Unfortunately there isn’t an easy answer to this question.  The short answer is that most handheld RFID readers can read most RFID tags anywhere from 1 to 20 feet.  Most fixed readers can read most RFID tags anywhere from several feet to 40 feet.  There are even a few very large tags designed for shipping containers that can achieve read ranges of well over 100 feet, but the size of these tags is not practical for most fixed assets.  These read ranges vary significantly, and don’t really answer the question sufficiently.  So let’s go into the details of the factors that will affect the range of an RFID tag.





It depends primarily on the following factors:

1.    The type of reader and antenna used (handheld or fixed reader)

2.    The type/size of tag used

3.    The type of asset being tagged

4.    The placement of the tag on the asset

5.    The environment

6.    The orientation of the tag in relation to the reader’s antenna



1.    Reader/Antenna Type

Generally fixed readers have more power and larger antennas than handheld RFID readers, so their effective read range is greater.  Although it depends on the vendor and model, fixed readers can often read 2-3 times the range of handheld RFID readers.


Another important variable that can affect the read range is the type of antenna on the reader.  The two most common types of antennas are circular and linear.  Linear antennas have a very focused wave propagation.  For maximum read range, the linear antenna and the antenna on an orientation sensitive tag need to be in the same orientation.  For example, if the linear antenna on the reader is in a horizontal position, the orientation sensitive tag also needs to be in a horizontal orientation.  If either the reader antenna or tag antenna orientation is changed, the read range can drop to a fraction of what it was when they were both at the same orientation. 


Circular antennas work well when the orientation of the tag will vary or cannot be controlled.  They have the ability to read a tag at almost any orientation, but the range is typically less than a linear antenna because the wave propagation is not focused in a particular orientation.



2. Type/Size of Tag

There is no “standard” passive RFID asset tag.  There are literally hundreds of types, sizes, and options to choose from.  Generally the larger the tag, the larger its antenna will be, so larger tags typically have greater read ranges than smaller tags.  However, there are exceptions to this rule.  A good example is tags that are specifically designed to mount on metal.  Many of these tags, although small, can achieve greater read ranges that larger tags when mounted on metal, because they are designed to use the metal to improve their performance.  Other specialty tags that are specifically designed for mounting on a particular type of material can also achieve greater read ranges than larger tags when attached to the type of material they are designed for. 


Many companies spend a lot of time and effort searching for the smallest tags they can find, thinking that all RFID tags have the same read range.  They don’t realize that these smaller tags are probably going to yield much shorter read ranges than larger tag options.


3.    Type of Asset being tagged

The material the asset is made of can have a significant effect on the read range of a tag.  Generally any asset with metal or liquid can cause interference.  Depending upon how close the tag is placed to the metal or liquid, the interference can be significant.  For instance, a tag that can be read by a handheld in “free air” at 20 feet, might only have a 6 inch read range when placed on a laptop.  Even though the outer shell of most laptops is plastic, there is a lot of metal underneath which causes a lot of interference.  For assets with metal and liquid, you will want to evaluate tags that are specifically designed to work on metal or liquid. 


4.    Tag Placement

The placement of the tag on the asset can affect the read range.  Some metal mount tags perform better if they have free-air on certain sides of the tag, so when they are placed dead center on an asset with a lot of metal, the performance can drop.  It is also sometimes difficult to tell if and where there might be metal on an asset.  PCs, laptops, printers, severs, digital projectors and similar assets that often have a plastic outer shell hide the underlying components.  Testing the tags in various areas of the asset will often result in varying read ranges.  Most assets have one or more “sweet spots”.  Finding these can improve the read range of a tag significantly.  Keep in mind that the “sweet spot” for one tag might not be the “sweet spot” for a different type of tag.



5. Environment

Different countries have different regulations and limitations on reader power and the frequency that they operate, which can affect read range.  Readers in Europe operate at a lower frequency and are limited to using less power than their counterparts in the U.S., so the read range for the same type of reader and tag is less in Europe than in the U.S.


Other environmental variables can be weather conditions.  Extreme cold or hot temperatures can affect read range. Humidity and rain can also cause unpredictable variations in read ranges.


In some cases, existing machinery or equipment being used can cause interference, especially equipment that might be operating at or near the same frequency.



6. Tag Orientation

Depending upon the design of the antenna in the tag, it may perform better at certain orientations (i.e. horizontal vs. vertical), depending upon the type of antenna on the reader.  Some tags are designed to be less sensitive to orientation and are usually symmetrical in size rather than long and thin. 


If the orientation of the tag will vary or cannot be controlled, consider using a circular polarized antenna (see number 1 above for more information on circular antennas). You could also consider using a tag that is not as sensitive to orientation.


For more information about RFID Asset Tracking solutions please visit www.inlogic.com.

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The opinions expressed herein are my own personal opinions and do not represent my employer's view in anyway.

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