Optical vs Static Dielectric Constant for E-field Simulation

[newengr]

TL;DR

When should I pick one over the other for E-field simulations?

I am just learning about e-field simulations and I came across two different types of dielectric constants: optical and static. I'm unsure which to use and in which cases. I would like to simulate e-field intensity to help ensure I'm always below the dielectrics breakdown strength.

 

[tech99]

The dielectric constant varies with frequency, so choose the value appropriate to the frequency of interest.

 

[Baluncore]

Welcome to PF.

I would like to simulate e-field intensity to help ensure I'm always below the dielectrics breakdown strength.

That strongly suggests DC or low frequency modelling.
If you are modelling capacitance, with the dielectric constant, in an electrical environment, use static.
If you are modelling light, with refractive index, in an optical fibre or lens system, use optical.

 

[sophiecentaur]

choose the value appropriate to the frequency of interest.

The values for a range of frequencies are always available - use Google. One shouldn't keep within the limitations of any simulation and rely on it whatever; there is a lot of real world information about these things. Simulations have a habit of making assumptions about what you want. This allows you to get an 'answer' out but it should always be scrutinised but there are pitfalls that you have to accept when you want too much 'help' in driving the software. (GIGO)

 

[newengr]

That strongly suggests DC or low frequency modelling.
If you are modelling capacitance, with the dielectric constant, in an electrical environment, use static.

It is for use in DC so it seems the static value is suitable. There will be some high frequency content since there is switching in the converter, but DC is dominant.

Most of the work that I've seen doesn't mention why they chose electrostatic vs DC simulation. Actually, a lot of papers I read just talk about their simulation results and don't even mention which one they used. How does one determine if DC or electrostatic is appropriate? I'm not really sure what the difference is between the two.

 

[berkeman]

Most of the work that I've seen doesn't mention why they chose electrostatic vs DC simulation. Actually, a lot of papers I read just talk about their simulation results and don't even mention which one they used. How does one determine if DC or electrostatic is appropriate? I'm not really sure what the difference is between the two.

In your thread title and first post you used the words "optical vs. static", but now you changed to "DC or electrostatic". DC is analogous to static, but optical and electrostatic are completely different. Can you say more about what you are simulating?

It is for use in DC so it seems the static value is suitable. There will be some high frequency content since there is switching in the converter, but DC is dominant.

This kind of implies that you are simulating capacitors in switched mode power supplies (SMPS, using SPICE?)? If so, you need to take into account the equivalent series resistance (ESR) of the capacitors, since that is a major part of what causes ripple voltage in the output of SMPS.

As to your original terms, "optical" means at optical frequencies like you would use for optoelectronic fiber calculations, or lens design. "DC" or "static" means measured at low frequencies (say less than 1kHz). The dielectric constant of materials for frequencies between 1kHz and light ("optical") varies with the material, and as mentioned already can be looked up with Google searches.

 

[newengr]

In your thread title and first post you used the words "optical vs. static", but now you changed to "DC or electrostatic". DC is analogous to static, but optical and electrostatic are completely different. Can you say more about what you are simulating?

Sorry for jumping all over the place. I want to design a FEA simulation for a capacitor considering different dielectrics and other things like dielectric thickness and other geometries. I found static and optical dielectric constants which is what prompted this post. I wasn't sure what the difference was or when to use which. You mentioned DC or low frequency modeling so I just wanted to confirm that I am interested in DC. I just mentioned the high frequency switching content in case that added something else to the discussion. Looking back, I don't think it did. I'm not doing converter or component modeling considering electrical performance, but I'm more so considering material properties dependent and the physical geometry. So I think FEA is appropriate here.

I asked about DC vs electrostatic because those are two different simulation types available. You mentioned using static dielectric constant for DC simulations, but I though DC simulations considered bulk resistivity. I though electrostatic is the simulation type for considering permittivity.

Again, sorry if that made it more confusing. To sum it up, I want to simulate a capacitor that will hold a DC voltage considering various parameters such as dielectric type and different geometries using FEA. I have COMSOL and Ansys so I would be doing either DC or electrostatic.

 

[berkeman]

I have COMSOL and Ansys so I would be doing either DC or electrostatic

What other parameters are available for dieletrics in that simulation environment? How can you model ESR, for example? And loss tangent?

 

[newengr]

What other parameters are available for dieletrics in that simulation environment? How can you model ESR, for example? And loss tangent?

Through DC simulation I'm able to model the conductivity, permittivity, and permeability of the plates as well as the dielectric. ESR should be able to be modeled through conductivity. Loss tangent is a function of capacitive current and resistive current so I suppose you could determine the loss tangent from simulation. If I wanted add loss tangent as a parameter, I would I have to use the RF module which I'm not using here. I'm mainly considering parameters that effect e-field intensity.

I know that e-field simulations can be done using DC or electrostatic. From my understanding, electrostatic is means there is no magnetic field present or it's slow moving and can be neglected. Do DC simulations typically consider permittivity AND conductivity whereas electrostatic assumes perfect electrical insulators and conductors and only considers permittivity?

The image attached are the parameters I have available in the current module that I'm using.