Inductive charging mats already exist for small items, such as mobile phones, laptops, even electric kettles. An electric bus line in Milton Keynes, UK, uses much larger inductive charging mats buried in the road to recharge the bus’ rechargeable batteries while the driver is on his break.
Automakers offering electric vehicles and plug-in hybrid electric vehicles have also been testing inductive charging systems as an alternative to the plug. Two different types of coils exist, angular and round, incompatible with each other, and having their own strengths and weaknesses.
Round Inductive Coils are, as the name suggests, circular in shape, the power transmission wire coiled around a doughnut-shaped ferrite core. The receiving coil is wired the same way, and must be located centrally over the transmission coil in order for efficient power transfer. Round inductive coils can be made more powerful with minimal escape of electromagnetic radiation.
Angular Inductive Coils are built in a square shape, the transmission and receiving coils wound around a square-shaped ferrite core. Instead of power transmission through the center of the coil as in the round shape, power is transmitted on the edges of the square. This configuration is not as powerful, but allows the receiving coil to be slightly offset from the transmission coil without affecting efficiency. This design also emits more electromagnetic radiation to the sides, which could become a problem with FCC’s radio laws.
It seems that about half the automakers are going round, and the other half is going angular. Toyota Motor Manufacturing Company is favoring the angular inductive coil, and is currently striving to adjust the design to limit leaking electromagnetic radiation to the sides. The angular coil would make it easier to park an electric vehicle for inductive charging without having to be so precise.