It's my understanding that in electromagnetics, if an attenuating device is functioning linearly, it means that 1) input and output signal strengths are proportional; and 2) input f = output f. How accurate and complete is this definition?
It's also my understanding that an attenuating barrier can become non-linear in the presence of a high-strength EM field (e.g., 50 kV/m, 133 A/m). Why/how does this occur? What properties of the barrier material affect this (e.g., permitivity, permeability, ferromagnetic properties, etc.)?
It's also my understanding that non-linearity causes a barrier's attenuation to be enhanced or diminished by frequency, depending on the detail of the non-linearity. What is meant by "the detail of the non-linearity"? Why/how does non-linearity cause attenuation to be enhanced or diminished at a frequency? In other words, what material properties determine whether attenuation increases or decreases?
Actually, if the definition of linearity in the first paragraph above is okay, then I think I understand, at least partially, why non-linearity might cause attenuation to increase or decrease at a frequency. If the non-linearity involves a frequency shift, then attenuation would increase at the input frequency and decrease at the output frequency. If the non-linearity involves a change in the proportionality of input and output signal strengths, then depending on how the proportion changes, attenuation would be increased or decreased. Do I have this right?
This is a rewrite of this question, which was titled and worded poorly. Selvek's answer was helpful, though. I would have asked him for clarification, but it didn't seem to make sense to contribute further to an unclear question that misses what I had intended to ask and that's inviting down votes. So, re-asking seemed a good solution. Apologies if this isn't correct procedure. I'm new here. I did reach out for help from a moderator, but I haven't received a reply yet.