A graphite nanoplatelet-based highly sensitive flexible strain sensor

Flexible strain sensors, as crucial components in smart wearable devices, have recently drawn considerable attention due to their long-term monitoring abilities and facile interaction with the human body. However, low sensitivity, sluggish response, poor repeatability, sophisticated, and expensive fabrication process have notoriously limited their further deep applications. Herein, a graphite nanoplatelet (GNP) based capacitive-type strain sensor has been developed by a cost-effective gap coating method. The prepared sensors can be stretched up to 30%, and unlike other traditional capacitive-type strain sensors which have a limited theoretical maximum gauge factor of 1, it exhibits an interesting negative gauge factor, whose absolute value can go up to ∼3.5. Additionally, this work also investigated the layout design of shunt capacitors, and the pseudo-interdigital capacitor sensor demonstrated a substantial increase in the cyclic stability compared to the parallel plate capacitor. Furthermore, the as-prepared sensor has a fast signal response, whose response time is less than ∼140 ms and recovery time less than ∼90 ms. Also, the cyclic stability test of stretching proves the long-term durability of the sensor. Moreover, a microcontroller unit (MCU) system has been developed in the circuit level to realize the real-time control of a robotic hand.