Korean engineers have broken a record by transmitting enough power wirelessly over a distance of about 16 feet to charge up to 40 smartphones at the same time.
The researchers, from the Korean Advanced Institute of Science and Technology (KAIST), created a "Dipole Coil Resonant System" (DCRS) made specifically for an extended range of inductive power transfer between transmitter and receiver coils. The development of long-distance wireless power transfer has attracted a lot of attention by researchers in recent years.
The Massachusetts Institute of Technology (MIT) first introduced a Coupled Magnetic Resonance System (CMRS) in 2007. It used a magnetic field to transfer energy for a distance of 2.1 meters (about seven feet).
According to the Korean researchers, CMRS has unsolved technical limitations that make commercialization difficult. For one, CMRS has a rather complicated coil structure (it's composed of four coils for input, transmission, reception, and load); bulky-size resonant coils; and a high frequency (in a range of 10MHz)
The KAIST team uses a lower, 20kHz frequency.
While that may seem like a unique move, the KAIT engineers are using the same technology as WiTricity, a company in Watertown, Mass.
WiTricity has been developing magnetic resonance charging over distance for sale to manufacturers since 2009. What the KAIST researchers did was build a bigger system.
Overall configuration of KAIST's DCRS system, showing primary and secondary coils (Image: KAIST).
WiTricity's wireless charging technology is designed for "mid-range" distances, which it considers to be anywhere from a centimeter to several meters, according to Kaynam Hedayat, Witricity's product manager.
Magnetic resonance wireless charging works by creating a magnetic field between two copper coils. The larger the copper coils and the greater the power being pushed through them, the bigger the size of the magnetic field.
What KAIST researchers did was build a 10-foot-long, pole-like transmitter and receiver that was able to create a magnetic field large enough to transmit 209 watts of power over a distance of five meters (or about 16 feet). Over that distance, the wireless transmitter still emitted enough power to charge up to 40 smartphones, if plugged into an outlet powered by the wireless transmitter. But, as the distance increased, the power dropped off significantly.
The Korean engineering team conducted several experiments and achieved "promising results." For example, at 20kHz, the maximum output power was 1,403 watts at a three-meter distance; 471 watts at four meters; and 209 watts at five meters.
"For 100 [watts] of electric power transfer, the overall system power efficiency was 36.9% at three meters, 18.7% at four meters, and 9.2% at five meters," Chun Rim, a professor of Nuclear & Quantum Engineering at KAIST, said in a statement. "A large LED TV as well as three 40 [watt]-fans can be powered from a five-meter distance."
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