Understanding Passive RFID

All RFID tags contain a wireless radio, processing circuitry, and an antenna. But a passive tag does not contain a battery or internal power source; the power needed is supplied by a reader (also known as an interrogator). When radio waves from the reader are encountered by a passive RFID tag, the tag draws power from reader’s electromagnetic field, energizing the circuits in the tag. The tag then powers-up quickly, initializes, and then sends the requested information encoded from the tag’s memory.
The features of Passive RFID systems are:

  • A passive tag can generally be read at distances typically ranging from a few inches up to about 30 feet (10 meters) – depending on the the type of tag.
  • Sensors can be used with passive tags, if the sensor power requirements are very small.
  • Passive tags can have very long useful lifetimes; up to dozens of years after tag is attached to the asset being tracked.
  • Passive tags typically cost less than $0.50/ea. to manufacture; however, the passive RFID readers are general quite complicated and expensive.
  • The tag can be very small (some tags are smaller than a grain of rice).
  • These tags have many applications in a wide variety of industries.
  • Most passive tags implement one of the global industry standards, enabling interoperability between a number of suppliers.
  • Some asset materials may dramatically affect the performance of some passive tags (depending on the tag design).

Understanding Active RFID

An active RFID tag is equipped with a battery (or power source) that can power the tag’s circuitry. Some active tags contain rechargeable or replaceable batteries; others are sealed units. Active RFID tags can autonomously transmit their identifier (id) periodically, or upon some received signal or other event to a reader (interrogator) using their own internal power. Simple active RFID readers usually just receive transmissions from tags, and rarely transmitting any information. More complicated active RFID systems such as RTLS, may require sophisticated readers and protocols.

The features of Active RFID systems are:

  • Active tags can be read at distances of up to 300 feet or more.
  • On-board power can enable independent sensor monitoring or control
  • An active RFID tag’s battery lifetime may range from a few hours up to about 5 years; depending on the design, after which the batteries must be recharged or replaced.
  • Active tags are typically more expensive than passive tags, often costing $20 or more each; howver, active RFID readers are generally quite simple and inexpensive.
  • Active tags are often physically larger than passive tags.
  • Because of their cost, active tags are used to mange more expensive assets.
  • Some types of active RFID tags are able to implement mechanisms to determine and transmit their location along with their id.
  • Most active tags implement proprietary communication protocols.