Question on the rule of thumb for faraday cage

Discussion in 'Wireless & RF Design' started by Titanpick, Sep 9, 2017.

  1. Titanpick

    Thread Starter New Member

    Sep 9, 2017
    16
    4
    Hi,

    I would like to know when they say in this website (http://wiki.backyardbrains.com/Exper...e_Faraday_Cage)
    One rule of thumb often used for Faraday cages to prevent transmission is that the holes need to be no larger than 1/10 of the wavelength of the signal

    I would like to know what does it really mean out of these 5 options?

    a) we need a hole smaller that a square hole whose sides =1/10 of the wavelength to prevent propagation
    b) we need a hole smaller than a rectanglar hole which has one side = 1/10 of the wavelength to prevent propagation
    c) we need a hole smaller than a square hole whose diameter = 1/10 of the wavelength to prevent propagation
    d) we need a hole smaller than a circle hole whose diameter = 1/10 of the wavelength to prevent propagation
    e) the perimeter of the hole has to be smaller than 1/10 of the wavelength to prevent propagation

    Thank you
     
  2. dendad

    Distinguished Member

    Feb 20, 2016
    2,522
    679
    I would take it to indicate the largest dimension needs to be less that 1/10th wavelength, and that applies to any shape hole, round, square or slot.
     
    shortbus likes this.
  3. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    7,826
    1,309
    The hole hase to be less than 1/10 of the wavelength signal,

    so like the Example given for a mobile phone signal of 14cm, in a square hole the diagonal has to be less than 14cm,

    which give the sides length of 9.8cm.

    Most Faraday cages are made from multiple layers of shielding.
     
  4. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
    7,499
    1,817
    Does it matter how much of the area is hole and how much of it is metal? I'm thinking of 1/2" mesh wire netting where the hole size is small but most of it is hole not metal.
     
  5. ArakelTheDragon

    Well-Known Member

    Nov 18, 2016
    1,243
    101
    It means the area (square mm) needs to be less than.... The shape does not matter but its best if its synchronized with the shape of the electro magnetic field probably.

    The bigger.the holes, the smaller.the efficiency.
     
  6. crutschow

    Expert

    Mar 14, 2008
    21,714
    6,262
    Wouldn't the diagonal need to be less that 1.4cm?
    Obviously the more metal, the better the attenuation.
    But if the wire netting has a 1/2" maximum diagonal opening then it will significantly attenuate any signal wavelengths of 5" or greater.
     
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