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complex relative permittivity: definition of the imaginary part in a look-up table

Posted Apr 2, 2013, 5:59 a.m. EDT Version 4.3a 2 Replies

Andrea Marie Scholl
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Dear all,

I'm quite confused right now as regards the definition of the complex relative permittivity.

In a previous discussion I've read that a complex permittivity of a+jb should be entered as a-jb as COMSOL would always regard the imaginary part as a negative entry.

Now I'm wondering whether this also applies to the definition of the complex permittivity in a lookup table.

Is it either: eps_real(freq)+j*eps_imag(freq) or
eps_real(freq)-j*eps_imag(freq) ?


Thank you!
2 Replies Last Post Apr 2, 2013, 8:47 a.m. EDT
Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago Apr 2, 2013, 7:21 a.m. EDT
Andrea,

it may be best to look at the equations. You can find that in the help pages:

RF Module > The Radio Frequency Branch > Theory for the Electromagnetic Waves Interface > Introducing Losses in the Frequency Domain

Here it states that losses are described with eps_c = eps_0 ( eps' - j eps'')

It appears that COMSOL is using the engineering convention here, whereas the physics convention is eps_c = eps_0 (eps' + j eps'').

I am wondering how often courageous science projects fail because physicists and engineers use different conventions ;-).

Cheers
Edgar

--
Edgar J. Kaiser
www.emphys.com
Andrea, it may be best to look at the equations. You can find that in the help pages: RF Module > The Radio Frequency Branch > Theory for the Electromagnetic Waves Interface > Introducing Losses in the Frequency Domain Here it states that losses are described with eps_c = eps_0 ( eps' - j eps'') It appears that COMSOL is using the engineering convention here, whereas the physics convention is eps_c = eps_0 (eps' + j eps''). I am wondering how often courageous science projects fail because physicists and engineers use different conventions ;-). Cheers Edgar -- Edgar J. Kaiser http://www.emphys.com
Andrea Marie Scholl
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Posted: 1 decade ago Apr 2, 2013, 8:47 a.m. EDT
Thank you, Sir!
Thank you, Sir!

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