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Passive tags
Passive tags are a subset of RFID tags, that use an external
power source to 'trigger' their operation, and to allow tracking.
These tags are suitable for the following purposes:
- For tracking items within a facility - without having
to necessarily know exactly where they are at any
point of time (which would require 'active' technology).
This requirement falls within the realm of “Access
Control and Management”, and is usually accomplished
by protecting all entry and exits in the facility
with readers, which capture movement of tags in and
out of the facility.
- For automated inventory management, including expiration
tracking/notification, ad-hoc operations (e.g. The
“Smart Shelf” concept where the system should
track when items are taken off or put back on the
shelf without any human intervention), and for fast
and efficient (and automated) tracking of material
movement and placement within a facility.
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Technology
Passive tags operate on principle of parasitic power transfer
through electromagnetic induction. The core RFID chip on a
passive tag contains a unique ID, and also necessary circuits
to power (and operate) this chip when any current flows through
the circuit.
The power is provided by the external reader to the passive
RFID tag through electromagnetic induction, as the copper
loop in the tag generates a current as it travels through
the electromagnetic field created by the reader. Since the
electromagnetic field power falls off as the square of the
distance, hence passive RFID systems are limited in the distance
of operation - often operating between only 2 to 5 centimetres.
Each tag has a unique ID that is set during manufacture,
and cannot be changed. When the RFID chip is triggered, it
uses the copper loop as an antena, and broadcasts it's unique
ID, which is picked up by the RFID reader, thus triggering
a “tag read”. This tag read can then be transmitted
to an Enterprise information system, and processed accordingly.
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