Radio Frequency Identification
(RFID)
By Ike Mowete
Monday, April 18, 2005
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“Papa,
when I said I needed a monitor, I meant one for my computer
and not a security guard.” |
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Radio Frequency Identification (RFID) is the name given to
the technology involving a set of small electronic devices
consisting of small chips and antennas and having the typical
capabilities of storing up to 2,000 bytes of information.
These devices, like bar codes or small magnetic strips on
the back of credit/ATM cards, offer a method for the unique
identification of objects, using electromagnetic waves. In
the typical device, a reader communicates with a tag, which
contains digital information in a microchip. Each device may
be regarded as a radio-frequency identification system, whose
component parts include a scanning antenna, a transceiver
equipped with a decoder to interpret data and a transponder
or radio-frequency tag, containing programmed information.
It may be said that radio-frequency identification technology
began in the 1900s, following the demonstration of the first
continuous wave radio by Ernst Alexanderson. According to
historical records, modern-day RFID applications were conceptualised
in the 1940s, first in a 1948 paper written by Harry Stockman
and the patent entitled ‘Radio transmission systems
with modulated passive responders’, filed in the 1950s
by D. B. Harris. By the 1960s, the theory of RFID had been
developed through the contributions of several other scientists,
(including notable contributions from Roger F. Harrington
of Syracuse University) to the extent that field application
trials were possible. An explosion of RFID development was
witnessed by the 1970s and after the Los Alamos Scientific
Laboratories (LASL) published its celebrated paper on the
subject (´Short-range radio-telemetry for electronic
identification using modulated backscatter’) in the
open literature in 1975, several companies began the manufacturing
of RFID devices. By the time standards for RFID emerged in
the 1990s, the technology had been widely deployed in such
commercial applications as multi-protocol traffic, control
and toll collection systems, security and access control and
supply chain management, to mention a few.
When in operation, the device’s scanning antenna radiates
radio-frequency signals over a relatively short range and
to serve two purposes. First, the radiated signal facilitates
communications with the transponder tag. That is, the RFID
chip, which is also equipped with an antenna with which it
picks up signals and sends signals’– identification
code or electronic product code, EPC–– to a reader.
Second, in the case of–passive RFID tags, it provides
the device with the energy with which to communicate. Scanning
antennas may be permanently attached to a surface, but some
handheld types are also available. They can be of any desired
shape and can be built in door frames, to accept data given
out by human traffic through the doors. When an RFID tag enters
into the field of a scanning antenna, it detects the activation
signal emanating from the antenna and it responds by activating
its RFID chip to transmit information on its microwave chip
to the scanning antenna.
There are two types of RFID tags, namely: the active tag and
the passive tag. The battery-powered active tag is characterised
by a longer range, of between 6m and 30m and which may be
of the ‘read-only’ or ‘read/write’
varieties. On the other hand, the passive tag, is powered
by the reader, whose range extends to about 6m. Because of
the obvious cost benefits involved, the tendency is for RFID
deployments to utilise frequencies in the unlicensed regimes
of RF spectrum. Frequencies in use include 125/134.2 kHz in
the LF regime; 13.56 in the HF region; 869 and 915MHz in the
UHF spectrum and the microwave frequency of 2459MHz in the
band favoured by the ISPs. Choice of frequency of operation
is specified by intended application, which also prescribes
the range of the device. Thus, whereas tags in the LF-HF band
have a range of between 2.5cm and 45cm, passive tags in the
UHF band are able to reach up to 6m, (1.8m for passive microwave
tags) depending on the type of surface on which the tag is
mounted.
(Source: transpondernews.com)
Magnetically coupled transponder systems operating at 125
kHz are arguably the most common transponders available today.
Antennas for such tags are typically made of several turns
of wire wound round a coil former. Use of magnetic coupling
implies that the range, which is determined by the fields
generated between the effective North and South poles of the
reader, is limited to a few centimetres. Tags using magnetic
coupling but operating at 13.56MHz have been in use since
1998. Antennas for these tag types do not require the high
number of turns characteristic of the 125 kHz tags and are
consequently cheaper to manufacture. In addition to having
read-write capabilities, such tags also often have ‘anti-collision’
properties, which enable the simultaneous recognition of many
tags entering the reader beam at the same time. Although some
manufacturers claim a range of up to 1m for the tags, it is
generally held that their range should be about 50cm, on account
of the use of the magnetic field for propagation. Transponders
utilising the electric field for coupling provide tremendously
increased ranges over those using the magnetic coupling.
In this case, use is made of the electric field propagation
properties of radio communication to facilitate information
exchange (energy and data from reader to transponder, data
from transponder to reader) between reader and tag. Electric
field propagation uses antenna systems with antennas being
about half a wavelength (at the operating frequency; for example,
1.5m at 100MHz) in size, which means that there are practical
limits for frequencies located in the lower regimes, at which
electric coupling may be utilised. Higher frequencies, on
the other hand, require components that are more expensive
and at these frequencies, the inverse relationship between
energy transfer and the square of wavelength is lost. Because
energy radiated by electric field tags can be detected by
sensitive receivers, the tags are required to operate in a
systematic spectrum management system, in order to eliminate
the possibility of interference.
In order to communicate with the tags, the RFID reader/interrogator
is typically required to have several antennas in many deployments.
For example, a fixed reader located on a factory’s conveyor
belt might operate satisfactorily with one antenna, but another
fixed reader on the same factory’s massive door might
need several antennas for satisfactory operation. Readers
can be any of fixed mounts, handheld, or PCMCIA cards.
PCMCIA card readers may be used to enable the collection of
RFID data in situations where fixed mounts or handhelds would
not work, a common, often cited example being data collection
from computers on forklifts.
Circularly polarised antennas are preferred for handheld readers
because it may not always be possible to have line-of-sight
situations during the interrogation process. Interrogators
of the handheld variety usually have only one antenna, which
may be linearly or circularly polarised. Readers are said
to be ‘agile’’when they have the ability
to read tags operating at different frequencies or utilising
different methods for information exchange between interrogator
and tag.’‘Intelligent’ readers, according
to conventional wisdom, are those that are able to filter
data (or even run applications) in addition to being able
to run different protocols. Unlike what obtains with the’‘intelligent’
reader, where communication with the tag is essentially carried
on by a computer, in the ‘dumb’ reader, which
has very little computing power, only one type of tag may
be read, using only one frequency and one protocol.
One problem that RFID technology faces in the field concerns
the possibility of interference from signals from different
readers when coverage overlaps. This problem is often avoided
through the use of multiple access (TDMA in this case) techniques.
With this technique, readers are instructed to read at different
times rather than two or more trying to read at the same time.
However, it means that any RFID tag present in area of coverage
overlap will read twice, requiring that the system be set
up to ensure that once a tag has been read, another reader
does not read it again. RFID offers a number of distinct advantages
over the optical technology, using barcode. Communication
in the barcode domain depends on the availability of a line-of-sight,
(RFID is non-line-of-sight) unlike RFID which may be’‘read
only’ or ‘read/write’. The barcode is’‘read
only’ and barcodes can carry data on 2D data and whereas
the attendant requiring barcode is not reusable, the non-attendant-requiring
RFID is reusable.
One myth about the RFID is that it will ultimately replace
the barcode. The reality is that both are complementary technologies,
for while the RFID can store more data than the barcode, the
latter is much cheaper. Because the barcode is reliable and
cost effective, it is reasonable to expect that it will serve
as a useful backup to RFID.
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