Building a NFC extension Antenna

Question

I'm trying to find out how to build a circuit to extend the NFC range. NOT the range from the chip itself, but like following example:

I have NFC enabled Tablet that has an built-in NFC chip. I want to extend the range of that NFC chip with a circuit that would be attached to the back of the Tablet (where the NFC chip is located) and through a wire all the way to another NFC Chip, which would be lest say 60cm from the Tablet itself, without diss-asembling the tablet!

There is an idea here, but this requires to diss-asemble the Tablet. I dont want to do that, nor do I seek for a USB External NFC Readers (as they have poor Android supported Libraries). I need to find a way to extend the range though a cable.

Hope someone can help me out.

Answer 1

If you have a near-field-communication system that operates at 13.56 MHz (or lower) I suspect, that with a little bit of clever coil winding, you can passively extend the working range (via a decent cable) to several metres.

I'm thinking you could use a local coil (by the android device) to pickup the magnetic field and connect this to a cable and, at the far end of the cable you could use a similar coil for re-emitting the magnetic field.

This would rely on good coupling to the android's magnetic field in order to capture as much energy as possible because, without "stealing" as much as possible from the originating field, the remotely placed TAG will only collect a fraction of the energy it would otherwise have received.

Some capacitive tuning on both coils (either end of the cable) may be needed.

Just an idea that might make life a lot easier than trying to build an active system that can retransmit in both directions simultaneously. The other thing is that if this idea doesn't work (even when devices are really close) then it tells you maybe that any retransmission system probably won't work due to (as yet) unforeseen technical problems.