The fallacy of wireless power

Induction chargers promise convenience but use more power and take more space -- and they're not wireless

They're back -- wireless chargers, that is. If you believe the hype in the product blogs and from some consulting firms, by 2016 you'll have them nearly everywhere: hotel rooms, conference rooms, airports, lobbies, cafés, and on your desks and entryway tables.

I'm not so sure.

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Despite years of vendor attempts, the fairly old technology underneath wireless charging -- inductive charging -- has simply failed to take root in computing devices.

Wireless charging isn't wireless
Perhaps the most obvious strike against wireless charging is that it is not in fact wireless. You run a wire from your power source (wall outlet or USB port) to the charger. Then you need to have physical contact between that charger and the flagging device. It's the contact method that changes in inductive charging, a switch from a plugged-in cable to overlapping charging surfaces.

And you don't want true wireless charging anyhow, even though demonstration versions exist. Why? Because most of the energy gets lost heating the air as the power travels between its emitter and the device. Also, you're sending a strong electromagnetic beam or waves through the space that you and other people (and the occasional pet) exist. We have all sorts of radio waves and electromagnetic radiation in our environments, but they're low-level or have very limited range at troublesome intensities. That changes, and not in a good way, at the intensities needed to charge devices in a room or even on a specific table. It'd be like living in an always-on microwave oven.

Is the convenience enough to matter?
What these devices promise is convenience: Each time you charge a smartphone or tablet, you save a few seconds by not having to link the MicroUSB, Dock, or Lightning connector to your phone or tablet or to place it precisely in its dock. Instead, you just place the device front side up on a mat. As long as the two inductive surfaces touch, the charging commences. With a big enough mat, you can charge multiple devices at the same time, using just one wall outlet or USB power source; gone are splitters and multiple cable types. "The convenience may look trivial, but if you start using it, you find it isn't," says Menno Treffer, chairman of the Wireless Power Consortium, an industry standards group whose Qi (pronounced "chee") measure is used by several smartphone makers.

Convenience is a powerful motivator, and as additional manufacturers build wireless charging into their devices' skins, more and more users could take advantage of that expedience. Lack of convenience has been a big barrier to adoption, even though wireless charging has been around for a decade; different devices have used proprietary technology, requiring a separate mat for each device. Alternatively, you have to plug them into a sled or other add-on, thus increasing bulk and effort over hooking up the charging cable. The development of inductive charging standards such as Qi removes both barriers, Treffer says.

But the no-plug convenience of inductive charging is not as simple as you might think. You have to ensure the contact surfaces touch over sufficient area and in the correct areas -- placement still matters. That's because only part of the device will have a charging surface; the entire case won't be inductive due to issues around circuitry design, increased power wastage, and radiofrequency interference.

Charging pads are also large, and you need to uncover them when in use so that the device can make contact. On a cluttered desk, that extra space matters. A spare cable or typical wired charging dock takes much less space, and it serves as a syncing and transmission conduit for video and audio. (Yes, I know Bluetooth and Wi-Fi are increasingly taking over those other roles, but their use typically eats up battery life.)

Space matters on tables and office furniture as well -- just where will they be placed in your conference room, near your airline seat, or in a Starbucks café? At least that challenge is not much greater than where to put charging docks or cables in such environments. Such shared-facility deployments might be plausible for induction charging mats, especially if the device manufacturers converge on a single standard.

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