Radio Frequency Identification (RFID) systems use
radio frequency to identify, locate and track people,
assets and animals. Three components compose passive RFID systems – a reader (interrogator),
passive tag and host computer. The tag is
composed of an antenna coil and a silicon chip that
includes basic modulation circuitry and nonvolatile
memory. A time-varying
electromagnetic radio frequency (RF) wave that is
transmitted by the reader energizes the tag. This RF signal is called a
carrier signal. AC voltage is generated across the coil when the RF field passes through an
antenna coil. This voltage is rectified to result in DC voltage
for the device operation. When the DC voltage reaches a certain level, the device becomes functional. Reflecting, or loading, the reader's carrier transfers the
information stored in the device to the reader.
This is often called backscattering. By detecting the
backscattering signal, the information stored in the
device can be fully identified.
remote sensing applications, specifically in access
control and animal tracking applications, use the passive RFID system because of its simplicity for use.
Application demands increased dramatically in recent years. In most cases, unique packaging form factor, communication protocol, frequency, etc., are used in each application. The passive tag deals with very small power (~ µw) because it is
remotely powered by the reader’s RF signal. Thus, the read range
(communication distance between reader and tag) is
typically limited within a proximity distance. Design parameters, such as
frequency, RF power level, reader’s receiving sensitivity,
size of antenna, data rate, communication protocol,
current consumptions of the silicon device, etc., cause the read range to vary.
the availability of silicon devices, low frequency bands (125 kHz to 400 kHz) were traditionally
used in RFID applications. Typical carrier
frequency (reader’s transmitting frequency) in today’s
applications range from 125 kHz to 2.4 GHz.
In recent years with the advent of new silicon devices, the applications with high frequency (4
to 20 MHz) and microwave (2.45 GHz) bands have
frequency band has advantages and disadvantages.
of both low (125 kHz) frequency and microwave
(2.4 GHz) bands are offered by the 4 to 20 MHz frequency bands. Therefore, this frequency band
becomes the most dominant frequency band in
passive RFID applications.