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. However, the second half of 2017 and early 2018 has seen a major shift in the industry’s balance of power, led by Apple’s decision to pick a side.

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There are currently only two major groups producing wireless charging technologies for mobile products – the Wireless Power Consortium and the AirFuel Alliance (formerly A4WP and PMA). However there’s clearly a single dominant player when it comes to market share, and that’s the WPC’s Qi standard, which accounts for approximately 90 percent of all wireless charging products.

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 Charging Spot 4.0.

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, but there are questions lingering over the group’s potency now that its biggest contribuer, 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 devices regardless of their orientation in the magnetic field and can also power multiple devices from a single transmitter coil.

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.

Although Qi may have the advantages associated with early adoption, AirFuel is now attempting to push both inductive and resonant technologies into single products. This would provide the best of both worlds and has added an interesting dynamic for device manufacturers to consider.

Building products

So far, major mobile semiconductor players, including Qualcomm and MediaTek, have been working to provide integrated circuits that support at least one of the various standards. We have already seen the standard war produce products that support more than one type of technology too. For example, flagship products from Samsung and LG support both the inductive Qi and PWA standards.

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.

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.

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. However, its long range 15 foot technology remains unapproved. At CES 2018, the company unveiled its first product partnership, wirelessly chargeable smart underwear produced by Myant called SKIIN.

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? 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 may finally see some meaningful product and consumer adoption.