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Wireless charging technology: what you need to know

With AirFuel, Qi, and various other wireless charging standards all making their case, we take a look at the pros and cons of the different technologies.
January 11, 2019
Anker wireless chargering pad

Wireless Charging has had a hit-or-miss relationship with the mobile industry, dipping in and out of product ranges and flitting between spec sheet features and accessory status. These days, a number of high profile smartphone ranges support wireless charging, including Google latest Pixels, Samsung’s Galaxy S and Note products, and the Huawei Mate 20 Pro.

After years of battles over standards, there is now only one major player left in the smartphone game – the Wireless Power Consortium. The Wireless Power Consortium’s Qi standard (pronounced chee) accounts for approximately 90 percent of all wireless charging products. The Powermat (PMA & AirFuel) and Wireless Power Consortium (Qi) merged in January 2018, putting an end to the threats of market fragmentation and hopefully making it easier for manufacturers to pick a standard for the long term.

Coalescing around a standard

After a long period of industry indecision between the WPC and AirFuel standards, 2017 saw Apple adopt Qi technology for its iPhone 8 and iPhone X, adding major clout to the standard that in essence forced the industry to finally pick a group. Although Samsung — a larger smartphone manufacturer by global volume — adopted wireless charging long before Apple, it’s latest products hedge their bets with support for both Qi and PMA.

Come 2018, Apple’s decision proved to have trickle-down effects for the wireless charging industry. Powermat joined the WPC, specifically citing Apple’s use of the Qi standard as a determining factor. Powermat is now contributing its technology to the WPC, and the partnership will likely end up producing chargers with both Qi and PMA standards like its newest flexible wireless charging products.

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Powermat produces standards for products which incorporate its own and Qi technology, and has rolled out software updates to many of its existing products to support the standard. For example, those Powermat locations at Starbucks now work with Qi phones. Similarly, the company’s SmartInductive and AgileInductive product lines both also support Qi.

It’s also important to note that Powermat was a founding member of the PMA (Power Matters Alliance) that combined with A4WP to produce AirFuel. This group is still working on its own versions of inductive and resonance charging. In fact, some of PowerMat’s products continue to support AirFuel PMA inductive charging. However, there are questions lingering over the group’s potency now that its biggest contributor – Powermat – is working with Qi and the WPC.

How the technology works

Even before Apple’s adoption and the Powermat partnership, the Wireless Power Consortium’s inductive Qi standard had a prominent industry profile, as it powers a range of smartphones, accessories and products. The PMA standard, which is now folded into AirFuel, has also appeared in a number of smartphones and also struck deals to provide charging stations to businesses such as Starbucks. Both of these standards are based on inductive charging technology, which is typically quite short range and can be quite finicky. Rezense, the old A4WP standard was based on resonance technology, but this design has yet to appear in any smartphones.

magnetic fields
Coils of wire create magnetic fields, which can be used to generate a current flow in a separate, insulated coil. This is the basis of transformer technology and both inductive and resonance chargers.

Inductive- and resonance-based technologies produce quite different results from an end user’s perspective, despite being based on the same engineering principle that coils of wire can be used to transmit power over the air.

If you are interested in the science, inductive charging uses tightly coupled coils with a slightly “off-resonance” frequency for high transfer efficiency, resulting in an efficient use of power but at the cost of high sensitivity to coil misalignment. This is why Qi and PMA devices often use magnets to line-up devices with the receiving pad and are limited to very short charging distances, typically just 45 mm.

The only real differences between Qi and PMA are the transmission frequencies and connection protocols used to communicate with devices and control power management. Resonant charging is a little different, typically operating over a larger distance of a couple of inches by tuning the frequency of the oscillation to precisely match between the receiver and transmitter. This allows for a longer transfer distance before power diminishes but with less optimal power transfer than induction technology. One of the other big benefits of a resonance design is that power can be transferred to multiple devices regardless of their orientation in the magnetic field and can also power multiple devices from a single transmitter coil.

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OnePlus 8 Pro on wireless charger from side

Qi also now has a resonance design in its 1.2 specification for longer power transfer up to 2.8cm, but due to ensuring compatibility with existing Qi transmission frequencies, Q factor and heat limitations, it is not as effective at transmitting power over long distances as a system designed specifically for that purpose.

