Hacker News Reader

Comment by pkaye | Hacker News Reader

> The FCC rules for wireless charging devices like AirPower are quite strict, and limit exposure to 20 cm (8 in) above the device to 50 mW/cm^2.

I'm surprised they waited till the end to do the testing. When I used to work on hardware products at smaller companies, some preliminary tests are done on early designs to make sure we have a comfortable margin. A company like Apple should have dedicated in-house facilities to do this earlier.

View on HN

I'm quite sure they didn't "wait until the end" to do the testing. First, this article is iFixit's speculation. Second, they probably did something similar to what iFixit envisioned: they did test early and knew it didn't pass muster, but thought they could eventually engineer themselves a fix, until they finally just hit a brick wall (aka physics) and found it wasn't an issue they could overcome.

A good engineer hits the "physics limit" brick wall pretty early in the design process...

I would think it more likely that they thought they could change FCC regulation via lobbying efforts in time for release.

Lobbying > engineering.

They probably knew they were close to the legal limit and their engineers probably said on a hunch "we can stay beneath the limit and retain adequate power with the right mix of tricks" and then just ended up being wrong on that hunch by a little bit.

The laws of physics are very unforgiving.

That's why we have to bend them so often in real life with tricks. In media they can just make something up, we've got to find real solutions. I'm sure that one exists but it's either too expensive currently or not consistent enough yet. Yet being the key word there. I'm sure this will be an elegantly solved issue at some point, just might require some more smarts on the hardware side.

For example detecting where the device is and adjusting the current in separate coils accordingly?

I don't buy the explanation that this is about interferences. It doesn't seem like an insurmountable problem to me.

C(32, 3) is 4960. That means almost 5,000 different interference patterns to deal with. Since every manufactured device will vary (since each of its 32 manufactured coils will differ slightly from the next), that's 5,000 calibrations that need to be done on every single manufactured device. And that's best case, assuming (for example) that calibration is a single metric per coil over time.

Reply on news.ycombinator.com