What’s the big deal about Resonant?

Wireless power has made significant advancements in the last few years with many inductive technologies becoming mainstream and widely available – notably Qi and PowerMat products. Major players like Samsung are building wireless power receivers into their phones along with a huge number of transmitters widely available from companies like AirCharge, TYLT and of course Samsung themselves. Currently there are nearly 700 different products on the market that are Qi certified alone.

However, inductive wireless charging is not without its limitations – amongst them include slower charging speed and the requirement for precise alignment of the receiver (smartphone) and transmitter (wireless charger). This is where resonant technology can deliver a number of advantages and truly represents the future for charging wirelessly. Unlike inductive technologies, there are still zero finalized resonant products in the marketplace. A4WP has long promised an option and now the Wireless Power Consortium is in the process of developing a resonant specification called Resonant Qi. I've been working on the specification personally along with other top member companies at the WPC. The new Resonant Qi specification will overcome existing limitations with Inductive Qi and provide those consumer benefits which OEMs are looking to integrate into their devices.

What’s most important?

The discussion on how inductive and resonant perform must be framed in respect to what is valued by the end user. Specifically, what are the factors that will increase the appeal of wireless charging for the consumer?

  • Speed: Is the technology able to charge at the same or better speed than current wired chargers?
  • Multiple devices: Are you able to charge multiple devices (and multiple types of devices) at the same time?
  • Efficiency: How much power being delivered from the source is actually getting through to the device and not being lost? Will it still work efficiently if it is integrated into the surfaces of furniture etc.?
  • Alignment (spatial freedom): Are you able to charge devices in multiple positions and orientations on the charger (X & Y axis)? Or does it require precise alignment of the device? How does it perform on the Z axis over greater height?
  • Power level: Can the technology charge a range of devices – including higher power devices (>10W)?
  • Design: Can it be integrated into devices through miniaturized receivers, without the need for charging cases or sleeves?
  • Safety: Does the technology meet stringent industry guidelines i.e. 1998 and the 2009 ICNIRP (International Council on Non-Ionizing Radiation Protection)? Safety is determined by how much radio frequency (RF) exposure can be applied without being harmful to human health.
  • Interference: Will the technology affect the operation of the devices themselves, or peripheral devices and appliances? Specifically, are the EMF and EMI below industry limits?
  • Interoperable: Will the technology be able to work with existing wireless charging solutions currently on the market?

Based on the above factors, how do inductive and resonant technologies stack up?

I have used examples of current inductive products that we find on the market today (Qi and PMA) to compare functionality and performance with the Resonant Qi specification, currently in the works – see Table 1 below:

Overall, resonant presents a wireless charging future with greater convenience, performance and flexibility. The main areas where we will see the greatest advantages are:

  • Faster charging – You can’t charge at “wired speeds” if you are wasting energy as heat. Either you just won’t get enough power or you will cause you phone to overheat because you exceeded its thermal budget. This is why, for example, when using the Galaxy S6’s wireless charger, the phone is charged approximately 1:30 hours slower than when I plug it into the wall (it takes 2:55 hours instead of 1:25 hours). A wired charger is 2.2x faster than the current inductive wireless charger. With Qualcomm’s wired quick charger technology and the new USB standard now available this is going to be even more important in the future.
  • Multi-device charging – Inductive systems can only charge one device at a time. Resonant systems can charge many devices simultaneously and at different power levels. This makes it particularly useful for shared-use environments like table tops in the home or office.
  • Full Spatial freedom – For all three axis, x, y and z. One of the benefits of resonant technology is that it makes it really easy to drop and go, as well as charge through table tops or furniture. One of the biggest complaints about inductive charging is the requirement to precisely align the device. This is why inductive transmitters tend to have sticky rubber rings on their surface. This stops your device sliding off the charge when you bump your bedside table, for example.

Resonant Qi technology provides the next evolution to an already widely available set of products. It will provide a noticeable step-up in performance over the current inductive solutions, and will help wireless charging technology become more pervasive. Today, inductive solutions continue to be the only option for consumers wanting to purchase their own wireless charging system despite a lot of noise from other rival resonant standards. One has to ask why there are no (zero!) A4WP products shipping in the market to date.

The key for the WPC, and arguably the industry at large, will be to deliver a Resonant Qi specification that remains fully compatible with the hundreds of millions of existing Qi products on the market, while also delivering greater user performance over inductive systems. This approach puts the consumer first, and the best technologies always do.

2 comments on “What’s the big deal about Resonant?

  1. Scott Elder
    September 18, 2015

    70% effciency delivering 20W to a load means that 8.6W goes primarily into heating back-to-back coils at the surface of a charger.  That will blister a child's hand.  Wired 20W means that 750mW x 2 is spread across two distant objects.  Warm yes, blisters no.

    Wireless is a convenience if one has 2-3 hours of time to wait for a charge.  Wired means 50% recharge in 15 minutes plus the 5 seconds to plug in a cable.

    Smartphones are mobile devices.  There is nothing mobile about 2-3 hours of idle charging time.

    I can think of only one benefit of wireless power in mobile products: sealed computing.

    Isn't it interesting that on one hand we have future mandated efficiencies above 80% for wired wall chargers, but no one is complaining about 70% wireless charging efficiencies for the same purpose?





  2. peter.clarke
    September 24, 2015

    I think you make a very good point.

    The industry is so keen to add “convenience” factors to try and increase sales they seem to be blind to the important ecological implications.





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