General Discussions, page-28649

You essentially require a coil of wire at both ends. In the transmitting end (maybe underground) a current flowing through the coil produces an electromagnetic field which is normally amplified by means of an iron former (flux). The receiving coil in the car links with the field and a current flows through the coil. AC is required for induction to take place. The two coils are a kind of transformer, the number of turns in the coil determining the voltage that will be produced. The current flowing in the receiver coil can be converted to DC and used to charge the battery, all with a very good, as you say in excess of 90% efficiency. Lots of applications. There are drawbacks, one being the effects of electromagnetic radiation and cancer links. The good news is that EM radiation will travel long distances if the frequency is high. Most induction coils operate at frequencies of a few hundred to a few thousand hertz (low frequencies). This means that the radiation is confined to a short distance from the coil. Depends if you believe in this kind of stuff on your health. A mobile phone for instance operates at very high frequencies, so radiation travels further, but the power is confined to a few Milli-watts. In the case of cars, the radiation travels short distances (a few feet) but the power is in Kilowatts!