RFID Tags Overview - Different Types, and How to Choose
SageData is based in Ottawa, Ontario, Canada
RFID - Radio Frequency Identification is a technique which uses a radio signal to
communicate with a small tag,
and, by extension, the item to which that tag is attached. These are
commonly small items, goods in transit, fixed assets or file folders, but use can extend up to
vehicles and agricultural or construction machinery.
RFID tags can be grouped by a number of characteristics, specifically:
Active or passive tags, circular or linear antenna, operating frequency.
Active or Passive RFID Tags
Passive tags have no internal energy source. They have an antennae or receiving coil, which collects and stores energy transmitted by the reader. The tag then emits a short burst of energy, encoded with the critical information it is communicating. Passive tags only transmit when they have been energized by a reader.
Passive tags tend to be cheaper and smaller, and their life is only limited by the reliability of their components. They can be expected to function for decades. The range at which the tags can be read depends on their frequency of operation, and the power of the reader. Range can vary from less than a centimeter to several meters.
The ability to read a tag is affected greatly by the reader. Readers can be fixed, or integrated with a portable handheld computer. In mobile applications some readers are still relatively bulky and large, with the transmitting and receiving antennae being three or four inches high and just as wide. Others are smaller, sometimes with a reduced read range as a consequence.
Active tags get their power from a small internal battery.
They can be read at greater distances, but they tend to be slightly larger and more expensive. The life of an active tag is limited by the life of the battery, which generally cannot be replaced. The life of an active tag is of the order of several years, though this can be modified as the tag is set up, with speed of response being traded for battery life. From the time of manufacture, until the battery expires, these tags regularly transmit a small message which uniquely identifies them whether in range of a reader or not. A typical cycle would be once per second.
Antennae types - circular or linear
The two different formats of antenna result in different reading capabilities.
The linear antenna can give a longer read range, but requires a specific alignment for the tag
read. If the reader is held
on its side, then range is dramatically diminished. For a
the orientation of the reader with respect to the tag does not affect read range.
As an example, a typical mobile circular antennae may have a read range of six feet, regardless of orientation, compared to a similar linear reader, which might have a read range of twelve feet when properly aligned, but only twelve inches when either the tag or the reader is rotated through ninety degrees.
Frequency Range - passive tags
Tags can today be broken down by frequency into three categories. Each has specific
benefits and drawbacks,
and choosing the
best tag depends very much on the application.
Low Frequency tags operate in the range 125 KHz. These were the first tags to be developed, and are frequently used in animal tracking. Their physical design makes them thicker and more expensive to manufacture. Range is of the order of an inch or so.
High Frequency RFID tags operate in the range 10-15 MHz. These are frequently used for access controls. These tags are thinner and typically occupy a similar surface area to a credit card, though smaller button versions are available which can be sewn into the hem of a garment. Read range is typically up to twelve inches.
Ultra High Frequency tags operate in two bands, around 900 MHz and 2.4 GHz. These are the most recently developed tag, and are used in unit tracking and supply chain applications. These tags use a simple design, though the antennae still needs to be a few inches long to give a reasonable read reliability. Often, the tags are encapsulated, and may be artificially thick, to enable the tag to be mounted on a metal surface. Read ranges can be up to twenty feet of more, but the tags are more affected by metal or liquid.
We can provide a variety of tags in LF, HF or UHF variants, with different package options available in each category. RFID tags must be carefully selected for each specific application.
If you would like further and more detailed information on your specific application, one of our experts will be pleased to help.
Follow these links for more information on:
- RFID overview
- asset management using RFID
- RFID limitations