The concept of charging smartphones, tablets and other electronic devices wirelessly is now closer to becoming a reality after scientists at Korea Advanced Institute of Science and Technology (KAIST) announced they have transmitted electricity between transmitter and receiver at a distance of five metres, just over double the distance electricity had previously been wirelessly transmitted by an American university.

Scientists announced last month that their new Dipole Coil Resonant System (DCRS) had not only improved the distance of wireless electricity transmission but also increased known efficiency. The team hopes its continuing work will mean in the future wireless electricity will be as commonplace as WiFi internet connections.

"Our technology proved the possibility of a new remote power delivery mechanism that has never been tried at such a long distance," said KAIST professor of nuclear and quantum engineering Chun T. Rim.

"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," he added.

Refining wireless power

In 2007, the US-based Massachusetts Institute of Technology (MIT) developed the Coupled Magnetic Resonance System (CMRS), which, using a magnetic field, transferred energy between a distance of 2.1 metres, just under half of what the KAIST scientists have achieved.

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The CMRS system has faced many barriers to commercialisation, such as a problematic and bulky coil structure and high frequency required to resonate the transmitter, which creates low transfer efficiency. And due to a high Q factor of 2,000, the resonant coils are very sensitive to the surrounding environment.

The KAIST scientists who developed the DCRS, which is not commercially usable yet, have corrected some of these problems. For example, the DCRS is an optimally designed coil structure that has two magnetic dipole coils; a primary coil to induce a magnetic field and a secondary coil to receive electric power.

The coils are made up of compact ferrite core rods with windings at their centres, unlike the CMRS, which has large and thick loop-shaped air coils. With a size of 3m in length, 10cm in width, and 20cm in height, DCRS is also significantly smaller than CMRS.

It is also less sensitive to the environment due to a Q factor of 100 – significantly lower than the CMRS – and works well at low frequency of 100kHz.

Several experiments with the DCRS have revealed very promising results. Under the operation of 20kHz, the maximum output power was 1,403W at a three-metre distance, 471W at four metres, and 209W at five metres.

For 100W of electric power transfer, the overall system power efficiency was 36.9% at three metres, 18.7% at four metres and 9.2% at five metres. This showed that "a large LED TV as well as three 40W fans can be powered from a five-metre distance," according to Professor Rim.

Work in progress

"Just like we see Wi-Fi zones everywhere today, we will eventually have many Wi-Power zones."

Efficiency improvements are still needed. Professor Rim has said the technology is still very much in the "early stages of commercialisation" and is "quite costly to implement".

However in the future it could be used not only for charging electronic devices such as smartphones but for making high-risk environments, such as nuclear power stations and even oil rigs, safer by eliminating hazardous electricity leads and wires that can become tangled and dangerous when wet.

In this regard, the KAIST team successfully completed a research project with South Korea’s Hydro & Nuclear Power Co. in March. Using the DCRS they remotely supplied electric power to essential instrumentation and control equipment at a nuclear power plant. The team successfully transferred 10W of electricity to the plant, which was located seven metres away from the power base.

These early results are an encouraging sign that one day in the near future, leads and wires for powering batteries and electronic devices will be as rare in the home and in public spaces as dial-up internet is today.

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