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The ABCs of RFID
(Released June 2007)

  by Marianne Stanczak  


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The ABCs of RFID


Since RFID is often compared to UPC code technology, we will begin here. When a UPC code is scanned, information - usually product name and price - is displayed on a computer or cash register screen. RFID is a wireless technology that uses radio waves to scan or "identify" a product/substance/animal that contains a tag.

RFID technology is normally comprised of three parts: an antenna, a tag and a reader. A tag, also called a transponder, contains a printed circuit board and/or semiconductors. A reader, also called a transceiver, decodes information sent by the transponder. An antenna, generally found on the tag itself, obtains or gives out energy, in this, case radio waves. The data from the tag is sent out through the antenna and read by the reader.

To continue the UPC comparison, an RFID reader reads a tag like a scanner reads a UPC code. Unlike UPC code scanning, RFID tags do not require "direct-line-of-sight," i.e. they do not require the reader to "see" the tags. They also may contain more product information than a UPC, although this is not always the case. Multiple products, like items on a pallet in a warehouse, can be read simultaneously, whereas UPC is restricted to one coded item at a time. RFID tags can be scanned if the item is dirty, wet or otherwise obstructed since they are read via radio waves and not optical means (again, RFID does not require "direct-line-of-sight"). The reading speed is less than 100 milliseconds even in obstructed conditions or extreme temperatures.1 Another unique feature of RFID is the so-called "kill" option in which an RFID tagged item is deactivated once a consumer leaves a store.

While UPC codes are fairly standard, RFID technology comes in many different shapes, sizes, and capabilities. Subcutaneous implants, like those used to identify missing pets, can be as small as a grain of rice or pencil lead (~10 mm long). Other RFID tags are small enough to be built into casino chips, or as big as credit cards. The plastics tags found on clothing in stores are a familiar example of RFID tags. For especially large applications, such as scanning the contents of railroad cars, an RFID tag may be as large as 120 by 100 by 50 mm.

antenna and tag placed inside tube
RFID tag (V720-D13P07) and reader antenna (V720-HS03) used in an experiment. The RFID tag was attached on the inner surface of a PVC conger-eel tube

There are two types of RFID tags - passive and active. Passive RFID tags do not use batteries and must be used at a close range of 3m or less. The antenna, tuned to a particular radio frequency, sends out radio waves. The reader then sends out a radio signal to the tag/antenna, which is activated to transmit the pertinent information. The radio signal contains enough energy to power the tag long enough to send out its information. Most passive RFID tags use Electrically Erasable Programmable Read Only Memory (EEPROM) for small amounts of data.

table of  RFID attributes

The more sophisticated active tags use batteries, which make them more expensive; however, the reader can read tags that are ~100m (300 feet) away.2 Many use Static Random Access Memory (SRAM), which means the information in the tag is available as long as it is being powered, for instance with a battery. In summary, an active tag uses an internal power source (battery) while a passive tag uses an external power source (radio waves from the reader).

There are a few frequency ranges in which RFID technology can operate (different applications use different ranges).

LOW FREQUENCY ~ 125 KHz <0.33 m (1 foot or less)
HIGH FREQUENCY 13.56 MHz 1m (3ft)
ULTRA HIGH FREQUENCY (UHF)* 860 - 960 MHz up to 100m (10-20ft . . . 300ft)
MICROWAVE FREQUENCY** 2.45 GHz Various distances
* Television operates at this frequency; some mobile phones use 900 MHz frequency
** Only some applications, e.g. toll collection

Drawbacks of RFID technology often depend on what is being scanned/read. Because of the conductivity of metals, objects/products containing them may be hard to read. The tag itself may be comprised of an aluminum or copper foil antenna or silver ink. Other obstacles that may need overcoming are orientation of RFID tags and contents of scanned item:

Contents of packages can dramatically reduce the read rate. Only 25% of the tags on shipping containers containing water filled bottles could be read. Rice filled jars had a higher reading rate (80.6%) Even empty boxes did not have a 100% read rate...The orientation of the tag does make a difference, especially when coupled with a filled package between it and the reader antenna. Tags facing outwards, towards the reader antenna, had the highest likelihood of a successful read. When tags for the boxes of water filled bottles were all facing downward, no tags were read.3

Go To The Many Uses of RFID

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