What are RFID Tags and How do They Work?

by ASAP Partner, HID Global

What are RFID Tags?

RFID Tags are small objects that contain a chip and an antenna for wireless identification of the objects they are attached to (or embedded in) with the help of an RFID reader. Unlike barcode technology, RFID tags do not require line of sight from the tag to the reader and support read/write functionality. Most RFID tags are passive, which means they work maintenance-free, without battery power, for many years.
How Does RFID Tag Technology Work?

There are 2 main types of RFID tags: “passive” and “active.”

  • Passive RFID tags are powered by a stationary or mobile RFID reader that emits an electromagnetic field. The tag’s antenna harvests energy from this field to release a signal to the reader. The frequency of the reader must match the frequency of the tag. For passive tags, there are low-, high- and ultra-high frequencies standardized (LF, HF, UHF).
  • Active RFID tags use a battery to broadcast via BLE (Bluetooth Low Energy) or WiFi.
Can an RFID Reader Read Multiple Tags?

Some low frequency (LF) readers are designed to read only one tag at a time, e.g. the ID of a single cow, sheep or other livestock’s ear-tag. High Frequency (HF) and especially Ultra High Frequency (UHF) readers are designed to read multiple RFID tags concurrently, e.g. a stack of tagged books or a pallet of goods moving through a reader gate.
What Do RFID Tags Cost?

The least expensive RFID tags typically cost a few cents and are like sticky labels. Often tags like these are used for retail or logistics applications and are meant for one-time use in non-rugged environments. Depending on the tag’s required RFID chip capabilities, memory size, durability to survive flames, impact, freezing, direct sun, chemicals etc. and the type of tag, cost may go up to a few USD. Active tags with a battery are more expensive than passive tags.
Where Can I Buy RFID Tags?

RFID tags for end users are sold by system integrators of HID Global.
What are the Common Problems with RFID Tags?

Passive RFID tags are maintenance-free and generally robustly built. Problems most typically arise in the form of poor readability from a longer distance. Additionally, environmental factors like metal or water located near the tag can cause difficulty in the tag being read.

  • Metal: Most RFID tags experience reduced performance when used near metal. A tag placed directly on a metal surface will likely not read at all.
    • There are RFID tags that have been specifically designed for use on or near metal. These tags typically have a special housing which provides a gap of controlled thickness between the tag antenna and the metal surface or have a built-in metal foil and are tuned to optimized performance near metal.
  • Proximity: RFID tags placed too closely can interfere with each other. This is especially true for UHF tags. There are minimum spacing guidelines for each type of tag that must be followed to ensure proper functioning.
  • Water and moisture: The majority of tags are physically unaffected by water, however, the read range of some tags diminishes significantly in the presence of moisture. As a rule, the higher the frequency, the more likely the read-range will be impacted by moisture. While LF read range is essentially unaffected by water, UHF read range is strongly reduced while the tag is wet.
  • Fixation: There are multiple ways to affix tags to surfaces, and it is important to choose the right method for the application. It is important to ensure maximum contact between the tag and the surface. This is especially important for adhesive fixation. Maximum contact will help to ensure that the tag remains in place when exposed to mechanical shock and vibration.
What is the RFID Tag Format for Data?

In general, an RFID Tag represents memory that can be written in any data format. Some chips are more capable than others, e.g. by providing a file system or reserved memory areas for certain standardized pieces of data. Many proprietary formats exist on the market, but there are also some standardized formats that allow interoperability between tags, readers and applications from different vendors. Some public data format examples would be:

  • 64-bit UID – LF Tags – typically read-only
  • ISO/IEC 11784/11785 (FDX-B) – LF Tags – Animal ID
  • EN 14803 – LF Tags – Waste Management
  • NDEF – HF NFC Tags – defined by NFC Forum
  • EPC – RAIN UHF Tags – defined by GS1
What are typical RFID Tag Form Factors?

RFID tags can come in various form factors depending on use case, fixation and requirements for robustness. Typical form factors include:

  • Sticky label or dry inlay
  • Glass capsule
  • Disc (coin shape with hole)
  • Rectangular block (often with screw holes or steel ring to weld)
  • ISO card
  • Special form factors e.g. with built-in cable tie, tamper protection, keyfob, etc.
What are the Advantages of RFID Tags?

Advantages of passive RFID tags are typically compared to alternative technologies like barcode or QR-code. The main advantages compared to other technologies are:

  • Line of sight is not required to read the tags; they may be embedded or dirty and still function correctly
  • Supports read/write of data as opposed to read-only
  • Large memory (up to 32KB)
  • Optional cryptographic or password-based security
  • Long reading distance of several m/ft (UHF)
  • Ability to read multiple tags at once, e.g. an entire pallet of goods
What is the Distance/Range of RFID Tags?

RFID reading distance depends on several factors including:

  • Size of the tag’s antenna
  • Tag chip
  • Tags orientation in the reader field
  • Strength of the reader field
  • Environmental factors like metal, water or other material around the tag
  • LF, HF and UHF near-field tags typically have a reading distance of ~1 ft (30 cm).
  • UHF far-field tags typically have a reading distance of several m/ft but are strongly dependent on the environment.
  • NFC Tags (HF) are designed for near-field communication with a smartphone or similar device and typically have a reading distance of ~1 in (2 cm).
RFID Tag Uses

RFID tags are typically used to uniquely identify the item to which they are attached or embedded. The use cases are extremely diverse, supporting anything that is a physical object. The common denominator of all RFID tag use cases are:

  • Improved inventory speed and accuracy
  • No human error
  • Optimized logistics workflow of handling an item
  • Contactless payment
  • Access control
Where are RFID Tags Used and Who Uses Them?

RFID tags are used whenever a physical object needs to be uniquely identified in a quick and reliable way. Applications are very broad and are constantly expanding. Some main areas of RFID tag use today are:

  • Animal identification (pets, livestock, lab animals)
  • Contactless access control systems
  • Contactless payments
  • Electronic passports and citizen ID cards
  • Retail logistics
  • Automation & manufacturing
  • Returnable transport Items
  • Commercial laundry
  • Medical and health equipment
  • Waste management
What are NFC Tags?

NFC (Near Field Communication) tags are passive, high-frequency (HF) RFID tags that contain a NFC Data Exchange Format (NDEF) compliant data structure as defined by the NFC Forum. NDEF data, like a URL or contact, is understood by any NFC compliant reader device, such as a mobile phone, without requiring an extra API.
NFC Tag Uses

  • NFC tags are often used as a convenient replacement of a QR code, and simply host a URL that is opened when the tag is tapped with an NFC phone.
  • NFC tags may also host other information such as contacts, images, actions or phone numbers.
  • Public transport tickets may be NFC tags.
  • Secure NFC tags like the HID Trusted Tag open up new proof-of-presence use cases for guard tours, electronic visit verification, or service records.