How Do UHF RFID Readers Interrogate Cards Individually?

By RFID Journal

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Ask The ExpertsHow Do UHF RFID Readers Interrogate Cards Individually?
RFID Journal Staff asked 4 years ago

Please explain how this is accomplished. Can a reader determine every tag’s exact position?

—Sajan (India)

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Sajan,

Each passive ultrahigh-frequency (UHF) RFID transponder contains a unique serial number. When one transponder enters a read field, the reader interrogates the tag and captures its serial number. Conventional UHF readers cannot tell precisely where a transponder is located within the read field, only that a transponder is present. If multiple transponders are present in the field, the reader undergoes an algorithm to communicate with each transponder separately, capturing each transponder’s unique ID. Again, the reader usually doesn’t know each tag’s position.

If you have 100 students, you would enter their names into a database and associate a serial number in a transponder with each student. So, when student #1 walked in, his or her tag would be read and software would indicate that he or she was present. When student #2 walked in, his or her transponder would then be interrogated and software would indicate that he or she was present. And so forth.

—Mark Roberti, Founder and Editor, RFID Journal

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