how to determine mass of a sphere in a HFSS or FEKO diagram?

I need urgent help on how to determine the mass of a sphere or any 3D object in HFSS or FEKO. I need this for Specific Absorption Rate (SAR) project.

Thank you.

Right click on the Material Icon (ie test_mat) and select properties to get to material property window.

Select the tab for "Material Filters"

Change radio button selection to "All Products"

Go back to "Materials" tab

select the material that you would like to input a mass density and enter it

Once the Mass Density is specified, you can actually plot the Local SAR, Average SAR, or IEEE SAR (cell phone applications). Note that you should read the help concerning the deifference between Local (fast) and Average (slow) SAR. The average SAR involves many incremental integrations of SAR in a given unit mass spheres.

You will have to do this each time you enter the material properties window, and also, there are many common materials whose thermal properties, including mass density, are already available. Once you have turned on the "all products" option, you can see these properties of many of the materials in HFSS.

Hope this helps!

Re: how to determine mass of a sphere in a HFSS or FEKO diag

Thanks a lot for your reply.

I could see mass density. I take it the units are in 1kg/m^3. Also, the default is zero for the material I created and for most materials. Doesn't SAR need a value for mass density in order to calculate power absorbed over mass? How does HFSS solve SAR values when mass density variable is set to zero?

I guess if I want to find the mass, then mass = mass density x volume. What if the volume shape is irregular, how could I find the volume in HFSS?

I wish HFSS could just calculate mass of object for me, instead of I hand-calculate it.

To get the volume of an object is easy enough...right click in 3D modeler window, go to measure -> Object. Then select the object and both the volume and surface area are given.

If you want the mass this is fine, but why would you expect any electromagnetic solver to return this by default??? Mass density play little if any roles is most EM applications until thermal considerations are looked into, and even then there are relatively few thermal consideration in High Frequency EM if you look at the market as a whole. If you want this value without hand calculations, use the field calculator to create a calculator function that returns the mass.

The point about the material properties is that you can CHANGE the mass density to represent the material of interest for you.

Have Fun

Re: how to determine mass of a sphere in a HFSS or FEKO diag

Thanks. I right-clicked on an object that is made up of 2 different dielelectric properties (it was unioned) and was able to get its volume. Now I need to get the mass of this object. So, I take it I need to set the mass density in the material properties window for each dielectric separately. The question now is do I calculate the mass for each dielectric object separately using the mass = mass density*volume equation then add them up?

Also, I need to get the average SAR in the whole object which consists of 2 different unioned materials. How can I get this in HFSS? Do I add up all the SAR values from one end of the object to the other end on the SAR line? It seems that HFSS gives you average SAR at specific points. I am under the impression I need to add up the SAR values across all the points that fall within the object, is that correct?

Is there a way in HFSS other than using SAR to calculate the power absorbed in an object? That's really what I am trying to accomplish. I would like to measure power absorbed per unit mass. I am trying to get that now using this equation:
Power(absorbed) = Total Average SAR * mass.

I really appreciate your help. I am relatively new to HFSS and the world of EM simulation. Please bear with me.

Thank you.

HFSS has a MUCH easier way of determining the power loss in either volumes or surfaces. In the field calculator this is call Surface Loss Density and Volume Loss Density. If you integrate these values over either surfaces or volumes, you will have total power lost in the structures due to electromagnetic attenuation.

hope this helps

Re: how to determine mass of a sphere in a HFSS or FEKO diag

ok. If it's not too much to ask what are the steps I need to take to integrate the Volume Loss Density over the specific volume in the Fields Calculator. I can see the Volume Loss Density at the bottom of the Named Expressions list in the Fields Calculator window. I have not used the Fields Calculator before and I honestly don't have the time for trial and error since my project deadline is coming up soon.

Does HFSS produce a *.out file like FEKO does? Basically all power losses per dielecteric, etc.. would be listed there.

Thanks.

Sure, actually HFSS has a very nice Field Calculator Tutorial that walks one through the 4 steps to calculate the power lost in a dielectric.

1) go to HFSS help.
2) search "calculator cookbook"
3) select first entry returned, "Named Expression Library"
4) scroll to bottom of page and select the link for "HFSS Field Calculator Cookbook"
5) once the pdf is open, go to page 23 (in document, not pdf pages 27/34) this walks one through the calculation of loss in volume.

Process for surface loss is similar. If you want an out put for all diectrics you will need to create a calculator function for each dielectric, plot in data table, and export. No Problem.

Have Fun

Re: how to determine mass of a sphere in a HFSS or FEKO diag

ok. I have HFSS version 11. I think you may have a newer version. I searched for calculator cookbook and nothing came up. I then searched for Named Expression Library and I opened the help page for it, but it reads "Calculating Derived Field Quantities" at the bottom of its page. Could you upload the pdf or do for the calculator cookbook?

Also, I have a question about calculating SAR. Since I am using SAR calculation Do I need to have a receiving antenna on the other end of the body I am trying to measure power absorbed through? It seems that SAR line I draw through the body takes care of the power absorption calculations. I assume HFSS measures SAR in the entire body that the line goes through. It gives SAR measurements across the line, and I would have to add them up to get Total SAR. Hope I am right on that.

