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  1. I know that magnetic stripes used in credit cards and audio tapes are typically read by a magnetic reader head. But is it theoretically possible for the stripe to be read by a laser in a similar fashion to a barcode scanner?

I also heard of technologies like magnetic secure transmission by Samsung that emulate the magnetic stripe within 3 inches of a card reader. I'm guessing the smartphone or device that does the MSE is using more power to ensure the magnetic field reaches the card reader's reader head from a distance of 3 inches.

  1. I'm curious about the opposite. Could a magnetic reader head theoretically read a magnetic stripe with a gap distance (even a very small gap say 0.01mm) or without physically touching the magnetic stripe? Or is the magnetic field generated by the magnetic reader head too weak to handle any gap between the reader head and the magnetic stripe?
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    $\begingroup$ You might be able to do it with visible light (lasers) and surface plasmon games, but it would be absurdly difficult and expensive to set up. $\endgroup$
    – Carl Witthoft
    Feb 19, 2019 at 20:40
  • $\begingroup$ @CarlWitthoft You might also be able to do it if you can construct some sort of LIDAR microscope that has a sufficiently small resolution to be able to resolve images of the individual particles of charged materials and then determine their orientation based on those images. Needless to say, it wouldn’t be using visible light to do so. $\endgroup$
    – nick012000
    Nov 17, 2019 at 4:17

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  1. Reading a magnetic field with a laser or other light source will be "difficult" because light is not charged and it does not have its own magnetic field.... except it is electromagnetic radiation. I will speculate that it is "science fictionally possible" to affect the phase of a laser with a rapidly (~10^14 Hz) changing magnetic field but that is not going to happen with a magnetic strip.

    1a. Magnetic secure transmission (MST) appears to produce a magnetic field that looks to a card reader as if it had a card being scanned. Pretty neat, I never heard of it before but I can see how it would work. If an external coil produced a magnetic field that looked like a magnetic card was being swiped, the reader would not know the difference.

  2. Magnetic card stripes are effectively the same media as magnetic disks, in a different shape. The heads of old style (and maybe new style) magnetic disks never touched the surface; they rode along on a cushion of air about 0.1 micron thick. I can't find a good picture but this web site may give you the idea. The magnetic field is in the magnetic media (disk or stripe), not in the reading head. As the media moves near the coil in the head, it induces a very small current which is amplified to be used as ones and zeros. As a card moves in the reader, different parts move under the read head and the associated computer can put the pieces together to form a card number. One of the tracks on a payment card is recorded at 210 bits per inch. Each bit is about the size of the thickness of a thin plastic bag. To tell the bits apart, you need to be close, VERY close. From a distance, the best you can tell is there is a magnetic field on the card, but you knew that already.

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