Fundamentals about RFID TAGS

RFID tags, commonly identified as RFID transponders, typically consist of three basic components: an integrated circuit (IC), an antenna or coil, and a substrate in which the above elements are housed.

The illustrations above depict two typical RFID tag designs. The design on the left depicts a coil, optimized for use in LF/HF (low/high frequency) RFID systems, which operate in a lower frequency range. The tag uses the induction method as a means of power and communication. The UHF (ultra-high frequency) RFID tag on the right uses a dipole antenna design. The Tag uses RF transmission (radio frequency operation at a much higher frequency) to obtain power and realize communication. The higher the frequency of the Tag, the faster the information is transmitted and the less power is required to receive/transmit information compared to a tag that uses a lower frequency; lower frequency require more time. The antenna that transmits the signal can also be smaller at higher frequencies, achieving greater reading distances.

However, it is important to note that the choice between a UHF tag and an HF tag depends on the specific application and can therefore be right or wrong based on the specific needs. A tag that can be read over long distances can be advantageous in some situations, but can become problematic if it is necessary to interact with a specific tag while ignoring those nearby. Therefore, it is critical to understand the different characteristics and apply them based on the specific needs of the application.

IC chip for RFID tag

The IC chip on the RFID tag is very small, no larger than a grain of sand (see photo above). This compact size makes the tag suitable for a wide range of applications. However, the cost of the IC chip is directly proportional to its memory capacity and functionality. 

For its operation, the IC chip depends on the energy it receives, which is captured through its antenna. When a read command is issued from the RFID reader, the reader generates an RF energy field through its antenna. There is a maximum distance within which the antenna can effectively capture the RF energy required to activate the tag. This distance depends on the transmission power of the RFID reader and the size of the tag coil. In general, a larger coil allows the tag to be activated at a greater distance than a smaller coil. When the tag receives enough power for its operation, the IC chip immediately activates and responds to the RFID reader's command. Typically, the tag reads the binary information stored within it and responds to the reader. The basic information often read is the tag's unique identification number. If the tag contains additional data entered by the user, the reader can issue a command to retrieve all this data. This whole process takes place in a few microseconds, making RFID communication extremely fast and efficient.

The RFID tag is essentially similar to a flash memory card that is commonly used for one's digital camera. the RFID tag, however, is wirelessly powered and has much less memory. The available memory can range from the few bytes needed to store the tag ID, to about 8Kbytes to store other user data. Each letter of the alphabet takes up about 1 byte of space, so an 8Kbyte memory can store about 8000 characters. Tags with larger memory capacity usually have a higher cost. Depending on the chip, tags can be pre-programmed during production and contain either the same ID or a unique ID (Identification Number). A unique ID allows the reader to differential communication with multiple tags read in the same range. Some IC chips are capable of destroying the tag, preventing subsequent readings and rendering the tag useless. LF and HF tags use induction methods for short range (less than 10 centimeters) readings. UHF tags can reach up to 10m. The distance varies depending on the power transmitted by the RFID reader and the size of the antenna on the tag.