Flexible electronic devices are a rising interest in both research and industry due to their facile interaction with the human body and surrounding environment. In particular, demand is dramatically increasing for flexible sensors due to their potential applications in personalized health monitoring, human-machine interfaces, and soft robotics. Examples of such electronic devices include sensors for strain, pressure, touch, temperature, and a variety of bio-sensors.
In this project, we have developed highly stretchable strain sensors by combining graphite thin films as strain responsive conductive films and a flexible polymer support (Figure a). To boost the sensitivity, controllable microcracks have been generated in graphite films that can dramatically reduce the conductive passways upon stretching (Figure b). As a result, the strain sensors can simultaneously detect deformation amplitudes ranging from microscale ($\geq$ 10 $\mu$m) to millimeter scale ($\geq$ 10 mm) with ultrasensitivity (GFs $\geq$ 100) and high stretchability (e $\geq$ 100).
We have demonstrated the advantages of our strain sensors in various potential applications such as human motion detection, sound visualization, pressure sensing, and soft robotics. Figure (c) shows the resistance change of a strain sensor mounted onto the chest area for respiration rate and pattern monitoring. As shown, there is an obvious resistance change during deep breathing since larger strain is accommodated by the sensor. Figure (d) illustrates the integration of our strain sensors with a soft gripper robot as feedback control and sensory skin. The integration enabled touch and grasp sensing through resistance change of the embedded sensors.