NFC Tag Antennas

NFC Tag Antennas
NFC Tag Antenna. Image: 123rf

How do NFC tags work ?

An active device (usually a mobile phone) generates a local magnetic field which induces an electric current in the antenna of the passive device (the NFC Tag). This electrical energy powers the NFC Chip which creates a further magnetic field in it’s antenna which can be read by the active device (the phone). Thus allowing data to be transferred.

The antenna bit

The antenna on an NFC Tag (sticker/inlay) is made of etched aluminium or occasionally copper. Copper is more expensive to use than aluminimum but performs slightly better so is only used in the smallest of NFC tags where getting that extra bit of scan distance is important.

NFC tag antennas are not really, technically, antennas at all. They are actually just inductors designed to convert nearby magnetic fields into energy. The antenna is very carefully designed to resonate at the desired frequency (13.56Mhz) and ensure that this happens as efficiently and as effectively as possible.

The performance of the antenna is not affected by it’s thickness which is why NFC tags can be very thin. However, with a powerful magnetic field, the larger the antenna size, the better the performance. In reality, mobile phones don’t produce much ‘power’, so there’s a limit to the optimum size of antenna. As such, you often get a decreasing performance as the antenna gets larger than the optimum size.

The bonding bit

This is the NFC tags’ Achilles heel – the bit that gets broken when you bend them too much ! The bond is the connection between the tiny chip and the antenna.

A number of companies are developing and have developed ‘flexible’ bonds which mean, for example, tags can pass through a regular printer. However, so far, the costs and reliability of production aren’t worth the effort.

Other antenna options

While NFC Tags are made using etching, NFC Products (wristbands, keyfobs, etc) use other types of antenna. These usually fall into two categories, a coil of usually copper which we is often called an ‘E-Unit’ and PCB (printed circuit board) tags. These formats are more durable and allow for encapsulation into plastic mouldings. These are very specialised units and unless you make NFC products or are integrating NFC tags into products (and can’t use a sticker), you aren’t likely to need these.

Printable NFC Ink

One of the problems with NFC Tag design is that, relatively speaking, they are expensive to make. While NFC Tags will get cheaper, the antenna etching and bonding process means that the unit price of NFC tags is always going to reach a lower limit.

To be cheap enough for NFC tags to make it onto mass market product packaging such as a jar of peanut butter or included in the pages of a magazine, the price per tag has got to fall to a few pennies/cents. This is where printable NFC ink is likely to comes in. This allows the tag to be ‘created’ by printing.

At the moment, there are a couple of companies testing printed NFC antennas bonded to NFC chips. The reality is that this is an expensive process still and reliability is not great. There’s little overall cost benefit against using an integrated standard inlay.