Resonator with magnetically adjustable natural frequency for vibration energy harvesting

The recent years have witnessed a wealth of research on energy harvesting technologies. To maximize the output power, vibration-based energy harvesters are normally designed to exhibit natural frequencies that match those of the excitation. This has spurred interest into the design of devices that possess tunable natural frequencies to cope with sources which exhibit varying frequencies. In this work, an energy harvester is proposed in the form of a base excited cantilever treated with a piezoelectric layer. The cantilever carries a tip mass in the form of a magnet which is placed in close proximity to a stationary magnet with opposite polarity. Different values of axial tensions, and hence different natural frequencies, are obtained by adjusting the gap between the magnets. A dynamic model to predict the system performance is presented and verified experimentally. Based on the findings of this paper, natural frequencies ranging from 3.19 to 12 Hz were achieved.