Designing a "lossy metal" dipole in CST

[victor50]

lossy metal

As a biotechnology student at Rome university I have to prepare my thesis on a medical device which requires the design of a high frequency dipole (1-3 GHz) by means of CST, software for which I am a beginner. Nevertheless, following the tutorials and some examples I was able to design a dipole made of PEC (and vacuum) my professor was somewhat satisfied about. Now she asked me to perfect the design using a real material instead of PEC and suggested to select "lossy metal" with a conductivity of 1e+007 (10 millions) S/m. Now I changed the material of the solid bar selecting this new "lossy metal" material and ran it (!T) all from scratch but "unfortunately" the results were not that different from those of the PEC material. The polar graph of theta in the farfield section was overlapping almost perfectly the same graph for PEC material. I tried an extreme and impossible case using a conductivity of 1e+003 S/m and in this case the results were somewhat different from the PEC material. Unfortunately my professor dismissed my extreme test (1e+003) and said that I should work on the 1e+007 S/m lossy metal to find what was wrong with it. Is there anyone able to help me?

 

[GVVIN]

Yaa I too have noticed the same . I have used aluminium lossy metal 3.72e+007. for my antenna. there is no change in S11, also a very minimal change in surface current and Magnetic energy density when compared with PEC.Far field is also same.

 

[mauloftin]

Hi,
may be, you don´t use "lossy metal", but try use "normal" and set conductivity.

 

[loucy]

It will be much easier to simulate the "lossy" dipole using a MoM based tool such as Zeland IE3D or EMSS Feko. The FIT in CST (or other FDTD tool) is not adept at modeling "lossy metal" and the thin object--think about how small the time step should be when the material is as "lossy" as you specified or when the cell size is very small in order to capture the real dipole shape.

 

[victor50]

Thanks for the many helpful replies. Now, an additive problem arises. I Selected for the dipole "lossy metal", then I selected to monitor the "Current Density" (symbol J). When I ran !T, well it said
"Warning- the monitor current is only available for lossy materials and will b e ignored"
I'm now quite confused. I already chose "lossy metal" with the conductivity indicated in my first message! what else should I do?

 

[mauloftin]

The dipole have two "parts", have you sure, that you have both parts as "lossy metal" ?

ok ok, i am try it only

 

[shameemkabir]

Now, an additive problem arises. I Selected for the dipole "lossy metal", then I selected to monitor the "Current Density" (symbol J). When I ran !T, well it said
"Warning- the monitor current is only available for lossy materials and will b e ignored"
I'm now quite confused. I already chose "lossy metal" with the conductivity indicated in my first message! what else should I do?

Hi victor, It's not a problem I guess. Current density is calculated for the material which has dielectric and magnetic losses. Since you use lossy conductor, you have conduction loss. Therefore, Current Density monitor cannot be used. If you want to take a look at the current distribution, use H-field/surface current monitor.

Now, about your first problem: PEC and conductors like aluminium, copper etc. will give you almost the same result for your dipole antenna which has small length like 70 or 80 mm. Loss over this length is very small thereofre, no significant differenece can be obeserved between PEC and lossy metal simulation. In my view your simulation is alright, just build such an antenna with available material and it will definitely work.

regards,
shameem