Scientists propose high-efficiency wireless power transfer system

January 26, 2016 by Lisa Zyga feature
(Left) Illustration and (right) experimental setup of the wireless power transfer system. Power is transferred from one ceramic sphere to the other using the spheres' identical magnetic resonance. Credit: Song, et al. ©2016 AIP Publishing

(Phys.org)—Currently, commercial wireless power transfer is limited mainly to charging pads for phones: instead of plugging your phone directly into the wall, simply place it on top of a wireless charging pad. In the future, the same concept could be extended to much larger distances and higher transfer efficiencies, enabling entire rooms and even buildings to serve as wireless charging zones for phones, computers, and other electronic devices.

Although (WPT) was famously pioneered by Tesla in the early 20th century, it was not until 2007 that a team of scientists from MIT demonstrated the feasibility of WPT (or "WiTricity"), by powering a 60-watt light bulb from a distance of two meters at 45% transfer efficiency.

Building on this work and others that have followed, a team of researchers led by Polina Kapitanova at ITMO University and Elizaveta Nenasheva at Giricond Research Institute, both in Saint Petersburg, Russia, have proposed a new WPT system. According to numerical simulations, their proposed system can maintain an 80% transfer efficiency across a distance of 20 centimeters, while experiencing only a very small decrease in the efficiency as the distance increases. Their work is published in a recent issue of Applied Physics Letters.

Like almost all WPT proposals, the new proposal is based on resonance coupling. Similar to how an opera singer's powerful voice can transfer enough energy to a wine glass having the same resonant frequency to cause the glass to shatter, a resonant copper coil can transfer energy to a second resonant copper coil if the two coils resonate at the same frequency. Other nearby objects are not affected because they do not have the same resonant frequency. In WPT systems, the resonant frequencies of the two coils are often coupled using magnetic fields to further reduce unintended interactions because magnetic fields interact very weakly with most other objects, including the human body.

A comparison of the efficiencies with respect to distance of the proposed system operating at magnetic quadrupole mode (green line), at magnetic dipole mode (red dashed line), and the system proposed by MIT (blue dashed line). Credit: Song, et al. ©2016 AIP Publishing

In the new paper, the researchers demonstrated that they could decrease power loss—and therefore increase efficiency—in WPT systems in two ways. First, they replaced the traditional copper coils with "high-permittivity low-loss dielectric resonators," which look like two ceramic spheres. These resonators have a high refractive index, meaning that an electromagnetic wave traveling through them is greatly slowed down. For WPT, this property translates to stronger magnetic resonances in the ceramic spheres, and stronger resonances lead to higher efficiencies.

The second change the researchers made to decrease radiation loss was to use a higher-order resonant frequency mode than is normally used (they used the magnetic quadrupole mode instead of the magnetic dipole mode). These two frequency modes differ in terms of the shapes and magnitudes of their magnetic fields. The researchers found that the WPT efficiency of the system operating at quadrupole mode is not only more efficient, but also more resistant to the random orientation of the transmitter and receiver in space. As owners of wireless phone chargers know, the phone must be perfectly aligned on the pad to receive power. The quadrupole mode does not require such exact alignment.

"The main idea of this work is to demonstrate the near-field magnetic resonance WPT based on high refractive index dielectric resonators," Kapitanova told Phys.org. "In contrast to the traditional copper coils, the high refractive index dielectric resonators support higher order modes. So we propose to operate at the magnetic quadrupole mode rather than the magnetic dipole mode. This results in the higher WPT efficiency due to a reduction in the ohmic and radiation losses."

In the future, the researchers plan to further improve the WPT system by designing the receiver with better resistance to random orientation at all angles. They also plan to reduce the size of the resonators for practical use.

"Now we are working on fabrication and experimental investigation of the next WPT system prototype," Kapitanova said. "In cooperation with the Giricond Research Institute, we have fabricated new ceramic resonators with higher dielectric permittivity and low loss tangent. We believe this prototype will be very close to practical application."

Explore further: Getting in tune: Researchers solve tuning problem for wireless power transfer systems

More information: Mingzhao Song, et al. "Wireless power transfer based on magnetic quadrupole coupling in dielectric resonators." Applied Physics Letters. DOI: 10.1063/1.4939789

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12 comments

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greenonions
5 / 5 (6) Jan 26, 2016
Can they make sure they don't hit the resonant frequency of my ceramic dentures? That might not be fun....
wolfkeeper
1 / 5 (1) Jan 26, 2016
Actually Tesla's wireless power worked fine across the laboratory, it had similar range to Witricity's system, but it was a bit less safe because it used high voltages; but he lit his lab using wireless power, no problem.

