This blog post suggests that apple dropped their promised AirPower wireless charging mat because it didn't pass EMI standards, specifically due to the (unconfirmed) idea that they were using a large number of coils to make the product simpler for consumers to charge multiple devices without having to carefully position them over individual coils.
One quote stood out to me:
We asked an engineer with experience building wireless charging systems what obstacles Apple was working to overcome. “Over time, these harmonics add up and they become really powerful signals in the air,” explains William Lumpkins, VP of Engineering at O & S Services. “And that can be difficult—that can stop someone’s pacemaker if it’s too high of a level. Or it could short circuit someone’s hearing aid.” If Apple’s multi-coil layout was spinning off harmonics left and right, it’s possible AirPower couldn’t pass muster with US or EU regulations.
Specifically the bolded part surprised me, and I'm not sure if it's just because he's simplifying for a lay audience. I would have thought that the resultant field due to harmonics at any reasonable distance would be established near-instantly since it's just EM waves travelling in free space around the speed of light.
Is there something I'm missing that causes this to be different in the case of wireless charging devices?
Secondly, is this just a power conditioning issue, or do the coils themselves generate the harmonics? That is, if you had a perfect sine generator at the resonant coil frequency, would it also generate harmonics in the emitted EM?