Numerical-experimental study of a multi-branch l-shaped broadband piezoelectric energy harvester based on modal densification

Abstract

Piezoelectric energy harvesting (PEH) offers a sustainable power solution for low-power electronic devices, such as internet of things nodes, wireless sensor networks, and micro-electromechanical systems, by converting ambient mechanical vibrations into electrical energy. Among various multimodal PEH designs, the L-shaped cantilever beam has attracted significant attention due to its closely spaced first two resonant modes, which are beneficial for broadband PEH. However, an untuned L-shaped structure inherently suffers from a narrow operating bandwidth, limiting its practical application in broadband vibration environments. To overcome this limitation, this paper proposes a novel multi-branch L-shaped broadband piezoelectric energy harvester (MB-LPEH). The proposed design synergistically integrates multiple independent cantilever branches onto a primary L-shaped beam, thereby introducing multiple closely spaced resonant modes and significantly broadening the effective operating bandwidth. A comprehensive approach combining theoretical modeling, finite element simulation, and experimental validation is employed to analyze the vibrational characteristics of the MB-LPEH under multi-modal resonance and assess its performance under multidirectional excitation. Parametric studies reveal the influence of key structural parameters on the resonant frequencies and output characteristics. Experimental results confirm the accuracy of the theoretical and simulation predictions. It is demonstrated that replacing a single branch beam of the MB-LPEH with a stiffer material sequentially excites four bending resonant modes within the 5–45 Hz range, substantially broadening the effective operating bandwidth. Compared to a low-stiffness configuration, this design achieves a 27.3% increase in operating bandwidth and a 536% increase in output power at the third mode. Additionally, at an operating frequency of 15.6 Hz, the normalized power density reaches 248 mW (cm3⋅g2)−1. The proposed MB-LPEH presents an effective and innovative solution for enabling self-powered wireless sensor nodes in structural health monitoring applications.