Finding the right RFID tag
Selecting an RFID tag can be a daunting task, so how do you decide?
- Passive tags are the lowest cost tags, but have the shortest range.
- Active tags can transmit at will, have sensors added, and provide verification that the message is received. However, they have a finite battery life.
- 2.4 GHz, and 13.56 MHz are two frequencies that are the most universally accepted.
By Ronald Pulvermacher
RFID stands for Radio Frequency Identification. It normally refers to passive tags, but it can also be applied to active tags.
What is a passive RFID tag?
Tags that receive enough power from the interrogating reader device to power up the tag allowing it to transmit a unique identification number and some extra optionally information are called passive tags. These tags do not contain batteries and are the lowest cost tags in the marketplace. The read range is relatively short from fraction of an inch to 30 feet depending on tag frequency, antenna size, and power of the interrogator field. There are low frequency (LF), high frequency (HF), ultra-high frequency (UHF), and micro-wave tags available.
What is an active RFID tag?
Tags powered by battery, either rechargeable or non-rechargeable, are active tags. This allows the tag to transmit “at will” and typically does not have to be in close proximity to the interrogator. Because active tags have an on-board power source, its transmit range is much greater than passive tags and can be 35-1,000 feet and further. In the U.S., the FCC limits the amount of power it can transmit at, and that varies by frequency. Other countries have similar but often different transmit power restrictions. Active tags can also interface to sensors for collecting, temporary data logging, and reporting sensor data along with its identification (ID) number. Active tags can incorporate a passive wake-up antenna to allow it conserve power until it receive a wake up signal typically at a door way or other choke point.