A passive tag is an RFID tag that does not contain a battery. The RFID reader supplies the power for a passive tag. When radio waves from the reader are encountered by a passive RFID tag, the coiled antenna within the tag forms a magnetic field. The tag draws power from it, energizing the circuits in the tag. The tag then sends the information encoded in the tag's memory. See also active tag.
Advantages of a passive tag:
- With no battery to rely on, the tags can be in use for up to 20 years.
- Passive tags are inexpensive to manufacture.
- The small size of the tag allows nearly unlimited applications in a wide variety of industries.
Disadvantages of a passive tag:
- The tag can be read only at very short distances, typically a few feet at most.
- It may not be possible to include sensors that can use electricity for power.
- The tag remains readable even after its product has been sold and is no longer being tracked. This raises privacy concerns.