Beginner Comsol RF parallel transmission line

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I am trying to model a parallel transmission line in several different materials at 300MHz in the electromagnetic waves frequency domain modal analysis. I have followed the comsol guide (Finding the Impedance of a Parallel-Wire Transmission Line) and have yielded the same results for air, however, when i change the surrounding material domain from air to water i get strange responses in electric field and my current value drops significantly (to the order of e-9), resulting in a massive increase in impedance (calculated using Z = V/I). I am also seeing very strange electric field distributions (i have looked at multiple modes).

So far i have tried the following, but nothing leads to an expected impedance: -changing the domain size -changing the int_H size for -int_H(emw.Hxt1x+emw.Hyt1y) -changing between perfect magnetic conductor and diffusion outer boundary conditions. -changing the conductivity of water to 0

I have attached some images for reference of my model, one for air (electric field strongest between conductors) and one for water. What might be causing low current? Why are the electric field distributions for air and water so different?



1 Reply Last Post 2026年6月15日 GMT+8 22:09
Robert Koslover Certified Consultant

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Posted: 4 hours ago 2026年6月15日 GMT+8 22:09

Water has a very high dielectric constant compared to air. It also looks to me like you are exciting a higher order mode in the model with the water, or perhaps you just have poorly chosen boundary conditions. There are many possible sources of errors in Comsol models. You might get better advice if you post your .mph file(s) to the forum to allow readers here to inspect them in detail.

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Scientific Applications & Research Associates (SARA) Inc.
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Water has a very high dielectric constant compared to air. It also looks to me like you are exciting a higher order mode in the model with the water, or perhaps you just have poorly chosen boundary conditions. There are many possible sources of errors in Comsol models. You might get better advice if you post your .mph file(s) to the forum to allow readers here to inspect them in detail.

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