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The figure 1 below shows how the reader sends the signal to power and queries
the tags. It sends a signal whose magnetic field will power the tag. Once the tag is
turned on it can received and decode the signal. As the signal contains a query for the
tag, if the tag corresponds to the query it answers to the reader, if not it stays quiet. The
following figure (fig2) explains the exchanges between the reader and the tags. In this
example the reader use a filter, that means that it doesn’t query all the tags but only
those who corresponds to the specific criteria.
Figure 2 - Exchanges between the reader and the tags
Example of direct application
In a supermarket’s warehouse, all the items here have a tag attached
to identify them. If the director wants to know how many milk bottles he
has in the warehouse, instead of sending a trainee counting all the bottles
he will used his RFID reader to query all the tags with a particularity in
their ID. If this particularity signifies that the tag is attached to a bottle
of milk the director could have his answer quicker than with the trainee.
This is of course a schematic view of a RFID system, actually it can’t work like
this because of the tag collision. Like in all wireless communication technology there is
Julien David
Design of a RFID Controller
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