# Question on the rule of thumb for faraday cage

#### Titanpick

Joined Sep 9, 2017
16
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

Joined Feb 20, 2016
3,602
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

#### Dodgydave

Joined Jun 22, 2012
9,479
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.

#### AlbertHall

Joined Jun 4, 2014
10,417
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.

#### ArakelTheDragon

Joined Nov 18, 2016
1,350
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.

#### crutschow

Joined Mar 14, 2008
25,460
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.
Wouldn't the diagonal need to be less that 1.4cm?
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.
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.