They use multiple coils: "we can confirm is comprised of between 21 and 24 power coils".

Presumably they detect where the device is and engage an appropriate coil. Quick search on amazon found a few charging pads with multiple coils.

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).

Phased array inductive charging. Fascinating!

21-24 is a weird range

As someone who knows basically nothing about designing electronic devices, my initial thought is 3 rows of 7 coils or 3 rows of 8 coils? This wouldn't make it a range, though, so much as an either/or situation.

Would probably make more sense to choose some hexagonal pattern.

Oh, good point!

It's a weird design.

But there already exists something like that https://www.amazon.com/Wireless-Charger-JE-Charging-QI-Enabl...

That is just three wireless chargers stacked next to each other. Apple's design was to have no required orientation or position, just drop it wherever on the mat, along with whatever other devices.

Still, it is "multi-device charging mat" and if Apple could provide something like that their customers would be more than happy - I guess.

Could you expand on this?

It's easy -- just use variable position wireless power transmitted through multiple cooperative flux generators!

I'd submitted https://news.ycombinator.com/item?id=17980168 a few days ago, links to a landing page for a white paper and presentation.

Direct link: https://www.wirelesspowerconsortium.com/technology/multiple-...