måndag 27 maj 2013

RFID Journal Glossary terms

RFID Journal Glossary terms
Near-field communication: RFID reader antennas emit electromagnetic radiation (radio waves). If an RFID tag is within full wavelength of the reader, it is sometimes said to be in the "near field" (as with many RFID terms, definitions are not precise). 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)
Orientation: The position of a tag antenna vis-à-vis a reader antenna. With UHF systems, readers can be either circular-polarized or linear-polarized. When using a linear polarized antenna, the tag reader and antenna reader must be in alignment in order to achieve the longest reading distance. If that tag antenna is aligned vertically and the reader is sending out signals horizontally, only a small portion of the energy emitted by the reader will hit the tag antenna.
Passive tag: An RFID tag without its own power source and transmitter. When radio waves from the reader reach the chip’s antenna, the energy is converted by the antenna into electricity that can power up the microchip in the tag. The tag is able to send back information stored on the chip. Today, simple passive tags cost from U.S. 20 cents to several dollars, depending on the amount of memory on the tag, packaging and other features.
Reader module: The electronics of a reader, including a digital signal processor, on a circuit board. Modules can be put in an RFID label printer or other device, as opposed to a standalone reader.
RFID tag: A microchip attached to an antenna that is packaged in a way that it can be applied to an object. The tag picks up signals from and sends signals to a reader. The tag contains a unique serial number, but may have other information, such as a customers' account number. Tags come in many forms, such smart labels that can have a barcode printed on it, or the tag can simply be mounted inside a carton or embedded in plastic. RFID tags can be active, passive or semi-passive.
SAW: A technology used for automatic identification in which low power microwave radiofrequency signals are converted to ultrasonic acoustic signals by a piezoelectric crystalline material in the transponder. Variations in the reflected signal can be used to provide a unique identity.
Signal attenuation: The weakening of RF energy from an RFID tag or reader. The energy emitted by the reader naturally decreases with distance. The rate of decrease is proportional to the inverse square of the distance. Passive UHF RFID tags reflect back a signal at very low power levels. A tag’s reflected signal decreases as the inverse fourth power of the distance between tag and reader. Attenuation can be increased by external factors as well. For instance, water absorbs UHF energy, causing signal attenuation.
Attenuation: The reduction of energy. See signal attenuation.
Surface acoustic wave: A technology used for automatic identification in which low powermicrowave radio frequency signals are converted to ultrasonic acoustic signals by a piezoelectric crystalline material in the transponder. Variations in the reflected signal can be used to provide a unique identity.
Radio Frequency Identification: Any method of identifying unique items using radio waves. Typically, a reader (also called an interrogator) communicates with a transponder, which holds digital information in a microchip. But there are chipless forms of RFID tags that use material to reflect back a portion of the radio waves beamed at them.
Synchronization: In RFID, the term refers to timing readers or reader antennas near one another so that they don't interfere with one another.

2009-11-10 01:20 

2 kommentarer:

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