, no significant signal distortions were identified in 5000–cycle press/release testing, which demonstrated the long–term durability of the FCPS. The FCPS was capable of distinguishing between different external mechanical stimuli, including stretching, pressing, bending, and twisting by multiple responses (i.e., two electrode resistances and the capacitance between the electrodes). The FCPS was also employed to detect joint movements, body pressure, and arterial pulse. To study the spatial pressure distribution in depth, an FCPS array was developed by designing a LIG pattern into an electrode array. As a result, there was a mapping between the measurements and the spatial pressure. In our study, FCPS and its array were prepared for multiple stimuli identification and tactile sensing using a simple, efficient, and low–cost technique. The results from this study demonstrated that the FCPS and its array demonstrated potential for being fabricated into wearable medical devices, virtual reality/augmented reality (VR/AR) devices, or E–skin.