Post-apocalyptic movies have always depicted a war over scarcest resources and energy is an every depleting resources. Counties around the world are trying to invest in the energy research and technology. Now, researchers from the Graduate School of Engineering, Osaka City University have succeeded in storing electricity with the voltage generated from the conversion phenomenon of ferromagnetic resonance (FMR) using an ultra-thin magnetic film of several tens of nanometers.
Ferromagnetic
resonance is a state where electromagnetic waves and an electrostatic magnetic
field when applied to a magnetic media makes the electromagnets inside the
media to undergo precession at the same frequency as that of the
electromagnetic waves. This technique is used to investigate the magnetic
properties of a variety of media, from bulk ferromagnetic materials to
nano-scale magnetic thin films.
The research was conducted under the
leadership of Prof. Eiji Shikoh. "We are interested in efficiently using
the Earth's natural resources to harvest energy," states the professor,
"and capturing the energy from electromagnetic waves that surround us through
the electromotive force (EMF) they generate in magnetic films under FMR shows
potential as one such way". Their research was published in the journal
AIP Advances (Yuta Nogi et al, An energy harvesting technology controlled by
ferromagnetic resonance, AIP Advances (2021).)
"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."
How they did
it:
The team
first, ensured that the two alloy films generated electricity under ferromagnetic
resonance and found that Ni80Fe20 generated about 28
microvolts while Co50Fe50 generated about 6 µV (microvolts)
of electricity.
Then 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.
Following
that, 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.
"This is due to the respective
magnetic field ranges for the FMR excitation," concludes Prof. Shikoh.
Upon probing the different energy storage characteristics of the thin films,
the team found when they were in the same thermal states during the
experiments, Co50Fe50 could maintain FMR in a detuned
condition, while Ni80Fe20 was outside the FMR excitation
range. "By appropriately controlling the thermal conditions of the FM
film," continues the professor, "EMF generation under ferromagnetic
resonance can be used as an energy harvesting technology."
Another fascinating
point about this research is that the team centred on EMF generation itself,
independent of its origin. Meaning that as long as the FMR conditions are met,
energy can be stored from any electromagnetic waves source we interact with
daily—for example the Wi-Fi at your favorite café.
The paper is open to public and those who are interested can download it from the publication website: https://aip.scitation.org/doi/10.1063/5.0056724
