Self‐Powered Piezoionic Strain Sensor toward the Monitoring of Human Activities

Wearable sensors for the detection of human activities including subtle physiological signals and large-scale body motion as well as distinguishing the motion direction are highly desirable, but still a challenge. A flexible wearable piezoionic strain sensor based on the ionic polymer membrane sandwiched between two conductive electrodes is developed. This ionic polymer sensor can generate electrical signal output (≈mV) with rapid response (≈50 ms) under the applied bending deformation due to the internal mobile ion redistribution. Compared with the currently studied resistive and capacitive sensors, this sensor can generate sensing signals without the requirement of additional power supply, and is able to distinguish the direction of the bending strain by observing the direction of generated electrical signals. For the sensor with metallic electrode, an output voltage of 1.3 mV is generated under a bending-induced strain of 1.8%, and this voltage can be largely increased when replacing the metallic electrodes by graphene composites. After simple encapsulation of the piezoionic sensor, a wearable sensor is constructed and succeeded in monitoring the diverse human activities ranging from complex large scale multidimensional motions to subtle signals, including wrist bending with different directions, sitting posture sensing, pulse wave, and finger touch.