Laser-induced graphene (LIG) has the advantages of one-step fabrication, prominent mechanical performance, as well as high conductivity; it acts as the ideal material to fabricate flexible strain sensors. In this study, a wearable flexible strain sensor consisting of three-dimensional (3D) wavy LIG and silicone rubber was reported. With a laser to scan on a polyimide film, 3D wavy LIG could be synthesized on the wavy surface of a mold. The wavy-LIG strain sensor was developed by transferring LIG to silicone rubber substrate and then packaging. For stress concentration, the ultimate strain primarily took place in the troughs of wavy LIG, resulting in higher sensitivity and less damage to LIG during stretching. As a result, the wavy-LIG strain sensor achieved high sensitivity (gauge factor was 37.8 in a range from 0% to 31.8%, better than the planar-LIG sensor), low hysteresis (1.39%) and wide working range (from 0% to 47.7%). The wavy-LIG strain sensor had a stable and rapid dynamic response; its reversibility and repeatability were demonstrated. After 5000 cycles, the signal peak varied by only 2.32%, demonstrating the long-term durability. Besides, its applications in detecting facial skin expansion, muscle movement, and joint movement, were discussed. It is considered a simple, efficient, and low-cost method to fabricate a flexible strain sensor with high sensitivity and structural robustness. Furthermore, the wavy-LIG strain senor can be developed into wearable sensing devices for virtual/augmented reality or electronic skin.

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.