Radio Frequency Identification (RFID): Definitions
(some of the of terms used in RFID technology)
Low-frequency tags typical operate at 125 kHz or 134 kHz. The main disadvantages of low-frequency tags are they have to be read from within three feet and the rate of data transfer is slow.
They are less subject to interference than UHF tags.
They can be read at no more than three feet and the data transfer rate is slow. This type of tag is widely used in retailing because it is relatively inexpensive.
Some blocks might be locked, so data can't be overwritten, while others are not.
They have very high transfer rates and can be read from as far as 30 feet away, but they use a lot of power and are expensive. Some people refer to any tag that operates above about 415 MHz as a microwave tag.
Waves be changed in a variety of ways that can be picked up by the reader and turned into the ones and zeroes of binary code.
Waves can be made higher or lower (amplitude modulation) or shifted forward (phase modulation).
The frequency can be varied (frequency modulation), or data can be contained in the duration of pulses (pulse-width modulation).
Some RFID readers use Time Division Multiple Access, or TDMA, meaning they read tags at different times to avoid interfering with one another.
Each antenna scans the field in a preset order. This reduces the number of readers needed to cover a given area; such as, a dock door, and prevents the antennas from interfering with one another.
If an RFID tag is within full wavelength of the reader, it is said to be in the "near field."
If it is more than the distance of one full wavelength away, it is said to be in the "far field."
The near field signal decays as the cube of distance from the antenna, while the far field signal decays as the square of the distance from the antenna.
So passive RFID systems that rely on near-field communication (typically low- and high-frequency systems) have a shorter read range than those that use far field communication (UHF and microwave systems).
Noise can be caused by other RF devices, robots, electric motors and other machines.
This is essentially the reader's blind spot. It is a phenomenon common to UHF systems.