Energy harvesting technique uses ferromagnetic resonance

August 26, 2021 // By Jean-Pierre Joosting
Energy harvesting technique uses ferromagnetic resonance
Osaka City University succeeds in capturing energy generated through electromotive force from a ferromagnetic metal thin film under ferromagnetic resonance

Researchers from the Graduate School of Engineering, Osaka City University have succeeded in storing electricity with the voltage generated from ferromagnetic resonance (FMR) using an ultra-thin magnetic film of several tens of nanometers.

“We are interested in efficiently using the Earth’s natural resources to harvest energy and capturing the energy from electromagnetic waves that surround us through the electromotive force (EMF) they generate in magnetic films under FMR,” states the leading researcher, Professor Eiji Shikoh. The research was published in the journal AIP Advances.

Ferromagnetic resonance is a state in which applying electromagnetic waves and an electrostatic magnetic field to a magnetic media causes the electromagnets inside the media to undergo precession at the same frequency as that of the electromagnetic waves. As a technique, it is often used to probe the magnetic properties of a variety of media, from bulk ferromagnetic materials to nano-scale magnetic thin films.

“Research has shown that an EMF is generated in a ferromagnetic metal (FM) that is under FMR,” states Yuta Nogi, first author of the study, “and we explored energy storage possibilities using two FMs that are highly durable, well understood, and thus commonly used in FMR research – an iron-nickel (Ni80Fe20) and iron-cobalt (Co50Fe50) alloy thin film.”

First, the team confirmed the two alloy films generated electricity under ferromagnetic resonance and found that Ni80Fe20 generated about 28 microvolts while Co50Fe50 generated about 6 microvolts of electricity. To store the electricity, they used an electron spin resonance device to pressurize the electromagnetic wave, and the electromagnet of the device for the static magnetic field. Connecting a storage battery directly to the membrane of the sample via a conductor, the team observed that both FM samples successfully stored energy after being in a state of FMR for 30 minutes. However, as the resonance time extended, the amount of energy stored with the iron-nickel alloy film did not change while the iron-cobalt alloy film saw a steady increase.

Picture: 
Image credit: Yuta Nogi; Yoshio Teki; Eiji Shikoh.

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