Omni-directional Deformable Shear Sensor with Shear-Pressure Decoupling by Analyzing Frequency-Dependent Ion Dynamics

Artificial tactile sensor realizes touch by mimicking human skin and receptors. They have been used for healthcare monitoring devices, human-machine interfaces, and artificial skin for robots. Especially, this sensor is attached to the robot's skin and recognizes the stimuli, as if it was felt by a human. When human grabs an object, they feel applied normal and shear force and control the pressure to prevent the object from breaking or falling. To realize this delicate grasping motion in the robot, a shear force sensor is essential. However, the shear force sensor is structurally complicated because the electrode must be configured in a three-dimensional structure to recognize the force applied horizontally. Moreover, during the grasping motion, also minimal pressure is applied so that both pressure and shear force need to be recognized.<br/>Herein, we fabricated an ionic conductor-based soft sensor that can detect pressure and shear force separately. In an ionic conductor, various information can be obtained because the behavior of ions varies depending on the frequency. To use these advantages, the ion gel is placed between a hemispherical upper electrode and a flat lower electrode. The pressure is measured in low frequency to detect the electrical double layer(EDL) capacitance between the ion gel and the dome-shaped upper electrode, and the shear force is perceived in high frequency to detect bulk resistance of the ion gel. Therefore, with only ion gel, the sensor can perceive and differentiate pressure and shear force in different frequencies. Furthermore, the sensor can recognize shear force in any direction with 1 x 4 electrodes. Finally, the sensor can perceive various grasping in any direction and even delicate gestures such as opening a bottle cap.