RFID Tags & Readers: How an RFID system works

RFID Tags and Readers:


Radio Frequency Identification or RFID is an Automatic Identification and Data Capture technology that uses electromagnetic fields for the automated identification and tracking of marked objects.

Automatic Identification and Data Capture (AIDC) encompasses systems and technologies that enable the automated identification and acquisition of data from a variety of objects with little or no human input. Alongside RFID, other examples of AIDC include QR codes, barcodes, and biometrics. An AIDC system uses a transducer to capture specific information from objects and convert this information into digitally communicated data. This data is stored for later analysis and comparison by computer which in the case of IoT can be internet-linked.

RFID is distinct in that it is wireless, contactless, read/write and can be used in a range of environments and industries where the use of other forms of AIDC is precluded (moving objects or degraded labeling). RFID is also exceptional because it does not require contact or a ‘line of sight’ for the marked object to be identified, saving time and cost of personnel for this task.

How an RFID system works:

  • Radio Frequency Identification tags or labels are attached to the objects to be identified or tracked. They consist of transponder, receiver and transmitter components usually in the form of an antenna with attached micro processing chip.
  • The electromagnetic fields necessary for activation of RFID tags are generated by RFID reader devices also known as interrogators.
  • Contact with the generated electromagnetic fields of a particular frequency known as an interrogation pulse facilitates the yielding of the digitized data encoded within the tag. This transmitted data, typically numerical, can then be used for inventory purposes.

Two forms of RFID transponder exist.

  1. Active tags are battery powered and can be read at a significant distance from the relevant RFID reader.
  2. Passive tags are activated (‘energized’) and powered by the electromagnetic energy supplied by the interrogating signal. These will require proximity to the RFID reader to function. These RFID tags tend to be cheaper, low maintenance and can remain functional in-situ for many years.

Most common frequency band used in RFID is UHF:

  • Ultra high-frequency (UHF) bands which can range between 300 MHz and 3 GHz. Typically UHF bands lie between 865–868 MHz in the EU and 902–928 MHz in the US. UHF RFID is faster than its LF and HF counterparts and has reading ranges of up to 12 meters. It is, however, susceptible to interference, but this can and has been mitigated by alterations in design.
  • Low-frequency (LF) bands ranging between 30 and 300 kHz (typically between 120 and 150 kHz). This form of RFID operates at close range, around 10 centimeters (3.9 inches) and has slower read speeds than the other frequencies.
  • High frequency (HF) bands are found within the range of 3 and 30 MHz and can offer reading ranges of up to 1 meter (3.2 feet).
  • Microwave frequencies of up to 300 GHz include RFID systems also known as super high-frequency systems. These typically operate at the frequencies of 2.45 GHz and 5.8 GHz, have fast read speeds and can be read at distances up to 300 feet (91 meters).

UHF RFID, in particular, is gaining recognition and prominence as a form of RFID with excellent utility across a range of industries and commercial activities. Both passive and active UHF RFID tags are available. These offer full visibility of supply chains and inventory as, unlike LF and HF RFID, multiple tags can be read simultaneously. The cost of producing these tags has fallen greatly in recent years. Tags have also become smaller and their lifetime of operation has increased. Because of this, UHF RFID tags have become a fast-growing segment of the RFID marketplace, with increasing adoption by sectors as diverse and varied as:

  • Logistics
  • Transportation
  • Hospitality
  • Retail
  • Manufacturing
  • Healthcare
  • Agriculture
  • Food and beverage
  • Government

A single global standard for UHF RFID increases its appeal.

UHF RFID is the only form of RFID that is overseen by a single global standard. The lack of uniformity in RFID standards across frequency has hampered the worldwide uptake of this technology. The UHF Gen2 air interface protocol has been devised by EPC Global and ratified by the International Standards Organization (ISO) to provide a much-desired universal standard for RFID equipment. This has enabled the expansion of the manufacture of these tags and readers globally (particularly in Asia) and has improved their uptake. Most tags are also RoHS compliant, which has further facilitated uptake. The Gen2 standard was first published in 2004 and covers everything necessary to create a functional and compliant UHF RFID system of readers and tags.

