A Monolithic Strain–Proximity–Pressure Trimodal Flexible Sensor for Healthcare Monitoring and Wearable Perception

Flexible electronic skins capable of multifunctional signal acquisition are indispensable for both personalized healthcare and immersive human-machine interfaces. However, integrating strain, proximity, and pressure sensing into a compact device is impeded by structural redundancy and performance trade-offs. Herein, we demonstrate an all-in-one trimodal sensor via an electrode-multiplexed architecture, where serpentine conductive traces function as both piezoresistive transduction and capacitive sensing. By leveraging the dual function of these shared electrodes, the system achieves a reduction in integration complexity. The serpentine-patterned electrodes are utilized to provide high strain sensitivity (gauge factor of 3.69, 0-20% range), while their complementary stacking maximizes the fringing effect for long-range proximity detection (0-100 mm). Moreover, the integration of a hierarchical iontronic interface effectively alleviates the sensitivity-range trade-off in pressure sensing (3.75 kPa^-1 at 0-60 and 0.99 kPa^-1 at 60-200 kPa). Consequently, the system demonstrates versatile utility in healthcare monitoring, which accurately captures radial artery pulses, muscle dynamics, and noncontact respiration patterns. Furthermore, the sensor enables physics-informed wearable perception by synergizing tactile and proprioceptive information, which successfully distinguishes material softness from structural compliance. This work provides a robust solution for versatile multimodal sensors and facilitates advanced applications in ubiquitous human-machine-environment monitoring and interaction.