NFC tags/ reader system for position sensing

[LKUMA.1]

Hello ST team and Guys here.

We have a new project that requires us to measure the a position of a moving object with a range of 100 mm with an accuracy of +- 1 mm. I was wondering if by attaching a NFC tag to the object and a reader with a similar 100 mm read range, could we sample based on the time of flight or time stamps of tag read or tag count to achieve a +-1 mm of position accuracy. Can the algorithm based in NFC readers convert the tag time stamp or count to be used as position sensing with such high resolution.

 Thanks and best

LK

[Ulysses HERNIOSUS · Accepted solution]

Hi,

I cannot imagine such to work:

1. Tags are not designed to answer at an absolutely accurate timing. Even NFC-A which use a bit-grid for the tag responses allows a window of at least 0.4us (ISO14443-3 6.2.1.1)
2. A full period of 13.56 MHz is ~74ns
3. 1mm accuracy means timings in the 3.3ps range!
4. NFC readers are typically not built to measure response timings and for sure not at the required accuracy

What you could do is to look at the RSSI value in the reader but that will be very rough and can only work if you can limit your system to one reader with exactly one tag.

It sounds a little bit like CoVid-19 tracing apps which are trying to use the Bluetooth for ranging. Also Bluetooth despite its 2.4GHz is here very in-accurate as it was not built for ranging and they rely on RSSI (Received Signal Strength Indicator) instead of time of flight.

Even protocols built for ranging like UWB (https://www.st.com/en/ecosystems/spark-sr1010-sr1020-ultra-wideband-radio-modules.html) are orders of magnitude away from a 1mm accuracy.

Regards, Ulysses