I have read conductivity, permeability, and thickness of material affect the shielding of the electromagnetic energy such as radio frequency, microwave energy.
RF radiation is reflected by a change in impedance, such as going from air into ptfe. If the change is large enough this can have a large shielding effect.
RF radiation is also shielded by attenuation. This is what radar absorbing material (RAM) does. There is not much reflection, but the RF power turns into heat in the RAM, and very little makes it to the other side.
RF radiation is also reflected by metal. The currents in the surface of the metal generate a wave out of phase with the incident wave, going forward, that cancels it, and also generate a wave going backwards that is the reflected wave. The surface currents die away further into the metal, as does the incident field, as it is progressively cancelled. The power going forward turns into heat in the conductor.
In practice two or three of these effects are present to some extent in all shielding. Metal surfaces have a huge impedance mismatch to air, so not much power gets into the metal to be absorbed as heat due to the surface currents. Dielectrics not only reflect power due to impedance mismatch, but also absorb some due to dielectric losses (dragging dipoles back and forward).
Practically there are mu metals that is metals with high permeability and conductivity which are used for shielding. Electric field can penetrate significantly into even highly conductive metals at lower frequencies therefore hi mu metals are used to shield against these low frequencies.
There are two kinds of shielding.
1) Shields that protect shielding structure from a hazardeous irratiation.
They can be made of metals. Even thin metal sheet (the order of 1 micron)
can be used in this case. Such shields totally reflect the RF and microwave
e-m fileds.
2) Absorbing shields that are designed to minimize the reflected e-m radiation. They are typically used to make the shielded structure invisible
to radars. They are also used in anechoic chambers for antenna experiments, Such shields are constructed employing ferrites (at RF
frequencies) and various lossy dielectrics.
I recommend to read the chapter "Skin Effect and Shielding Theory of Schelkunoff" from this book:
http://www.springer.com/de/book/9783642032899 (Electromagnetic Compatibility for Device Design and System Integration by Gonschorek, Karl-Heinz, Vick, Ralf)
Have any of the informants addressing this question found any improvement in shielding using the metal sheeting discussed in these replies if the entire shielding is grounded through a highly conductive connection to ground? I think grounding has improved shielding in some applications in our experience. FlTabrah Honolulu.
it should be noted that metal foils even when they are very thin compared to the skin depth at the frequency under consideration can do VERY efficient shielding providet that the incident wave is has its vector of propagation othrogonal to the surface (or parallel to the surface normal vector)For grazing or near grazing incidence we have two cases(polarisation) .If the e-field of the incoming electric wave is parallel to the surface shielding will still be very good..otherwise not.
I think connection to ground can make a difference at low frequencies. At microwave frequencies it will make no difference whatever. At lower frequencies it probably helps keep different parts of the equipment at the same ground potential - there are inputs and outputs to the 'box', presumably, and these are connected to something else. If grounds are not at the same potential there can be extra currents in the leads that reduce shielding.
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