The base Qi standard supports up to 15W of power. This is what most smartphones on the market have made use of over the years, although not often maximizing the power output. Qi also has an augmented “Medium Power Simple Battery Charging” standard designed for use with higher power designed for appliances requiring between 35 and 60W.

Building products

So far, major mobile players have been working to provide products circuits that support at least one of the various standards. For example, flagship products from Samsung and LG support both the inductive Qi and PWA standards. However some devices, like the Huawei P20 Pro, only support Qi.

Other companies are taking the multi-mode approach much further, by supporting resonance on top of both inductive standards. NuCurrent, for example, support Qi, PMA and A4WP, and announced the world’s first 10-watt inductive and resonant charging antenna. In the future though, we may see manufacturers revert to supporting just Qi, as Apple has done. Safe in the knowledge that some of the biggest manufacturers are now rallying behind this standard.

Although some OEMs support Qi and PMA, we may now see the two refined into a single universal standard that simplifies product development.

The first generation of accessories were pretty much limited to power charging stations for your home, but the wireless charging market has expanded into lots of new product segments since then. Automotive is one of the growing sectors, and a number of manufacturers, such as Audi and Mercedes, have already announced wireless charging capabilities in their vehicles. The Wireless Power Consortium is particularly interested in building its technology into public spaces and businesses, and envisions future devices with smaller batteries but with enough charging points to easily keep them topped up.

Wireless charging is also branching out from its roots to become even more useful to consumers. The technologies have communication protocols built in to ensure the correct power transfer between devices, and this is being used to communicate with other systems. For example, it can be used with smart home solutions, such as controlling lights or temperature, or transmitting information about your favourite radio station or even your optimal seat position to your car’s on-board computer.

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Radio transmission and the future

While the Wireless Power Consortium is now the largest group with a range of products on the market, a number of smaller companies are also peddling other quite novel ideas. Many of them are now working with AirFuel to provide wireless charging at much longer ranges than before.

All the way back at CES 2016 we went hands-on with Humavox’s various pieces of wireless charging equipped gear. Unlike induction- or resonance-based designs, this technology is based on near field radio frequency transmission. Humavox is looking at similarly short ranges as existing wireless standards, but rather than large metal coils, the company’s technology uses a small integrated circuit to handle the power transfer and conversion, allowing for some discrete implementations. Humavox’s offers a platform dedicated to wireless headphone charging.

Energous is another company with a radio wave-based technology, but unlike Humavox it is touting much longer ranges from its standard, reaching up to 15 feet. Last year the company announced a rather expensive transmitter hub that is capable of delivering 5.5 watts of power to devices five feet from the hub, around 3.5 watts of power at 10 feet, and one watt at 15 feet. The extra range really is the selling point of Energous’ technology, but at close range it is still relatively competitive with existing chargers.

In early 2018, Energous received the first FCC certification for power-at-a-distance wireless charging for its medium range charging technology. This was filed under Part 18 which caters to industrial, science, and medical devices, rather than under the more regularly used Class B consumer electronics section of Part 15. At CES 2018, the company unveiled its first product partnership, wirelessly chargeable smart underwear produced by Myant called SKIIN. We’re still waiting on mainstream products though.

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Picture of a Huawei Mate 20 Pro wirelessly charging up the Google Pixel 3

If that wasn’t enough choice, it turns out that you can also use ultrasound to transmit power between devices. UBeam is one such standard based on this lower frequency transmission, and it boasts multiple device charging with a range of up to 4 meters with 1.5 watts of power. Unfortunately its power output and heat waste doesn’t quite match up with other ideas in the market, and the technology requires line of sight between devices in order to transmit power successfully.

Wrap Up

Clearly there’s lots of promising technology here, but there’s still one big question to be asked of wireless technology: why should consumers choose it over the convenience of a bedside USB cable with fast charging support? Honestly, it’s a tough one to answer, but ease of use and ubiquitous gadget support and charging stations will probably be required.

Despite being around for a number of years already, wireless charging still hasn’t become a critically important technology in the gadget market. However, now that the market is beginning to congregate around the Wireless Power Consortium and Qi, we’re starting to see some meaningful product and consumer adoption.