A tunable multi-arm electromagnetic pendulum for ultra-low frequency vibration energy harvesting

Autonomous electronic devices and sensors are essential to reduce expensive maintenance, increasing job security and reliability, avoiding battery replacements and wired systems. Industrial systems and civil structures vibrate dissipating an important amount of energy that can be harvested to power small devices. This work continues and extends a previous work from the authors (Castagnetti 2019 Meccanica54749–60). Here we improved that initial configuration by proposing a tunable multi-arm electromagnetic pendulum for ultra-low frequency vibrations energy harvesting. This configuration features five electromagnetic converters and a magnetic spring, each supported by a pendulum arm with different length: when excited by external vibrations, this six arms frame is free to oscillate around a central pivot. The paper starts from conceptual design, includes a detailed multiphysics dynamic simulation implemented with Matlab Simscape software, presents the prototype development through three-dimensional printing and experimental validation. Systematic experimental tests investigated different pendulum configurations for three stiffness levels of the magnetic spring and confirmed both the ultra-low frequency response (from 2 to 10 Hz), as predicted by the dynamic simulation, and the good voltage and power outputs. Specifically, for the higher stiffness of the magnetic spring, corresponding to an oscillation frequency of about 9.5 Hz, the power output was up to 8.4 mW and the output voltage of about 2 Volt.