Radio Frequency Identification (RFID): Definitions
(some of the of terms used in RFID technology)
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. The ability to address bits, fields, files, or other portions of the data on a tag.
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.
By changing the amplitude modulation wave, the RFID tag can communicate a string of binary digits to the reader.
The method of changing an amplitude modulation is known as "amplitude shift keying", or ASK.
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 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. 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.
Technologies normally considered part of auto-ID include bar codes, biometrics, and voice recognition.
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.
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.
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".