They use a grid of coils. By activating multiple adjacent coils, it behaves like one big coil. From a physics perspective it's really neat: the magnetic fields

They use a grid of coils. By activating multiple adjacent coils, it behaves like one big coil. From a physics perspective it's really neat: the magnetic fields of opposing currents in adjacent wires should cancel. But the price you pay is that you have the charging current flowing through more length of wire, and more resistive losses (heat).