Discussion Forum

Try searching for 'dielectric constant of _______'. Here's an MIT link for Au: www.mit.edu/~6.777/matprops/gold.htm

Hi,

the relative permittivity can be very frequency dependent. At low and RF frequencies you can use 1. At optical frequencies it is different and the value gets complex. There should be plenty of material on the web.

Cheers
Edgar

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Edgar J. Kaiser
emPhys Physical Technology

thanks..

Hy! Sorry for disturbing!
I am trying to implement a beam splitter configuration in COMSOL, but I'd like to use Gold, Aluminium or Chrome instead of Silver. The default COMSOL implementation uses Silver, with the relative dielectric constant: epsilon = -16.5-1.06*i. I need some similar values for the other three metals...
Do you have any idea for my situation? I searched all over the internet, but without any results... :( How could I determinate the relative dielectric constant (even if they are complex numbers) for Gold, Aluminium or Chrome?
Please answer!
Best regards: Ferencz Szilard, Technical University of Cluj-Napoca.

Ferencz,

a little Google search using 'permittivity of gold at optical wavelengths' already yields many hits. Among many others this one: fisica.ufpr.br/jfreire/EstadoSolido/optical%20contstants%20of%20noble%20metals.pdf
which should already answer your questions. It also describes how to measure the complex permittivity. And keep in mind, it is very frequency dependent in the optical domain.

Cheers
Edgar

--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com

The site refractiveindex.info/ has data files to download, which can easily be input into an interpolation function that defines your frequency-dependent permittivity or refractive index. The 1972 data from Johnson & Christy is available, for example.

-Bryan

Hi Bryan,

that's a good one, didn't know it so far. Thanks for sharing!

Cheers
Edgar

--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com

Hi Edgar,

To find the answer of a similar question, I just came across this post and I would be thankful if you illustrate the following points.

1-While the dielectric constant of the metals is usually reported infinity, how can it be assumed "1" (even at low frequencies)?

2-What is the difference between a metal and vacuum if "1" is considered as the dielectric constant of the metal?

I do really appreciate it if you resolve my ambiguity about this issue.

Cheers,

Farzam

Hi Edgar,

To find the answer of a similar question, I just came across this post and I would be thankful if you illustrate the following points.

1-While the dielectric constant of the metals is usually reported infinity, how can it be assumed "1" (even at low frequencies)?

2-What is the difference between a metal and vacuum if "1" is considered as the dielectric constant of the metal?

I do really appreciate it if you resolve my ambiguity about this issue.

Cheers,

Farzam

Hi I had the exact same question. Did someone solve this for you? Is it ok if we assume a permittivity of 1 for the metals?

Hello All,
Speaking a little bit more generally towards the underlying questions here, the following page is a good starting point for more in-depth reading on the subject:
en.wikipedia.org/wiki/Dielectric_spectroscopy

Also, we should point out that if you're using the Wave Optics Module or the Ray Optics Module, these do come with a library of several hundred materials (including gold and aluminum) with complex-valued refractive indices as a function of wavelength so that you don't need to look these up.

Hi Walter,
thank you for your answer. In my case the voltage that creates the electric field is constant and doesn't vary with time. So I am looking more for a static relative permittivity. In this case would the assumption of 1 be a good approximation for metals? I was using the boundary of my electrode to apply the voltage and then I changed my mind and used the whole domain which had as a result to assign a relative permittivity of 1 for my electrode by default (or maybe I did based on this thread I can't remember). Any suggestions on that would be helpful.