Flexible Bifunctional Proximity-Pressure Sensor Based on EGaIn/Silicon Dioxide/PDMS Nanocomposites for Human–Machine Interaction Applications

Abstract

Flexible bifunctional sensors are essential for human–machine interaction, yet achieving simple fabrication, structural flexibility, and accurate proximity-pressure detection remains challenging. This study presents a flexible bifunctional proximity-pressure sensor (FBPPS) based on gallium–indium alloy (EGaIn)/silicon dioxide (SiO₂)/polydimethylsiloxane (PDMS) nanocomposites and sodium chloride (NaCl) pore former. A composite structure with sandwich characteristics was constructed, namely the intermediate dielectric layer (porous microstructure) and the upper and lower electrode layers. NaCl templating creates a 3D porous microstructure, enhancing pressure sensitivity, while a gravity-induced process ensures uniform EGaIn hierarchical distribution in PDMS. SiO₂ nanoparticles improve electrode stability. The FBPPS demonstrates high pressure sensitivity (2.3463 kPa^–1), fast response/recovery (25 ms/37.5 ms), and a low detection limit (1.25 Pa). It also achieves 25 ms proximity response/recovery with fine distance resolution. With its dual functionality, the sensor enables applications in human–machine interaction, robotic grasping, and safety alerts, providing some ideas for the development of flexible electronic devices.