Ionic conductivity and excitation frequency effects in iontronic pressure sensing

Iontronic pressure sensors, which combine high sensitivity, superior signal stability, and resistance to electromagnetic interference, are regarded as promising candidates for next-generation pressure sensing systems. However, the roles of ionic conductivity and excitation frequency in determining sensing behavior remains unknown. Here, we employ an ionic-droplet-based research model to elucidate these effects through electrochemical impedance spectroscopy (EIS). Based on the equivalent circuit, we derived equations that link apparent capacitance change to ionic conductivity and excitation frequency. The equations reveal that droplet compression leads to larger apparent capacitance variation at lower ionic conductivity and higher excitation frequency, consistent with our experimental observations. Accordingly, tuning these parameters alone enhances the sensitivity of the droplet-based pressure sensor by up to 8772% without any structural modification. Under the optimized conditions, the sensor delivers highly repeatable pressure responses. Integrated into a robotic arm, it enables real-time pressure detection and discrimination of materials with different softness levels. By substituting ionic-droplets with hydrogels, the sensing model is successfully extended to solid-state ionic materials. A hydrogel sensor array of 4 × 4 with a pixel size of 2 mm is fabricated, enabling spatial pressure mapping. These findings provide new design principles for elastic ionic materials and underscore the critical role of measurement parameters in determining the sensing behavior of ionic sensing systems.