I am using a dipole, do I have to impedance match it first in the presence of the object I want to measure the power absorbed through or that's not necessary? Is there something in HFSS I could use like plane wave signal with radiated power that would replace the use of matched antenna?


Thanks a lot, you are God-sent.

I am running the latest version, HFSS12.1.2. You can find the older version of the cookbook in a quick google search...or you can update your version of HFSS to the latest version and it will be there.

The older version of cookbook does not include this example, but has several others to get you started.

The steps are easy as it gets.

1) Solve your model
2) go to HFSS -> Fields -> Calculator
3) Press "Quantitiy" button and drop down to VolumeLossDensity
4) Press "Geometry" button
5) Window pops up, select volume radio button
6) select the object that you want the total power loss
7) Press the button that looks like an integral symbol, in the third column
8) Press "Eval" to evaluate the amount

Also, if you go back through to step 7) and rather than hitting the eval button, you can save your function by hitting the "Add..." button above the entry window. This will ask you to give a name to a function that you can now access from the Reporter.

As for SAR, you do NOT need the receiving antenna as all power is being radiated from transmitter (unless of coarse you have substantial reflections from the receiving antenna, but they aren't usually designed this way ). Also, you DO want your antenna matched, or at least with the load that will be used for measurement as the field solutions will radiate power from the antenna according to the match. If it is poorly matched, then little power leaves the antenna.

good luck

Re: how to determine mass of a sphere in a HFSS or FEKO diag

Thank you for the fast replies.

Was I correct about this assumption: "I assume HFSS measures SAR in the entire body that the SAR line goes through. It gives SAR measurements across the line, and I would have to add them up to get Total SAR. Hope I am right on that."

Also, could you please answer this "maybe stupid" question:
"Is there something in HFSS I could use like plane wave signal with radiated power that would replace the use of an antenna?"
I have asked it before in some other forums and no one bothered to answer it maybe because it's so obvious.

I will try your detailed steps for VolumeDensityStep and let you know.

Thanks, man.

Re: how to determine mass of a sphere in a HFSS or FEKO diag

tallface,
what is the unit for volumelossdensity? Is it watts?

thanks.

You can look these kind of questions up in the HFSS help ;0)

The units are W/m^3 for volume loss density, hence integrating this quantity over a volume gives: Watts.

thanks again, man.

Could you please answer this urgent question for me:
Is there something in HFSS I could use like plane wave signal with radiated power that would replace the use of an antenna?


Basically the stupid dipole antenna I am using does not penetrate into the body 5mm away from it as much as I would like it to. The body is 10 cm wide, and I could tell from the SAR plot that E-field attenuates considerably after 1-2cm....

I need a wave that penetrates through a body with permittivity = 4.839 and conductivity=0.262. I am using 4GHz as solution frequency. Maybe I should use lower frequency, but some paper I read states the higher frequency penetrates better because it induces more field exposure to the body.

If all you are trying to do is increase penetration with such a lossy material, just crank the power up on the dipole. HFSS->Fields->Edit Sources

Re: how to determine mass of a sphere in a HFSS or FEKO diag

ok. good idea. Thanks.

I have 3 calculations results after my simulation ran:

1. Antenna Power Loss = Antenna Power Accepted - Antenna Power Reflected = 0.48214 W

2. VolumeLossDensity (integrated over the volume of object) =0.49011 W

3. Power (absorbed) = Total SAR * mass of object = 0.08916W ( I see other papers reporting similar low Power absorbed values through SAR calculation.)

Total SAR = Average SAR integrated over the SAR Calculation line.


How come the power (absorbed) does not match the VolumeLossDensity? It's much less.

I see the VolumeLossDensity matches closely with the Antenna Power Loss.


Thanks.

tallface65 said:

Right click on the Material Icon (ie test_mat) and select properties to get to material property window.

Select the tab for "Material Filters"

Change radio button selection to "All Products"

Go back to "Materials" tab

select the material that you would like to input a mass density and enter it

Once the Mass Density is specified, you can actually plot the Local SAR, Average SAR, or IEEE SAR (cell phone applications). Note that you should read the help concerning the deifference between Local (fast) and Average (slow) SAR. The average SAR involves many incremental integrations of SAR in a given unit mass spheres.

You will have to do this each time you enter the material properties window, and also, there are many common materials whose thermal properties, including mass density, are already available. Once you have turned on the "all products" option, you can see these properties of many of the materials in HFSS.

Hope this helps!

Click to expand...

Hi everyone! I really need your help!!!
Does anybody know exactly what choices do I have to make in order to plot SAR for a multilayered tissue model? I have already set the mass density values for each layer, but what do I have to do next? Do I have to choose all the layers together?
Is there a fastest way to calculate maxSAR and not to start a new simulation? How do I get either SAR 1g or SAR 10g? How do i change this setting?

One of the old HFSS user guides, I believe version 9, has a good tutorial on Specific Absorption Rate (SAR). You should be able to find it in edaboard with a simple search.

GL