Editing Radio-frequency identification (section)

===Tags===
RFID tags are made out of three pieces: 
* a micro chip (an [[integrated circuit]] which stores and processes information and [[modulation|modulates]] and [[demodulation|demodulates]] [[radio-frequency]] (RF) signals)
* an [[antenna (radio)|antenna]] for receiving and transmitting the signal 
* a substrate<ref name="constr">{{Cite web|url=https://rfid4u.com/rfid-basics-resources/dig-deep-rfid-tags-construction/|title=Construction of RFID Tags - RFID chip and antenna|date=n.d.|website=RFID4U|language=en-US|access-date=2020-03-01}}</ref>

The tag information is stored in a non-volatile memory.<ref name="constr"/> The RFID tags includes either fixed or programmable logic for processing the transmission and sensor data, respectively.{{citation needed|date=April 2021}}

RFID tags can be either passive, active or battery-assisted passive. An active tag has an on-board battery and periodically transmits its ID signal.<ref name="constr"/> A battery-assisted passive tag has a small battery on board and is activated when in the presence of an RFID reader. A passive tag is cheaper and smaller because it has no battery; instead, the tag uses the radio energy transmitted by the reader. However, to operate a passive tag, it must be illuminated with a power level roughly a thousand times stronger than an active tag for signal transmission.<ref>{{Cite journal|last1=Bays|first1=Barbara|last2=McGowan|first2=Mike|date=2016|title=Use of RFID for Tracking Government Property - Proof of Concept/Pilot|journal=Sandia National Laboratories|publisher=Sandia Corporation|page=24}}</ref>

Tags may either be read-only, having a factory-assigned serial number that is used as a key into a database, or may be read/write, where object-specific data can be written into the tag by the system user. Field programmable tags may be write-once, read-multiple; "blank" tags may be written with an electronic product code by the user.<ref>{{Cite journal|last=Want|first=Roy|date=January–March 2006|title= An Introduction to RFID Technology |journal= IEEE Pervasive Computing|volume= 5|pages=25–33|doi=10.1109/MPRV.2006.2|s2cid=130729}}</ref>

The RFID tag receives the message and then responds with its identification and other information. This may be only a unique tag serial number, or may be product-related information such as a stock number, lot or batch number, production date, or other specific information. Since tags have individual serial numbers, the RFID system design can discriminate among several tags that might be within the range of the RFID reader and read them simultaneously.