Discovery of Piezoelectricity in Natural Birch Bark for AI-Assisted Sports Violation Monitoring

The rapid advancement of wearable electronics has created an urgent demand for distributed, sustainable, and green energy sources to power various microdevices. As the conventional lithium battery is harmful to the environment, the biopiezoelectric nanogenerator is an ideal candidate to meet these requirements. Here, we develop a piezoelectric nanogenerator based on natural birch bark derived from Betula platyphylla, which exhibits a piezoelectric coefficient (d33) of 3.09 pm V–1, a piezoelectric voltage output of 29.3 V cm–3, a piezoelectric current output of 0.33 μA cm–3, and a power density of 3.42 μW cm–3. After over 10,000 cycles of mechanical impact or 180 days of storage, its piezoelectric output shows no significant degradation, confirming robust electromechanical conversion. As a proof of concept, an integrated sports violation recognition system is further designed by combining a birch-bark piezoelectric nanogenerator with a multilayer perceptron classifier. With the assistance of machine learning, the system can accurately identify rule violations, offering reliable technical support for referees. This study provides a new way of fabricating self-powered green micro/nanodevices in the Era of Artificial Intelligence, paving the way for sustainable energy solutions in smart electronics.