February 15, 2011

Metamaterials could enable wireless power beaming that is ten times more efficient

Arxiv - Metamaterial-Enhanced Coupling between Magnetic Dipoles for Efficient Wireless Power Transfer (23 pages)

Non-radiative coupling between conductive coils is a candidate mechanism for wireless energy transfer applications. In this paper, we propose a power relay system based on a near- field metamaterial superlens, and present a thorough theoretical analysis of this system. We use time-harmonic circuit formalism to describe all interactions between two coils attached to external circuits and a slab of anisotropic medium with homogeneous permittivity and permeability. The fields of the coils are found in the point-dipole approximation using Sommerfeld integrals, which are reduced to standard special functions in the long-wavelength limit. We show that, even with a realistic magnetic loss tangent of order 0.1, the power transfer efficiency with the slab can be an order of magnitude greater than free-space efficiency when the load resistance exceeds a certain threshold value. We also find that the volume occupied by the metamaterial between the coils can be greatly compressed by employing magnetic permeability with a large anisotropy ratio.

MIT Technology Review has coverage

A thin slab of metamaterial increases the efficiency of wireless power transmission by an order of magnitude. 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. 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.



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.

As typical for metamaterial superlenses, the performance can be theoretically arbitrarily good { in our case, the power transfer efficiency can be as close to 100% as needed { but only if arbitrarily small loss tangents can be implemented. The growth of the gure of merit with decreasing loss is very slow (typically, logarithmic). Nevertheless, even with practically attainable loss tangents is about 0.1 the metamaterial relay system can over-perform free space coupling efficiency by an order of magnitude or more, depending on the load resistance.

If you liked this article, please give it a quick review on ycombinator or StumbleUpon. Thanks

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