The kQ Product as Viewed by an Analog Circuit Engineer

People in the 20th century believed that magnetic induction is due to the coupling coefficient kbetween two coils. Dense flux was supposed to reach only in close proximity. This common-sense interpretation was drastically altered by Kurs et. al. in 2007. They demonstrated a strong power transfer in spite of low k, i.e. at a distance, by enhancing the coil's Q factor. The key index to this success was not k alone but k times Q in their experiment [1].