The Gen2 protocol specifies key aspects of UHF RFID including:

  • Classification of UHF tags and readers
  • Operating frequencies (the 860 to 960 MHz UHF range)
  • Channel bandwidth
  • Frequency hop rate
  • Bit coding
  • Modulation
  • Anti-collision protocols

What is the data transfer rate for UHF RFID?

Data transfer rates for UHF RFID can be anything from 40 to 640 kbps.

Key Gen2 UHF RFID system components.

  • RFID antennas emit and receive the UHF electromagnetic waves needed for the detection of RFID tags. Passive tags will be activated as they pass the field of an RFID antenna. Antennas may be 2D printed, with metallic ink or wire-based. There are three notable antenna types which can be used singly or in combination detect tags:
    • Circular polarizing antennas or omni-directional antennas can be used where the tag reading angle is variable.
    • Linear polarizing antennas are the ideal choice for reading tags which are always presented with a controlled orientation
    • Near-field antennas cover short distances of a few centimeters.

To overcome environmental electromagnetic energy, an RFID antenna is designed to have a gain that exceeds background noise by is 6 dB. The Q factor is also important for the performance of passive RFID antennas as they need to absorb energy from the reader to be activated. With these antennas, the Q factor needs to be between 30 to 40. This means the radiofrequency energy will need to cycle through an RFID antenna 30 to 40 times before energy is radiated from the transponder.

  • Gen2 RFID readers may be fixed or portable, depending on the application for which they are used. Readers can be selected for their accuracy (reading ratio, reading area, or ability to read high numbers or density of tags.
  • UHF RFID tags and labels are attached to the objects to be identified. The expansion of the market for these tags has meant that there is a broad range available which vary by a number of key characteristics:
    • The size of tags will affect not only the utility and attachment of the tag but also how much antenna it will contain, which will affect its sensitivity and ability to be detected.
    • The reading angle or orientation of the tag will determine the type of reader and antenna needed for successful detection, particularly where linear antennas are used.
    • Internal processing chip or integrated circuit (IC) These vary in the amount of memory from tens to hundreds of bits. Read-only IC chips are often factory written with a 64, 80 or 96-bit numerical code. Read/wrote functioning comes into play beyond 256 bits. Other capabilities can be included such as locking or 'kill' mechanisms and Near Field Communications (NFC).
    • Encasement of the RFID tag will determine the resilience of the RFID tag in a variety of environments. Tags may have to withstand extreme temperatures, moisture ingress, hot oil, high pressure, and other extremes. Materials such as ceramics, plastics, polymers, and glass can be used to create suitable encasements for high-wear environments in a range of industries without compromising tag function.
  • RFID printers enable the encoding necessary to store information on RFID chips, such as bar codes or numerical data. Factory programmed or read/write capable tags may be obtained. The Electronic Product Code (EPC) is the part of the tag that is typically modified.

UHF RFID is also emerging as a complementary technology for the Internet of Things (IoT) and Machine 2 Machine (M2M) communication. RFID is now proving to be of great advantage as an adjunct technology in a wide variety of internet of things and M2M applications. Internet-based communication is already expanding to include objects and machines. 'Things' rather than human-operated devices are expected to massively outstrip the number of servers and computer-based IPv4 addresses within a few years.

Both IoT and M2M communication require the ability to implement rapid, accurate identification of networked objects and components for the proper functioning of their systems, alongside efficient, often wireless, bidirectional data transfer for automated (human-free) regulation. RFID is therefore critical to the deployment of the increasingly complex networked solutions demanded by industry. It offers an as yet unrivaled opportunity for stakeholders to create systems and processes with superior levels of supervision and control.

