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Wireless charging explained: What is it and how does it work?

Wireless charging explained: What is it and how does it work?

Wireless charging technology has been around for more than 100 years, but its inclusion in devices such as Apple's new iPhone line has given it new life. Here's how it works, and why it could soon show up in everything from homes to robots.

Credit: Apple

"If in every restaurant and coffee shop you have it, then people will be more likely to use it and get a pad to charge at home," Freas said.

Most of these efforts are still just pilot programs, Freas said, adding that consumers and businesses are less likely to want tightly coupled charging and more likely to opt for loosely coupled resonant charging. That's because loosely coupled charging lets you simply plop down a phone, tablet or laptop on a desktop and have it charge.

WiTricity and wireless charging in vehicles

In July, Dell released a Latitude laptop that incorporates resonant wireless charging from WiTricity. The Dell wireless charger offers up to 30W of charging power, meaning  a Latitude laptop will charge at the same rate as it were plugged into a wall outlet.

dell laptop WiTricity WiTricity

Dell's new Latitude 7285 2-in-1 laptop and wireless charging pad.

But WiTricity's main focus is the auto industry. The company, which is part of the AirFuel Alliance, expects a number of electric car manufacturers to announce wireless charging for their vehicles, according to WiTricity CEO Alex Gruzen.

The company's electromagnetic resonant technology allows power to transfer at distances of up to about nine inches away from a charging pad. That would allow electric cars to charge just by parking on top of a large charging pad.

For example, Mercedes-Benz this year will roll out S550e plug-in hybrid sedans that can use WiTricity's technology; the S550e simply parks over a pad and begins charging even more efficiently than if it were plugged in.

The electric vehicle application is tailor-made for electromagnetic resonant charging, Kesler said. That's because a vehicle doesn't need a charging cable, and the wireless charging pad delivers electricity more efficiently. (Wired charging systems use electronics to convert AC to DC and regulate the flow of power, reducing efficiency to about 86%, Kessler said.)

Qi wireless charging damage your iPhone Wireless Power Constortium

Nearly 50 car models now offer Qi-based wireless charging in their cabins.

"Our wireless charging can be 93% efficient from end to end – from the wall to what's being delivered to the battery," Kesler said.

Wireless charging over distance

This month, Apple surprised some industry watchers by purchasing PowerByProxi, a New Zealand-based company developing loosely coupled resonant charging technology that's based on the Qi specification.

PowerbyProxi was founded in 2007 by entrepreneur Fady Mishriki as a spin-out from the University of Auckland. PowerByProxi has showcased charging boxes and bowls into which multiple devices can be placed and charged at the same time.

The Aukland-based company got its start selling large-scale systems for the  construction, telecommunications, defense and agriculture industries. One such  product is a wireless control system for wind turbines.

PowerByProxi, a member of the WPC's Steering Committee, has also miniaturized its technology and placed it into AA rechargeable batteries, eliminating the need to embed the technology directly into devices. The wireless technology takes up about 10% of the AA battery height.

Apple could use PowerByProxi's technology to expand its use of wireless charging beyond just smartphones – using it, for instance, to charge TV remote controls, computer peripherals or other devices that require batteries.

Though mobile device charging pads are popular, wireless charging technology is also making inroads into everything from warehouse robots to tiny IoT devices that otherwise would need to be wired or powered by replaceable batteries.

Both Ossia and Energous have demonstrated wireless charging beyond 15 feet. Ossia's charger can send about two watts up to several feet, but that drops off quickly as the distance increases. Even at 30 feet, however, the amount of power transmitted is "meaningful," according to Ossia CEO Mario Obeidat, alluding to trickle powering devices so as to maintain their charge.

Ossia Cota Wireless Charging system Mark Hachman

The Ossia Cota wireless power system includes this large cylindrical transmitter as well as receivers. 

"Let's say I'm in an office for eight to 10 hours a day and I'm receiving a half a watt or a watt of power; it's charging my device all the time," Obeidat said. "So if it takes five hours to fully charge that devise, that's fine because you're there all the time."

"I've used both [Ossia and Energous]; the technology works," Rob Rueckert, the managing director at Sorenson Capital, a private equity and venture capital firm, said in an earlier interview with Computerworld.

Rueckert believes charging at distance is a more compelling technology than rival technologies.

how wireless charging works resonant PowerByProxi

How wireless charging works.

Both Energous' WattUp and Ossia's Cota mobile device charging systems work much like a wireless router, sending radio frequency (RF) signals that can be received by enabled wearables and mobile phones. A small RF antenna in the form of PCB board, an ASIC and software make up the wireless power receivers.

Using a multi-antenna management chip about 4x4mm in size, the Cota power transmitter can be built into a variety of form factors – everything from ceiling tiles to  tables, desks, glass, televisions and automobile dashboards.

The transmitter automatically detects Cota-enabled devices and includes a temperature-sensing unit to prevent overheating.

"We call it real wireless power," Obeidat said. "The difference between our technology and others in market, like Qi, is we can deliver meaningful power remotely. Others require you to place your device on the pad. So, effectively you have to give up the device to charge it."

Obeidat also claims Cota charging can work through walls, just like a Wi-Fi router.

"Our technology is agnostic. You can envision having a transmitter in room where it powers a smartphone, a tablet or a smartwatch, all at the same time," Obeidat said.

Ossia has been piloting its technology on electronic labels for products on retail shelves. The labels can inform shoppers of product details or sales without requiring workers to place physical signs or change price stickers.

While some have scoffed at the idea of only transmitting a couple of watts of power over distance, investors have taken the idea seriously. For example, Pleasanton, Calif.-based Energous – an AirFuel member – raised about $25 million when it went public in 2014.

Energous' WattUp charger uses the Bluetooth wireless communication spec. Like Ossia's Cota technology, the amount of wattage WattUp can send is limited. As a result, Energous is focused on powering small mobile devices rather than laptops or batteries that require higher capacities.

energous wireless power Energous

Michael Leabman, founder and CTO of Energous, demonstrates how one of the company's wireless charging routers can send power at midrange and far-range distances.

A single WattUp transmitter can charge up to 24 devices, all under software control that enables or disables charging, according to Energous. The maximum amount of power – 4 watts – can only be delivered to four devices simultaneously. As more "authorized" devices enter a room, the charge to each device drops.

One potential obstacle to adoption of wireless charging at distance is that neither Ossia's nor Energous' can charge Qi-enabled devices; the technology is proprietary.

Only the beginning

Green believes Qi and Powermat provide a great start, but stresses the technology  isn't completely wireless. "Qi has started the conversation about wireless power. There is an important need to educate consumers about what is possible," he said.

By starting with a Qi pad charging, users will come to understand the premise of wireless power and will soon demand a much more flexible, robust solution: power at a distance with the flexibility to use a device while its charging.

"One thing is clear: in 2017, we're not going to see a device offering full-speed wireless charging across a room," Green said. "There's two ends of a scale instead, charging at the same speed as a wire but on a charging pad, or perhaps trickle charging very slowly but at a larger distance away."


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