Self-powered multilayer impact sensor consisting of CFRP integrated with soft and hard piezoelectric layers

This study presents the design, development, and evaluation of a multilayer sensor composed of carbon fiber–reinforced polymers (CFRP) integrated with soft and hard piezoelectric layers (hereinafter CFRP/Piezolayer-Hard&Soft) for advanced impact sensing and energy harvesting. This novel design incorporates hard and soft potassium sodium niobate (KNN) piezoelectric composites, optimized at 35 and 40 vol% KNN contents, respectively. The hard layer provides superior mechanical strength and energy-harvesting efficiency, and the soft layer enhances flexibility and sensitivity, thus redistributing stress and mitigating damage effectively. The CFRP/Piezolayer-Hard&Soft configuration exhibits the best impact-sensing performance, achieving a peak sensitivity of 1.5 mV/g and substantial energy-harvesting capabilities at resonance frequency. Failure analysis under high-energy impacts reveals distinct signal behaviors associated with brittle and ductile fracture mechanisms, offering insights into the composite failure process. The proposed sensor has exceptional durability, mechanical robustness, and sensing sensitivity and is thus a promising candidate for structural health monitoring and self-powered sensing applications.