Omnidirectional Wireless Charging Developed

Researchers have overcome a major obstacle in wireless charging with a device that allows charging in any orientation.

AsianScientist (Jul. 15, 2015) – A group of researchers at the Korea Advanced Institute of Science and Technology (KAIST) has developed a wireless-power transfer (WPT) technology that allows multiple mobile devices to be charged in any direction and up to 0.5 meters away from the charging device. Their results have been published in IEEE Transactions on Power Electronics.

Mobile devices, such as smartphones and laptops, have become indispensable portable items in modern life, but one big challenge remains: keeping their batteries charged.

Although wireless-power technology has been applied to smartphones, it currently does not offer any substantial advantages over traditional wired charging because the devices still require close contact with the transmitter, a charging pad. Existing wireless-charging technologies have a charging distance of less than 10 cm and can only be charged in a fixed position, restricting their use in three-dimensional space.

A team led by Professor Rim Chun T. of the Nuclear and Quantum Engineering Department at KAIST has now developed WPT that is capable of charging multiple mobile devices concurrently and with unprecedented freedom in any direction, even while holding the devices in midair or a half meter away from the power source.

Either 30 smartphones with a power capacity of one watt each or five laptops with 2.4 watts each can be simultaneously and wirelessly charged at a 50 cm distance from the transmitter with six degrees of freedom, regardless of the devices’ three-axes positions and directions. The maximum power transfer efficiency for the laptops was 34 percent.

They used high-frequency magnetic materials in a dipole coil structure to build a thin, flat transmitter (Tx) system. First developed in 2014, the dipole coil resonance system (DCRS) is composed of two transmitting and receiving magnetic dipole coils placed in parallel, with each coil having a ferrite core and connected with a resonant capacitor.

The ferrite cores were designed to reduce the core volume by half, and their ability to transfer power is nearly unaffected by human bodies or surrounding metal objects, making DCRS ideal to transmit wireless power in emergency situations. In a test conducted in 2014, Rim and colleagues succeeded in transferring 209 watts of power wirelessly to the distance of five meters.

In the present study, the research team rearranged the two dipole coils from a parallel position to cross them in order to generate rotating magnetic fields, embedding them in the Tx’s flat platform. This has made it possible for mobile devices to receive power from any direction.

In addition, the DCRS works at a low magnetic field environment. Based on the magnetic flux shielding technology developed by the research team, the level of magnetic flux is below the safety level of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guideline (27µT) for general public exposure to electromagnetic field (EMF).

“Our transmitter system is safe for humans and compatible with other electronic devices. We have solved three major issues of short charging distance, the dependence on charging directions, and plane coil structures of both Tx and Rx, which have blocked the commercialization of WPT,” Rim said.

Currently, the research team and KAIST’s spin-off company, TESLAS, Inc., have been conducting pilot projects to apply DCRS in various places such as cafes and offices.

The article can be found at: Choi et al. (2015) Six Degrees of Freedom Mobile Inductive Power Transfer by Crossed Dipole Tx and Rx Coils.

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Source: KAIST.
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