Scientists in Korea have developed a new wireless power transfer (WPT) technique using miniaturized receivers that enables more efficient wireless power transfer at greater distances than ever before.
WPTuses overlapping magnetic fields, rather than wires, to transmit electric power. This technology is believed to have wide range of potential uses, from wireless cell phone chargers to the powering of electric vehicles, and even medical implants.
However, real-world uses of WPT have been limited by a number of inescapable issues. For example, the WPT method of inductive coupling is crippled by the large size of the receivers (relative to most miniaturized handheld devices), as well as an unfortunate ineffectiveness over large distances. Additionally, using microwaves to wirelessly transfer power poses a number of potential health risks that need to be studied further before the technology is release widely into the consumer market.
To combat these problems, scientists Hyoungjun Kim and Chulhun Seo from Soongsil University have developed a novel WPT technique that uses a metamaterial slab and a resonant coupling method to maximize the effectiveness of the power transfer, even over large distances, and with smaller receivers. Their research is described in a paper titled “Highly efficient wireless power transfer using metamaterial slab with zero refractive property,” published in Electronic Letters.
WPT by way of a resonant coupling method—that is, manipulating the transmitting and receiving coils to resonate at the same frequency, in the hopes of maximizing transfer efficiency—was first studied in 2007 by scientists at MIT. This method was the most effective of its time, as it was able to transfer power over a relatively large distance. However, this method was limited by the large size of the receivers, which were determined by the resonant frequency they vibrated on, putting a roadblock on device miniaturization and thus commercial use.
With this knowledge in mind, Kim and Seo have found a way of miniaturizing the receivers, as well as how to improve transfer efficiency. To achieve this, they designed a metamaterial slab that uses the zero refractive index (ZRI) property to redirect leaked energy from the transmitter back to the receiver.
Specifically, the scientists manipulated the permeability of the material to be close to zero, using a spiral structure and a capacitor. The WPT setup was comprised of a transmitting coil and a receiving coil, which was approximately the size of a cell phone battery, bridged by a metamaterial slab. The distance between the two coils ranged from 100 to 150 mm.
At the experiment’s conclusion, Kim and Seo found that the power transfer efficiency of their system doubled at 100 mm and was sustained for longer distances, unlike past WPT systems.
The researchers believe that their novel ZRI technique not only has important implications for resonance coupling WPT systems, but also for high gain antennas and MRIs. However, because of the pricey low-loss board used in the system, the technique is still too expensive to be used in the real-world. If a low-cost alternative board could be found as a replacement, the scientists are confident that their system could be widely available for public use.
The team is currently researching negative refractive index techniques as a potential solution to these issues. Additionally, they are working on a WPT system that utilizes three-dimensional, rather than two-dimensional, structures, in order to facilitate wireless power transfer at any receiver location.
-Melanie Abeygunawardana
