Radio Frequency Identification or a RFID system employs an automatic
identification technology which uses radio-frequency electromagnetic fields to
identify objects carrying tags when they come close to a reader. In the past few
years, RFID has been increasingly used in various sectors as an alternative to
the barcode to uniquely identify an object, animal or a person as it does not require
direct contact or line-of- sight scanning. The major components that form an RFID
system are Transponder (tag), Transceiver (decoder) and Antenna.
The transponder commonly known as tag contains electronically programmed
unique information which is read or decoded by the transceiver also known as the
reader. RFID tags generally feature an electronic chip with an antenna in order to
pass information onto the reader. The assembly is called an inlay and is then
packaged to be able to withstand the conditions in which it will operate. The
reader antenna emits radio signals that activates the tag. Upon activation, the tag
transmits data back to the reader which is then decoded to extract information
and perform necessary action. The range within which an RFID system operates
depend on the power output and the radio frequency. Low-frequency RFID
systems (30 KHz to 500 KHz) have short transmission ranges (generally less than
six feet). High-frequency RFID systems (850 MHz to 950 MHz and 2.4 GHz to 2.5
GHz) offer longer transmission ranges (more than 90 feet). In general, the higher
the frequency, the more expensive the system.
The chip in the tag is activated when the tag antenna receives signal from the
reader. Generally, the larger the tag antenna's area, the more energy it will be
able to collect and channel toward the tag chip, and the further read range the
tag will have.
There is no perfect tag for all applications. It is the application that defines the
tag’s antenna specifications. Some tags might be optimized for a particular
frequency band, while others might be tuned for good performance when
attached to materials that may not normally work well for wireless
communication (certain liquids and metals, for example). Antennas can be made
from a variety of materials; they can be printed, etched, or stamped with
conductive ink, or even vapor deposited onto labels.
The polarization and designing of tag antennas also plays an important role in
determining its overall performance. The polarization can either be circular and
linear. Circularly polarized antennas will have shorter read range but will be less
orientation sensitive. You can select between right hand circularly polarized
antennas (RHCP) or left hand circularly polarized antenna (LHCP). Sometimes you
can see dual circularly polarized antennas that have both left hand and right hand
polarization. Linearly polarized antennas will provide longer read range and more
focused beam but will read only tags that have antennas parallel to the plane of
wave. If your tag orientation is not fixed, especially when using single dipole tag
antennas (which are most common), you should select a circularly
polarized antenna.