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Calculating Complex Permittivity

Posted 2025/03/12 7:30 GMT-4 Electromagnetics, Materials, Equation-Based Modeling Version 6.2 2 Replies

Karen Simonyan
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Hi, I'm trying to calculate the complex permittivity of graphene using this formula

here σ is the conductivity, ω=2πf is the angular frequency, ε0 is the dielectric constant of the vacuum, and t is the thickness of the material. In COMSOL, this formula should look like this

1-(j x sigma)/(epsilon0_const x comp1.ewfd.omega x d_eff)
(I changed asterisks to x, because on this forum asterisks turn text Italic)

But for some reason, COMSOL assigned an "rad" unit to this formula even though all variables are right

What's wrong and how do I fix this?

2 Replies Last Post 2025/03/12 8:45 GMT-4
Acculution ApS Certified Consultant
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Posted: 6 months ago 2025/03/12 7:53 GMT-4

From this [https://www.researchgate.net/publication/283380681_Optical_properties_of_graphene_on_quartz_and_polyethylene_substrates_in_terahertz_frequency_range] it looks like you are expecting unit less for that permittivity? I think what you get is correct seen from how omega here is rad/s, but you could also write omega as 2pifrequency, with frequency having unit Hz, in which case you have no resulting unit.

-------------------
René Christensen, PhD
Acculution ApS
www.acculution.com
info@acculution.com
From this [https://www.researchgate.net/publication/283380681_Optical_properties_of_graphene_on_quartz_and_polyethylene_substrates_in_terahertz_frequency_range] it looks like you are expecting unit less for that permittivity? I think what you get is correct seen from how omega here is rad/s, but you could also write omega as 2*pi*frequency, with frequency having unit Hz, in which case you have no resulting unit.
Karen Simonyan
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Posted: 6 months ago 2025/03/12 8:45 GMT-4

From this [https://www.researchgate.net/publication/283380681_Optical_properties_of_graphene_on_quartz_and_polyethylene_substrates_in_terahertz_frequency_range] it looks like you are expecting unit less for that permittivity? I think what you get is correct seen from how omega here is rad/s, but you could also write omega as 2pifrequency, with frequency having unit Hz, in which case you have no resulting unit.

It works thanks. I realized what the problem was. comp1.ewfd.omega is 2 x pi x ewfd.freq not the comp1.ewfd.freq

>From this [https://www.researchgate.net/publication/283380681_Optical_properties_of_graphene_on_quartz_and_polyethylene_substrates_in_terahertz_frequency_range] it looks like you are expecting unit less for that permittivity? I think what you get is correct seen from how omega here is rad/s, but you could also write omega as 2*pi*frequency, with frequency having unit Hz, in which case you have no resulting unit. It works thanks. I realized what the problem was. comp1.ewfd.omega is 2 x pi x **ewfd.freq** not the **comp1**.ewfd.freq

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