# Using RFID antenna to read NFC tag

I have a simple question, I want for a school project read NFC tags from a large range, can I use a RFID antenna to read the NFC tag ? I want to know if the RFID antenna is going to work and read the NFC tag.

The scope will be under 50cm to 1m, it's enough (if I could get more scope, tell me).

If the RFID antenna isn't possible, could you tell me if it's possible to build a reliable NFC antenna to read NFC tags with a scope of 50cm to 1m without to need a big antenna on a truck :D, I want a small thing, that I can by example put in a bag.

You will not be able to read NFC tags with such a distance. The read distance is limited by design, and you can't easily change that.

Now there are ways to extend the useful range to about half a meter, but that's really tricky to do and part of active security research. I doubt that you want to pull that off for a school project. You need a lab and several years of experience to pull this off.

I suggest you look for other RFID tags with medium range read characteristics such as ISO15683. Their read distance is longer, but you need a huge reader-device for that.

I cannot stress this enough: Nils is right, NFC is not really a technology where the term "radio wave propagation" applies; RFID in general isn't.

The point is that in real antennas, you generate a wave front that propagates through space, until it hits the receiver. For NFC, that is not the case.

Here, you essentially build a transformer with the primary coil being the reader and the secondary coil being the NFC tag. Through the amount of power the tag takes out of the magnetic field, data is exchanged. This is fundamentally different from antennas, and power goes down with $d^3$, instead of $d^2$ as with wave propagation (and antennas of a finite effective area), $d$ being the distance between transmitter and receiver.

So, no, without a big, powerful system you cannot extend the range of NFC, as dictated by physics.

Now, you say "carry in a bag": This can work, because the NFC coil in e.g. a smart phone is really small, and a bag can get pretty large. The question really is how far this will work. Assuming your original NFC range was 4cm, and you want to get e.g. to 40cm = 4cm * 10, your transmitter would need to be $10^3$ times as powerful and sensitive to allow for the necessary energy to inductively "couple over" from reader coil to tag coil.

Still, communication probably wouldn't work – the further you get from the coil, the less "reaction" you can measure when someone extracts energy from your field (hence the increase in necessary sensitivity). If you can build a device with $10^3 \cdot 10^3$ the dynamic range of commercial NFC readers, you'd definitely reached a level that would exceed "school project" ambitions and count as "serious commercial or academic research done by people with years of experience". Also, at some point, the energy that doesn't couple into the tag, but is lost due to being radiated as wave (involuntarily) or coupled into other conductive materials will be considered harmful interference.

• Nice long explanation why it doesn't work. Btw, those range extension techniques indeed work by increasing the output power by a huge factor and building an amplifier to pick up the weak "reaction" from the tag and make it larger. They're called load modulation amplifiers and are incredible hard to build because they are so close to be an oscillator. Jul 6, 2016 at 11:24