Information Technology Reference
Figure 10: Components of a RFID tag.
A basic RFID system consists of two components: a reader and a
transponder (tag) . The tag may be electronically programmed with
static data (read-only tags) or variable (read/write tags). The tags consist of
a chip (1 mm 2 , 0.2 mm thickness) connected to an antenna glued on a thin
layer of polyethylene terephthalate (PET), which can be inserted into labels,
tickets, bracelets, buttons, keys, etc. (Figure 10). All tagged objects become
smart since held data can be used to build some additional information (e.g.
by querying a database).
Tags can be classified by several criteria, such as the energy source, the
memory type, the working frequency, and so on. We will shortly discuss the
energy source that classifies tags in active and passive .
7.1 Passive tags
Passive tags are the most popular and cheap because they do not embed a
battery or any other power source. Besides, receiving and transmitting data
within a short range (25/120 cm), the antenna turns the received electro-
magnetic energy into electric energy to power up the transmitter. This is the
reason why the range of a passive tag depends on the amount of received
energy and therefore on the reader transmitted power.
The intelligent part of each tag consists of a simple RF signal transmission
circuit and a non-volatile memory containing a unique code, which is trans-
mitted to the reader. Some tags embed a more complex chip which is able to
carry on some computation and send back the results to the reader.
Most of the passive tags operate in the RF range of 13.56 MHz or
125 KHz, and their size can be very small as well as their cost, which is much
lower than active tags.