How to identify payment card chip model?

[typk]

@Satur9

The three values: capacitance, inductance, and resonant peak are related. If you know two you can determine the third.

Got it, used the chips load capacitance as I saw on a research paper that many card manufacturers are not very close to the resonance frequency.

I used my NanoVNA that has been calibrated and tested the load capacitance on the chip I found the data sheet for. Chip is reading 122pF load capacitance when the apparent datasheet says 62-74pF for the internal tuning capacitor.

Any suggestions for getting accurate measurements? Or checking?

[Satur9]

@typk

Any suggestions for getting accurate measurements? Or checking?

Check out these resources.

Designing NFC "Antennas"

I was talking over antenna design with another forum member and figured it would be good info to share. I would start by understanding what the circuit we’re building actually is, an LC Tank Circuit. There’s a resonant frequency where the coil/chip combination will naturally draw the most power and have the highest coupling efficiency. The farther your “resonant peak” is from 13.56MHz, the less power is being delivered to the chip. [PXL_20210701_210325620~2] Once you have an idea of what you…

Testing NFC antennas with a NanoVNA

If you’re willing to destroy the card you can sometimes measure the chip’s input capacitance directly with a meter after detaching the coil. Make sure you measure the resonant peak of the whole assembly with a VNA first though, or attach a known inductance afterwards and measure the resonant peak with that.

Otherwise go with the datasheet capacitance and your measured resonant peak and use a calculator like the one in the thread I linked to figure out the appropriate inductance.