NFC tags are a frequent target for experimentation, whether simply by using an app on a mobile phone to interrogate or write to tags, by incorporating them in projects by means of an off-the-shelf module, or by designing a project using them from scratch. Yet they’re not always easy to get right, and can often give disappointing results. This article will attempt to demystify what is probably the most likely avenue for an NFC project to have poor performance, the pickup coil antenna in the reader itself.
A selection of the NFC tags on my desk
The tags contain chips that are energised through the RF field that provides enough power for them to start up, at which point they can communicate with a host computer for whatever their purpose is.
“NFC” stands for “Near Field Communication”, in which data can be exchanged between physically proximate devices without their being physically connected. Both reader and tag achieve this through an antenna, which takes the form of a flat coil and a capacitor that together make a resonant tuned circuit. The reader sends out pulses of RF which is maintained once an answer is received from a card, and thus communication can be established until the card is out of the reader’s range.
Very Few NFC Tags And Readers Are On The Same Frequency
For the majority of tags likely to be experimented by Hackaday readers the RF frequency is 13.56 MHz, and the RF emissions are supposed to be in the magnetic field plane rather than the electric field. There’s nothing complex about the antennas, indeed it’s easy enough to make one yourself by winding a suitable coil and ..
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