Passive RFID Tag

A passive tag is an RFID tag that does not contain a battery; the power is supplied by the reader. 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.
         The advantages of a passive tag are:
• The tag functions without a battery; these tags have a useful life of twenty years or more.
• The tag is typically much less expensive to manufacture
• The tag is much smaller (some tags are the size of a grain of rice). These tags have almost unlimited applications in consumer goods and other areas.

          The major disadvantages of a passive rfid tag are:
• The tag can be read only at very short distances, typically a few feet at most. This greatly limits the device for certain applications.
• It may not be possible to include sensors that can use electricity for power.
• The tag remains readable for a very long time, even after the product to which the tag is attached has been sold and is no longer being tracked.