It's now possible to wirelessly charge 40 smartphones from 16 feet away

Korean engineers are using the same tech as U.S. companies

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."

KAIST's DCRS magnetic resonance system. Note the two coils on either side of the room (Image: KAIST).

The Korean researchers believe that wireless charging will eventually be as common as Wi-Fi in homes and public places.

WiTricity, a creator of wireless charging systems, has an intellectual property (IP) license agreement with Toyota Motor Corp. Under the agreement, Toyota is expected to offer wireless charging on future rechargeable plug-in hybrid electric and fully electric vehicles.

David Schatz, director of business development at WiTricity, demonstrates to Computerworld how a new prototype wireless charger called "Prodigy" can power a device from about 10 inches away.

The size of the coils in WiTricity's system are dependent on the application and the application environment (i.e., a vehicle, a smartphone, a wearable computing device, etc.), Hedayat said.

The size of the transmitting coil is limited by the deployment environment and user expectations, while the size of the receiver coil is limited by the physical size of the device receiving power, Hedayat said.

For example, WiTricity's wireless power transmitters for vehicles are about 19-in. square by 2-in. thick. The receiver coils that would be installed in a car or truck are about one foot square by .4-in. thick,

WiTricity has been able to stretch the distance of its magnetic resonance charging field by using a "repeater," a small disk-like object that retransmits the magnetic signal.

WiTricity is by no means alone in developing magnetic resonance charging devices, though it does claim its is the first based on the MIT technology. The company is a member of the Alliance for Wireless Power (A4WP). There are three major alliances backing various forms of wireless charging, including inductive magnetic charging.

To date, products on the market have been built around magnetic inductive charging techniques, which require that a mobile device be in contact with a charging surface, such as a charging pad. The leading charging pad supplier has been Duracell's Powermat technology, a member of the Power Matters Alliance (PMA).

Two of the three major wireless power consortiums have agreed to establish interoperability standards for wireless power.

The partnership, announced earlier this year, pits the A4WP and the PMA against the largest of the industry groups -- the Wireless Power Consortium (WPC), which touts the Qi (pronounced "chee") wireless charging specification.

Lucas Mearian covers consumer data storage, consumerization of IT, mobile device management, renewable energy, telematics/car tech and entertainment tech for Computerworld. Follow Lucas on Twitter at @lucasmearian or subscribe to Lucas's RSS feed. His e-mail address is

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