Researchers achieve wireless power transfer at a distance of 16 feet

Researchers at the Korea Advanced Institute of Science and Technology (KAIST) have demonstrated the ability to deliver a maximum output power of 209 W at 20 kHz or, in laymen’s terms, enough juice to charge 40 smartphones simultaneously, at a distance of 16 ft away.

Referred to as the Dipole Coil Resonant System (DCRS), the technology was demonstrated by Chun T. Rim, a professor of Nuclear and Quantum Engineering at KAIST, and his team at the KAIST campus in Daejeon, Republic of Korea. 

 
The Dipole Coil Resonant System turns a LED television on at a 5-meter distance

Speaking broadly, DCRS represents a tremendous improvement in the distance that electric power can travel wirelessly, which has seen steady, growing interest since the folks at MIT introduced the Coupled Magnetic Resonance System (CMRS) in 2007. It used a magnetic field to transfer power for a distance of 2.1 m, and a lot of its technical limitations can be attributed to commercialization that hasn’t been solved yet, including:
• A complicated coil structure (there are four coils: input, transmission, reception, and load);
• Bulky-size resonant coils;
• High frequency (in a range of 10 MHz) necessary to resonate the transmitter and receiver coils (results in low transfer efficiency);
• High Q factor of 2,000 that makes the resonant coils very sensitive to things like temperature, humidity, and human proximity

Professor Rim’s solution started with an optimally designed coil structure that consists of just two magnetic dipole coils: a primary one to induce a magnetic field and a secondary one to receive electrical power. Where the CMRS used thick, large loop-shaped air coils, the KAIST research team went the route of compact ferrite core rods with windings at their centers. The high frequency AC current of the primary winding generates a magnetic field, and then the linkage magnetic flux induces voltage at the secondary winding. 

 
DCRS configuration shows primary and secondary coils

The group’s approach allowed for an improvement in specs. The system is 3 m long, 10 cm wide, and 20 cm high (all in all, slightly smaller than the CMRS). It has a low Q factor of 100, showing 20 times greater strength against environment changes, and works well at a low frequency of 100 kHz. 

 
Simulation result of magnetic flux lines of DCRS coil configuration

Several experiments were conducted with the system, and many yielded promising results:
• Under the operation of 20 kHz, the maximum output power was 1,403 W at a 3-m distance, 471 W at 4 m, and 209 W at 5 m.
• For 100 W of electric power transfer, the overall system power efficiency was 36.9% at 3 m, 18.7% at 4 m, and 9.2% at 5 m.

“With DCRS,” Professor Rim said, “a large LED TV as well as three 40 W-fans can be powered from a 5-m distance.”

“Our technology proved the possibility of a new remote power delivery mechanism that has never been tried at such a long distance. Although the long-range wireless power transfer is still in an early stage of commercialization and quite costly to implement, we believe that this is the right direction for electric power to be supplied in the future. Just like we see Wi-Fi zones everywhere today, we will eventually have many Wi-Power zones at such places as restaurants and streets that provide electric power wirelessly to electronic devices. We will use all the devices anywhere without tangled wires attached and anytime without worrying about charging their batteries.”

Earlier in the year, Professor’s Rim’s team completed a project with the Korea Hydro & Nuclear Power Co., to remotely supply electric power to instruments and control equipment at a nuclear power plant in order to properly respond to an emergency situation like that experienced at the Fukushima Daiichi nuclear plant. Once the set-up was complete, the system proved capable of transferring 10 W or electricity to the plant 22 ft away from the power base.

To see the technology in action, check out the team’s demonstration of long-distance wireless power transfer in the video below:

The group’s research was published in the March 2014 issue of IEEE Transactions on Power Electronics .

Story via eurekalert.org