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Radio Frequency Identification (RFID) is the generic term used to describe systems that transmit the identity (in the form of a unique serial number) of an item, object or person wirelessly, using radio waves.

RFID is being used for everything from tracking farm live stock (birds, cows, etc), retail inventory (goods, bottles, packets, clothes) persons (both business personnel, individuals and pets) to equipment. It is even used for ticketing, automating toll and fare collection at toll booths.

This is a page for general information on understanding and utilizing RFID technology. Please click here to see QDnet's RFID optimized GPS solutions

Today, automatic identification procedures are popularly used in the logistics of resource management for service, purchasing, distribution, manufacturing and material flow industries. These systems are customized to provide timely, geo-referenced information about people, animals, goods or products.

RFID technology makes highly flexible, contact-less data transfer between the data carrying devices and readers possible.

How Does it Work?

Radio Frequency Identification or RFID consists of 2 parts
The entire solution consists of:

  1. A Reader - also called an interrogator or detector, and
  2. A Tag - this is an RFID transponder.
Both the reader and the tag are fitted with an antenna as part of their subsystem.

What is a RFID Reader?
A RFID reader usually contains a high frequency transceiver (i.e. a transmitter and receiver section), a control section and an antenna . The reader will have other interfaces (these may be RS232, RS 485, ethernet, GSM, etc.) to transfer the received data to another system.

What is a Tag?
The tag or transponder, which is where the data or ID resides, consists of a small antenna (coupling element) and a microchip. For most applications, the tag does not posses its' own power. The reader continuously emits electromagnetic waves or radio signals. In the vicinity of the these waves, the a charge is induced in the tag and it transmits a modulated radio signal in response. The reader decodes this signal to identify the tag and store or re-transmit the acquired data. These tags are called passive tags.

How does the Antenna function?
Antennae, the critical element of RFID design, are fitted in both the reader and tag and act as conduits between the reader and tag. Antennae are available in a variety of shapes and sizes; they can be built into doors, bottle covers or personal ID cards to receive tag data from persons or things in the vicinity. These antennae continuously transmit radio signals, to detect multiple tags that pass within its proximity.

What is the difference between Passive and Active Transponder RFID Tags?
Passive RFID tags
do not have a power source and draw power from the electromagnetic field radiated by the reader. This received power is used to kick-start the onboard microchip which then sends data back to the reader. As the signal gets diffused in free space, only a small amount of the reader's electromagnetic field reaches these tags, hence they can only be read from short distances.
Active RFID tags are fitted with a battery, that can be used as a partial or complete source of power for the tag's circuitry and antenna. These tags continuously emit radio signals which can be read at distances of one hundred feet or more. However, in comparison to passive RFID tags, they are far more expensive, much larger in size and have higher maintenance costs.

How are the tags read?
RFID readers use inductive coupling or backscatter to read the RFID tags.
Inductive coupling method
The tag, which is almost always passive, consists of a microchip containing the tag's data, and a cross-section of induction coil, which functions as an antenna. The reader's antenna generates a strong electromagnetic field (from an AC voltage) which penetrates the cross-section of the tag's coil and generates a charge, on the principle of induction. The AC voltage induced is rectified to activate the microchip in the tag. A small capacitor is connected across the tag's induction coil to form a resonant circuit which generates an electromagnetic signal, which is transmitted in response to the reader's signal. Inductively coupled systems are based on transformer-type coupling between the primary coil in the reader and the secondary coil in the tag.
Back scatter method
In the backscatter method, the tags does not transmit data independently, instead it reflects the electromagnetic signal sent by the reader, back to the reader. So it transfers data by modulating the reader's signal. This reflected signal is received by the reader's antenna where it travels in the backwards direction and is decoupled using a directional coupler. This decoupled signal reveals the tag's transmitted information, which is then stored by the reader.

What Frequency Bands are used by the RFID?
The frequencies generally used for RFID are:
Low Frequency - 125 Khz (Most commonly used)
High Frequency - 13.56 Mhz
Ultra High Frequency - 860-960 Mhz , 2.45 Ghz, 5.8 Ghz

Are there any standards for RFID?
The groups that have defined RFID standards include the International Organization for Standards (ISO), International Electro-technical commission (IEC), EPC (Electronic Product Code), ASTM (American Society for Testing and Materials) and DASH7 Alliance. Some of the common standards:
ISO/IEC 14443 - Identifications of Proximity cards (Short range RFID)
SO/IEC 15693 - Identifications of Vicinity cards (Long range RFID)
ISO 18000 - Item management (Extended long range RFID)

Which Tags do I use for my applications?
RFID tags come in various sizes from small grains that can be embedded under the skin of the live stock to the sized of a floppy disk. The size depends on whether the tag uses a battery to broadcast a signal or simply reflects a signal back from the reader. The other factor is the size of the antenna. As the antenna gets smaller the read range decreases. Tags that are the size of a grain of pepper have an antenna etched onto the microchip. Because the antenna is so small, the tags can only be read from less than an inch away.

Low-frequency tags use less power and are better able to penetrate non-metallic substances. They are ideal for scanning objects with high-water content, such as fruit, but their read range is limited to less than a foot (0.33 meter).

High-frequency tags work better on objects made of metal and can work around goods with high water content. They have a maximum read range of about three feet (1 meter).

UHF ie Utra High Frequencies typically offer better range and can transfer data faster than low and high frequencies. But, they use more power and are less likely to pass through materials. And because they tend to be more "directed," they require a clear path between the tag and reader. UHF tags might be better for scanning boxes of goods as they pass through warehouse doors.

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