Subtract structure in HFSS

When you are creating a cylindrical ring in HFSS, which one of the below is the right approach?

Method 1:

1. create an outer cylinder of metal
2. create an inner cylinder of metal
3. subtract 2(Tool part) from 1(Blank part), No clone option
Q? Will HFSS automatically assign the inner hollow area as Vacuum or Air?


Method 2:

1. create an outer cylinder of metal
2. create an inner cylinder of Air
3. subtract 2(Tool part) from 1(Blank part), No clone option

Q?HFSS replace the inner hollow area with Air, but the hollow part will not be visible in the Design Tree.



Method 3:


1. create an outer cylinder of metal
2. create an inner cylinder of Air
3. subtract 2(Tool part) from 1(Blank part), WITH clone option

Q?HFSS replace the inner hollow area with Air, and the hollow part WILL be visible in the Design Tree.

Do you have a dielectric material (box) outside the metal cylinder?
Make sure the enable material override is checked under HFSS Design Settings. This make it so that if a conductor and insulator overlap the overlap area is given the conductor properties.
Methods 1 and 2 will do the same thing. Having an outer air box will make the subtracted area air. The problem with having the dielectric cylinder inside the conductor with the same radius of the inner conductor radius is that sometimes the mesh can get messed up at the interface of two curved shapes if they are both explicitly defined. If you want to have the insulating material in the design tree, copy the insulator before the subtraction and increase the radius slightly.
Q1. Inner hollow area will be assigned box material properties. if no outer box defined then vacuum will be assigned.
Q2. Hollow part will not be in design tree as an explicit dielectric object.
Q3. Yes, you are correct.

Thanks! No dielectric box specified.

about the material override, wouldn't HFSS give error when the structures overlap?


Q1. Will the properties of the inner hollow area change based on the outer box created later on ( eg: Ring created first and then create outer box)? Or is the properties assigned during run/validation time?

If the box isn't checked then yes you will get errors or warnings. with the box checked, smaller objects take precedence over larger objects and coductors override dielectrics, but you still get errors if you overlap two different dielectrics.
Q1 yes, the properties of the inner hollow area change based on the outer box created later on.

When slots are created on a metal surface (Without enabling the material override)it gives an overlap error only when it intersect the metal outline, if the slot happen to be within the metal surface, no overlap error is shown. Is it how it works?

If the slots are made by subtraction, what is there to overlap? If there is no overlap there will be no overlap error.

Sorry, I should have made it more clear. I have created an air box with the dimension of slot and placed it within the larger metal box. Without subtract, there was no overlap error when the air box was enclosed within the metal box and if I change the position so that the slot air box cross the outline of the metal box, then overlap error is shown.