Piezoelectric-Excitation-Enabled Saturated-Charge Regulation for Active Noncontact Triboelectric Sensing

Abstract Surface charges on triboelectric materials inherently exist in a nonsaturated, dynamically decaying state. Consequently, passive noncontact inductive sensing produces signals with pronounced amplitude fluctuations and baseline drift. To address these limitations, we introduce an active excitation strategy based on a piezoelectric layer: periodic mechanical actuation induces reversible polarization, thereby modulating the local electric field to enable real-time replenishment and spatial redistribution of surface charges on the triboelectric layer. This mechanism markedly enhances both signal amplitude and long-term stability. Furthermore, intrinsic material properties, including relative permittivity, surface resistivity, thickness, and surface charge retention capacity, introduce systematic variations in coupling capacitance, induced charge transfer pathways, and charge relaxation dynamics across different target materials in noncontact configurations. By employing frequency-swept excitation, static dielectric and charge-related differences among materials are transduced into distinctive dynamic frequency-response signatures, substantially improving multimaterial classification accuracy. Critically, this approach retains the key advantages of noncontact operation and zero mechanical wear, while effectively reducing surface contamination and introducing active signal conditioning, thereby distinguishing it from conventional contact-mode triboelectric classification and passive noncontact sensing paradigms. Finally, by fusing time-domain, frequency-domain, and time-frequency features within a decision tree-based classification framework, the system achieves >95% recognition accuracy across diverse material classes, demonstrating a scalable, robust, and actively enhanced triboelectric sensing platform suitable for online material sorting, thin-film quality inspection, and robotic tactile perception.