Radio Frequency Identification (RFID): Definitions

(some of the of terms used in RFID technology)

active tag
1. An RFID tag that has a transmitter to send back information, rather than reflecting back a signal from the reader, as a passive tag does.

Most active tags use a battery to transmit a signal to a reader; however, some tags can gather energy from other sources. Active tags can be read from 300 feet (100 meters) or more, but they're expensive (typically more than US$20 each).

They're used for tracking expensive items over long ranges; for example, the U.S. military uses active tags to track containers of supplies arriving in ports.

2. Also defined as an RFID tag that includes a battery for powering the microchip's circuitry and transmitting a signal to a reader. Active tags are not used in library RFID systems.
1. The ability to write data to different fields, or blocks of memory, within the microchip in an RFID transponder.
2. The ability to address bits, fields, files, or other portions of the data on a tag.
agile reader
A generic term that usually refers to an RFID reader that can read tags operating at different frequencies or using different methods of communication between the tags and readers.
air interface protocol
The rules that govern how tags and readers communicate.
The orientation of the tag to the reader.
amplitude modulation, AM (s) (noun), amplitude modulations (pl)
The deliberate processing of a carrier signal which is used in ordinary radio and TV broadcasting: The amplitude modulation varies in accordance with the level of the modulating signal while transmitting the video portion of a television signal.

Variation of the amplitude modulation of a carrier wave, commonly a radio wave, presents fluctuations in the audio or video signals that are being transmitted.

A higher amplitude modulation wave is interpreted as a "1" and a normal wave is interpreted as a zero.

The method of changing an amplitude modulation is known as "amplitude shift keying", or ASK.

anchor-amplitude (s) (noun), anchor-amplitudes (pl)
The maximum absolute value of a periodic curve measured along its vertical axis (the height of a wave, in layman's terms).
The tag antenna is the conductive element that enables the tag to send and receive data.

Passive, low- (135 kHz) and high-frequency (13.56 MHz) tags usually have a coiled antenna that couples with the coiled antenna of the reader to form a magnetic field.

UHF tag antennas can be a variety of shapes. Readers also have antennas which are used to emit radio waves.

The RF energy from the reader antenna is "harvested" by the antenna and used to power up the microchip, which then changes the electrical load on the antenna to reflect back its own signals.

antenna gain
1. In technical terms, the gain is the ratio of the power required at the input of a loss-free reference antenna to the power supplied to the input of the given antenna to produce, in a given direction, the same field strength at the same distance.

Antenna gain is usually expressed in decibels and the higher the gain the more powerful the energy output. Antennas with higher gain will be able to read tags from farther away.

2. The conductive element that radiates or receives energy in the radio frequency spectrum to and from the tag.
anti-collision (s) (noun), anti-collisions (pl)
1. A general term used to cover methods of preventing radio waves from one device from interfering with radio waves from another. Anti-collision algorithms are also used to read more than one tag in the same reader's field.
2. A technique for keeping radio waves from interfering with one another, especially in the case of reading more than one tag in the same reader's field as with a stack of books.
auto-ID center
A non-profit collaboration between private companies and academia that pioneered the development of an internet-like infrastructure for tracking goods globally through the use of RFID tags.
automatic identification
A broad term that covers methods of collecting data and entering it directly into computer systems without human involvement.

Technologies normally considered part of auto-ID include bar codes, biometrics, and voice recognition.

A method of communication between passive tags (ones that do not use batteries to broadcast a signal) and readers.

RFID tags using backscatter technology reflect back to the radio waves from a reader; usually, at the same carrier frequency. The reflected signal is modulated to transmit data.

bar code
A standard method of identifying the manufacturer and product category of a particular item.

The barcode was adopted in the 1970's because the bars were easier for machines to read than optical characters.

The main drawbacks of barcodes are that they don't identify unique items and so scanners have to have "line of sight" to read them.

battery-assisted tag
These are RFID tags with batteries, but they communicate using the same backscatter technique as passive tags (tags with no battery).

They use the battery to run the circuitry on the microchip and sometimes an on-board sensor.

They have a longer "read range" than a regular passive tag because all of the energy gathered from the reader can be reflected back to the reader. They are sometimes called "semi-passive RFID tags".

List of Radio Frequency Identification or RFID articles.