ABC: U.S. Airport Full Body Scanners Too Unreliable to Use, Germany Says

Discussion in 'Aviation Passenger Security in the USA' started by Mike, Sep 2, 2011.

  1. Wimpie

    Wimpie Original Member

    Both of these "authorities" are incorrect.
    Modern WTMD's use multiple coils of wire which form the feedback of an oscillator circuit, which operates at a frequency somewhere between audio and very-low-frequency radio. 30-150Khz is typical.
    The reason for multiple coils is to create "zones" so they can pinpoint (sic) the area of disturbance.
    When metal comes within the field of a coil, it changes the frequency of the oscillator. Iron and ferrous metals cause the frequency to decrease, brass and non-ferrous metals increase the frequency. When the logic detects a change of frequency a certain amount (sensitivity) from the "set" frequency, it makes an alarm.
    This is the principle behind the White's metal detector, for finding coins on the beach.

    The frequencies involved and the power level have been universally agreed to be absolutely safe to human tissue, although it is remotely possible to upset electronic devices, like first-generation pacemakers.

    I hope this clears this up.
     
    Lisa Simeone and RadioGirl like this.
  2. RadioGirl

    RadioGirl Original Member

    Thanks - beat me to it. Spent some time looking - there's a lot of rubbish out there!

    Bungnoid, try this link instead. http://science.howstuffworks.com/transport/flight/modern/airport-security3.htm Here's a pdf document from the Dept of Justice on how they're calibrated: http://www.ncjrs.gov/pdffiles1/nij/193510.pdf See page 2, definition 1.2.3 and page 8, sect 2.1.3: "The level of the magnetic field generated by the detector shall be less than the exposure limits specified in ACGIH–0302 (1996), Sub-Radio Frequency (30 kHz and below) Magnetic Fields, as amended."
     
  3. Mike

    Mike Founding Member Coach

    Also most of the supermarket door openers I've seen use infrared sensors. They don't work so well on a hot 98.6 degree day. :D
     

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