Greetings ...

It is not abnormal to be confused because Science is an inconsistent Labyrinth ... where only Spirituality can show the direction ...

Now ... the reason because "permittivity of a material decreases" is because the speed of the "electrons" increase ...

I cannot give in this moment a mathematical example ... but is not complex.

Merci,

Giovanni.

Thank you Giovanni A. Orlando

The permittivity of a material is a complex number. The real and imaginary parts of the permittivity are function of the temperature and the frequency of the electro-magnetic wave.

For a fixed frequency, both the real and imaginary parts decrease with increasing temperature due to the higher mobility of the molecular dipoles.

However, for a fixed temperature, the variation with frequency is more complicated. For example, water at 25°C, the real part of the permittivit is about 79 at low frequency (a few hundred Herz) and decreases to about 4.2 at 1000 GHz, but the complex part of the permittivity is close to 0 at a few hundred Hz, inceases to about 35 around 15 Ghz, then deceases steadily to about 2.5 at 1000 GHz.

You can find explanations for the behaviour of permittivity in most textbooks on electro-magnetic waves and their interaction with matter.

Thank you very much dear William Ellison

But it depends the relaxation frequencie of the electron

The complex dielectric constant is ability of material to irradiate or absorb electromagnetic energy of EM wave.

As frequency increases loss of energy more and hence dielectric decrases