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I have posters with "Tap me to check in/out of this meeting room" drawn on them. I have NFC Stickers behind each poster to send the user to a specific URL in the application.

They are being placed on a glass door so the customer wants them to be placed back to back so you can't see the back of any of the posters. Each poster does different things so I don't want the tags conflicts.

If I put foil/copper mesh between two posters it blocks/absorbs the NFC signals so I can't read the one behind, but that also blocks the one "in front" of the mesh that I want to be able to read.

I'm looking for a sandwich of materials that would work, something like:

  • Acrylic Poster
  • NFC tag (stuck to the back of the poster)
  • Rubber/Silicone(?)
  • Ferrite(?)
  • Glass of the door
  • Ferrite(?)
  • Rubber(?)
  • NFC tag
  • Acrylic Poster

Apologies if I explained that badly, I'm an applications developer out of my depth on materials/engineering!

Thanks

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    \$\begingroup\$ The problem is that anything that would block radio interference effectively by getting placed in parallel with the tag, will also block the intentional signal/antenna. If possible mechanically, you could perhaps mount each tag so that it stands out horizontally from the door, then place a vertical metal screen between the two tags. \$\endgroup\$ – Lundin Mar 26 '20 at 12:13
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    \$\begingroup\$ Is there any way to redesign the poster with "tap-here" target offset (ie bottom right of poster), so that when they are back-to-back the targets are separated? Alternatively, is it possible to redesign the web side so that there's a per-room tag, not room-in and room-out tag? (Can't log out of a room you're not in, etc) \$\endgroup\$ – jonathanjo Mar 26 '20 at 12:36
  • \$\begingroup\$ Thanks for the input @jonathanjo, there is a left/right offset in the poster design but as we are using a credit card sized sticker to make the target as big as possible the two nearest edges will only be about 3cm apart. The urls are setup so there is one for check in and another for check out as they could happen in the same time window so we need to know which of the two actions are being taken. \$\endgroup\$ – Alex W Mar 26 '20 at 13:03
  • \$\begingroup\$ @Lundin thanks for the input, I'm not exactly sure what you mean by a "vertical" screen? I get moving the tags as far away as possible from each other horizontally, which we intend to do as much as possible without making the posters look silly / H&S eye gouging issue \$\endgroup\$ – Alex W Mar 26 '20 at 13:07
  • \$\begingroup\$ Bit hard to explain without drawing. I meant that if you could mount the tags so that they protrude 90 degrees from the wall on each side, you could have a vertical screen between them. At least that would be optimal RF-wise, but perhaps not mechanics-wise. \$\endgroup\$ – Lundin Mar 26 '20 at 15:51
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I think there are two possible solutions for back-to-back posters with NFC tags:

  1. You can buy special NFC tags that are for use on metal surfaces. (They have a built-in metal backing a short distance behind the NFC antenna, and everything is tuned to work with that gap. So they work on both metal and non-metal.) They do have a shorter range and are a bit more expensive, like $1 apiece. With those you could put foil between the two posters and have no worries.

  2. As commenters suggested, if your posters are wide enough you could do something like put the tag on the right side of each poster, so the tags are not back-to-back. This is error-prone if users wave their phones all around the poster though. (And, your solution of adding a gap between the posters also works.)

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