The key elements of RFID technology are the reader and the tag. The reader emits an electromagnetic wave at a UHF frequency and receives the backscattered modulated signal from each tag in its range. The label usually does not have a battery (ensuring sustainability) and costs a few minutes 0.02 €. For these reasons, RFID technology is fundamental to the adoption of the Internet of Things, as, at very low cost, it creates the conditions for interaction with the object to which it is attached.
The key elements of a label include an AC to DC converter (rectifier), a transistor and an antenna. The rectifier constantly received the incident power from the reader, converting it to the necessary DC voltage for the transistor’s operation. Particularly critical is the proper matching of the tag’s antenna to the rectifier's capacitive load to ensure maximum power transfer.
The RFID labels are manufactured in various sizes, shapes and different materials, according to the requirements of the applications. They may have a battery or not. The most common form is printed labels on self-adhesive paper without a battery. They cost only $ 0.02 and thanks to their low cost they can be used for each product without significantly increasing the cost of the product. There are special tags for metals, for liquids, waterproof-ones, etc. Depending on their size (surface), they demonstrate significant changes in their antenna gain and hence the maximum reading distance. For example, a small label of 1.5cm x 1.5cm size can be read just 1m away while a tag measuring 8.2cm × 3.2cm can be read from a 10m distance. However, the application itself requires the appropriate label size. That is, in a small box of medication one can attach the small tag, expecting a small read-region.
Readers may have the transmitter and the receiver together, so they are called monostatic readers, or separately so they are called bistatic. Depending on the number of transponders operating simultaneously, a reader can read labels on multiple frequencies (multiple channels).