Liquid Metal Interdigitated Capacitive Strain Sensor with Normal Stress Insensitivity

Abstract

Soft and stretchable sensors of strain are important for human–machine interfaces, soft robotics, and electronic skins. However, soft strain sensors generally cannot distinguish in‐plane strain from normal stress. For example, stretching a sensor often gives a similar signal to pressing the sensor. To solve this problem, a liquid metal (LM)‐interdigitated capacitive strain sensor that is insensitive to normal stress is introduced. The sensor contains LM‐interdigitated electrodes prepared by vacuum filling of LM into lithographically defined microchannels. The capacitance between the LM electrodes decreases with increasing strain due to geometric changes. Because of the liquid nature of the electrodes, the sensor exhibits high stretchability (100% strain) and repeatability with gauge factor of −0.3. Due to the elasticity of the device, the sensor has low hysteresis (<1%) and no crosstalk between strain and normal stress sensing. These types of soft sensors may find use in wearable devices.