[Hardware] nRF52 - NFC antenna design

[Konrad Traczyk]

Hi,

I'm developing a project based on nRF52 and utilizing NFC for my master's degree. One part of the project will be a beacon with as small PCB layout as possible. That's why I'm considering designing the NFC antenna on my own but I'm a newbie in this field. The question I have is about the position of the antenna relatively to the chip. In all of the designs I've already seen, the antenna is on the same layer as the chip but it's placed next to it. I'm wondering if I can place an antenna on another PCB which would lie exactly above the main PCB with a chip and CR2032 battery (like a sandwitch). Thanks to this I would save much space, but can the RF passing through the antenna and then the main PCB damage the chip or battery?

Best regards, Konrad

[butch]

The NFC antenna or the BT (or whatever) antenna? The NFC antenna that came with the NRF52DK is a separate piece and much larger than the 2.4gHz antenna built into the PCB. You can buy a tiny BT chip antenna, but an NFC one? Common wisdom is that antenna design requires skill and testing to get a good result. Is that a sidetrack?

[Konrad Traczyk]

Hi, thanks for your answer. I mean a NFC antenna. The provided one with a kit is too large for me. I need to fit in a circle board with radius about 22-23 mm. Thats why I had an idea to design this antenna. But it's totally a sidetrack, however tesing it would be great value for my thesis supervisor.

[butch]

I am not an expert. I read that NFC is for units less than 5 cm apart. Maybe larger antennas are used where you don't know the configuration of the matching antenna. If your units only interact with your units, and not some other maker's unit, then you might be able to design a small antenna and require that they are close and aligned when held together.

[FormerMember]

The optimal size and shape of the NFC antenna depends on the intended application. For a maximized range/power transfer, the NFC antenna should have similar shape and size to the antenna it is intended to work with.

The NFC antenna does not need to be placed in the same layer as the chip. A sandwich design with the NFC antenna placed above or below the chip will make the design a lot more compact, but it has some disadvantages.

If placed below the chip, under a ground plane, the ground plane will heavily decrease the NFC antenna performance. If you google "NFC on ground plane", there is quite a bit of information on what happens when the antenna is placed on a ground plane.

If the antenna is placed above the chip, there will be the effect of presence of ground. In addition, I don't know how/if the RF performance will be affected since the NFC operating frequency is quite different from the RF frequency. For this case I would recommend some testing.

To maximize the NFC performance, tuning of the NFC antenna is necessary. This whitepaper explains how to do it.

[Andrew Lohmann]

Another solution if you want a smaller NFC coil is to use an external NFC IC eg M24LR?? ST with a CoilCraft NFC aerial (ferrite coil).