An Ionic Hydrogel-Based 3D Force Sensor for Multidimensional Password Input and Enhanced Security
Flexible tactile sensors are pivotal for human-machine interaction, yet accurate decoupled sensing of three-dimensional (3D) forces and integration into functional systems remain challenging. Here, we present a piezoresistive 3D force sensor based on ionic hydrogels that detects and analyzes multi-directional forces. The sensor exhibits a linear response to normal forces from 1 to 25 N (R²=0.99) and maintains stable sensitivity for shear forces within 0–4 N. By incorporating both force magnitude and direction, the sensor enables multidimensional password input, expanding traditional one-dimensional passwords into numeric, alphabetic, and Morse code formats. Experimental results demonstrate significant potential for enhancing information security. The sensor's simple structure, mature fabrication, and ease of integration with flexible electronics underscore its practicality. This work addresses the bottleneck of unidirectional sensing in conventional flexible pressure sensors, offering a robust solution for multidimensional force acquisition in human-machine interfaces, soft robotics, and biomechanical monitoring.