I describe an old project in which a few friends and I designed an RFID tag that fits into a magnetic stir bar and measures temperature wirelessly. We decided to opensource the project, and you can see the PCB design and tag firmware at the github repo below. I don't think I have the firmware for the base station, unfortunately.

https://www.ti.com/product/TMS37157
https://www.digikey.com/en/products/d...

https://github.com/benkrasnow/Tempera...

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