Ξ May 3rd, 2009 | → Comments Off on RFID Tags Maximum Read Distance | ∇ General RFID Questions, RFID News |
There is so much confusion on RFID tag read distances and there is certainly a lack of standardization throughout the industry.
Each manufacturer seems to use a different method to calculate the read distance for their specific offerings. Some companies use the same reader for each tag and set at a specific power rating, others just make a read and write distance statement without offering any details on how they actually calculated the read and write distances.
Many companies provide a read and write standard based on free air – that is they actually read the tag in a relatively quiet environment but do not mount the tag to anything. So all that you are getting is a free air read – this means nothing other than in free air the tag will read to a specific distance. If you mount the tag onto cardboard – heavy paper materials, plastic, wood or other similar materials, there likely will be a maximum read distance change in the specification. Likewise if you mount the tag onto metal or another hard surface the tag read distance will probably drop dramatically.
For metal mount tags – many of the specifications are based on free air read distances and not actually attached to a metal surface. Sometimes manufacturers call the RFID tag – a “Surface Independent Tag” – meaning the tag can be mounted on a number of different surfaces and it will read. You may have only a short read distance compared to the “Free Air Specification” but the tag will read! With surface independent tags on what surface was the read distance calculated?
Metal mount tags also have their own unique issues for read distances. There are several different techniques for making a tag read on metal. Some manufacturers put an air cushion under the inlay so that the tag does not contact the metal. This allows the tag to be read but usually the read distance is not that great as it is dependent on the air spacer of the tag. Other manufacturers use an isolation material so that the tag inlay is protected from the metal surface by a material that re tunes the tag to a different frequency. In free air the tag will not read very well, but when attached to a metal surface the read distance increases. Some metal tag manufacturers use a combination of isolation materials plus the adjust the tag antenna properties so that the tag itself actually operates on a totally different frequency. In free air these tags really have short read distances, but when attached to the backing material and then placed on the metal the read distances dramatically improve. The longest read distance metal mount tags use a combination of isolation materials and retuning the tag to a different frequency.
The same concepts also go for windshield tags – using a standard tag will work but the read distance is poor when compared to a tag inlay that has been tuned to operate when attached to a vehicle windshield. Note that all vehicle windshields are laminated glass so attaching a windshield tag to a piece of glass does not work as well. In free air these windshield tags do not read very well, but when attached to the inside of a vehicles windshield the tags improve extremely well. SkyRFID windshield tags are tuned to the laminated glass so the free air read distances are under 3 meters (9 feet) but when installed the read distances go over 8 meters! (25 feet) without any problems.
Other problems with the maximum read distance is that the distance may have been calculated in a special environment to obtain the best results. So when you use the tag in a real world application your read distance is not the same as the specifications.
Last but not least of the problems with calculating read distances is the hardware itself – is it a hand held reader, is it a fixed reader, what manufacturer of reader, what is the power setting used to determine the read distance, what cables and antennas were used to calculate the read distance, mono-static, bi static, circular polarization, linear polarization, what attenuation, what beam width, and so many more that until the industry comes up with a standard way of calculating read distances your results will probably vary from the manufacturers specifications
Since there are all of these variables in the maximum read distance of any tag the best solution is to work with your vendor, understand the differences in manufacturing, ask questions and then obtain some samples and test in your environment before purchasing larger quantities.
About SkyRFID Inc.
SkyRFID is a privately held Canadian company specializing in Automated Data Collection (ADC) solutions that use Radio Frequency Identification (RFID) technology. SkyRFID has over 20 years of experience in ADC and provides customers with everything from a single consulting engagement to a complete turnkey global solution. SkyRFID personnel have implemented solutions in all of the Americas and many other countries with great success. SkyRFID provides solutions in Low Frequency (LF), High Frequency (HF), Ultra High Frequency (UHF) and Microwave (SHF) RFID technologies and has considerable expertise in Animal Management,Asset Management, Access Control, Document Management, Library Systems, Field Service, Manufacturing, Parking Management, Supply Chain, Warehousing and Distribution, Event Management, Fleet Maintenance, and Custom Tags.
For more information contact SkyRFID Inc. at +1 647-476-3265
Web Site: www.skyrfid.com
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