Editing Radio-frequency identification (section)

==Design==
A radio-frequency identification system uses ''tags'', or ''labels'' attached to the objects to be identified. Two-way radio transmitter-receivers called ''interrogators'' or ''readers'' send a signal to the tag and read its response.<ref>{{cite web|title=RFID-Tag|date=July 2018|url=https://www.behance.net/gallery/67918923/RFID-Tag|publisher=Behance|access-date=15 July 2018}}</ref>

===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.

===Readers===
RFID systems can be classified by the type of tag and reader. There are 3 types:<ref>{{cite web|url=https://www.makeuseof.com/tag/technology-explained-how-do-rfid-tags-work/|title=How Does RFID Technology Work?|website=MakeUseOf|date=June 2017|language=en-US|access-date=2019-04-22}}</ref>

* A '''Passive Reader Active Tag''' ('''PRAT''') system has a passive reader which only receives radio signals from active tags (battery operated, transmit only). The reception range of a PRAT system reader can be adjusted from {{convert|1|-|2000|ft|-2}}, allowing flexibility in applications such as asset protection and supervision.
* An '''Active Reader Passive Tag''' ('''ARPT''') system has an active reader, which transmits interrogator signals and also receives authentication replies from passive tags.
* An '''Active Reader Active Tag''' ('''ARAT''') system uses active tags activated with an interrogator signal from the active reader. A variation of this system could also use a Battery-Assisted Passive (BAP) tag which acts like a passive tag but has a small battery to power the tag's return reporting signal.

Fixed readers are set up to create a specific interrogation zone which can be tightly controlled. This allows a highly defined reading area for when tags go in and out of the interrogation zone. Mobile readers may be handheld or mounted on carts or vehicles.

===Frequencies===
{| class="wikitable"
|+ RFID frequency bands<ref name=Sen09>{{Citation|first1=Dipankar|last1=Sen|first2=Prosenjit|last2=Sen|first3=Anand M.|last3=Das|title=RFID For Energy and Utility Industries|publisher=PennWell|year=2009|isbn=978-1-59370-105-5}}, pp.&nbsp;1-48</ref><ref name=Weis>{{Citation|first=Stephen A.|last=Weis|title=RFID (Radio Frequency Identification): Principles and Applications|publisher=MIT CSAIL|year=2007<!-- Year from PDF document properties; 2006 from access dates in article -->|citeseerx=10.1.1.182.5224}}</ref>
|-
! Band
! Regulations
! Range
! Data speed
! [[ISO/IEC 18000]]<br/>section
! Remarks
! Approximate tag<br/>cost in volume<br/>(2006) 
|-
| LF: 120–150&nbsp;kHz
| Unregulated
| {{convert|10|cm|0|abbr=on}}
| Low
| [http://www.iso.org/iso/home/store/catalogue_ics/catalogue_detail_ics.htm?csnumber=46146 Part 2]
| Animal identification, factory data collection
| US$1
|-
| HF: 13.56&nbsp;MHz
| [[ISM band]] worldwide
| {{convert|0.1|-|1|m|sigfig=1|abbr=on}}
| Low to moderate
| [[ISO/IEC 18000-3|Part 3]]
| Smart cards ([[ISO/IEC 15693]], [[ISO/IEC 14443]] A, B),<br/>ISO-non-compliant memory cards ([[Mifare]] Classic, iCLASS, Legic, [[FeliCa]] ...),<br/>ISO-compatible microprocessor cards (Desfire EV1, Seos)
| US$0.05 to US$5
|-
| UHF: 433&nbsp;MHz 
| Short range devices
| {{convert|1–100|m|ft|sigfig=1|abbr=on}}
| Moderate
| [https://www.iso.org/standard/57336.html Part 7]
| Defense applications, Underground Miner Tracking with active tags
| US$5
|-
| UHF: 865–868&nbsp;MHz (Europe)<br/>902–928&nbsp;MHz (North America)
| ISM band
| {{convert|1–12|m|ft|sigfig=1|abbr=on}}
| Moderate to high
| [https://www.iso.org/standard/59644.html Part 6]
| EAN, various standards; used by railroads<ref>{{cite web|url=http://www.railway-technology.com/features/feature1684/|title=RFID and Rail: Advanced Tracking Technology – Railway Technology|date=16 March 2008|access-date=14 March 2018}}</ref>
| US$0.04 to US$1.00<br/>(passive tags)
|-
| [[microwave]]: 2450–5800&nbsp;MHz
| ISM band
| {{convert|1–2|m|ft|sigfig=1|abbr=on}}
| High
| [http://www.iso.org/iso/home/store/catalogue_ics/catalogue_detail_ics.htm?csnumber=62539 Part 4]
| 802.11 WLAN, Bluetooth standards
| US$25 (active tags)
|-
| microwave: 3.1–10&nbsp;GHz
| Ultra wide band
| up to {{convert|200|m|ft|sigfig=1|abbr=on}}
| High
| Not&nbsp;defined
| Requires semi-active or active tags
| US$5 projected
|-
| mm-wave: 24.125&nbsp;GHz <ref name="Kaleja">{{cite book|year=1999|volume=4|pages=1497–1500 |doi=10.1109/MWSYM.1999.780237|isbn=0-7803-5135-5|s2cid=22463766|chapter=Imaging RFID system at 24 GHZ for object localization|title=1999 IEEE MTT-S International Microwave Symposium Digest (Cat. No.99CH36282)|last1=Kaleja|first1=M.M.|last2=Herb|first2=A.J.|last3=Rasshofer|first3=R.H.|last4=Friedsam|first4=G.|last5=Biebl|first5=E.M.}}</ref><ref name="Hester">{{cite book|year=2017|pages=1557–1560 |doi=10.1109/MWSYM.2017.8058927|isbn=978-1-5090-6360-4|s2cid=20439390 |chapter=A Mm-wave ultra-long-range energy-autonomous printed RFID-enabled van-atta wireless sensor: At the crossroads of 5G and IoT |title=2017 IEEE MTT-S International Microwave Symposium (IMS) |last1=Hester |first1=Jimmy G.D. |last2=Tentzeris |first2=Manos M. }}</ref><ref name="Soltanaghaei">{{cite book|year=2021|pages=69–82 |doi=10.1145/3447993.3448627|isbn=978-1-4503-8342-4|s2cid=231833014|doi-access=free |chapter=Millimetro: MmWave retro-reflective tags for accurate, long range localization |title=Proceedings of the 27th Annual International Conference on Mobile Computing and Networking |last1=Soltanaghaei |first1=Elahe |last2=Prabhakara |first2=Akarsh |last3=Balanuta |first3=Artur |last4=Anderson |first4=Matthew |last5=Rabaey |first5=Jan M. |last6=Kumar |first6=Swarun |last7=Rowe |first7=Anthony }}</ref> 
| [[ISM band]] worldwide
| {{convert|10-200|m|ft|sigfig=1|abbr=on}}
| High
| Not defined
| Requires semi-passive tags. Uses retrodirective backscatter approaches to achieve extended ranges
| US$10 projected
|}

