1/6/2024 0 Comments Tagit mfg.![]() RFID uses the Federal Communication Commission's unlicensed industrial-scientific-medical (ISM) frequency assignments. Typical tag antenna sizes range from less than an inch to 4 or 5 in. The larger the tag antenna, the larger the signal and the greater the range. Signal strength at the tag is proportional to the cube of the distance (r) from the reader, or 1/r 3. The interrogator antenna is the primary winding of the transformer, while the tag antenna is the secondary. RFID uses transformer theory in the near field. ![]() The near field is essentially the magnetic field produced by the reader's antenna. The electric and magnetic fields regenerate one another along the way according to Maxwell's equations. Most wireless systems use the far field, in which the radio wave breaks away from the antenna and becomes a self-supporting electromagnetic wave. The near-field range extends up to about one wavelength (λ) from the transmitting antenna, where λ = 300/f MHz in meters. This short range is within what wireless engineers call the near field. But this varies with the frequency of operation as well as the antenna size, and it can range from a few centimeters to about 20 ft. To read a passive tag, the distance between the reader and the tag must be relatively close ( Fig. Most readers are fixed in place, but handheld readers are available, too. Working with a computer, the reader recognizes and/or records the tag info and takes the appropriate action, depending upon the application. Then they rectify and filter the signal into a dc that powers up the transponder circuits, which in turn transmit the tag's ID code back to the reader. Passive tags receive the RF signal from the reader. Also called an interrogator, this higher-power transceiver (usually 1 W or so) uses a larger antenna to interrogate the tag. The other major piece of the RFID system is the reader. Another huge time-saving benefit is the ability to scan or read multiple items concurrently. ![]() It's also possible to write to an RFID tag and change its code or content. In addition, automatic reading cuts costs and human reading errors, especially in supply-chain applications. Reading or scan time thus becomes much faster. Furthermore, reading can be automated because orientation of the labeled device isn't an issue. Unlike bar codes, readers don't need a line-of-sight (LOS) scan. A popular tag format is a chip mounted on a plastic sheet that contains an antenna in the form of a small loop ( Fig. Each tag consists of a single chip with an EEPROM containing the ID number and a radio transceiver or transponder. RFID uses electronic tags or smart labels to electronically store a unique identifying number instead of a printed bar code. It goes beyond bar coding to mark, identify, and track everything from products to people. RFID, or radio-frequency identification, is a short-range wireless technology.
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