Most wireless mobile charging solutions rely on inductive coupling. Here's a typical approach:
The charging station takes the form of a mat or other flat surface. Inside the mat are one or more inductive coupling coils. The mat itself is wired -- you have to plug it into a wall socket. Since the electricity coming to your house is alternating current, the mat provides the electricity the coils need to generate a changing magnetic field.
Your mobile devices need a special case or attachment to take advantage of this magnetic field. Some manufacturers make devices with cases and electronics that facilitate inductive coupling -- the Palm Pre had this feature. But most manufacturers make equipment that still requires cables or wires to recharge. For these devices, you may need to use special sleeves -- each sleeve fits a particular model of a device. Or you may have to attach an adapter that plugs into your mobile device's charging port. The sleeve or adapter will have the matching coil to the surface's inductor coils.
Whether your device natively supports inductive coupling or requires a sleeve or adapter, your next step is to place the device on the charging surface. The inductor coils inside the mat generate the magnetic field that induces electricity inside your device, sleeve or adapter. This electricity then recharges your device's battery. Because there's no direct current passing between the mat and the device, it's perfectly safe to pick up a gadget when you're on the go.
Inductive coupling is useful but there are some downsides. The largest drawback is that it doesn't work over large distances. Placing a device a little too far to one side might mean that you aren't actually recharging the battery. Some wireless charging surfaces try to compensate for this by outlining where a device should fit on the surface or by creating raised areas that devices fit inside to make sure the coils are close enough together to work.
While inductive coupling is the most common approach to wireless chargers, it's not the only game in town. Let's look at some alternatives to induction.