RFID and IoT

IoT system architecture comprises perception, network, and service layers. RFID is one of a number of technologies that has demonstrable utility in capturing and communicating real-world information from the perception layer for downstream processing and use. When attached to objects, RFID tags can be used to undertake the monitoring, supervising and tracking functions needed for IoT to effectively map a ‘real-world’ environment.

RFID and M2M

With decreasing deployment costs, RFID is also able to increase the complexity of interactions in M2M and Machine 2 Object (M2O) communication as it can be used as a near field communication alternative, to transfer status information on machines for upstream data processing. Both passive and active tags can be used to perform sensory functions in M2M setups, for example, automated reporting of the weight or positioning of a load, or the volume of liquid in a container.

UHF Tag characteristics can be matched to a variety of uses within IoT and M2M communication.

UHF RFID tags are further categorized by EPC Global into 5 classes that equip tags with increasing capabilities. The varied categories enable UHF RFID tags to be more precisely aligned with IoT and M2M setups.

  • Class 0 RFID tags are passive tags with only basic radio frequency capability. These tags are factory programmed only and offer no further functioning.
  • Class 1 RFID tags are basic passive tags which, unlike Class 0, are user-programmable. These tags have no in-built power source and receive energy from exposure to radiofrequency waves from a reader.
  • Class 2 RFID tags are passive tags with added capabilities like encryption and a simple read/write memory.
  • Class 3 RFID tags have greater functionality with an integrated circuit. This type of tag has the processing power for logic-based processes and longer-range communication.
  • Class 4 active RFID tags 4 These more sophisticated active tags have peer to peer communication and additional sensory capabilities.
  • Class 5 RFID tags are battery-powered tags that can activate other tags and have reader capability.

By combining tag classes, ever more complex RFID functionality can be achieved for a wide range of applications as described below.

UHF RFID applications in industry

Commercially available UHF RFID systems are used in a broad range of industries, with new applications being found all the time.

A key advantage of using a UHF RFID system is the scalability that can be achieved with RFID tags, as multiple tags can be read simultaneously. Their use and functioning most often include:

  1. Monitoring systems can be automated to enable continuous steady-state surveillance or supervision of assets, processes, behaviors or environments and early alerts if there is a change or non-compliant functioning.
  2. Tracking capabilities of RFID allow objects to be readily located or followed whilst in transit.

[A] RFID in manufacturing

Information technology is already well integrated into manufacturing processes across sectors such as the automotive, electronics and packaging industries. Data capture is critical for assessing and managing supply chains. The use of RFID for data acquisition equips manufacturers with ‘real-world’ insights, based on actual, rather than assumed data. Rugged hard-wearing UHF RFID tags can follow materials and products into harsh and hostile machining environments where other labeling or methods of observation would be hazardous or degraded rapidly. Tagging facilitates more informed decision making and enhances responsiveness when conditions change. The addition of RFID to manufacturing processes can further support:

  • Scheduling operations
  • Production control
  • Workforce management
  • Maintenance
  • Quality control

RFID can be integrated across the span of a manufactured product’s life cycle from production, through distribution and even to the end of product life and recycling.

The machinery involved in the manufacturing process can also be tagged with tool tracking for increased oversight, control, and efficiency gains in factory operation. Data acquired from strategically located RFID tags can be used with Enterprise Resource Planning Systems (ERPS) or Manufacturing Execution Systems (MES) to create a virtual representation of product flow with IoT networking to upload data to where it can be used to best advantage via online tracking and management.

RFID for logistics and Supply

Combining RFID with IoT/M2M provides the opportunity for industry stakeholders to gain greater control over entire supply chains and stock control. This provides the ability to claw back greater efficiencies and profits as networked RFID tags present the entire supply chain in real-time. UHF RFID solutions provide a number of key advantages including:

  • Supervision of supply chains.
  • Warning of accidents, adverse events, and incidents, so remedial steps can be taken.
  • Data transfer, analysis, and forecasting.
  • Real-time stock control and agility.
  • Facilitation of a more robust response to the market.
  • Increased supply chain transparency and management.

