I'm afraid my Google-fu is failing me. Try as I might, I can only find very basic descriptions online of how RFID tags (specifically passive ones) work. I'd like to actually know what the microcontroller in the tag does, and how it creates a signal the reader can pick up and decode. For example, many articles I've found say that the integrated circuit sends a signal by modulating the impedance of the tag antenna, but I'm interested in how it does so. I'm a physics student, not an electrical engineer, so I would ideally like to see an explanation that is quite detailed, but hopefully keeps the jargon to a minimum. If someone could point me in the right direction, I'd really appreciate it!