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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.

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  • \$\begingroup\$ What connectors does your android device have that can be used for connecting your NFC cable? \$\endgroup\$ – Andy aka Nov 24 '14 at 11:31
  • \$\begingroup\$ The only one is the uUSB, but adapters exist to USB. However, this is not what I want. I need to wirelessly transmit the NFC signal through the case (from the built in chip), to my transmitter that would be attached on the back of the case. And through the cable, to the External Receiever, which would detect NFC cards. \$\endgroup\$ – David Kasabji Nov 24 '14 at 11:36
  • \$\begingroup\$ What RF transmission frequency does your NFC system use? \$\endgroup\$ – Andy aka Nov 24 '14 at 11:43
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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.

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  • \$\begingroup\$ The ides is certainly good. I also noticed such ideas over the web. But I do not how to calculate parameters for the coil ? And yes, the operating frequency is 13.56MHz as you said. \$\endgroup\$ – David Kasabji Nov 24 '14 at 12:06
  • \$\begingroup\$ Maybe you can link to the ideas you have seen on the web? \$\endgroup\$ – Andy aka Nov 24 '14 at 12:42
  • \$\begingroup\$ Here is the youtube video: link but the instructions are in german (in description), which I dont understand well. \$\endgroup\$ – David Kasabji Nov 24 '14 at 12:57
  • \$\begingroup\$ I can't use youtube where I am - maybe a non-video link? \$\endgroup\$ – Andy aka Nov 24 '14 at 12:57
  • \$\begingroup\$ This is copy / paste on how to do it. It sounds too simple, what do you think? to build it yourself is quite simple. In the example shown above i used enameled copper wire to make the coils. The whole thing is one big loop. So you have to solder the 2 ends of your wire together. On each side (the reader side) and the side placed on the back of your tablet you have to form a coil with 7 loops. The coil on the back of your nexus 7 is about the size of a credit card. The coil on the reader side should be the size of your nfc tag. \$\endgroup\$ – David Kasabji Nov 24 '14 at 13:00

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