Advanced Flexible Physical Sensors with Independent Detection Mechanisms of Pressure and Strain Stimuli for Overcoming Signal Interference

Recently, flexible and wearable physical sensors have garnered significant research interest due to their potential applications in attachable devices, electronic skin, and multipurpose sensors. The physical stimuli detected by such sensors typically consist of pressure applied vertically and strain applied horizontally. However, due to the similar response characteristics between the two, signal interference can occur, complicating the clear distinction between pressure and strain stimuli. This interference leads to inaccurate data interpretation and reduces the specificity of the sensors. To address this issue, we developed novel dual-sensing mode physical sensors with separate response mechanisms for the two types of physical stimuli, based on a unique structural design that independently induces changes in piezocapacitance for pressure stimuli and in piezoresistance for strain stimuli. The sandwich-structured sponge-piezocapacitive pressure sensor demonstrated high sensitivities (GFs) across various pressure ranges: 0.1034 ± 0.01624, 0.0129 ± 0.0017, and 0.0062 ± 0.00019 kPa-1 in low, medium, and high-pressure sections, respectively. In particular, the high linearity reached 0.995 at pressures ranging between 5 and 30 kPa, and there was minimal hysteresis between the response signals during the loading/unloading cycle process. As a piezoresistive strain sensor, it demonstrated a remarkable GF of 0.1462 ± 0.00325%-1 and exceptional linearity of 0.998 across a strain ranging from 0 to 30%, highlighting its potential as a precise strain-sensory device in advanced applications. The asterisk-shaped piezoresistive strain sensor highlighted its ability to distinctly respond to the external stress intensity and direction. Maximum resistance change rates occurred at a strain direction of 0° (parallel to the electrode), whereas minimum values occurred at a strain direction of 90° (perpendicular to the electrode), clearly demonstrating a linear sensing performance depending on the direction of the tensile stimulus. These findings were demonstrated via real-world tests, including the weight changes, water droplets, and monitoring of the finger, wrist, and knee movements. Our study suggests the feasibility and effectiveness of the dual-sensing-mode physical sensors with a sandwich-structured sponge-piezocapacitive and asterisk-shaped piezoresistive architecture, which demonstrate promising application prospects in wearables, healthcare, and human-machine interfaces. (DOI:10.1021/acsami.4c09337)