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An RFID tag is a uniquely identified (or identifiable) object, that
can be embedded (or attached) to any physical body to track its position
or location. Tags are of various kinds, covering the entire spectrum
the passive tags powered in the presence of a reader, to a continuously
signal-emitting active tag.
Both active as well as passive RFID tags consist of a small microchip
that contains a unique ID encoded within it. The rest of the tag consists
of a mechanism to transmit this unique ID to an "Interrogator"
or a reader that can identify this tag.
In the case of a passive RFID tag, the construction consists of an
antenna that serves a dual purpose - it acts as a "coil"
that generates enough electric current when placed within an electromagnetic
field (i.e. Close to a passive reader) to "power" the microchip.
The unique ID encoded within the microchip is then transmitted in
an electromagnetic pulse that uses the antenna to broadcast the pulse
back to the reader.
In the case of an Active tag, an internal power source (battery) is
used to power the transmission - which broadcasts the tag's unique
ID to all sensors/receivers that are listening on the specified frequency.
The signals are non-directional, and may be received by one or more
sensors. These signals then need to be interpreted by the system to
determine the location of the tag within a facility.
Both active as well as passive tags fall within a range of frequencies
that are used according to the international ISO specifications for
air interface (ISO-18000 2-7). Some of these specified frequencies
are more suitable to passive operation (i.e. shorter range, larger
bandwidth, lower power) while some are more suitable to active RFID
technology. Passive tags in the HF range are commonly found in the
125 KHz and the 13.56 MHz range. Some of the newer tags are also available
in the UHF range, with larger bandwidth, read speeds, as well as larger
read ranges. However, these technologies also require higher power
readers than those with correspondingly lower frequencies.
Most active RFID badges usually work between 420 - 450 MHz. Some of
the tags also work between the 63.57 MHz frequency range, which compensate
for the lower range (90m) with much longer battery life, which is
a very practical consideration for an actual deployment.
Features
- All tags use some kind of FM modulation in order to transmit
the tag's unique ID to the Interrogator
- Interrogated remotely via RF/inductive signals (passive) and
direct broadcast (active)
- Long life - can withstand mechanical shocks, dirt etc
- Non-directional, with non line-of-sight functioning that enables
complete automation of RFID enabled (or supported) systems and
processes.
- Non-contacting (tamperproof) and non-obtrusive (transparent
to user)
- Robust protocol - fault tolerant transmission, inherently engineered
for error-handling and recovery
- Flexible with minimal interference
- Unique identification number allows stronger authentication
of personnel and systems.
Comparison of Active vs. Passive Tags
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Feature
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Active Tag
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Passive Tag
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Frequency
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420-450 Mhz, 63.57 Mhz
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125Khz, 13.56Mhz, 920-930Mhz, 2.4-5.8Ghz
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Typical usage
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Position tracking, location-based computing, "Aware"
systems that can react to specified physical signals
and stimuli
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Object identification, process automation, Retail
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Typical environment
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Hospitals and healthcare facilities, Warehouses
& Freight management facilities, Defense and high-security
installations
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Retail sales, Warehouse and freight management,
Logistics, Manufacturing & Supply chain management,
Agriculture
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Range
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1 - 100 m
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2 - 50 cm
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Cost
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Medium, Re-usable for long-term cost recovery
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Low, but non-reusable tags
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