Active tags transmit radio waves signals periodically using its on-board battery. A battery-assisted tag activates its battery to transmit radio waves signal only when a RFID reader is close for detection. RFID passive tags has no battery and uses the energy of radio waves that are transmitted from the RFID reader to function. The passive tag is a lot cheaper to operate, but the transmitted radio waves have to be significantly high in order to achieve sufficient harvested power, leading to exposure to higher radiation environment and more vulnerable to interference.
Active RFID tags have a battery, which is used to run the microchip’s circuitry and to broadcast a signal to a reader (the way a cell phone transmits signals to a base station). RFID Passive tags have no battery. Instead, they draw power from the reader, which sends out electromagnetic waves that induce a current in the tag’s antenna. Semi-passive tags use a battery to run the chip’s circuitry, but communicate by drawing power from the reader. Active and semi-passive tags are useful for tracking high-value goods that need to be scanned over long ranges, such as railway cars on a track, but they cost a dollar or more, making them too expensive to put on low-cost items. Companies are focusing on passive UHF tags, which cost under a 50 cents today in volumes of 1 million tags or more. Their read range isn’t as far — typcially less than 20 feet vs. 100 feet or more for active tags — but they are far less expensive than active tags and can be disposed of with the product packaging.