The weird properties of artificially engineered metamaterials are at the core of research into invisibility cloaking, but engineers from Duke University in North Carolina suggest that these materials could also provide a boost to another of technology's quests - wireless power transmission. In this latest hard-to-get-your-head-around metamaterial scenario, it's not the cloaked object that "disappears" - it's the space between the charger and the chargee.
Close-range wireless charging of mobile devices has become a reality for consumers in recent times but there's room for improvement, particularly if bigger fish - like electric vehicles - are to be caught in the wireless-power net.
The problem with transmitting small amounts of power over longer distances is that most of it will be scattered before it reaches the receiving device. And if you up the energy, radiation becomes a problem.
"We currently have the ability to transmit small amounts of power over short distances, such as in radio frequency identification (RFID) devices," said Yaroslav Urzhumov, assistant research professor in electrical and computer engineering at Duke's Pratt School of Engineering. "However, larger amounts of energy, such as that seen in lasers or microwaves, would burn up anything in its path.
"Based on our calculations, it should be possible to use these novel metamaterials to increase the amount of power transmitted without the negative effects," Urzhumov said.
The theory is that metamaterials placed between the transmitter and the receiver would create a strange kind of lens, "focusing" the energy so that most of it gets to the device being charged.
"The metamaterial would make it seem as if there was no space between the transmitter and the recipient," Urzhumov said. "Therefore the loss of power should be minimal."
Duke researchers lead by Professor David R. Smith were the first to demonstrate that metamaterials could act as a cloaking device in 2006 and Urzhumov's research is an offshoot of "superlens" research conducted in the same laboratory.
The key to all of this is a property displayed in metamaterials called a negative refract index. This means they can refract light in a way that nothing found in nature can, resulting in "superlens" designs that give researchers greater control over light than can be attained using traditional optics. The same theory applies to any electromagnetic waves, so wireless power transmission can also make use of the phenomenon.
(There's a useful explanation of what a negative refractive index entails at the David R. Smith Research Group site.)
The wireless power transmission metamaterial would be similar to that used for cloaking, using thousands of individual thin conducting loops that can be arranged in an almost infinite variety of configurations.
"The system would need to be tailored to the specific recipient device, in essence the source and target would need to be 'tuned' to each other," Urzhumov said. "This new understanding of how matematerials can be fabricated and arranged should help make the design of wireless power transmission systems more focused."
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