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I'm discovering RFID applications and I would like to be able to read an RFID card I strapped to the back of my phone (the most convenient location for me) by just putting the phone face down on the reader.

At the moment the reader (MFRC522) reads the card at 10cm distance without anything in between, but can't read the card this way even when the phone is placed on top of the reader.

I don't know if that's because it's attenuating the signal too much (in which case perhaps I could boost the reader's signal, somehow) or even completely (Faraday? Is that you?), or if the phone's NFC chip interferes with the card (I've got a Pixel 4, which should have one) - and I don't know how to find out which it is.

Note: I'd like to avoid reading the NFC chip inside the phone itself because I read it's got a much smaller range, and I don't even know how to read it from this reader.

Any ideas?

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  • \$\begingroup\$ yes, hold the phone face up \$\endgroup\$
    – jsotola
    Mar 23, 2022 at 1:24

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Use this phone instead...

Otherwise, the metal of your phone is going to block the chip from being read. The card is powered by coupling to the reader, so it won't be "boosted" like a far-field signal.

You can use NFC chips that are meant to be placed on metal surfaces; but this wont let you read the chip from the opposite side of a phone with a metal body. The chip is outside the phone so it's not acting as a Faraday cage. The oversimplified answer is that the phone is reflecting the signal.

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  • \$\begingroup\$ In that case, how come we can read tags from the back or the front of phones, when reading them from the phone itself? \$\endgroup\$
    – user42875
    Mar 22, 2022 at 16:58
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    \$\begingroup\$ Because the NFC reader is inside the phone, and tuned to use the phone body as part of the antenna. It is also usually to one side (near the top) where there is a gap in the metal of the phone and away from the battery. \$\endgroup\$
    – Alphy13
    Mar 22, 2022 at 17:01

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