Passive Shape‐Adaptive Fluidic Interface for Enhanced Skin‐Sensor Coupling in Wearable Devices

Optimal coupling between sensors and the skin is critical for accurate physiological signal acquisition in wearable devices for healthcare, fitness, and human‐machine interaction. Accurate sensing relies on maintaining stable skin‐sensor contact that can adapt to the body's complex geometry under both static and dynamic conditions. Conventional sensor‐mounting structures, such as flexible or elastic straps, suffer from contact loss during movement and can cause discomfort due to excessive localized pressure. This article presents a passive shape‐adaptive fluidic (PSF) interface that enhances skin‐sensor contact quality and comfort by employing flexible, fluid‐filled pouches to redistribute pressure from high‐stress regions toward areas requiring additional pressure to maintain sensor contact. A computational model accurately predicts the mechanical response of the interface, showing excellent agreement with quasi‐static and dynamic measurements. A wrist‐worn PSF prototype improves pressure uniformity by 32% across eight sensing sites and six hand poses vs. a band without the interface, and increases skin‐sensor contact quality by 93% relative to a compliant foam, achieving superior performance at 80% lower thickness (2‐mm‐thick PSF) without power or bulky components. PSF interfaces provide a compact, adaptable, and low‐energy platform that advances wearable systems by maintaining ideal sensing pressure, enabling enhanced physiological signal fidelity and user comfort.