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RFID tags...How do they work?

Discussion in 'Electronic Repair' started by [email protected], Feb 12, 2008.

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  1. Guest

    I am a senior industrial design major and I am have been asked to give
    a brief presentation on RFID tags and how they work. I understand the
    general concept but I am not sure the specific technical aspects of
    the system. I was wondering if someone could explain the basic
    principle of how these tags work (in layman's terms!) I have
    conducted some research but I am not sure I completely understand the
    difference between active, passive and semi active. Another thing I
    am a little confused with is that I read that they are used in
    library's and theft deterrent devices in retail. I have taken some of
    these tags apart (specifically the ones found in CD's ) and it appears
    they are a plastic housing with thin sheets of steel in them. Are
    these considered RFID or strictly magnetic detectors that must be
    demagnetized in order to pass through the detector. If anyone can
    shed some light on this issue, I would be most appreciative. Thank you
    very much.


    Jesse Stein
  2. Mr. Stein, how thoroughly have searched the Web? Have you gone to the sites
    of companies manufacturing RFID tags? Have you contacted them or their

    With all the resources available that you have apparently not made use of,
    it appears you haven't done your homework, and you're asking for assistance
    too early, from the wrong people.
  3. Jerry

    Jerry Guest

    They work very well for something so small. A couple of months ago, I
    started setting off the theft prevention alarms in just about every
    store that had them. Walmart, Target, Kohls, Mervyns - you name it, I
    set off their alarm. Started to be annoying when I would be walking
    out of the store with nothing, and the security people would be
    looking at me like they were thinking whether to ask if I had anything
    in my pockets.

    Took me a while to figure out what was setting off the alarms. I had
    bought a new leather checkbook cover recently. Hidden in bottom of one
    of the credit card slots was an RFID tag, paper-thin, and about 1 inch
    square. Took it out and no more dirty looks from the "loss prevention

  4. Jim Yanik

    Jim Yanik Guest

    I had a Hooter's refrigerator magnet in my pocket and the alarm went
    off;there's also a magnetometer.
  5. Arfa Daily

    Arfa Daily Guest

    Try having a look on Elektor magazine's website

    Sometime last year as I recall, they did a feature issue on RFID with lots
    of articles on how they work. All articles are archived, searchable, and
    available for download - allbeit for a small fee, although I think you can
    get enough 'free' credits to download a couple, just by registering with the
    site (it's reputable, and this will not cause you to be bombarded with spam)

  6. David Harmon

    David Harmon Guest

    On Tue, 12 Feb 2008 12:06:44 -0800 (PST) in,
    You can't repair them. If it's broke, you have to get a new one.
  7. LOL! you are pointing out that this is a .repair group..

    Mr. Stein, I'd help you out if I knew something abou these things, but it
    sounds like you understand them as well as I do. Active RFID's have a
    battery or power supply. IIRC Passive work by low frequency radio freq about
    1hz to power the device by an antenna. It also detects it like this by some
    means. Semi-active devices? I have no clue. I'd assume that it is some sort
    of mix of the two. Maybe they store recieved energy by capacitance of some
    sort. I suggest checking wikipedia and

  8. N Cook

    N Cook Guest

    I don't see how they can be used for the purposes of identity.
    Say the sub-cutaneous implants for pedigree dogs.
    All you do is pass a scanner near the dog, obtain the code, buy a blank slug
    for a few cents/dollars , clone that one, and plant in your phoney dog or
    dogs. Then which is the genuine one?
  9. Baron

    Baron Guest

    They have a predefined identity code built in.
  10. default

    default Guest

    Spoofing store anti theft systems is becoming entertainment. Walmart
    was/still uses the white plastic strip theft prevention. It is a
    simple device that tells when a strip of metal is magnetized inside
    the plastic. At the cashier, the strip passes a degausser in the
    counter. When you pass the largish loop detectors on the way out,
    they alarm on magnetized strips.

    The spoofing comes in when people save the strips from purchases they
    made then walk into the store with a magnet in one pocket and strips
    in the other. They remagetize the strips and attach them to store
    patron's clothing or just shopping carts, then sit at the lunch
    counter and monitor the doors and wait for the fun to begin.

    Disabling the devices is also becoming hacker entertainment. Pocket
    degaussers and a device to disable the fusible RFID tags - the ones
    that are just coming into use. They take the guts from a disposable
    camera flash (tons of those available) and mate it to a coil with an
    SCR trigger circuit. Hold the coil against the tag and discharge the
    cap and it is supposed to kill the RFID device.

    They claim that the price is still too high on the tags to make them
    universal - I sort of doubt it. The ones I've seen look like a tiny
    blob of plastic with a larger loop antenna that appears to be printed
    on to the paper tag. With some ICs in the 20 cent range in quantity
    rfid should be dirt cheap in the quantities they anticipate using -
    especially with Walmart pushing it.

    Our google groper needs to do a little research of his own.

  11. N Cook

    N Cook Guest

    I sliced open one from the back of a pack of batteries.
    Other than a nice source of ferrous shim of 0.03 mm or 1.2 thou/mil thick ,
    not much in there. 3 such pieces , 2 the same length and one a bit shorter.
  12. Bill Jeffrey

    Bill Jeffrey Guest

    At least some of these things are not magnetic at all, and I think that
    applies to the one you cut open.

    The two "wings" you saw are antennas. At the junction of the wings is a
    tiny dot which is actually a subminiature diode. When you walk through
    the detection loop, you enter an RF field that is set up (transmitted,
    if you will) by one of the loops. The wing antennas pick up the RF, and
    the diode creates harmonics, which are re-radiated through the wings.
    The detection part of the operation involves looking for the 3rd
    harmonic of the original frequency.

    The tag is disabled at the checkout counter by placing it on a pad that
    contains a transmit antenna. The pad transmits enough energy to burn out
    the tiny diode. Once burned out, the diode does not generate harmonics
    on the way out of the store, so the detector isn't triggered. The field
    strength at the surface of the pad is also strong enough to scramble the
    magstripe on your credit card, of course - hence the warning not to put
    your card on the pad.

    Note that everything happens in what the RF engineers call the "near
    field", so the field strength drops off very rapidly with distance.

    Finally, the little theft prevention thingies are not "RF ID" devices -
    that is a different kettle of fish.


  13. would be the appropriate newsgroup to ask
    this question.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida

  14. You set off their biohazard detector with the chicken fat on the
    magnet. ;-)

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  15. default

    default Guest

    No, he's correct. The magnetic thingee is not an RFID just anti theft.
    There are three very thin pieces of metal in there. Two of the strips
    appear to be mu metal (I'm guessing) and another magnetic iron.

    These are "electronic article surveillance" tags, or EAS

    I had the operation backwards. From what I'm reading the tag can be
    deactivated with a magnet and activated with a degaussing device.
    The Electromagnetic (EM) system, which is dominant in Europe, is used
    by many retail chain stores, supermarkets and libraries around the
    world. In this technology, a magnetic, iron-containing strip with an
    adhesive layer is attached to the merchandise. This strip is not
    removed at checkout -- it's simply deactivated by a scanner that uses
    a specific highly intense magnetic field. (One of the advantages of
    the EM strip is that it can be re-activated and used at a low cost.)
  16. N. Morrow

    N. Morrow Guest

    I too set off the alarm at Walmart and the nice 'greeter' suggested that I
    may have a tag somewhere on my person that had not been deactivated .. like
    in my shoes. Sure enough, I found it embedded into a slot in the insole of
    my shoe. I now happily hop through the security antennas without the
    embarassing beeps.
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