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Radar cross section calculation problem

Posted 6 août 2010, 21:16 UTC−4 Version 4.1 3 Replies

COMSOLoholic
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Hello,

I am new to COMSOL and I want to find the radar cross section of a simple cylindrical structure. I found an example in the models (www.comsol.com/showroom/documentation/model/8613/) but I could not transform it into my desire simulation. My structure is a lossy dielectric cylinder and I want to find both its far field and near field scattering fields. In the model example, there is a perfect conductor (boat) in the middle of the simulation window and the boat is used as a "general extrusion". The name of this extrusion area is "back" and the RCS is calculated as [4*pi*(back(Efarz(x,y)))^2].

---what is general extrusion and how can it be useful for far field calculation? It is mentioned that the field will be calculated at points (x*cos(phi),x*sin(phi)). What is x in this relation?

---In the case of a lossy dielectric cylinder, do I require to define a boundary (Impedance matching boundary) around the desired dielectric cylinder?

---Which one is better and more accurate: cylindrical PML or cubic PML? How thick should it be? How far should it be from the object?

---What is far field calculation, which is used in the boundary of the boat? Should it be always at the boundary of the desired structure? In the case of dielectric object what should I do?

--- In the case of half space dielectric object, PML should include both the air and the half space dielectric. What is your suggestion for that?

Thanks for your help in advance.
3 Replies Last Post 29 févr. 2012, 14:41 UTC−5
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Glenston Miranda
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Posted: 1 decade ago 18 août 2011, 09:33 UTC−4
I have the same problem... what is the purpose of using general extrusion(back) in this model .
Been stuck on it for a while.

Help would be greatly appreciated!
I have the same problem... what is the purpose of using general extrusion(back) in this model . Been stuck on it for a while. Help would be greatly appreciated!
Guy Lipworth
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Posted: 1 decade ago 29 févr. 2012, 11:55 UTC−5
Draw an imaginary circle around your object - the points in X,Y are functions of cos and sin of the angle phi around that circle.

Then, at each point on the circle, Comsol is measuring the fields.

It then uses the Efarz command to calculate what the far-fields would be based on the fields it measured around the circle, which are not far-fields.

From the far-fields, it then calculates the RCS.

Hopefully that helped

-Guy
Draw an imaginary circle around your object - the points in X,Y are functions of cos and sin of the angle phi around that circle. Then, at each point on the circle, Comsol is measuring the fields. It then uses the Efarz command to calculate what the far-fields would be based on the fields it measured around the circle, which are not far-fields. From the far-fields, it then calculates the RCS. Hopefully that helped -Guy
Pu
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Posted: 1 decade ago 29 févr. 2012, 14:41 UTC−5

Hello,

I am new to COMSOL and I want to find the radar cross section of a simple cylindrical structure. I found an example in the models (www.comsol.com/showroom/documentation/model/8613/) but I could not transform it into my desire simulation. My structure is a lossy dielectric cylinder and I want to find both its far field and near field scattering fields. In the model example, there is a perfect conductor (boat) in the middle of the simulation window and the boat is used as a "general extrusion". The name of this extrusion area is "back" and the RCS is calculated as [4*pi*(back(Efarz(x,y)))^2].

---what is general extrusion and how can it be useful for far field calculation? It is mentioned that the field will be calculated at points (x*cos(phi),x*sin(phi)). What is x in this relation?

Far field values don't depend on x. Here the significance of far fields is the angular distribution.

---In the case of a lossy dielectric cylinder, do I require to define a boundary (Impedance matching boundary) around the desired dielectric cylinder?

Far fields are calculated according to near fields on a closed boundary enclosing the scatterer. The boundary is not necessarily the surface of the scatterer.

---Which one is better and more accurate: cylindrical PML or cubic PML? How thick should it be? How far should it be from the object?

Just use PMLs conforming with the computational domain. U need to try and see how field attenuates inside, then decide the proper thickness.

---What is far field calculation, which is used in the boundary of the boat? Should it be always at the boundary of the desired structure? In the case of dielectric object what should I do?

--- In the case of half space dielectric object, PML should include both the air and the half space dielectric. What is your suggestion for that?

Generally, use PMLs to enclose all structures.

Thanks for your help in advance.
[QUOTE] Hello, I am new to COMSOL and I want to find the radar cross section of a simple cylindrical structure. I found an example in the models (http://www.comsol.com/showroom/documentation/model/8613/) but I could not transform it into my desire simulation. My structure is a lossy dielectric cylinder and I want to find both its far field and near field scattering fields. In the model example, there is a perfect conductor (boat) in the middle of the simulation window and the boat is used as a "general extrusion". The name of this extrusion area is "back" and the RCS is calculated as [4*pi*(back(Efarz(x,y)))^2]. ---what is general extrusion and how can it be useful for far field calculation? It is mentioned that the field will be calculated at points (x*cos(phi),x*sin(phi)). What is x in this relation? Far field values don't depend on x. Here the significance of far fields is the angular distribution. ---In the case of a lossy dielectric cylinder, do I require to define a boundary (Impedance matching boundary) around the desired dielectric cylinder? Far fields are calculated according to near fields on a closed boundary enclosing the scatterer. The boundary is not necessarily the surface of the scatterer. ---Which one is better and more accurate: cylindrical PML or cubic PML? How thick should it be? How far should it be from the object? Just use PMLs conforming with the computational domain. U need to try and see how field attenuates inside, then decide the proper thickness. ---What is far field calculation, which is used in the boundary of the boat? Should it be always at the boundary of the desired structure? In the case of dielectric object what should I do? --- In the case of half space dielectric object, PML should include both the air and the half space dielectric. What is your suggestion for that? Generally, use PMLs to enclose all structures. Thanks for your help in advance. [/QUOTE]

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