13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- A Vibration Energy Harvester with Internal Impact and Hybrid Transduction Mechanisms Songmao Chen, Jing Sun, Junhui Hu* State Key Lab of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, 210016, Nanjing, P. R. China. * Corresponding author: ejhhu@nuaa.edu.cn Abstract To increase the power harvesting capability of an internal impact type vibration energy harvester (VEH), the authors have developed a novel hybrid VEH integrating both piezoelectric and electromagnetic (EM) modules for energy conversion. The proposed VEH transforms a low frequency external base vibration into an internal impact vibration of the tip of a cantilever beam, which is used to cause energy conversion by the piezoelectric effect and electromagnetic induction. A prototype is designed, fabricated and tested; the optimum load resistances are determined experimentally, and the power output performance and the total power density of the proposed VEH have been experimentally characterized with respect to the excitation amplitude and frequency. The dependence of the optimum excitation frequency for maximum total power output on the excitation amplitude has also been experimentally investigated. The total output power and power density are 0.8 mW and 15 µW/cm3, respectively, when the excitation amplitude and frequency are 1 mm (rms) and 15 Hz, respectively. Keywords Vibration Energy Harvesting, Impact, Piezoelectric, Electromagnetic, Hybrid 1. Introduction With the evolution of low power electronics, harvesting the structural vibration energy, which is clean, ubiquitous and renewable, has gained increasingly extensive attentions from worldwide researchers in the recent decade [1-4] for its great potentials for applications in areas of wireless sensor networks (WSNs), autonomous low power microsystems, distributed computing and portable alternative power sources, remote sensing and actuation, etc., to replenish or even replace traditional power supply such as battery. A number of vibration energy harvesters (or vibration-powered generators) using the piezoelectric effect [5-9] and electromagnetic induction [10, 11] have been proposed and developed. Generally, a typical piezoelectric VEH employs a cantilever beam structure with a proof mass at its tip and excitation at its base [6]; thus only d31 mode is used. To increase the vibration energy harvesting capability of such mechanism, a piezoelectric VEH combining the d31 mode caused by flexural vibration and the d33 mode caused by direct impact was proposed [7]. It was found that piezoelectric components operating in the d33 mode can significantly increase the power generation of the conventional cantilevered piezoelectric VEH. Similar work using impact method has also been carried out by other researchers [12-15]. Nevertheless, to widen the application range of VEHs, the output power still needs to be increased. To further enhance the energy harvesting capability and more efficiently utilize the space of VEH structure, the authors have developed an evolutionary version based on their previous work [7]. In the evolutionary version, the VEH converts low frequency external vibration into its internal impact vibration and uses the piezoelectric effect and electromagnetic induction to convert the internal vibration energy into electric energy. The VEH topologically consists of three modules. The first one is a piezoelectric module harvesting the energy of internal impact directly; the second one is another piezoelectric module harvesting the impact induced vibration energy in the frames of the VEH; the third one is an electromagnetic module comprised of one hand-wound enameled copper coil and two pairs of anti-symmetrically placed bulk NdFeB permanent magnets, using the magnetic
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