RFID System Overview

RFID relies on radio frequency or "waves" between a card or tag and a reader in order to make an identification. Because RFID is a "contact less" technology, it requires neither contact with a reader or a direct line of sight to a reader (as does bar code technology). RFID, therefore, reduces the problems associated with those "contact" or "line-of-sight" technologies. For instance, a "good" read can occur through sunlight, wet, cold (-30°C ), frost, dirt, grease, and many corrosive chemicals.

Radio frequency (RF) refers to electromagnetic waves that have a wavelength suited for use in radio communication. Radio waves are classified by their frequencies, which are expressed in kilohertz, megahertz, or gigahertz .
Radio frequencies range from very low frequency (VLF), which has a range of 10 to 30 kHz, to extremely high frequency (EHF), which has a range of 30 to 300 GHz.

RFID system’s typically includes the following components:

• RFID device (transponder or tag) that contains data about an item
• Antenna used to transmit the RF signals between the reader and the RFID device
• Radio transceiver that generates the RF signals
• Reader that receives RF transmissions from an RFID device and passes the data to a host system for processing

In addition to this basic RFID equipment, an RFID system includes application-specific software.

Transponder RFID Tag

Historically, an RFID device that did not actively transmit to a reader was known as a tag. An RFID device that actively transmitted to a reader was known as a transponder (transmitter + responder). However, it has become common within the industry to interchange the terminology and refer to these devices as either tags or transponders. For the purposes of this overview, an RFID device that actively transmits to a reader is termed an “active” tag; an RFID device that only reflects or backscatter's transmission from a reader is termed “passive.”

The tags are programmed with data that identifies the item to which the tag is attached. Tags can be either read -only, volatile read/write, or write one/read many (WORM) and can be either active or passive. In general, active tags
use batteries to power the tag transmitter (radio) and receiver. These tags usually contain a greater number of components than do passive tags. Therefore, active tags are usually larger in size and are more expensive than passive tags. In addition, the life of an active tag is directly related to battery life.

Passive tags can be either battery or non-battery operated, as determined by the intended applications. Passive tags reflect the RF signal transmitted to them from a reader or transceiver and add information by modulating the reflected signal. A passive tag does not use a battery to boost the energy of the reflected signal. A passive tag may use a battery to maintain memory in the tag or power the electronics that enable the tag to modulate the reflected signal.

Antenna

Each RFID system includes at least one antenna to transmit and receive the RF signals. In some systems, a single
antenna transmits and receives the signals; in other systems, one antenna transmits and one antenna receives the signals.
The quantity and type of antennas used depend on the application.

RF Transceiver

The RF transceiver is the source of the RF energy used to activate and power the passive RFID tags. The RF transceiver may be enclosed in the same cabinet as the reader or it may be a separate piece of equipment. When provided as a separate piece of equipment, the transceiver is commonly referred to as an RF module. The RF transceiver controls and modulates the radio frequencies that the antenna transmits and receives. The transceiver filters and amplifies the backscatter signal from a passive RFID tag.

Reader

The RFID reader directs the RF transceiver to transmit RF signals, receives the encoded signal from the tag through the RF transceiver, decodes the tag’s identification, and transmits the identification with any other data from the tag to the host computer. The reader may also provide other functions. For example, ETC applications include accepting data from other input devices such as a vehicle detector and controlling gate and lights. Firm ware in the reader controls reader operations. The user can change or customize the reader’s operations to suit a specific requirement by issuing commands through the host computer or a local terminal.

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