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Wireless Charging: Magnetic Induction or Magnetic Resonance?

Wireless Charging: Magnetic Induction or Magnetic Resonance?
by Majeed Ahmad on 01-18-2015 at 7:00 pm

Standard wars are no stranger to technology business. In fact, they are the norm. Take, for instance, the rock star technology of 2015—wireless charging. Magnetic induction or magnetic resonance: which standard will dominate the wireless power ecosystem?

That’s the crucial question while wireless charging continues to win the prominence in the technology industry, and the same time, looks akin to an assortment of workable ideas with a number of pros and cons. The stellar promise of wireless power comes down to a critical premise: clarity that OEMs like smartphone makers need for making decision about incorporating wireless charging as a standard feature in their products.

Ask Integrated Device Technology Inc., the company that offers wireless charging products for both magnetic induction and magnetic resonance technologies and is a board member of the Wireless Power Consortium (WPC) and Alliance for Wireless Power (A4WP) standard bodies. According to Arman Naghavi, Vice President and General Manager of the Analog and Power Division at IDT, “right now the wireless power technology is at step one if there are going to be ten steps.”

So it’d be worthwhile to have a look at the wireless power standards maze and make a sense of the technology merits amid this standards battle and the possible consolidation of these standards later this year.

Magnetic Induction: Device on Mat

The technology is powered by two coils of wire: the coil at the charging station produces an oscillating magnetic field, which in turn induces an alternating current that is received by the coil at the device being charged.


Image credit: IDT

Qi (pronounced as chee) is driving the magnetic induction wireless charging standard and boasts more than 200 members. The Qi standard—developed by WPC, which was established back in 2008—won early adoption but has taken the back seat due to a number of compromises. First and foremost, it’s slightly more expensive to produce compared to methods without a coil.

Second, because Qi uses tightly coupled coils for high transfer efficiency, the arrangement is sensitive to coils misalignment that eventually leads to smaller distances between device and docking station.

Another wireless power standard, which uses inductive charging, has been developed by the Power Matters Alliance (PMA). The PMA standard, which is quite similar to Qi, has Starbucks and MacDonald’s among its early adopters. It has recently joined hands with A4WP, the standards body driving the adoption wireless charging based on magnetic resonance technology.

Magnetic Resonance: Proximity

The magnetic resonance technology still uses a loosely coupled coil arrangement that creates a usable magnetic field; but it also tunes the frequency of oscillation to precisely match between transmitter and receiver. As compared to closely-coupled coils in magnetic induction, magnetic resonance technology increases transfer distance, but looser coupling between the coils leads to suboptimal power transfer.

The Rezence standard, spearheaded by A4WP, promises to charge multiple devices without having to worry about alignment and states 5 cm as a typical operating distance. The charging accessories and mobile devices based on the Rezence standard are expected to be available later this year.

Rezence block diagram (source: A4WP)

Consolidation Ahead

Chipmakers like Broadcom, IDT and MediaTek are launching board and coil designs that support both inductive and resonant coil systems. The partnership recently announced by A4WP and PMA is another harbinger of the coming consolidation within the wireless power standards domain that will encourage device OEMs to commit to the highly promising but still embryonic wireless charging feature.

Another notable indication of the imminent consolidation in the wireless power standards comes from the fact that industry heavyweights like Qualcomm and Samsung, once staunch supporters of A4WP, are now backing up Qi as well. The fragmented world of wireless power merely shows the infancy state of the technology and the fact that there are still missing links within wireless charging technology landscape.

Bridge standards and dual-standard products could fill the void and bring more OEMs into the wireless power fold. Meanwhile, the two competing wireless charging technologies will most likely continue to collide and converge. Steve Goacher, Business Development Manager for TI’s Analog Wireless Power Group, believes that both magnetic induction and magnetic resonance wireless charging standards will have relevance in the future. “Each technology has its pros and cons and I don’t see one dominating the other.”

Majeed Ahmad is author of books Smartphone: Mobile Revolution at the Crossroads of Communications, Computing and Consumer Electronicsand The Next Web of 50 Billion Devices: Mobile Internet’s Past, Present and Future.


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