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Radio Frequency Identification Tags (RFID)
A basic RFID system consist of three components:
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An antenna or coil
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A transceiver (with decoder)
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A transponder (commonly called an RF tag) that is electronically programmed with unique information
The antenna emits radio signals to activate the tag and read and write
data to it. Antennas are the conduits between the tag and the
transceiver, which controls the system’s data acquisition and
communication. Antennas are available in a variety of shapes and sizes;
they can be built into a door frame to receive tag data from persons or
things passing through the door, or mounted on an interstate toll booth
to monitor traffic passing by on a freeway. The electromagnetic field
produced by an antenna can be constantly present when multiple tags are
expected continually. If constant interrogation is not required, the
field can be activated by a sensor device.
Often the antenna is packaged with the transceiver and decoder to become
a reader (a.k.a. interrogator), which can be configured either as a
handheld or a fixed-mount device. The reader emits radio waves in ranges
of anywhere from one inch to 100 feet or more, depending upon its power
output and the radio frequency used. When an RFID tag passes through the
electromagnetic zone, it detects the reader’s activation signal. The
reader decodes the data encoded in the tag’s integrated circuit (silicon
chip) and the data is passed to the host computer for processing.
RFID tags come in a wide variety of shapes and sizes. Animal tracking
tags, inserted beneath the skin, can be as small as a pencil lead in
diameter and one-half inch in length. Tags can be screw-shaped to
identify trees or wooden items, or credit-card shaped for use in access
applications. The anti-theft hard plastic tags attached to merchandise
in stores are RFID tags. In addition, heavy-duty 5- by 4- by 2-inch
rectangular transponders used to track inter-modal containers or heavy
machinery, trucks, and railroad cars for maintenance and tracking
applications are RFID tags.
RFID tags are categorized as either active or passive. Active RFID tags
are powered by an internal battery and are typically read/write, i.e.,
tag data can be rewritten and/or modified. An active tag’s memory size
varies according to application requirements; some systems operate with
up to 1MB of memory. In a typical read/write RFID work-in-process
system, a tag might give a machine a set of instructions, and the
machine would then report its performance to the tag. This encoded data
would then become part of the tagged part’s history. The
battery-supplied power of an active tag generally gives it a longer read
range. The trade off is greater size, greater cost, and a limited
operational life (which may yield a maximum of 10 years, depending upon
operating temperatures and battery type).
Passive RFID tags operate without a separate external power source and
obtain operating power generated from the reader. Passive tags are
consequently much lighter than active tags, less expensive, and offer a
virtually unlimited operational lifetime. The trade off is that they
have shorter read ranges than active tags and require a higher-powered
reader. Read-only tags are typically passive and are programmed with a
unique set of data (usually 32 to 128 bits) that cannot be modified.
Read-only tags most often operate as a license plate into a database, in
the same way as linear barcodes reference a database containing
modifiable product-specific information.
RFID systems are also distinguished by their frequency ranges.
Low-frequency (30 KHz to 500 KHz) systems have short reading ranges and
lower system costs. They are most commonly used in security access,
asset tracking, and animal identification applications. High-frequency
(850 MHz to 950 MHz and 2.4 GHz to 2.5 GHz) systems, offering long read
ranges (greater than 90 feet) and high reading speeds, are used for such
applications as railroad car tracking and automated toll collection.
However, the higher performance of high-frequency RFID systems incurs
higher system costs.
The significant advantage of all types of RFID systems is the
non-contact, non-line-of-sight nature of the technology.
Tags can be read through a variety of substances such as snow, fog, ice,
paint, crusted grime, rubber, and other visually and environmentally
challenging conditions, where barcodes or other optically read
technologies would be useless. RFID tags can also be read in challenging
circumstances at remarkable speeds, in most cases responding in less
than 100 milliseconds.
The read/write capability of an active RFID system is also a significant
advantage in interactive applications such as work-in-process or
maintenance tracking. Though it is a costlier technology (compared with
barcode), RFID has become indispensable for a wide range of automated
data collection and identification applications that would not be
possible otherwise.
Developments in RFID technology continue to yield larger memory
capacities, wider reading ranges, and faster processing. It is highly
unlikely that the technology will ultimately replace barcode — even with
the inevitable reduction in raw materials coupled with economies of
scale, the integrated circuit in an RF tag will never be as
cost-effective as a barcode label. However, RFID will continue to grow
in its established niches where barcode or other optical technologies
are not effective. If some standards commonality is achieved - whereby
RFID equipment from different manufacturers can be used interchangeably
- the market will very likely grow exponentially.
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