How Metamaterials Will Boost Wireless Power Transmission
Power cables are the bane of modern existence. If you own a desktop PC, a phone and perhaps a media player, you’re likely to have at least one power socket that looks like spaghetti junction.
Which is why there is a growing interest in wireless power transmission. RFID chips have become ubiquitous in the western world thanks to the ability to provide them with small amounts of power power wirelessly.
But there have been many much more ambitious attempts to devise more powerful ways to transmit power. The Japanese have a long-standing interest in beaming power to the ground from solar panels in space. With limited natural resources of their own, they see this as one way to secure their energy supply.
One of the limitations of aircraft is the amount of fuel they can carry so there have been various attempts to beam power to them using microwaves and lasers. Some researchers have even looked at the possibility of launching and powering a spacecraft on the tip of a powerful laser beam.
Closer to home, the idea of wirelessly recharging portable devices such as smartphones, laptops and media players has obvious appeal. And in recent years, various wireless charging devices have hit the market. Researchers have even demonstrated the possibility of beaming power across a room to these machines.
There are numerous problems with all these ideas. Microwave and laser beams can carry significant power but they also tend to fry anything that gets in their way.
Inductive chargers are safer because they rely on a resonant effect between two closely spaced coils. But they are not particularly efficient at the best of times and what efficiency they do have drops off a cliff as the distance between the coils increases. In mathematical terms, if the distance between the coils is d, the efficiency of power transmission is inversely proportional to d^6. Nasty!
Today, Yaroslav Urzhumov and David Smith at Duke University in North Carolina say there is a way to dramatically improve this using metamaterials, the strange artificial stuff that researchers can use to bend electromagnetic waves to their will.
One of the first discoveries about metamaterials about ten years ago was that they can be used to create a perfect lens, that is a lens capable of focusing and electromagnetic beam with subwavelength resolution. Another way of saying this is that the lens works when it is closer than a single wavelength of the source.
The new idea is relatively simple. Urzhumov and Smith simply suggest placing a superlens between the two coils in an inductive charger. And that’s it.
The work they publish today is a detailed theoretical account of the improvements that such a system would produce. They say that such a lens would take the form of a thin, flat slab of metamaterial and that it would increase the efficiency from being inversely proportional to d^6 to inversely proportional to d^3.
In practical terms, that translates into a big increase in efficiency. “The power transfer efficiency with the slab can be an order of magnitude greater than free-space efficiency,” they say.
That’s a big deal in a discipline where engineers struggle to increase efficiency by a few per cent.
So when could we expect to see such a device? Urzhumov and Smith don’t say but it’s possible to make an educated guess.
Smith is one of the top bananas in the world of metamaterials–he built and demonstrated the first invisibility cloak back in 2006. In fact, he unveiled the device just a few months after the idea of using metamaterials to make invisibility cloaks was first mooted. Clearly, he’d been working on it for some time before the theory paper was published
It makes sense to keep an interesting new idea under wraps until you’ve worked out how to build it (and protected the IP).
So judging by his past form, my guess is that Smith has a working version of his wireless power transmission device now and that he’ll demonstrate it publicly in the coming months.
Ref: arxiv.org/abs/1102.2281: Metamaterial-Enhanced Coupling between Magnetic Dipoles for Efficient Wireless Power Transfer
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