Inductive and Magnetic Resonance

Wireless inductive power transfer can enhance user convenience and safety in the charging of electric vehicle batteries. This method can be used for transmitting high power through an air gap of 0.01–0.2 m at the efficiency of up to 90%, a quality factor (Q factor) of approximately 5–100, a coupling factor of approximately 0.2–0.5, and a fundamental operating frequency of hundreds of hertz to several hundred kilohertz. A longer wireless power transmission distance can be achieved by using resonant tanks with magnetic coupling in which the source and load are not in contact than can be achieved through wireless inductive power transfer. With the aforementioned tanks, efficient wireless power transmission can be achieved with a Q factor of approximately 100–10 000, a coupling factor of less than 0.2, and an operating frequency range of 0.2 to 20 MHz. The aforementioned two methods are based on the principle of electromagnetic induction. Implementation of these methods requires the use of advanced semiconductors, high-frequency switching components with low power loss, a tuned compensation network that can tolerate lateral misalignment between coils, and a power pad design that enables high magnetic flux to be generated for transmission over a relatively long distance.