===Signaling===
[[File:A3tag.jpg|thumb|RFID hard tag]]
Signaling between the reader and the tag is done in several different incompatible ways, depending on the frequency band used by the tag. Tags operating on LF and HF bands are, in terms of radio wavelength, very close to the reader antenna because they are only a small percentage of a wavelength away. In this [[Near and far field|near field]] region, the tag is closely coupled electrically with the transmitter in the reader. The tag can modulate the field produced by the reader by changing the electrical loading the tag represents. By switching between lower and higher relative loads, the tag produces a change that the reader can detect. At UHF and higher frequencies, the tag is more than one radio wavelength away from the reader, requiring a different approach. The tag can [[backscatter]] a signal. Active tags may contain functionally separated transmitters and receivers, and the tag need not respond on a frequency related to the reader's interrogation signal.<ref name="Dobkin08">Daniel M. Dobkin, ''The RF in RFID: Passive UHF RFID In Practice'', Newnes 2008 {{ISBN|978-0-7506-8209-1}}, chapter 8</ref>

An [[Electronic Product Code]] (EPC) is one common type of data stored in a tag. When written into the tag by an RFID printer, the tag contains a 96-bit string of data. The first eight bits are a header which identifies the version of the protocol. The next 28 bits identify the organization that manages the data for this tag; the organization number is assigned by the EPCGlobal consortium. The next 24 bits are an object class, identifying the kind of product. The last 36 bits are a unique serial number for a particular tag. These last two fields are set by the organization that issued the tag. Rather like a [[Uniform resource locator|URL]], the total electronic product code number can be used as a key into a global database to uniquely identify a particular product.<ref>John R. Vacca ''Computer and information security handbook'', Morgan Kaufmann, 2009 {{ISBN|0-12-374354-0}}, page 208</ref>

Often more than one tag will respond to a tag reader. For example, many individual products with tags may be shipped in a common box or on a common pallet. Collision detection is important to allow reading of data. Two different types of protocols are used to [[Singulation|"singulate"]] a particular tag, allowing its data to be read in the midst of many similar tags. In a [[ALOHAnet|slotted Aloha]] system, the reader broadcasts an initialization command and a parameter that the tags individually use to pseudo-randomly delay their responses. When using an "adaptive binary tree" protocol, the reader sends an initialization symbol and then transmits one bit of ID data at a time; only tags with matching bits respond, and eventually only one tag matches the complete ID string.<ref>Bill Glover, Himanshu Bhatt,''RFID essentials'', O'Reilly Media, Inc., 2006 {{ISBN|0-596-00944-5}}, pages 88–89</ref>
[[File:RFID search environment.png|thumb|right|An example of a binary tree method of identifying an RFID tag]]
Both methods have drawbacks when used with many tags or with multiple overlapping readers.{{Citation needed|reason=See talk page|date=July 2021}}

