What’s the big deal mounting inductive based RFID tags on metal?

Many times I find myself being asked by customers why the range of inductive-based RFID tags are so limited when mounting on metal or especially in metal. That’s a great question to ask as it also reminds me that the principals of inductive based RFID are not always well known.

For industrial RFID users, there are two main frequencies that are most commonly dealt with. Low Frequency, typically between 70 and 400 KHz and High Frequency, typically using 13.56 MHz. With both of these frequencies, the tags are passive, meaning they do not contain a power source like a battery. So the way these tags are powered are when they come into contact with a magnetic field created by the coil in the read/write head. The coil in the tag then has a voltage “induced” in it, there by powering the tag. For those interested, this is based on a principal called Faraday’s Law.

The problem is that metal around the tags coil also absorb the magnetic field, similar to the way you magnetize other metal objects when you put them near a magnet. But that also means the strength or amplitude of the read/write heads signal suffers degradation or is weakened to the point where it will no longer power the tag reliably.

This is why many industrial RFID vendors make special tags specifically designed with special antennas to isolate and maximize the strength of the heads signal. In some cases, proving ranges as much as 60mm to 150mm in packages smaller then 40x30mm (see Balluff’s offering at www.balluff.com/M-M.). So when mounting on metal is a must, but a desire for maximum range is needed, don’t loose heart, there are products out there designed to solve this for you.


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