Unlike with other materials, RF waves cannot penetrate metal. Metal blocks and reflects RF waves, which poses quite a challenge when using RFID technology for tracking metal assets or in environments with a lot of metal objects. And that’s not all, metal also couples with the tag antenna and detunes the tag so the read range is drastically shortened. This means that a common passive RFID tag placed on a metal asset cannot be read from a distance even within the line of sight or performs very poorly. But what to do when you need to track tools, machines, kegs, containers, auto parts and other metal items?
Fortunately, there are several options that help mitigate this issue.
1. Do not place the RFID tag directly on the metal surface
Are there non-metal surfaces on the item? Can you place the tag on the (non-metal) packaging? Can you use hang tag or folding tab tag that does not touch the metal surface? These are classic avoidance methods that work in many circumstances and allow you to use a standard RFID inlay or label without the extra expense of a specialized tag. Non-specialized labels are produced by companies like Alien Technology, Smartrac, Omni-ID and other vendors.
RFID Folding Tab Tag used for servers
There are several manufacturers on the market that specialize in tags that are made to be used on metal surfaces. These tags are usually encapsulated. The encapsulation serves several purposes. First of all, the tag instantly becomes more rugged and often reusable. The tag is also offset from the attachment surface, so that the tag antenna does not touch the metal item directly. The offset is precisely calculated so that the tag can harvest the signal not just coming from the reader but also the signal reflected off the metal surface behind the tag. This can happen only if the antenna and the offset are perfectly matched. In some circumstances this design extends the tag read range beyond a standard distance. Such tag will not perform as well when mounted on other surface materials, however, it will excel when mounted on metal. There are several vendors that make metal mount encapsulated tags, such as Omni-ID, Confidex, Metalcraft, Vizinex, HID and others.
Encapsulated Metal Mount Tags
Note: Sometimes, the tag antenna is completely insulated from the metal surface and does not use the metal to increase performance. In this case, the tag is universal and can be used for any surface, not just metal.
Metal Mount RFID Tag Diagram
Universal Encapsulated RFID Tag
3. Use mount on metal labels
Besides encapsulated tags, you can also find mount on metal labels. These labels are usually thicker than common paper or polyester RFID labels, again because they need the offset layer from the metal surface. They are also specifically tuned to work with metal, therefore, these labels may not perform as well when placed on other types of materials. While most mount on metal labels need to be preprinted by the manufacturer, there are some new labels on the market that can be printed by a desktop RFID printer encoder, such as Confidex Silverline.
4. Use semi-passive or active RFID tags
Active and semi-passive tags are always encapsulated, therefore, insulated from the surface. In addition, their power and presence of a transmitter (in active tags) provides stronger signal, which due to reflections and signal bending can provide solid performance even on metal assets and in metal environments. However, active and semi-passive tags come with higher cost and therefore are suitable for high value assets. Some of the manufacturers of semi-passive tags are CAEN, Omni-ID and active Savi Technology, Identec Solutions, Omni-ID and others.
Semi-passive RFID Tag