Cutting the cable: Wireless charging becomes a reality

Computerworld - Imagine sitting down at work, plopping a mobile device on the desk and having it wirelessly charge itself while, at the same time, synchronizing new data to your PC.

In that world, one could also wirelessly charge a phone set on a car's dashboard or armrest while it plays music through the speakers, and never have to search for the one open electrical outlet at the coffee shop or airport.

That world may not be too far off for the masses of smartphone, tablet and other mobile device users.

With the launch of the Windows Phone 8-based Lumia 920 smartphone last week, embedded wireless charging is hitting the U.S. mainstream.

The built-in wireless charging capabilities offered in the Nokia 920 doesn't require that widgets be plugged into the USB port of a smartphone in order to charge it from a magnetic induction power pad. That's the typical wireless charging process today.

The Lumia 920 only has to be laid on a power pad to be charged.

Charging Pads

William Stofega, an IDC mobile device analyst, said wireless charging pad business is currently dominated by Duracell's Powermat technology, which is based on magnetic induction technology, one of two forms of wireless charging.

Duracell's Powermat wireless phone charger

But that choice is likely to change soon, thanks in part to the Wireless Power Consortium's Qi (pronounced "chee") open wireless charging standard, Stofega said.

Already, some products from 120 companies are certified as compliant with the Qi standard.

The certified products run the gamut, from the LG Optimus LTE2 and Panasonic Eluga smartphones, to charging pads, gaming controllers, Blu-ray Disc recorders, smartphone docking speakers, automobile phone chargers, alarm clocks, battery packs and charging modules that can be installed in tabletops and furniture.

Magnetic induction vs. resonance charging

Analysts note, though, that there are some slight differences in the Qi-compliant wireless charging products being developed today.

Some use magnetic induction charging techniques, which require that the mobile device be in contact with a charging device. Others use resonance charging, which allows a mobile device to be placed near the power source for charging.

Magnetic induction charging uses two coils: a transmitter coil and a receiver coil. Alternating current in the transmitter coil generates a magnetic field, which induces a voltage in the receiver coil.

In contrast, resonance charging offers wireless AC transmission to a device at a distance ranging from 5mm to 40 millimeters (about 1.5-in) from the power source.

Resonance charging is based on the same transmitter/receiver coil technology as magnetic induction, but it transmits the power at a greater distance. So, for example, a mobile device could be charged when laid next to a laptop with resonance charging capability.