Asymmetric Structure Based Flexible Strain Sensor for Simultaneous Detection of Various Human Joint Motions

Joint motion is a very common activity which involves tensile or compressive bending motions. Distinguishing and monitoring of joint motions are important for an interactive human–machine interface or rehabilitation of human joints. Here, we present an asymmetric structure based, liquid metal embedded, resistive strain sensor, which is prepared by a stereolithography-based 3D printing process. Electromechanical characterization results of sensors confirm that the current sensor can monitor the angle and direction of joints even if the angle amplitude remains the same. The sensor exhibits good mechanical stability and minimum resolution angle of 1°, ranging from 70° to −70°. Sensor performance is enhanced with the increase of its thickness, which is due to an additional deviation produced at the center. This deviation causes the resistance of the sensor to change greatly during both compressive and tensile bending. Finally, a sensor’s capability is practically demonstrated by the monitoring the motion of index of the finger, wrist, and neck joints under various human activities. Our sensor paves a way for real-time continuous monitoring of human or artificial robot joint motions.