Electromagnetic induction (EI), or the production of voltage across a conductor by varying the magnetic field or by moving the conductor through a fixed magnetic field, is one of the most traditional methods of converting other forms of energy to produce electrical energy. Consequently, its principles are widely understood, and the technology is highly mature. However, the principles of EI have not been rigorously applied so far in implementing energy conversion mechanisms on a smaller scale, such as energy harvesters that collect small amounts of energy.
Notably, the major limitation of energy harvesters is their relatively low power output compared to their size. Consequently, much research has been dedicated to increasing their power output by developing new energy conversion mechanisms, often incorporating hybrid structures that combine these mechanisms with the relatively higher power output of EI. Many studies have sought higher power output by simply choosing larger and stronger magnets and more turns of coils. However, an innovative approach is to try to optimize the topology of magnets and coils based on the principle of maximizing the magnetic flux change.
With this motivation, a team of researchers from the Republic of Korea, led by Associate Professor Dahoon Ann from the Department of Mechanical System Design Engineering at Seoul National University of Science and Technology (SeoulTech), focused on cylindrical EI coils and magnet cores, the most commonly used components in energy harvesters, to come up with a novel design for energy-efficient and high-power-output EI-type vibration energy harvesters (VEHs). "This can help achieve higher power output in a smaller volume. If such energy harvesters are realized, it could herald a future where all battery-powered devices use energy harvesters as their primary power source," claims Dr. Ahn.
Their findings were made available online on September 10, 2024 and published in Volume 9, Issue 4 of the Journal of Science: Advanced Materials and Devices on December 01, 2024.
The researchers studied the conversion of mechanical energy to electrical energy in cylindrical EI-VEHs with disc- or ring-shaped magnets and coils. Their simulations reveal that using a repulsive magnet pair instead of a single magnet, incorporating a yoke (a structure for guiding and concentrating magnetic flux in a desirable part of a magnetic circuit), and optimizing the position and thickness of the coil are promising strategies. These approaches modify the path of the magnetic flux so as to maximize the magnetic flux gradient at the position of the coil winding, leading to better EI-VEHs.
Specifically, a yoke enhanced the power consumption at the external load by about 5.8 times. The team also determined the points in the magnetic circuit where power generation is unfeasible as a result of zero magnetic flux gradient and observed a remarkable 5.3-fold uptick in power generation upon optimizing the coil placement.
Based on these results, the study proposes two novel designs for EI-VEHs: one with a moving coil winding and fixed disc magnets with a yoke to the housing and another based on moving ring magnets and fixed coil winding to the housing with a yoke enclosure. While the first design demonstrates high power output, it's not structurally sound. In contrast, the second configuration has no structural limitations and can also generate power at about 85% of the first design's level.
"The potential applications of the optimized energy harvester designs proposed by us are directly linked to those of electromagnetic induction cores. Some examples include wearable devices, switches, and wireless sensors," concludes Dr. Ahn.
