Acoustic Wave Assisted Lotus Leaf Papillae Lead-Free Piezoelectric Material Humidity Sensor

To address the long-standing challenges of slow response, weak signal, and poor mechanical robustness in conventional flexible humidity sensors, A novel flexible multifunctional sensor is developed based on a "lotus-leaf acoustic wave collaborative lead-free piezoelectric" technology strategy. Specifically, a lotus leaf surface is used as a template, which is replicated with PVDF and then combined with a cellulose matrix embedded with niobium-based perovskite crystals, resulting in a sandwich-structured, flexible, lead-free piezoelectric composite film. Under acoustic wave excitation, the local piezoelectric coupling at the bio-inspired papilla interfaces significantly accelerates water adsorption/desorption kinetics, achieving an exceptional humidity response/recovery time of 0.98/1.2 s and a high sensitivity of 97%. The sensor demonstrates superior performance compared to commercial hygrometers. In addition, it has a high response signal of 130 V and a voltage sensitivity of 4.33 V N^-1 under a stress of 40 N, thus achieving dual parameter sensing. This humidity sensor, with its sub second response, high sensitivity, and dual-mode sensing capability of force and humidity, is expected to capture the slightest humidity and mechanical changes in real-time medical monitoring, motion tracking, and environmental IoT, providing unprecedented secure and green core components for intelligent health, and sustainable sensing systems.