===Bulk reading===
"Bulk reading" is a strategy for interrogating multiple tags at the same time, but lacks sufficient precision for inventory control. A group of objects, all of them RFID tagged, are read completely from one single reader position at one time. However, as tags respond strictly sequentially, the time needed for bulk reading grows linearly with the number of labels to be read. This means it takes at least twice as long to read twice as many labels. Due to collision effects, the time required is greater.<ref>{{cite web|url=https://www.rfidjournal.com/site/faqs|archive-url=https://web.archive.org/web/20130328095357/http://www.rfidjournal.com/site/faqs|archive-date=March 28, 2013|title=Frequently Asked Questions|website=www.rfidjournal.com|access-date=2019-04-22}}</ref>

A group of tags has to be illuminated by the interrogating signal just like a single tag. This is not a challenge concerning energy, but with respect to visibility; if any of the tags are shielded by other tags, they might not be sufficiently illuminated to return a sufficient response. The response conditions for inductively coupled [[High frequency|HF]] RFID tags and coil antennas in magnetic fields appear better than for UHF or SHF dipole fields, but then distance limits apply and may prevent success.{{Citation needed|reason=See talk page|date=July 2021}}<ref>{{Cite book|last=Paret|first=Dominique|title=RFID at ultra and super high frequencies: theory and application}}</ref>

Under operational conditions, bulk reading is not reliable. Bulk reading can be a rough guide for logistics decisions, but due to a high proportion of reading failures, it is not (yet){{When|date=January 2021}} suitable for inventory management. However, when a single RFID tag might be seen as not guaranteeing a proper read, multiple RFID tags, where at least one will respond, may be a safer approach for detecting a known grouping of objects. In this respect, bulk reading is a [[Fuzzy mathematics|fuzzy]] method for process support. From the perspective of cost and effect, bulk reading is not reported as an economical approach to secure process control in logistics.<ref>{{cite web|url=http://www.nerc.com/files/SGTF_Report_Final_posted_v1.1.pdf|title=STGF Report}}</ref>

===Miniaturization===
RFID tags are easy to conceal or incorporate in other items. For example, in 2009 researchers at [[Bristol University]] successfully glued RFID micro-transponders to live [[ant]]s in order to study their behavior.<ref>{{cite news|url=http://news.bbc.co.uk/1/hi/england/bristol/8011998.stm|title=Ants' home search habit uncovered|work=BBC News|date=2009-04-22|access-date=2013-09-03}}</ref> This trend towards increasingly miniaturized RFIDs is likely to continue as technology advances.

Hitachi holds the record for the smallest RFID chip, at 0.05&nbsp;mm × 0.05&nbsp;mm. This is 1/64th the size of the previous record holder, the mu-chip.<ref>{{cite web|url=https://www.engadget.com/2007/02/14/hitachis-rfid-powder-freaks-us-the-heck-out|title=Hitachi's RFID powder freaks us the heck out|date=15 February 2007 |publisher=Engadget|access-date=2010-04-24}}</ref> Manufacture is enabled by using the [[silicon-on-insulator]] (SOI) process. These dust-sized chips can store 38-digit numbers using 128-bit [[Read Only Memory]] (ROM).<ref>{{cite web|author=TFOT|year=2007|title=Hitachi Develops World's Smallest RFID Chip|url=http://thefutureofthings.com/news/1032/hitachi-develops-worlds-smallest-rfid-chip.html|access-date=2009-03-27|archive-url=https://web.archive.org/web/20090416235559/http://thefutureofthings.com/news/1032/hitachi-develops-worlds-smallest-rfid-chip.html|archive-date=2009-04-16}}</ref> A major challenge is the attachment of antennas, thus limiting read range to only millimeters.

====TFID (Terahertz Frequency Identification)====
In early 2020, MIT researchers demonstrated a [[terahertz (unit)|terahertz]] frequency identification (TFID) tag that is barely 1 square millimeter in size. The devices are essentially a piece of silicon that are inexpensive, small, and function like larger RFID tags. Because of the small size, manufacturers could tag any product and track logistics information for minimal cost.<ref>{{cite news|last=Zewe|first=Adam|url=https://news.mit.edu/2021/ruonan-han-circuits-1118|title=Pushing the limits of electronic circuits|work=MIT News|date=2021-11-18|access-date=2021-11-18}}</ref><ref>{{cite news|last=Matheson|first=Rob|url=https://news.mit.edu/2020/cryptographic-tag-supply-chain-0220|title=Cryptographic "tag of everything" could protect the supply chain|work=MIT News|date=2020-02-20|access-date=2021-11-18}}</ref>