We are defining we have a problem with no proof it exists or hasn’t been addressed, first of all. Let’s get that out of the way.
Second, if we did have a problem what solves it? Our cases act like faraday cages by design. We also don’t want to use magnetic cases (Faraday cases are usually copper mesh such the they shield the proper wavelengths).
Faraday cages shield their contents from electromagnetic radiation. Basically, when an electromagnetic field hits something that can conduct electricity, the charges remain on the outside of the conductor rather than traveling inside.
When a metallic (stuff a magnet will stick to) material is charged and discharged it creates noise. The name of the phenomenom evades me 40 years since physics class. Remembered it - Barkhausen basic definition is the effect given to the noise in the magnetic output of a ferromagnet when the magnetizing force applied to it is changed. To remove this noise, we use non magnetic stuff that is STILL a low permeability to RF like aluminum. RF is easily attenuated through the thickness of the shield (case). Look at a case and stuff inside like a coaxial cable. Our circuits are on the inside, the case is the braided shield on the outside.
The ends of our cable braid (case) shield needs to be at the same potential as earth. This means the RF ground produces zero voltage (voltage = I * R). If we keep R at zero, we have no inductively coupled noise. That’s impossible since the shield has a resistance due to length.
We can’t adhere to the absolute ideal, so we measure shields ground differential using transfer impedance and SEED (Shield Effectiveness Evaluation Device) tests. A shield is measured for it’s isolation to ingress or egress in dB. That’s our induced voltage trying to get through, and how much it is attenuated. Numbers are typically 80 dB (single braid) to 110 dB (quad shields). Curiously, a shield also shields the same amount to stuff radiating OUT of the signal wire! Yes, we need to keep that to ourselves, too. Go back and look at the real basic definition of a Faraday cage. Our shields all looks like one and act like one from the basic principal of RF.
Alternatively, we can indirectly measure the induced voltage by the resitance at specific frequencies (shield transfer impedance is not linear to frequency, see the graphs in the .PDF) using transfer impedance in mill-ohm/mtr. The lower the better as this means a smaller induced voltage can be inductively coupling to the inner wire (circuit board). Notice the shield works better at higher frequencies as the B-field drops away to just an E-field.
One method measure the attenuation factor based on the shields properties, the other calculates a number that can allow a ratio to be used to differentiate shields across frequency.
RF is pretty easy to mitigate in proper designs. But you have to know the technicalities to do it. Guesses in the RF region are seldom accurate or right. RF is weird stuff, but it isn’t impossible to understand it even if it’s properties are aggravating.
Last, RF doesn’t have Return Loss on a Faraday cage or conductive case. RL is caused by VERY, VERY periodic ground changes caused by distance (diameter changes on a coaxial cable dielectric). That alters the Impedance because the capacitance is changing and this differs the cable’s impedance properties to the fixed resistive load. The variation in impedance causes the reflections.The Faraday cage or component case isn’t a transmission line, it is an end point ground. The RF stays on the outside and goes to ground. The higher the RF, the less it penetrates the shield. We’ll assume we are talking true electric E- fields and not magnetic B-fields, which are not the same problem at all.
Go here - https://www.iconoclastcable.com/techpapers/shieldsandgrounding.pdf