Question on faraday cage formula for hole size

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 4 choices?

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 rectangle 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

Thank you

you can take it as a hole smaller than a circle hole whose diameter less than 1/10 of the wavelength. If you made a square hole with a side of lambda/10, bisector/median of that square hole will be lamda*sqrt(2)/10 which is bigger than lambda/10

As with any rule of thumb, the answers depends on the thickness of your thumb...

Please realize that there's no simple threshold. Smaller holes will still leak RF to some extent. You would perform an EM simulation with exact geometry to get the screening factor of a specific faraday cage.

As for the lambda/10 rule, looking at the hole diagonal seems reasonable as a first guess.

I remember trying to use copper screen as a component shield, and the shielding effectiveness was poor, compared to a purchased solid shield. The rule of thumb did not work in that instance.