https://www.kickstarter.com/projects/142464853/hendo-hoverboards-worlds-first-real-hoverboard I see that it says it's based on Lenz's law, which says that the induced currents will generate a field that opposes the change in the field. So, I figure they have some kind of oscillating magnetic field coils on the bottom of the board, which generates an oscillating field which generates eddy currents in the non-ferromagnetic floor, which generates an opposing field that lifts the board. But, I don't see how the floor's field can always oppose the field from the board. If the board's coils are oscillating, wouldn't the fields attract each other 50% of the time? What's going on here? Is there some kind of trick so the changing field can always have the same sign?