Liquid Metal-Based Flexible Sensor for Perception of Force Magnitude, Location, and Contacting Orientation

Flexible sensors have the advantage to enable intelligent systems to interact with the environment with high safety and versatility. Liquid metal is a useful element for flexible sensors due to its stretchable, reconfigurable, and healing characteristics. However, it is difficult to decode the stimuli position using uniform liquid metal because of its homogeneity and fluidity. Current sensing systems for the perception of force magnitude and contact location mostly rely on sensing arrays and massive crossover electrodes. In this article, we proposed a novel method for simultaneously sensing the force magnitude and contact location without crossover electrodes. In the new design, we encapsulate the liquid metal electrodes with varying cross sections in two silicon layers that function as protective skin and govern the geometry of liquid metals. When a force is applied to the flexible sensor, the change of resistance is dependent on both location and stimuli magnitude. Three liquid metal channels with different gradient resistance are embedded in the prototypes with parallel distributions. Combining the signals collected from the three channels, we can simultaneously measure the force magnitude, stimuli location, and contacting orientation. The overall force resolution is sub-Newton in the range from 0.5 to 20 N. The position can also be determined with a 100% success rate for the segmented sensor and a position resolution of 2 mm for the continuous sensor. The error for contact orientation measurement is 4.58° when the orientation ranges from 45° to 135°. The proposed multifunctional sensing device with high accuracy and wide sensing range has significant potential for developing interactive interfaces for human–machine interactions and industrial applications.