Wireless power transfer breaks all connections, Part 3

April 07, 2015 // By Sanjaya Maniktala
Sanjaya Maniktala offers a third part of a high-level review of the current state of wireless power transfer (WPT).

WiPowering the Future

There was another almost concurrent success story based on another ongoing university project. In 2004, a spinoff company called WiPower had emerged from the shadows of University of Florida, where its founder Ryan Tseng had been exploring WPT for some time, reportedly having been thoroughly disgusted carrying bags of wall-warts/adapters all over the world on his many trips. He had dreamed of a charging pad on which he could just throw his mobile phone along with any other rechargeable battery-powered gadgets such as mp3 players, media tablets, PDAs and perhaps even laptops, and have them charged overnight. Over the following three years, his new-born company continued R&D efforts along with the University of Florida.

Note that to dispel the “inherently poor efficiency’ popular myth of MR-based systems, WiPower had declared back in 2009 that its prototype wireless chargers operated at about 60% efficiency, and that it had achieved higher than 75% in testing.

In September 2010, Qualcomm acquired WiPower. The A4WP group was formed in May 2012 by Samsung and Qualcomm, with some help from Powermat (pioneers of PMA surprisingly), SK Telecom, Ever Win Industries, Gill Industries and Peiker Acustic (no spelling mistake here). By June 2013, Intel had also thrown its weight behind A4WP. A4WP’s Board of Directors by then also included Broadcom and IDT.

In Dec 2013, the first version of their Rezence standard was released. This was an inductive standard, but as mentioned, the frequency was set to 6.78 MHz, because that is the lowest, almost unlimited frequency band in terms of “intentional” electromagnetic interference (EMI) as described in the international applicable standard known as CISPR 11. Microwave ovens also get a “free pass” in effect, because 2.45 GHz is also permitted by CISPR 11. So do radio-controlled toys working at 27 MHz. And so on.

Rezence is a combination of the words “resonance” and “essence”. It describes a single power transmitter unit (“PTU”) and one or more power receiver units (“PRUs”). This interface standard supports power transfer up to 50 Watts, at distances up to 5 centimeters (“z-freedom”). The power transmission frequency is 6.78 MHz, and up to eight devices can be powered from a single PTU depending on transmitter and receiver geometry and power levels. A two-way bluetooth smart link operating at the standard frequency of 2.40 to 2.48 GHz is also unique to the A4WP system. It is intended for control of power levels, identification of valid loads and protection of, and from, non-compliant devices.

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