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Qi seeks safety, efficiency over distance

Posted: 08 Aug 2014  Print Version  Bookmark and Share

Keywords:Qi  WPC  John Perzow  wireless charging 

The Wireless Power Consortium has improved Qi, its wireless charging spec, with officials saying that the new resonant option is on the right track for the safest method of charging.

Qi is an open, flexible standard based on a close-coupled magnetic induction charging system—the only wireless charging method on the market today, though it has drawbacks in mobility. Following industry trends, the WPC is working on a loosely coupled magnetic resonance solution, and it has previewed updates that would be backward compatible with its early charging method and offer slightly more freedom of movement.

New receivers are not only compatible with Qi's inductive and resonant standards, but they also allow for a 15mm increase in possible charging distance. WPC officials hope the ability to charge devices over a 45mm distance will increase the likelihood of Qi charging pads being embedded into furniture. Other resonant-only companies offer charging at up to 10in (254mm), but John Perzow, the WPC's vice president of market development, told us it doesn't believe in maximising distance.

 Qi1.1 and Qi1.2 resonant systems

Multiple manufacturers demonstrating Qi1.1 and Qi1.2 resonant systems. (Source: WPC)

"Power is limited for safety reasons, and efficiency [in longer-distance resonant chargers] is low because there's a physical relationship between distance and efficiency," Perzow said. "I don't want to suggest we're on a path to greater and greater distance. We don't see that as safe or an efficient path. That's not our goal."

Responsible organisations and manufacturers will plan for charging capabilities at up to 3in, while most will aim for 25mm to 45mm (0.9in-1.7in), Perzow said. "One gets closer to those safety limits as switching frequency and transmitted power increase, and as system efficiency decreases. Since Qi uses a lower switching frequency and is inherently more efficient, it's easier to increase the power of a Qi system while staying well within safety limits."

None of the major resonant charging groups, which include the Association for Wireless Power and the Power Matters Association, have been found to conflict with regulations set by the International Commission Non-Ionizing Radiation Protection (ICNIRP). Nevertheless, in a blog post on Planet Analog (a sister site), Perzow said transferring power efficiently, safely, and with low electromagnetic interference is tricky.

- Jessica Lipsky
  EE Times





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