Electronic – Why does smart card antenna follow a “snake” pattern when approaching the chip

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This image is from this post which shows MasterCard plastic card being dissolved in acetone to have the circuitry extracted for further analysis (TL;DR further analysis failed because of chip protective features). Wires are a bit off because acetone made them unbind from the plastic.

Note the area close to the chip – two wires approach the chip and each of them follows a "snake" pattern – down, then up, then down, then up again, that repeats at least four times.

What's the purpose of this "snake" pattern?

Best Answer

The module is connected to the antenna using conductive adhesive. At the backside of the module there are two pads that are glued to the antenna. For this reason the antenna needs some pads as well or a meander-shaped region that serves the same purpose.

A more detailed discussion can be found here: http://arxiv.org/pdf/1507.06427.pdf.

Related Solutions

Detecting whether the card is present or not in a smart card reader

The code examples for the card reader is well hidden on their site. Nice products. hard to find docs. Look for the smart card code examples.
enter image description here

And dont worry if you dont give us enough information, It was hard for me to find it too.

**'' Define Smart Card connections  
' allows non-contiguous pin usage  
  cd := cdpin 
 dira[cd] := 0 
 pub detect | ok 
'' Detects insertion and presence of Smart Card  
  if (ina[cd] == 1)               ' inserted?  
    start                         ' check card  
   ok := (write($A0) == ACK)  
   stop  
  else  
  ok := false  
 return ok  *

http://obex.parallax.com/objects/649/

enter image description here http://www.parallax.com/Portals/0/Downloads/docs/prod/rf/32320-SmartCardReader-v1.0.pdf

Electronic – What’s the purpose of such weird wiring inside this smart card

This stripe is a patch antenna, which is nothing else than a wire, printed on a PCB or similar, that radiates like an antenna.

The unconnected strip on the right is likely a reflector element, which doesn't receive any current from a direct connection but is electrically coupled with the rest of the patch to improve the radiation properties or the input impedance (these antennas are very sensitive to resonance).

While there is theory about microstrip (patch) antennas, they're not as easy as dipoles or "normal" antennas to analyze for human beings, anda great part in their design is done numerically. They can easily be considered black magic.

I'm trying to understand If AB are really connected or not:

at a first glance I'd say that tey are not connected, but the rounded areas are the pads to connect the ends of the antenna to the transceiver. It would be consistent with the dark path going to A.
Or, but this may be or may not be: some patch antennas are made of two "independent" radiating elements, of which one or both is feeded by the signal; these elements interact together like a Yagi antenna, providing a more directional radiation. So it also may be possible that there are two different loops, but it's only an hyphotesis.

Best Answer

Related Solutions

Detecting whether the card is present or not in a smart card reader

Electronic – What’s the purpose of such weird wiring inside this smart card

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