'Superlens' extends range of wireless power transfer

Jan 10, 2014
This small copper coil created the electromagnetic field by running an alternating electric current through it. In the background is the metamaterial "superlens" that focused the electromagnetic field onto another identically sized copper coil on the other side, which greatly increased the wireless transfer's power. Credit: Courtesy of Guy Lipworth and Joshua Ensworth, graduate student researchers at Duke University

(Phys.org) —Inventor Nikola Tesla imagined the technology to transmit energy through thin air almost a century ago, but experimental attempts at the feat have so far resulted in cumbersome devices that only work over very small distances. But now, Duke University researchers have demonstrated the feasibility of wireless power transfer using low-frequency magnetic fields over distances much larger than the size of the transmitter and receiver.

The advance comes from a team of researchers in Duke's Pratt School of Engineering, who used metamaterials to create a "superlens" that focuses magnetic fields. The superlens translates the magnetic field emanating from one power coil onto its twin nearly a foot away, inducing an electric current in the receiving coil.

The experiment was the first time such a scheme has successfully sent power through the air with an efficiency many times greater than what could be achieved with the same setup minus the superlens.

The results, an outcome of a partnership with the Toyota Research Institute of North America, appear online in Scientific Reports on Jan. 10.

"For the first time we have demonstrated that the efficiency of magneto-inductive wireless power transfer can be enhanced over distances many times larger than the size of the receiver and transmitter," said Yaroslav Urzhumov, assistant research professor of electrical and computer engineering at Duke University. "This is important because if this technology is to become a part of everyday life, it must conform to the dimensions of today's pocket-sized mobile electronics."

This is a side view of the metamaterial "superlens." Both its width and thickness affects how far it can boost the wireless transfer of power using electromagnetic fields. Credit: Courtesy of Duke University

In the experiment, Yaroslav and the joint Duke-Toyota team created a square superlens, which looks like a few dozen giant Rubik's cubes stacked together. Both the exterior and interior walls of the hollow blocks are intricately etched with a spiraling copper wire reminiscent of a microchip. The geometry of the coils and their repetitive nature form a metamaterial that interacts with magnetic fields in such a way that the fields are transmitted and confined into a narrow cone in which the power intensity is much higher.

On one side of the superlens, the researchers placed a small copper coil with an alternating electric current running through it, which creates a magnetic field around the coil. That field, however, drops in intensity and power transfer efficiency extremely quickly, the further away it gets.

'Superlens' extends range of wireless power transfer
A closer look at the metamaterial “superlens” that beams electromagnetic fields to increase the range of wireless power transfers. The squares are actually long coils of copper wire reminiscent of the surface of a microchip. Credit: Duke University

"If your electromagnet is one inch in diameter, you get almost no power just three inches away," said Urzhumov. "You only get about 0.1 percent of what's inside the coil." But with the superlens in place, he explained, the is focused nearly a foot away with enough strength to induce noticeable in an identically sized receiver coil.

Urzhumov noted that metamaterial-enhanced wireless power demonstrations have been made before at a research laboratory of Mitsubishi Electric, but with one important caveat: the distance the power was transmitted was roughly the same as the diameter of the power coils. In such a setup, the coils would have to be quite large to work over any appreciable distance.

"It's actually easy to increase the power transfer distance by simply increasing the size of the coils," explained Urzhumov. "That quickly becomes impractical, because of space limitations in any realistic scenario. We want to be able to use small-size sources and/or receivers, and that's what the superlens enables us to do."

Each side of each constituent cube of the "superlens" is set with a long, spiraling copper coil. The end of each coil is connected to its twin on the reverse side of the wall. Credit: Courtesy of Guy Lipworth, graduate student researcher at Duke University

Urzhumov said magnetic fields have distinct advantages over the use of electric fields for .

"Most materials don't absorb magnetic fields very much, making them much safer than electric fields," he said. "In fact, the FCC approves the use of 3-Tesla magnetic fields for medical imaging, which are absolutely enormous relative to what we might need for powering consumer electronics. The technology is being designed with this increased safety in mind."

