Faraday Cage Concept and Building Questions

[kandrey89]

I have a few questions and verifying statements regarding the concept as well as practical building of Faraday Cages.

1. A Faraday cage's mesh must have a grid with a spacing less than that of the wavelength that is intended to be stopped.
2. Why is it that foil and mylar also work as faraday cage devices when wrapped around an object, I saw this on quite a few websites and don't understand how this works with the Faraday Cage concept.
3. Does the material used ie. copper, steel, ... or the diameter of the rods that make up the cage's mesh matter, are certain materials better, do diameter of rods matter in practical applications or the size of the rod doesn't matter (begs the question regarding wavelength size because a 10 inch rod mesh would not be able to stop radio wavelength... right?)?
4. What is the harmful to electronics EM spectrum that is emitted by a nuclear bomb? This should hopefully identify what wavelength the equipment should be protected against.
5. Must a Faraday Cage be grounded when working against an EMP? Musr a Faraday Cage be grounded when working against a lightning bolt\or Van de Graff generator?

Thank You

 

[Baluncore]

1. A Faraday cage's mesh must have a grid with a spacing less than that of the wavelength that is intended to be stopped.

No. It needs a mesh with holes smaller than about one tenth of a wavelength. But even those will not stop all energy. Any hole will allow some energy to pass through. Currents flowing on the outer surface of the cage will cause a current to flow along the edge of the hole. That edge current will direct some energy into the cage.

2. Why is it that foil and mylar also work as faraday cage devices when wrapped around an object, I saw this on quite a few websites and don't understand how this works with the Faraday Cage concept.

The Mylar has no effect on the waves. Mylar coated with a metal film, or a foil can act as a screen since the conductive layer makes a mirror that reflects EM energy.

3. Does the material used ie. copper, steel, ... or the diameter of the rods that make up the cage's mesh matter, are certain materials better, do diameter of rods matter in practical applications or the size of the rod doesn't matter (begs the question regarding wavelength size because a 10 inch rod mesh would not be able to stop radio wavelength... right?)?

The more conductive the metal the better the reflection. Thicker wires and smaller holes increase the effective conductivity, so improve the isolation.

4. What is the harmful to electronics EM spectrum that is emitted by a nuclear bomb? This should hopefully identify what wavelength the equipment should be protected against.

The Electro-Magnetic Pulse, EMP, radiated by a nuclear bomb is a fast step that contains all frequencies. Equipment must be protected against all wavelengths, from DC to gamma rays. Any exposed semiconductors will be destroyed.

5. Must a Faraday Cage be grounded when working against an EMP? Musr a Faraday Cage be grounded when working against a lightning bolt\or Van de Graff generator?

No, it does not need to be grounded. The strike will flow over the outside of the cage. There will be little charge inside the container.