Types of RFID readers   Handheld RFID readers Selecting kinds of RFID readers

Images credits: Motorola; Barcoding Inc.; CNet

 

RFID readers are devices that perceive, interrogate, and amend RFID tags which have assigned a unique electronic identity to a physical article. These two devices exchange information by the use of short-range RF signals.

 

RFID Reader Operation

RFID tags are used to designate various assets with an electronic identity which can be encoded and read by RFID readers. The RFID reader propagates a particular radio frequency and once a compatible RFID tag enters the reader's detection range, the tag transmits a return signal. This return signal has been modulated to include the tag's protocol, managing organization, asset description, and serial number. Such information is commonly stored as a 96-bit string of data called an electronic product code and the reader determines EPC accuracy by the use of an error correcting code algorithm. At this point the reader relays the tag identification to the system user, server, or database, which updates the data of the RFID tag as needed.

Selecting RFID infrastructure

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The way in which the reader perceives the RFID tag depends on whether the tag is active or passive. Active tags periodically transmit the tag's RF signal which is then registered by the reader. Active tags require a charge in the circuit and antenna, and have a larger range because of an integrated battery. In the instance of semi-active (the circuit is charged, but not the antenna) or passive (there is no battery and no charge) RFID tags, the tags wait for the initial RF from the reader before broadcasting the return signal. Since passive tags have no battery to charge the circuit, the initial magnetic field radiated by the reader must be threefold the field needed to maintain communication. Readers compatible with passive tags require a larger, in-phase coil antenna as well.

 

Frequencies

The accompanying table represents the most common frequencies used by RFID equipment.

Band Range Data speed Common uses
120—159 kHz (low frequency) 10 cm Low Animal identification; factory data collection; auto keys
13.56 MHz (high frequency) 10 cm—1 m Low to moderate Smart cards; shelf inventories; transactions
433 MHz (ultra-high frequency) 1—100 m Moderate Defense applications; tracking pallets

Eurasia: 865—868 MHz (ultra-high frequency)

North America: 902—928 MHz (ultra-high frequency) 

1—12 m Moderate to high Inventory; hard-to-read RFID applications
2450—6800 MHz (microwave) 1—2 m High 802.11 WLAN, Bluetooth standards
3.1—10 GHz (microwave) >200 m High Road toll accounts

 

Bulk Reading

An RFID reader will frequently sense multiple RFID tags within its detection range. While it seems like the reader is capable of reading hundreds of tags immediately, it actually must read them sequentially in order to comprehend each individual identity. Readers which are expected to bulk read must be programmed with collision detection to formulate a protocol to scan and organize each tag; otherwise the time to identify each item grows exponentially. Two anti-collision algorithms can be encoded into an RFID reader signal.

  • For probalistic detection, the RFID tag is assigned a random time delay. If a collision occurs, the tags with signals that are not read are randomly assigned an available timeslot. This continues until all tags within the detection range are read. 

Selecting slotted ALOHA readers

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  • Deterministic detection is typically quicker than probalistic detection. This method relies on the underlying binary code of the tag, which is read bit-by-bit. In this method, no tags are read more than once, and the scan time is directly related to the number of tags.

RFID adaptive binary tree

Image credit: Great Note

 

Instances where two readers have an overlapping detection field are common. To prevent the readers from scanning the same tag simultaneously, the RFID readers will alternate between random frequencies within its bandwidth in a process known as frequency hopping.

 

Reader Implementation

The method by which the reader is employed is largely dependent upon application. There are three formats in which readers are manufactured.

  • Handheld readers are battery-powered, mobile devices which allow system users to read and alter RFID tags once they are scanned. These readers usually include a keyboard to allow immediate updates to the tag. Handheld readers are wirelessly connected to database software.
  • Fixed readers are stationary and the RFID tag must be placed within the detection range of the reader. In some instances the fixed reader is incorporated into an archway so pallets of inventory can be automatically logged as it passes through.
  • Vehicle-mounted readers are placed on forklifts, pallet trucks, or on other freight handling equipment to automatically read and record the locations of cargo as it is relocated or loaded for transportation.

Handheld RFID readers Selecting Fixed RFID readers  Selecting vehicle RFID readers

Handheld reader; fixed reader; fixed reader; vehicle-mounted readers

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RFID Reader Standards

The intrinsic relationship between RFID tags and readers means most standards apply to the operation of both devices. An extensive list of standards is available from the IHS Global Standards Store; the ones listed below are important to many applications.  

 

-ISO 18000 RFID use for item management across many frequencies

-ISO 21481 RFID information exchange and protocols

-ISO 18046 RFID devices, performance and test methods

 

RFID Reader Applications

While the quantity of RFID tags in the field vastly outnumbers the quantity of RFID readers, the two devices are inoperable without one another. There is a limitless number of applications for RFID equipment. RFID readers appear in the same arenas as RFID tags, including:

  • Encrypted readers are employed in scenarios where the RFID is directly linked to a credit or banking account. These readers will sometimes feature a keypad, so the user can enter a PIN and supplementary info.
  • In asset tracking, fixed readers are placed at access points so tags can be automatically scanned as it passes. This includes factories and warehouses, as well as retail stores which utilize electronic article surveillance.
  • Readers are used to scan ID badges and electronic keys; they identify the user and determine access authorization.
  • Fixed RFID readers are placed around oil rigs so personnel can be identified and found quickly.
  • RFID readers are used by veterinarians and animal control workers to identify and update information which has been stored on an RFID implanted in the animal's skin. They are also used to keep track of livestock.

  • RFID readers are utilized in road tolls. This system allows drivers to begin a toll account and the transactions are recorded by a reader scanning tags that are placed in vehicles.

Resources

 

Intermec - RFID (scanners)

 

Motorola Solutions - RFID Readers

 

Wikipedia - Radio-frequency identification

 

RFID Journal - FAQ