A passive tag
does not have its own power source (there is no onboard battery) or a radio transmitter. It obtains power from the RF waves emitted by the reader. Therefore, it can communicate only when inside the read
zone and while energized by the RF waves. Power from the radio waves operates the tag’s integrated circuit, sending data
back to the reader. These tags usually have read range
of anywhere from few inches to 20 feet and inlays cost approximately $0.10 when purchased in large quantities. They are primarily used in the applications requiring low cost, simple and light-weight tags.
Semi-passive (or also sometimes called Semi-Active) tag has a battery but no radio transmitter. The battery powers its integrated circuit (IC), which helps it to modulate the reflected signal.
The advantage of this type of tag is that it does not entirely rely on power from the reader. Therefore, you can use low-power readers and store more data on the tag. This type of tags is used to get longer read range or to couple the tag with environmental sensors such as temperature, pressure, relative humidity, etc. This tag can be read at a longer range of up to 100 feet.
Active tags have their own battery and radio transmitter. This tag communicates at a longer distance because it is not dependent on a reflected signal. Its communication distance ranges from 100 to 750 feet and it can have more memory
to store data. However, the cost is higher, and tags have larger size and higher weight than passive tags.