RFID tags (Radio Frequency Identification) are the most common and common form of packaging for RFID devices. They are self-adhesive intelligent devices that allow information to be stored[1]​ and are characterized by their flexibility, their "thinness", the ability to be printed with human readable code on their front face and the memory capacities that will depend on the integrated circuit that is incorporated.

The most common or mass-consumed passive RFID tags are made up of the following layers:

The entire conglomerate of layers exposed above comes on a silicone backing paper that allows each of the labels to be dispensed at will or in automatic application machinery.

There are other layer compositions for RFID tags and they depend on whether the inserted inlays come with a component called strap. However, its composition is very similar and its behavioral implications once applied are not relevant to the user.

In addition to passive RFID tags, there are active and semi-active tags. Active tags incorporate an internal power supply that allows them to emit signals autonomously. For their part, semi-active tags are activated by a signal received by an RFID reader, but unlike passive tags, these have a battery that powers the chip, allowing a greater reading range.[1]​.

It is a point that generates a lot of confusion when defining the type of technology to be used in RFID tags, since the most used frequency bands of RFID, within the electromagnetic spectrum, are those shown in the following graph:

Specifically, it is not the same antenna for a frequency of 13.56 MHz as for one of 868 MHz.

In the image on the right you can see two forms of antennas for RFID tags, highlighting the differences between the copper turns for the different HF and UHF frequencies. It will be evident that in order to obtain reasonable costs for the use of RFID technology, working with UHF frequencies provides greater advantages in the cost of RFID tags.