sentences:  Most mains-frequency induction coils are designed for single phase operation, and are low-current devices intended for localised heating, or low-temperature surface area heating, such as in a drum heater.The basic principle involved in induction heating was discovered by Michael Faraday as early as 1831.Faraday's work involved the use of a switched DC supply provided by a battery and two windings of copper wire wrapped around an iron core.