In RFID systems, there are two types of RFID tags widely used - passive and active.

Passive RFID Tags

Passive RFID tags are powered by RFID reader that emits an electromagnetic field.

Once the RFID tag is detected by the RFID reader (via the antenna), the reader transmits energy to the tag which powers it enough for the chip and antenna to send information back to the reader. Then the reader transmits this information back to an RFID computer program for interpretation. 

The frequency of the reader must match the frequency of the Passive RFID tag, which mainly use three frequencies to transmit information, including: 

125-134 KHz, Low Frequency (LF)

13.56 MHz, High Frequency (HF) and Near-Field Communication (NFC)

865 – 960 MHz, Ultra High Frequency (UHF)

Passive RFID tags generally fall into two categories: inlays and hard tags. Inlays are typically quite thin and can be stuck on various materials, whereas hard tags are just as the name suggests, made of a hard, durable material such as plastic, metal or ceramic.

Active RFID Tags

Active RFID tags are powered by an internal battery to continuously broadcast their own signals via BLE (Bluetooth Low Energy) or WiFi. There are three main frequencies used by active systems - 433 MHz, 915MHz and 2.45 GHz.

Active RFID systems contain three main essential parts- a tag, antenna, and reader or interrogator. Active RFID tags possess their own power source – an internal battery that enables them to have extremely long read ranges as well as large memory banks.

The battery in an active RFID tag can supply enough power to last between 3-5 years, but when it runs out, the active tag will need replacement, as the batteries are not replaceable in current market.

Two different kinds of active RFID tags are available: beacons and transponders.

Beacons - In a RFID system that uses an active beacon tag, the tag will send out its specific information every 3-5 seconds, and their signal is readable up to several hundreds meters away. But in order to conserve battery life, they may be set to a lower transmit power to reach about 100 meters reading distance.

Beacon tags are very common in the oil and gas industry, as well as cargo tracking applications.

Transponders - In a system that uses an active transponder tag, the reader will firstly send out a signal to the transponder, which then send back with the relevant information. Because they only activate when near the reader, transponder tags are much more battery-efficient than beacons. 

Active RFID transponders are commonly used in secure access control and in toll booth payment systems.