Method to model a dipole in saltwater or other mediums?
Altair EmployeeI have a 2.7Ghz dipole antenna with length of one wavelength and radius of 1/10 wavelength.
I want to see how the radiation pattern changes for a dipole antenna in various mediums - different gases, water, salt water, etc.
What would be the easiest way to accomplish this?
I've tried two different ideas without much success:
Idea 1) Directly change the properties (relative permitivity, conductivity, density) of the free space medium.
When I start changing these properties far from their defaults I start getting a lot of geometry errors. For example, to model salt water, I give the free space medium a relative permitivity of 80 and a conductivity of 4 S/m. But then trying to solve this model gives 'ERROR 114: Segmentation rules have been violated (wire segment is too long)'. I attempt to resolve this by shortening the length of the dipole antenna to wavelength/10, but then I start getting mesh errors like 'WARNING 18189: The geometry is much smaller than the model extents. This could cause tolerance issues.' Is this normal? Do I need to just keep playing with the antenna vs mesh dimensions until it works?
Idea 2) Create a sphere surrounding the antenna and assign the region a new medium with the correct properties.
I create a sphere with a width several times the length of the antenna, but no matter what medium I assign to the region inside, FEKO treats it as a lossy space. For example, giving the region the default free space medium, and the faces are all perfect electric conductor, results in all gain from the antenna being destroyed and 'WARNING 3397: The power loss is larger than the active power'. Shouldn't a spherical region of free space be treated the same as the rest of the free space geometry? Why does FEKO treat it differently?
I know this is possible because I've read several research papers talking about using FEKO to model antenna underwater, but so far I haven't figured out the key. Can anyone provide some help?
Edit: Attached my models.
Answers
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Your first approach is correct.
The problem with your model is to do with how you have set up the meshing. If you remove the Local mesh settings for the dipole wire the correct wire segment lengths will be used to mesh the dipole (i.e. adapted to the local wavelength in the seawater). However, this triggers a new error, which is related to the ratio of the radius of the dipole wire and the mesh segments - basically your dipole radius is too large. If these dimensions are physical and match the real antenna - you can use a cylinder instead of a wire to model the dipole. However, the radius does look very thick. I changed your radius to h/500 and the simulation runs without errors.
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