Going forward, Urzhumov wants to drastically upgrade the system to make it more suitable for realistic power transfer scenarios, such as charging mobile devices as they move around in a room. He plans to build a dynamically tunable superlens, which can control the direction of its focused power cone.

"The true functionality that consumers want and expect from a useful system is the ability to charge a device wherever it is – not simply to charge it without a cable," said Urzhumov. "Previous commercial products like the PowerMat™ have not become a standard solution exactly for that reason; they lock the user to a certain area or region where transmission works, which, in effect, puts invisible strings on the device and hence on the user. It is those strings—not just the wires—that we want to get rid of."

Explore further: New approach advances wireless power transfer for electric vehicles

More information: "Magnetic Metamaterial Superlens for Increased-Range Wireless Power Transfer," Lipworth, L., Ensworth, J., Seetharam, K., Huang, D., Lee, J.S., Schmalenberg, P., Nomura, T., Reynolds, M.S., Smith, D.R., and Urzhumov, Y. Scientific Reports, Jan. 10, 2014. DOI: 10.1038/srep03642

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5 / 5 (1) Jan 10, 2014
not rated yet Jan 10, 2014
A massive block of "lens" in order to focus the field so you don't have to have an enormous block of coil...
Whydening Gyre
not rated yet Jan 10, 2014
Reception is possible via the perpendicular property of magnetic induction.
not rated yet Jan 10, 2014
This is like those telephone / telegraph systems used for near-shore islands & lighthouses before sub-sea cables were workable. Also, trench phones in WW_1 ?
To get an adequate audio signal across gap, transmitter and receiver antennae had to be as long as their separation...
not rated yet Jan 10, 2014
This might be already patented by Mitsubishi.

They have been doing wireless power at over 70% efficiency for a couple years using arrays of sprial MM.

not rated yet Jan 11, 2014
I think the idea they are working on here, is to have some kind of tracking device, say on your phone, and have the meta material wireless transmitter focus a cone of magnetic energy to your phone. The tracking device is needed for the transmitter to adjust the focal point of the cone, to match the location of your phone. Obviously limited to buildings.

I'd buy one, when they get it working right.
4 / 5 (4) Jan 11, 2014
Wired is better. This is just a novelty for "tech junkies," which is ultimately less energy efficient than just using the wire.
3 / 5 (2) Jan 11, 2014
" "This is important because if this technology is to become a part of everyday life, it must conform to the dimensions of today's pocket-sized mobile electronics." "

Yet another reference to "charging a cell phone". Is that the only thing that matters to the general public any more?
2 / 5 (4) Jan 11, 2014
Inventor Nikola Tesla imagined the technology to transmit energy through thin air almost a century ago,

"I am not an inventor. I am a discoverer of new scientific principles." Nikola Tesla
not rated yet Jan 11, 2014
For once Returners I'd have to agree that it would be good for tech junkies.

Personally I'm not tethered to hand held devices, but I do see the benefit in this technology. Imagine all hand held devices permanently being at full charge (hence full speed CPU/GPU capable) whilst in a building. As soon as you walk out, you can safely assume your device is fully charged. Walk back in, and bingo charging commences automatically. I bet Executive Directors and business types the world over would love this technology. How about hand held devices in hospitals? Though they might ban a projecting, self focusing magnetic cone in hospitals!! Work places will love this stuff, followed by the home consumer.
Also I can't see it being all that wasteful, as tracking the device allows for dynamic feedback of the device being charged. The super-lens system could reduce power or increase as necessary. In fact if you're only using one wireless charger then some kind of multiplex charging is required.
not rated yet Jan 12, 2014
See: http://en.wikiped...mulation and http://www.popsci...tell-lie
The apparant fact that technology is being developed which can, from a distance, affect the mood, personality traits, and other functions of the brain is a little disturbing. Isn't there something in science fiction called a "tasp"? A device which can remotely activate the pleasure center of a "target"s brain?
5 / 5 (1) Jan 14, 2014
powering satellites from central solar power station?