Material heating from AC electromagnet

Question

What material property decides how much will that material heat up when inside solenoid with alternating current applied to it?

I am trying to research what type of ceramic will absorb as little energy as possible inside the AC magnetic field so it stays cool.What is great mystery to me is,when you have a glass tube with gas and the whole thing is inside solenoid coil,why does the gas becomes plasma,while the glass doesnt melt?

I want to know how to calculate how much will certain ceramic material heat up by AC magnet so I can chose the right ceramic.Is it electrical conductivity? Permeability? Permitivity? Density? Or maybe certain freqency is transparent to glass but will heat gas? Is it becose gas atoms are free to move and heat up by collisions as they are accelerated and ceramic atoms cant move so cant heat up?

Gases and ceramics like fused silica are very similiar in the electrical properties,both are electrical insulators,both are non-magnetic,both have extremly low thermal conductivity,only thing really different is density,less amount of atoms requires less energy to turn it into plasma,but then it will only delay the melting of glass and the devices using induction coupled plasma technology operate continuously for long time.

akhmeteli · Answer

First of all, there are linear and nonlinear mechanisms of heating. That means that electric properties of materials and, therefore, heating efficiency, depend on the strength of the field. Each material has a breakdown threshold above which plasma may be formed. So at some field strength there is a discharge in gas, but not in glass. However, there will be a breakdown in glass at higher field strength. The breakdown threshold, say, in gas, depends, among other things, on density and frequency.

Linear mechanisms, in general, include electric and magnetic losses. Typically (in non-magnetic media), electric losses are more important and depend on the complex permittivity (https://en.wikipedia.org/wiki/Permittivity#Complex_permittivity), which depends on the frequency, among other things. You may find some formulas, say, at http://www.engr.sjsu.edu/rkwok/EE142/Lossy_Medium.pdf .

Material heating from AC electromagnet

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