Why can't wireless charging be used through front glass?

https://news.ycombinator.com/item?id=17639739

by chintan_io • 8 years ago

1 1 8 years ago

news.ycombinator.com

magicpat2010• 8 years ago

Wireless charging can't be used through the front glass of a phone because it needs to have a receiving (Rx) coil and not cause electrical interference with the parts between the receiving and transmitting coils by the magnetic flux produced by wireless charging.

If you look at the bottom of page 4 of this PDF document (numbered page 11 if it were printed), https://www.mouser.com/pdfDocs/TI-Designing-a-Qi-compliant-r..., you can see a picture (Figure 8) that shows the construction of wireless charging coils for phones. The Rx portion would be inside the phone. Notice that there is a part titled "Rx Shield". The Rx Shield is to protect components of the phone above it.

Figure 5 (on page 2 of the document) has a picture that shows the magnetic flux density graphed. The fields produced are in the low mT range, so parts need to be able to handle it without heating or interference and boards will need to have appropriate filtering, if you wanted to charge through the front glass.

Why can't wireless charging be used through front glass?

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