What Tesla failed at was sending power wirelessly over hundreds of miles.

Witricity's system uses magnetic fields, which is much safer, but they didn't even invent that, there'd been similar systems back in the 80s and 90s, and they'd even been fairly widely deployed, anti theft tags and wirelessly powered credit and Id cards used it.

TheGhostofOtto1923
3.5 / 5 (8) Jan 26, 2016
Soon enough we will have new and entirely unanticipated power sources so (what's the word?) enormously productive that toward the end of this century waste heat will be the single greatest contributer to global warming.
indio007
5 / 5 (1) Jan 26, 2016
First Tesla transmitted through the ground not air.

tgoldman
1 / 5 (1) Jan 26, 2016
If quadrupole is better than dipole, wouldn't octupole be even better? Etc.
big_hairy_jimbo
3 / 5 (4) Jan 27, 2016
Please correct me if I am wrong, but does such a system WASTE energy radiating into space if their ISN'T a device to receive it? Call me stupid, but I keep relating this to the sun. The sun is wirelessly radiating energy (Photons) in a sphere. The Earth is capturing but a minute fraction, the rest just escapes to the universe. What am I missing?? How is this different? How can this be efficient if it isn't FOCUSSED??? What you need is a device that can shift the focus continually like a spotlight following an actor on stage. Wasn't there an article awhile back utilising meta-materials to do exactly that? The device to charge would transmit it's location and the wireless charger would focus ON THE DEVICE, with a continual feedback loop, in order to make sure energy wasn't being wasted?
axemaster
5 / 5 (6) Jan 27, 2016
I can't wait for this to become widespread, the massive electromagnetic interference will make everything work better... oh wait...
Mike_Massen
2.7 / 5 (7) Jan 27, 2016
TheGhostofOtto1923 guesses
Soon enough we will have new and entirely unanticipated power sources so (what's the word?)
The word is scam but, admittedly artfully contrived over long period but, with Nil actual definitive evidence ie A. Rossi & ecat co :-(

Note
Sol produces ~270Watts of heat per cubic meter but, at massive pressure via tunneling nuclear fusion
https://en.wikipe...lar_core

Rossi/e-cat has never offered *any* mechanism *ever* which explains Multi Kilo watt per ~ 1/50th of a cubic meter & worse appears Rossi's relies on input fossil fuel gas to start & keep his reaction going in commercial products ie A scam artfully progressesd & a Fail !

Furthermore TheGhostofOtto1923 claims
.. toward the end of this century waste heat will be the single greatest contributer to global warming
No but, if you think so then offer a basic rationale, better yet a journal/paper which goes towards a proof ?

Opposite far more likely for many reasons
Uncle Ira
4.2 / 5 (5) Jan 27, 2016
I can't wait for this to become widespread, the massive electromagnetic interference will make everything work better... oh wait...


Yeah, that is what I was thinking too. Using the near field resonance will work (that is the simple transformer), but for any kind of distance you are working with far field radiation and that will cause havoc with all kinds of devices (and you lose a lot of power out in the "aether").

Non you couyons, I know there is non "aether", it's just what we use for slang to mean "space".
promile
Jan 27, 2016
This comment has been removed by a moderator.
TheGhostofOtto1923
4.3 / 5 (6) Jan 27, 2016
The word is scam but, admittedly artfully contrived over long period but, with Nil actual definitive evidence ie A. Rossi & ecat
Please visit the other thread for the unlikelihood of sustaining conspiracies at this level.

Rossi continues to enjoy $millions in support from his big deal owner, IH. Mills is giving a public display of his hydrino engine tomorrow which is the product of $15M and 12 months of engg by independent engg firms.

But healthy skepticism is... healthy I guess.
TheGhostofOtto1923
4.3 / 5 (6) Jan 27, 2016
No but, if you think so then offer a basic rationale, better yet a journal/paper which goes towards a proof ?
Unsubstianted opinions are protected by the 2nd amendment, which is how Cosby got out of his latest civil suit.

But IF these new clean, compact, and almost unlimited power sources prove to be viable, and they replace all conventional sources, then we can expect that their waste heat will become a problem as well.

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