Low-hysteresis Flexible Strain Sensors Based on Liquid Metal for Human-Robot Interaction

Flexible strain sensors have aroused great interest in the fields of human-machine interaction, human motion detection, and wearable devices. However, developing flexible strain sensors with low hysteresis, large strain range, fast response time, and excellent dynamic and static stability remains a challenge. In this paper, we prepared three types of flexible strain sensors: wave-shaped, triangle-shaped, and line-shaped by injecting liquid metal (EGaIn) into the silicon elastomer (Ecoflex) microchannel. Then, the performance of the three types of flexible strain sensors was tested. The results show that these sensors can withstand more than 150% strain and have extremely low hysteresis. Among these sensors, the triangle-shaped strain sensor exhibits a negligible hysteresis of 0.049% and the line-shaped strain sensor has the most obvious hysteresis of 1.406%, followed by the wave-shaped strain sensor with a hysteresis of 0.146%. However, the line-shaped strain sensor has the highest sensitivity with the value about 1.2, while the wavy-shaped and triangle-shaped strain sensors have a lower value of 0.95 and 0.83, respectively. In addition, the three types of sensors simultaneously exhibit many excellent performance characteristics such as excellent dynamic and static stability, long durability, and fast response time. To demonstrate the capability of the sensors in practical application, we used the triangle-shaped strain sensor to detect the bending motion of the robot finger. The results indicate that the developed flexible strain sensors are expected to be used for human-robot interaction.