RFID for inventory tracking and warehouse management

Inventory and warehouse management are one of the more mature applications for RFID with demonstrable gains in efficiency and labor savings. The tagging of stock means that items can be readily tracked in both warehouse and retail environments with an overview of stock levels and ready recovery or reordering of depleted items. Security is also improved as oversight of the entire inventory can be achieved with less manpower and greater precision.

The Auto-ID technology of RFID means that individual items and product lines can be uniquely identified by applying a serialized tag. UHF RFID also delivers high read rates that mean the status of large quantities of stock can be monitored quickly and accurately without the need to separate or group them manually. Barcodes only store very limited amounts of data but RFID tags are capable of storing a large amount of information via their programmable IC chips.

Tags also move with the stock if attached to pallets or packaging for monitoring of goods in transit, being loaded or unloaded or put away. Unlike barcodes and QR codes that can be worn down by moving stock or poor storage conditions, RFID tags remain in place and functional for many years at a time. When it comes to order-fulfillment, processes are tightly controlled using a combination of RFID and complimentary internet-based order management software that can track orders from the warehouse straight to a customer’s hands.

RFID applications in transportation

The advantages of RFID in industry, point to the potential for similar utility in the transportation sector. When applied in a targeted manner, RFID provides the ability for operators to manage vehicle fleets and cargo across the world with greatly increased efficiency. The combination of RFID and IoT delivers high visibility with a reduction in the labor costs associated with identifying objects and relaying data. This auto-ID technology has been deployed worldwide in transportation sectors such as:

  • Air cargo
  • Shipping
  • Road haulage
  • Rail freight

UHF RFID technology has also been put to use in transport infrastructure. Consumer-facing toll-roads, where vehicle payment transactions are handled via RFID. Smart Parking Control is another recognizable use of RFID which provides seamless, time-saving, automated access control which is greatly appreciated by users.

Problems and limitations of RFID

Despite widespread uptake, RFID is not without challenges and concerns. Understanding the limitations of RFID systems will guide the judicious use of this technology, but the efficacy of these protocols varies widely in live settings

  • Technical problems. The non-contact communication between RFID tags and readers is vulnerable to electromagnetic interference.
  • Collision problems have the potential to drastically erode the sensitivity and specificity of these systems as multiple tags are read at an identical frequency. Large scale deployments of RFID tagging need to have an anti-collision or singulation protocol in place for the simultaneous identification of numerous tags to take place reliably. Examples of anti-collision protocols are:
    • frame slotted ALOHA protocol (FSA)
    • binary tree protocol (BT)
    • query tree protocol (QT)
  • Security challenges. Tags can be interrogated by any reader that broadcasts the correct signal. They can also be overloaded and jammed by continual radio frequency signaling. An RFID tag may also be cloned or spoofed which could lead to theft of inventory or interference with assets.

Protocols and access control mechanisms need to be developed that overcome this stark vulnerability.

  • Privacy Issues: Tags can remain in place for years after their initial deployment, and unless specifically programmed, remain able to be read by anyone with a tag reader. Tags may be found in consumer or personnel items such as clothing or uniforms and therefore used as a means of locating or tracking individuals and private property.
  • Cost: The last decade has seen a massive expansion in the global production of RFID tags with unit prices falling dramatically. This has been one of the main drivers of uptake of these tags, but improving the security and utility of generic passive tags still comes at a premium. The cost of RFID tags is also not yet equal to the price of printed barcode labels, which further limits their use. Enhancing RFID tags with more powerful antennas, batteries or greater processing capability still adds significantly to the unit cost of RFID tags.
  • Integration with other technologies: Deployment of RFID systems with IoT and M2M infrastructure requires careful design and middleware development to enable RFID to seamlessly communicate with allied technologies.

Posted by George Hardesty on 6th Feb 2021

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