You will need to ensure the mesh is continuously conductive and that the holes are sufficiently small. If the mesh has breaks and is not continuously conductive you can get transmission through it. As for the holes, think of them as very short waveguides. The holes need to be small enough that all of the modes in those little waveguides are cutoff. You will stop getting transmission when the size of the holes fall below a quarter to a tenth of a wavelength in size. If you have a way to do electromagnetic simulations, you could simulate your mesh as a frequency selective surface and determine if any transmission will occur.

Steel will not be as good as copper because it is less conductive, and if it is magnetic steel it will be even worse, because the skin depth will be reduced, making the surface conductivity even worse.

I recommend to read the chapter "Skin Effect and Shielding Theory of Schelkunoff" (pages 377-392) from the book "Electromagnetic Compatibility for Device Design and System Integration" by Karl-Heinz Gonschorek and Ralf Vick (see Book Electromagnetic Compatibility for Device Design and System Integration

Magnetic steels will usually not degrade the shielding efficiency, but rather improve it, as a higher relative permeability will reduce the skin depth and therefore increase absorption loss inside the metal. Nevertheless, a smaller skin depth also leads to a higher wave impedance inside the metal, which reduces reflection loss.

Mathias

I think that what you say about magnetic steels may be true for solid (sheet) material, but may not be true for mesh, where the currents in the wires are what does the shielding, and absorption is not relevant.

Malcom, you are probably right about this. Another issue: Magnetic steel will lose its higher relative permeability already in the lower megahertz frequency range. So at real RF frequencies, there will be almost no magnetic effect anymore.

The use of metal mesh is a good idea for protecting radio waves. It is light and has low wind resistance. Aluminum mesh is also a good choice for weight loss.

It will depend upon the desired attenuation. Steel will not be as effective as aluminium or copper but will still attenuate. Keep the size of the holes less than lambda / 20 for highest frequency. My personal experience is that magnetic shields sometimes cause interference in electronic equipment inside the mesh if it is located close to the mesh structure.

My personal experience shows that shielding is a very complex task. Metal mesh must be closed and earthed. The complexity of the task confirms the simple experiment I conducted this past weekend. I put the mobile phone in an aluminum case. Sent the call from a landline to a mobile phone. The call was received. I assume that the currents flow through the gap between the two halves of the case.

I also tried to put my phone inside the microwave and I tried to call it with other phone by face time. The phone still rung. It means that my phone inside the microwave was still connected to the WiFi signal. The WiFi frequency is quite similar with the frequency of microwave. Therefore, microwave has still leakage even though there meshed metal shield. The size of meshed metal is so small compared to wavelength of MW. However, there is still leakage but it is not noticeable because it has a low power capacity and the time duration is short. If we increase the power of the microwave in the household and have long duration of usage, we can detect the its leakage. I think it is similar of what I have experienced.

Your microwave oven has chokes (stop-band filters) in the door surrounds to stop the microwave frequencies. The door does not make metal-to metal contact. The chokes will almost certainly not work for mobile phone signals, so the signal will get in round the door, not through the mesh.

The mobile phone frequencies are deliberately not the same as the microwave oven frequency.

The mobile phone is different frequencies. What I am using is the Wifi. You can facetime in iphone with WiFi. Without it, it will not ring. The WiFi frequency is around 2.4 GHz. It is the same with the household microwave oven 2.45 GHz.

Firstly, perfect shielding needs a Faraday's cage. So, any wire mesh will never provide complete isolation. Secondly, WiFi needs picowatts to communicate, So even a door-mesh with 100 dB shielding cannot block it. Shielding effectiveness should not be measured in terms of blocking advance communication protocols but in terms of continuous waves isolation.

Dear Roland, you may want to read the recent paper about the Mathematics of the Faraday Cage:

https://people.maths.ox.ac.uk/trefethen/chapman_hewett_trefethen.pdf

and eventually this one:

https://arxiv.org/ftp/arxiv/papers/1609/1609.05567.pdf