There are several frequencies that are used for RFID. These include LF, HF,
UHF, and Microwave frequencies. The exact frequencies may vary depending on the
country where it is used.
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Frequency Range
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Description
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Typical Applications
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<135khz span="span">
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Low Frequency, Inductive coupling
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Access Control & Security
Widgets identification through manufacturing processes Ranch animal identification OEM applications |
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13.56 MHz
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High Frequency, Inductive coupling
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Access Control
Library books Laundry identification OEM applications |
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868 to 870 MHz 902 to 928 MHz
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Ultra High Frequencies (UHF), Backscatter coupling
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Supply chain tracking
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2.400 to 2.483 GHz
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SHF, Backscatter coupling
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Asset tracking
Highway toll tags Vehicle tracking |
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.
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):
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).
