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.
To date, there are no resonance-charging devices available, according to Stofega. But that may soon change as Intel ramps up its wireless chip development.
Intel Labs first demonstrated in 2008 technology that could wirelessly charge mobile devices. Intel's Wireless Charging Technology (WCT) would let a user charge a smartphone wirelessly from a notebook PC. Intel late last month announced a partnership with Integrated Device Technology Corp. (IDT) to develop chipsets for WCT products.
Products using the chipsets are expected to come out in 2013, Intel said.
Some reports have said the next Apple MacBook laptop will have wireless charging capability based on the Intel-IDT technology.
"[The jointly developed] product is important and new because it leads to a solution that isn't limited to inductive charging and 'smartphone on a charging mat' usage," Intel spokesman Dan Snyder wrote in a blog post.
"Although we are not yet giving out timeframes for consumer products with WCT enabled, IDT has stated they will be delivering their full chipset solution for reference design work in early 2013," Snyder added. "The ecosystem is already excited about this technology so we assume there will be a race to the finish line for sure."
Currently, wireless chargers can supply up to 5 watts of power, the equivalent of most USB-style chargers available today. By comparison, a USB port on a laptop, which shares it's bandwidth with data I/O, offers only 2.5 watts of power.
Some of the latest USB chargers, however, offer fast charging with 10 watts of power.
The Wireless Power Consortium is already working to extend its Qi specification to allow 10 watt power charging, said Menno Treffers, chairman of WPC.