Anti-metal tags

Making your tags work on metal surfaces

Nov 7, 2016 - 2 minute read

If you’ve ever tried to attach an NFC sticker to the back of your iPhone or perhaps put a Bluetooth pairing tag on a metal peripheral, you’ve probably noticed that the tag will no longer scan. Even if the tag isn’t directly on metal, just being close to metal is sometimes enough to cause your scan performance to take a dramatic turn for the worst. In this whitepaper, we will look at why this happens and how you can make your tags work again.

What is happening?

Simply, eddy currents are killing your tag performance. When an NFC reader is attempting to interact with a tag, it produces a radio-frequency electromagnetic field that both powers the tag as well as allowing the reader to communicate with it. When the tag is affixed to a surface that is not electrically conductive, this process works very well and you get the smooth tag reading performance you expect.

However, something very different happens with the surface is electrically conductive. When a conductive material is placed inside a changing electromagnetic field, a current is induced in the conductor - these currents are called eddy currents. When these eddy currents form, they interfere with the reader and tag’s ability to communicate with each other, resulting in a tag that seems to be unreadable.

Eddy currents in the underlying surface cause a disruption of communication

Communication with a tag on a non-conductive (left) vs conductive surface (right)

How do we fix it?

In order to restore tag communication, we have to use a special iron-containing ceramic material called ferrite. When a sheet of ferrite is placed between the tag and the metal surface, it reduces the interferenced caused by the surface, allowing us to create a tag that can be affixed to metal structures while still being readable.

A ferrite layer prevents eddy currents from disrupting communication

A ferrite layer prevents powerful eddy currents from disrupting communication

Where to get these tags

There are two ways to get these ferrite backed “anti-metal” tags - the most common is to purchase a tag with the ferrite layer already included, although it is also possible to purchase adhesive ferrite “stickers” seperately and combine them when you apply the tag. While just about any tag can be made into an anti-metal tag, due to their specialized nature, they’re often only readily available in a handful of form factors with just a couple of different types of NFC chips. However, if you place a custom tag order with TapTrack, we can provide anti-metal tags with just about any combination of chip, form factor, and custom printing that you may need.

Luke Van Oort

Chief Developer, fan of immutable data structures and functional reactive programming. Guitar noodler and cycling enthusiast.

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