Tags: A tag is the data carrier and normally contains
the ID number, and unique EPC code programmed into the Tag
Tag Antenna: The tag antenna is connected to the chip
in tag. It could be wire or printed using conductive ink.
Reader Antenna: It is a coil included in plastic or similar
case, and normally measures 12 -18 inches square
Reader: A reader captures the data provided by the tag
within the detectable area of the Reader. There can be one
or more tags within the capture area. A reader is typically
capable of reading multiple tags simultaneously.
Savant: This is normally a middleware that interacts
with the readers, and communicate with External databases.
A simplified block schematic of an RFID tag (also called
transponder) is shown in the diagram below. Various components
of the tag are as shown. Normally, the antenna is external
to the tag chip, and large in size.
The operation of the RFID tag is described below:
Handshaking with the Reader (interrogator):
The reader continuously emits RF carrier signals, and
keeps observing the received RF signals for data.
The presence of a tag (for our discussion, we consider
only passive tag) modulates the rf field, and the same is
detected by the reader.
The passive tag absorbs a small portion of the energy
emitted by the reader, and starts sending modulated information
when sufficient energy is acquired from the rf field generated
by the reader. Note that the data modulation (modulation
for 0s and 1s) is accomplished by either direct modulation
or FSK or Phase modulation.
The reader demodulates the signals received from the
tag antenna, and decodes the same for further processing.
Backscatter is one of the most widely used modulation schemes
for modulating data on to rf carrier. In this method of modulation,
the tag coil (load) is shunted depending on the bit sequence
received. This in turn modulates the rf carrier amplitude as
shown in the diagram below. The reader detects the changes in
the modulated carrier and recovers the data.
The above diagram provides a simplified modulated carrier
signals from the RFID tag. As seen in the diagram, the encoded
binary digits modulate rf carrier. A 1 is represented with high
carrier level, and a 0 is represented by a low carrier level
(tag coil shunted). The reader demodulates the signals to recover
the data, and note that this data is still encoded. The reader
decodes the data using suitable decoder, and forwards it for
further processing to a computer (or any backend server).