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The truth about wireless power transfer (Part 3)

Posted: 14 Apr 2015     Print Version  Bookmark and Share

Keywords:Wireless power transfer  WPT  electromagnetic interference  EMI  <i>Rezence 

To access previous instalments, click Part 1 and Part 2.

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 6.78MHz, 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 2.45GHz is also permitted by CISPR 11. So do radio-controlled toys working at 27MHz. 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 6.78MHz, 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 2.48GHz 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.

In Feb 2014 WiTricity decided to throw its entire weight behind the similar, evolving standard from A4WP. So, its products also now work at the Rezence frequency of 6.78MHz not their initial 9.9MHz.

In June 2014, WiTricity announced an enhanced working relationship with another powerful member of A4WP: Intel. But interestingly, prior to all that, as early as in May 2013, WiTricty, an obvious pioneer of MR-based systems had gone and joined PMA, a supposedly "opposing" MI-based standard. But on second thought, this only emphasizes the fact that though the three standards under discussion here may seem "different" to some people, their underlying principles are the same—Faraday's law of induction as applied to resonant circuits. The only real difference between MI and MR is the operating point on the resonance curve, as mentioned previously.

Yet, Rezence is different when it comes to its "use-cases". The major claim to fame of Rezence is that it enables significantly more "z-freedom" (separation), yet at safe frequency levels, unlike microwave power transfer (MPT). Rezence also offers multiple devices to be charged simultaneously on a single transmitter/charging pad. And it is safe too, based on the same magnetic induction principle.

Many consider the Rezence standard immature when compared to the infrastructure already set up by WPC. Testing and certification labs are just coming up for Rezence. Over the period Dec 2013 to Jan 2014, Telecommunications Technologies Association (TTA) and AT4 wireless (AT4w) became the first Rezence Authorised Test Labs (ATLs).

What about commercialisation? In June 2014, Gill Electronics announced a partnership with Qualcomm and in the same month debuted the "first commercially available resonant (Rezence) wireless products" at Neocon 2014. This was a 16W transmitter to be sold under the brand name TesLink. NuCurrent announced their high-frequency resonant antennas were being used in this Tx unit.

Where were the Rezence receiver units though?—many asked. There always needs to be an ecosystem in place, after all. In September 2014, Gill Electronics uploaded a photograph without comment, indicating forthcoming TesLink branded aftermarket sleeves for iPhone 5/5s. Though, clearly this has added significantly to the size of the phone. But that will likely be overcome soon.

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