“Almost universally, all the carmakers have learned…that consumers find plugging in a vehicle is inconvenient, and the carmakers have concluded they need to offer some type of wireless, hands-free charging,” says David Schatz, director of business development and marketing for WiTricity Corp. in Watertown, Mass., which makes wireless chargers for phones and cars. With WiTricity’s system, a user would not have to park his or her car directly on a charging mat, let alone deal with wires. As long as the car is within range of the charging station, energy begins to flow into the battery.
The process relies on a principle called magnetic resonance coupling (pdf). The charging device, made of a coiled wire with capacitance plates on either end, uses electricity to create a magnetic field that resonates at a specific frequency. Just as an opera singer can shatter a wine glass by singing the right note, the emitting coil transfers energy only to a receiving coil that resonates at the same frequency. Magnetic resonance coupling is thought to be safer than other methods of wireless charging because the intensity of the field can be increased without affecting other, non-resonant objects nearby.