Free Space Wireless Charging

Wireless charging technologies usually require devices to stay in one place within a few inches of a charging pad. Now, a group of Korean researchers developed a wireless-power transfer (WPT) technology that charges mobile devices even when they are away from the power source, in a similar way that Wi-Fi works for internet connections. According to the researchers, as long as mobile users stay within one and a half feet of the transmitter, the devices will pick up power automatically, at any location and in any direction. The team is from the Korea Advanced Institute of Science and Technology (KAIST), an institution that has also pioneered wireless charging for transportation.

Just like Wi-Fi, several users can use the system at the same time, without worrying about the exact position of their devices. The work was published in IEEE Transactions on Power Electronics and demonstrated on July 7 at a lab on KAIST’s campus. The researchers used high-frequency magnetic materials in a Dipole Coil Resonance System (DCRS) to build a charging pad. Anywhere within a 19-inch zone, either 30 smartphones with a power capacity of one watt each or 5 laptops with 2.4 watts each can simultaneously charge. The maximum power transfer efficiency for the laptops was 34%.

The DCRS is made up of a transmitting and a receiving magnetic dipole coil placed parallel to each other, with each coil having a ferrite core and connected with a resonant capacitor. To make it possible for mobile devices to charge from any direction, the researchers rearranged the two dipole coils from a parallel position to cross them in order to generate rotating magnetic fields, which was embedded in the transmitter’s flat platform.

The researchers say the wireless charging system is safe for humans and compatible with other electronic devices, with magnetic flux below the safety level of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guideline (27µT) for general public exposure to electromagnetic field (EMF). Now the research team and KAIST’s spin-off company, TESLAS, Inc., are conducting pilot projects to install wireless charging systems in public places such as cafes and offices.

Source: KAIST | New Electronics

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