Learn about the function and construction of RFID tags and how screen printing and other imaging methods are used to produce these devices.
By Wim Zoomer
HF tags are equipped with antennas consisting of four to six windings of copper coil and are sensitive to a frequency of 13.56 MHz . These tags support a maximum read distance of 3.25 ft (1 m). HF tags are used for "smart cards," such as those issued by libraries and for luggage tags in airline baggage-handling systems.
UHF tags respond to a frequency range of 862-950 MHz and have a read/write distance of 16 ft or more. In the US, the UHF standard frequency is 915 MHz. In other parts of the world, different frequencies may be used. The large read distance requires a dipole antenna. Such tags allow postal and courier services to determine the nature of the products piled up on a pallet without having to inspect each package individually. These tags are also used in cards issued to motorists for automatic toll collection.
The microwave RFID tag has a read distance of approximately 3.25 ft and responds to frequencies of 2.45 or 5.8 GHz. Microwave RFID tags are used for logistics applications.
HF and UHF tags are the most popular RFID systems. These tags consist of three main components:
• Antenna—the silver, copper, or aluminum antenna communicates with the reader by transmitting and receiving data.
• Chip—the chip is mounted on the antenna and stores data for transmission.
• Inlay—an inlay is the assembled chip and antenna on a carrier sheet. The RFID inlay can be placed on adhesive paper or plastic to function as a label or tag, or it can be mounted on a plastic card.
Producing RFID Antennas
Manufacturing the antenna is the initial step of the RFID production process. Antennas for HF and UHF RFID tags can be produced in three different ways:
• direct printing with a silver conductive ink
• removing copper or aluminum from a laminate by etching (subtractive method)
• applying an electrically conductive medium and then galvanizing it (additive method)
Each of these methods for manufacturing RFID antennas can be accomplished with a printing process. Depending on the run length and the characteristics required from the antenna, flexography, gravure printing, or screen printing may be used (Table 2).
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