The main factor that characterizes the RFID system is the Tags. Before we dive into the details of the tags it’s important to know about the readers, it is to be noted that generally a Passive Tag reader can’t read an active tag and vice versa, however these days there are these multi-protocol readers which can read more then one type of tags.
The RFID reader is a device that creates an electromagnetic signal, which is transmitted to the RFID tags through one or more antennas. Under normal operation, the reader is continuously transmitting the electromagnetic signal in search of one or more RFID tags. The RFID reader also performs a second function of monitoring for electromagnetic signals from the RFID tags via the same antenna.
Passive RFID Tags
The Passive tags do not contain a power source. To power the tag circuitry, the tag
relies on electromagnetic power obtained from the RFID systems antenna. Since passive tags do not contain their own power sources, the designs can be simpler and less expensive.
They can also have an unlimited shelf life in comparison to active tags. This has made the passive tag the focus of most government and commercial RFID mandates. The downside of all passive tags is their extremely limited range. Since passive tags depend on power from the reader and antenna, with the current technology, passive tags must be in close proximity to the reader and antenna in order to obtain sufficient power to transmit a signal.
Semi Passive RFID Tags
Tags can also be designed with features found in both passive and active tags. These
are attempts to retain the advantages while eliminating the disadvantages of each type. Semi-active tags typically use an internal battery to power circuitry that is internal to the tag itself. Typically, circuitry on semi-active tags includes sensors for monitoring environmental conditions such as temperature and humidity. Sensors can also be powered to detect vibration or movement. These are typically used to monitor the possibility of damage or unauthorized movement during transport or storage.
However, in contrast to active tags, the semi-active tag does not use its internal power
source to communicate with the antenna. For communications functions, the semi-passive tag relies on electromagnetic field power received from the system’s antenna. By conserving its internal power in this manner, the internal battery life can be greatly extended.
Active RFID Tags
In contrast to passive tags, active tags contain an onboard power source. This is
usually in the form of a small battery. The battery powers both the tag’s internal circuitry and the onboard antenna. The additional circuitry required by the battery as well as the battery itself requires that active tags be larger and more expensive than passive tags. Many active tags, for example, have plastic housings. These cannot simply be adhered to high-volume inventory in the same manner as a film or Mylar-based passive tag. Because of this, specific consideration must be made to affixing the active tag to the inventory
or pallet being tracked.
As a result of the additional power offered by the battery, the range of active tags is generally far superior to that of passive tags. Active tags can have transmission ranges measured in hundreds or even thousands of feet instead of just a few feet, as is normal in the case of passive tags. Active tags conserve battery power by normally existing in a sleep mode. The tag is woken up or activated by entrance into an RFID system interrogation zone.
For more information about RFID and our research in this area, see: