Developing and testing a palm-sized shaking energy harvesting device

Abstract

In the development of technology today, the energy problem remains one of the most challenging issues that electrical engineers must carefully consider. Although people use electricity daily, generating it is a relatively unfamiliar concept to those outside the engineering field. To raise awareness of this issue, the idea of creating a simple, compact power generator has emerged. One objective was to make the principle sufficiently accessible to be demonstrated and understood by younger students, while also investigating its potential for small-scale energy generation and storage. Improving understanding of energy generators for the next generation could open another potential for energy technology. The project investigated the feasibility of converting human-generated mechanical motion into electrical energy using a compact vibration-based electromagnetic energy harvester. The system was based on Faraday's law of electromagnetic induction, in which a permanent magnet moved axially inside a copper coil during manual shaking. A numerical model was developed in MATLAB to calculate the magnetic field, magnetic flux linkage, induced voltage, and generated current. Electromagnetic behavior was also simulated using COMSOL Multiphysics and ANSYS Electronics Desktop, while LTspice was used to investigate the Schottky bridge rectifier and capacitor-smoothing circuit. A physical bench prototype consisting of the magnet-coil generator, rectification and filtering circuit, TP4056 charging module, and 18650 lithium-ion battery were constructed and experimentally tested. The constructed system remained a bench prototype and was not developed into a complete enclosed palm-sized product suitable for use by children. Experimental measurements showed that the electrical output was intermittent and strongly dependent on the speed and consistency of manual shaking. The TP4056 charging indication and the measured positive battery-side current showed that current was transferred toward the battery during operation. However, a complete battery charge or a controlled long-term increase in battery state of charge was not quantitatively demonstrated. At the measured mean battery-side current of 0.2625 mA, the ideal constant-current equivalent charging time for a nominal 2600 mAh battery is approximately 9905 hours. This is not an experimentally demonstrated charging time and excludes the intermittency of manual shaking, conversion losses, and the battery-charging profile. The developed prototype demonstrated the feasibility and educational value of shaking-based energy harvesting, while the limited output power remained an important area for future improvement.