In an RFID device, how does the reader send data to interrogate the tag and how does the tag respond with the data stored in it ?
closed as too broad by uint128_t, PeterJ, Autistic, DoxyLover, Daniel Grillo May 8 '16 at 18:35
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You need to research about how RFID works.
Photo 1. Inside of an RFID card showing the loop antenna and chip.
The RFID reader emits a radio wave. The wire loop antenna in in the card picks up enough power (when close to the transmitter) to power the chip. which is also visible in your photo.
The chip modifies the radio signal in a way that the transmitter can sense and encodes the ID back to the reader as a modulated binary data stream. The reader demodulates the signal to extract the data which is then handled like any other digital data.