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RFID technology

 

 

General principle of operation of any RFID system is rather simple. System shall always include two basic components: Reader and Identifier (card, tag, badge.) Reader generates electromagnetic waves into environment. Identifier receives the signal from Reader and forms a response received by Readers antenna and processed with its Electronic Control Unit.

 

Two types of RFID systems are distinguished: passive and interactive. Passive system is rather simple: Reader's signal generation is continuous in time (non-modulated) and works as Identifier power source only. Having received the required power Identifier is initiated and modulates Reader's wave with its code that is accepted by Reader. Most of Access Control Systems use this philosophy, where Identifier serial number is required only. Systems applicable in logistics are operated in interactive mode. In such a system Reader generates modulated electromagnetic wawve, i.e. forms the request. Identifier decodes the request and forms appropriate response, if necessary.

 

Anticollision

The demand in interactive systems has resulted from the necessity of simultaneous operation of more than one Identifier, e. g., when it is required to read all tags at goods packaging in the warehouse. In such cases anticollision mechanism capable to provide random alternate performance of several Identifiers simultaneously located within Reader's field will be a must. Otherwise Identifier signals would overlap each other. In the course of anticollision procedure Reader detects all Identifiers by their unique serial numbers and then processes them one-by-one.

 

Writable Identifiers

To make a decision on person access to premises or to calculate boxes on a pallet it is sufficient that each Identifier has its unique serial number. On the other hand there is a wide range of tasks, when the tag shall include additional data reflecting the progress of operating procedure.
In this case writable Identifiers shall be used with additional non-volatile memory keeping data in case of power failure. Such memory capacity may vary from dozens of bits to dozens of kilobytes with regard to the application task.

 

Frequency Range and Standards

RFID technology includes two key definitions:

  • Proximity cards and badges are short range Identifies with coverage about 10 cm. They are used in vehicle access control systems
  • Vicinity Identifiers are medium range Identifiers (about meter and a half coverage.) They are used for goods and products identification in logistics systems. From the point of view of operating frequency the low frequency (125 or 134 kHz), high frequency (13.56 MHz) and ultra high frequency (800 MHz - 2.45 GHz) ranges are the basic.
Low frequency range is mostly used with Access Control Systems, as well as for identification of animals and metal things (such as beer cans.)
Currently the high frequency range is the most popular. It is used ticketing systems and similar applications, where writable cards are required. ISO 14443 is the basic standard and actually all smart-cards are produced in accordance with this standard.
Two standards are of interest within medium frequencies range: ISO 15693 and EPC.
ISO 15693 is mainly used for writable tags fabrication with rather wide functionality. EPC (electronic product code) has a simpler structure and is an electronic analogue to strip codes.
Ultra high frequency range (800 MHz - 2.45 GHz) has recently come into use and it is of great interest due to the fact that under existing standards of generation power within this range passive Identifiers have coverage up to 4 - 8 m that is critical for warehouses, for example. Two standards prevail in this range: ISO 18000 and EPC.
Nowadays it can be taken for granted that EPC for medium and high frequency ranges is very promising for logistics systems in particular.

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