A Stretchable AI‐Enhanced Patch with Low‐Drift Iontronic Pressure and Vibration Sensor for Soft Film Thickness Recognition and Knee Motion Decoding

ABSTRACT Flexible iontronic mechanical sensors that mimic ion flow mechanisms in human mechanoreceptors can precisely sense physical stimuli, such as strain or pressure. An easily neglected issue is that these sensors often suffer from irreparable signal‐drift under continuous static pressure owing to mechanical hardening in the sensitive interface. Additionally, a mechanical mismatch between the flexible sensor and the rigid circuit limits the reliable application on the dynamic surface of human skin. Here, inspired by the tip conductor to non‐contact guide lightning, a non‐hardening solid‐liquid contact interface is engineered to form the electric double layer under pressure or vibration, which enables low‐drift and pressure‐vibration iontronic sensing. The iontronic sensor exhibits exceptional pressure sensitivity 23 550.6 kPa − 1 , and detects subtle vibration as low as 0.03 g. Leveraging low drift and high sensitivity, the sensor measures the thickness of soft films, distinguishing minimum thicknesses down to 10 µm, and CNN model enables recognition of 7 distinct film types with 93.6% accuracy. Furthermore, a stretchable circuit patch integrating an iontronic sensor and electronic chips is applied to the knee for motion monitoring. Using a transfer learning model, the patch system achieves real‑time decoding of 30 knee motions with 94.3% accuracy by mapping bending degree and shaking counts to x/y coordinates in a character matrix.