Pepperl+Fuchs specializes in producing components for factory automation. This means a very metal-intensive environment is inevitable. RFID low- and high-frequency tags must often be mounted to a metal carrier or metal part.
When mounting an RFID tag to a metal surface, special consideration must be taken to ensure that too much read range is not lost when mounting to this type of surface. The read range is defined as the maximum distance between the RFID tag and the read head while still allowing communication between the two. A proper maximum read range number will be 99.9% accurate even when all slight variations in tag and read head manufacturing performance are taken into consideration. Here are some typical metal mounting options:
Tags with ferrite material
For 20 years we have seen RFID tag coils wound around ferrite cores. These tags give you a very short read range but can be embedded in metal. This ferrite material amplifies or focuses the read field to increase the range. This technology can be extended to tags that are surface mounted on metal as well. Ferrite material is adhered to the back of an RFID tag and the results are similar. The range goes from only a few millimeters to almost 50 mm. That is a huge increase, and this option should be considered when a very thin tag is required.
Tags with built-in spacers
If you know that you are going to mount a tag to a metal surface and you want to maximize range and minimize size it is best to design the tag specifically for the application. This is done by tuning the RFID tag specifically for metal mounting and then also making it thick. The “thick” tag is basically a tag with a built-in spacer. You don’t have to worry about picking the right spacer for the application. You just buy it and mount it. When space or tag size is not a consideration, this is the best way to go.
What about the hundreds of standard tags that are available? The best way to mount these is with a nonmetallic spacer. The thicker the spacer the closer to the “in air” read range you will get. We say “in air” to refer to the read range you would get when no metal is around the tag. When the RFID tag is more than 1.5” away from metal, the range can be approximated by this value. Make sure the spacer is made out of a material that's right for the application. If you use a high-temperature RFID tag good to 250 °C, then make sure the spacer is also rated for this temperature. You don’t want the spacer to fail prematurely. In the RFID RFID Read/Write Ranges manual (PDF), tables are available that provide the read/write ranges of most standard tags when mounted on steel with 10 mm spacers. Our 10 mm Teflon spacers are available in 30 mm and 50 mm diameters, and they are good to 250 ºC. This will cover most application requirements. Spacers less than 10 mm thick will provide less range, while thicker spacers give you more range. If you need more range, then a thicker, 25 mm spacer might work.
Specially designed tags for metal mounting may get you the most range, but selection may be limited. Think about using a tag spacer when mounting your tag to metal in your next application.