RFID tags consist of a microchip connected to an antenna that is constructed of a small coil of wires. The assembly is usually covered with a protective layer (such as a laminated card), which is determined by the type of application. The RFID tag can be a passive tag or an active tag. The RFID tag is also known as an inlay.

Components of passive RFID system:

• An antenna is attached to a microchip.
  
  
• The antenna allows the chip to transmit information to a reader, which also has an antenna.
  
  
• The reader is the device that actually sends out the radio waves to create a magnetic field. A passive RFID tag draws its power from this magnetic field, which powers the circuits in the microchip allowing it to transmit data back to the reader.
  
  
• The reader transmits data to a computer system.
  
  
• The computer passes the data onto a network.
  
  
• Software determines how the data received should be used.

Microchip

The most expensive read/write, active RFID transponders may have microchips with a memory capacity of up to one megabyte (1,000,000 characters). Most tags are inexpensive, passive transponders that can store only 32 to 128 bits (characters) of information, so an identification number is basically the only data that the read-only tag will contain. When the number is read, detailed information stored in a database in a computer can be accessed. This is similar to a barcode system in which data, such as a price, is accessed when the barcode is read; however, the barcode must come in direct contact with an optical scanner/reader and the RFID tag is capable of transmitting data to the reader via radio waves and therefore, it does not have to be in direct physical contact with the reader.

Antenna

The antenna allows the chip to receive and relay information, such as an ID number of an individual product. Some antennas are constructed of metal and are etched or stamped from metal, such as copper. Other types of antennas are printed with digital or conventional equipment. Advances in technology are allowing printed antennas to achieve the functionality of traditional materials. Printed antennas are also less expensive. One of the most popular methods of printing antennae is with the use of silver conductive inks printed on plastics substrates or paper. Testing of RFID antennae is usually performed with ohmmeters, milliohm meters, RF network analyzers, impedance-measuring equipment, and other types of similar devices.

RFID tags can be manufactured in several different shapes and sizes depending on the type of application in which they will be used.

• Some RFID tags are the size of a pencil lead or are less than a half-inch in length and can be inserted under the skin of animals and livestock.
  
  
• Screw-shaped RFID tags are used to identify specific trees.
  
  
• Rectangular RFID tags found in some products are used as an antitheft device.
  
  
• Large, heavy duty tags that are several inches in length, width, and depth are used to track large containers or large vehicles such as trucks or rail cars.

RFID tags operate under different radio frequencies, depending on the application. The FCC of the US government determines the limits on power output of RFID systems as well as the different radio frequencies that can be used. Low, high, and ultrahigh (UHF) frequencies are used with RFID transponders.

• Low and high frequency tags are less expensive than UHF and are best used for merchandise tracking, animal and livestock identification, and security access.
  
  
• Tags with UHF frequencies use more power than low and high frequency tags, but they have a greater range and the data transfer rate is faster. They are best suited for applications in which the tag and the reader have a more direct path with one another. Rail car tracking and automated toll booths are some of the uses.

The communication range between the RFID tag and the reader depends on the frequency, the antenna size of the tag, the antenna size of the reader, and the output power.

• Low and high frequency devices have communication ranges of a few inches to several feet, depending on the application.
  
  
• Ultrahigh (UHF) may have ranges of 25 feet or more.

The radio signals can transmit through many substances such as rain, fog, snow, dirt and grime, painted surfaces, etc. This gives RFID tags a distinct advantage over optically read items, such as barcodes, which would be useless under similar conditions. An RFID reader can receive data from as many as 1,000 tags per second.

RFID quality control is a necessity because groups of manufactured inlays may have experienced some damage before they reach the printer or converter. The chips in the inlays can also be damaged during the printing or converting process, which renders the RFID tag useless. Special substrates can be used to limit the damage to the chips. Quality control after printing or converting is also important to ensure that the chips were not damaged and will be functional.

When RFID antennae are manufactured, they are usually tested with ohmmeters, milliohm meters, RF network analyzers, and impedance-measuring equipment. It is also important to remember that RFIDs are electronic devices and therefore should not be exposed to, or stored near, areas where high levels of electromagnetic or static energy may exist.