This type of wireless power transfer depends on magnetic fields that radiate outward from a source coil and generate a current in a receiving coil. The team of researchers was able to construct a superlens that, when exposed to the magnetic field, resonates at a particular frequency and focuses those fields on a specific point nearly a foot away. The focused field can then generate a stronger current and charge an electronic device remotely, an improvement from current wireless power transfer technology.
“There are certain mats that can charge a phone wirelessly, but the phone has to be right on top of the mat,” said Guy Lipworth, first author of the study and graduate student researcher. “By increasing the distance, you can imagine that if there’s a coil in the ceiling or anywhere in the room, you can charge your phone on the go.”
The superlens used in the team’s experiments was about 40-by-40 centimeters, a few centimeters thick and built from electromagnetic devices called metamaterials. This setup allowed a current to be measured about a foot away, but Lipworth noted that given a larger source coil, a stronger power source or a larger lens, the functional distance would increase proportionally.
“You want it bigger than the [source] coil to capture more of the emanating fields,” he said. “We could have made it go a longer distance, but after a certain point it becomes impractical.”
From a biological perspective, charging devices using a magnetic field poses almost no threat of bodily harm. Organic matter does not tend to have strong adverse reactions with these types of fields, Lipworth said.
“That’s a big benefit of this kind of charging,” he said. “Hospitals have MRIs that use magnetic fields that are much more powerful, so it’s something we don’t have to worry about.”
Additionally, concerns regarding the harmful effects of magnets on magnetic hard-drives and credit card strips have mostly been resolved because the fields used in wireless power transfer are a type that are fundamentally less damaging to these devices, said Yaroslav Urzhumov, adjunct assistant professor in the department of electrical and computer engineering and author on the study. Furthermore, advances in magnetic shielding research have allowed these scientists to push the boundaries of wireless power transfer at a very low cost.
“Magnetic shielding films have been widely used, and you can get a [magnetic field-safe] wallet for 10 bucks at Walmart these days,” Urzhumov said.
Fully developed wireless power that transfers via magnetic fields, however, has implications that span beyond charging phones. Lipworth noted that after publication of his superlens research, one of his friends sent him a link to an article that featured a type of bus in London that charges wirelessly.
“They power the bus through coils installed in the road and in the bus, separated by a short distance,” Lipworth said. “With the superlens, we can potentially make that system work more efficiently by focusing the field.”
The research team at Duke was funded by and collaborated with the Toyota Research Institute, an industry partner. Toyota has worked with the team on previous projects as well and these types of partnerships between industry and academia are quite common, Lipworth said.
“The people at Toyota might not have the expertise on this kind of research, so that’s why they hire us,” he said. “We have biweekly meetings with them, usually through conference calls, and they are always interested in how we are doing with the project.”
Although it is unclear what Toyota plans to do with the new superlens technology, it seems as though there are a number of developmental obstacles that must be overcome before wireless power transfer becomes an aspect of everyday life.
The first is that, currently, the superlens cannot shift the direction of the focal point. As it stands, the lens can only focus the magnetic fields to a point directly opposite the source. Lipworth said that directional control is theoretically possible, and will be a good challenge for future researchers.
Senior Kushal Seetharam, an author of the study who worked on the computational design of the superlens, mentioned that transitioning from experimental to real-world applications of the superlens will require some modifications of the materials that the researchers used.
“We designed and tested non-resonant transmitting and receiving coils,” he said. “Most applications of mid-range [wireless power transfer], however, require resonant coils in order to transfer useful amounts of power.”
Despite the amount of work that still has to be done, the superlens certainly brings us closer to what physicist Nikola Tesla first conceptualized a century ago—a world where usable power moves freely through the air, Lipworth said.
“Tesla is a role model for most scientists and engineers,” he said. “On the one hand, he’s this crazy scientist figure, and on the other hand, he’s a genius. Here we are 100 years later, and we’re still researching things he worked on back then.”