SEMCAD Tutorial

Michael Burdumy

Michael.Burdumy@ibt.uni-karlsruhe.de

January 29, 2009

1 Two Metallic Spheres

The goal of this exercise is to become familiar with the low frequency solverof SEMCAD. We’ll create two metallic spheres, assign different potentialsto them and let SEMCAD calculate the electric field. Be aware that this isthe first version of this tutorial, so any comments would be appreciated.

1.1 Creating the Model

1. Set the model unit to cm

2. Create a sphere by using the Sphere icon in the modeling toolbar. Setthe radius to 1cm.

3. Create a second sphere. Set the radius again to 1cm. Set the translationto x = 17cm. You can also change the color of this sphere.

1.2 EM-Simulation

1.2.1 Simulation Settings

Next we have to set up the simulation settings.

1. Click on the EM-Simulations tab. There will already be a defaultsimulation entered.

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1.2 EM-Simulation 1 TWO METALLIC SPHERES

Figure 1: Two metallic spheres

2. Change the solver in Settings→ Solver to Low Frequency Solver.

3. Make sure the Solver Type is set to Electro Static. This is the defaultsetting.

1.2.2 Solid Regions

Now we have to change the material of the spheres and assign the potential.

1. Click on Solid Regions

2. Choose Sphere1 and select PEC/Metal as Type. Set the PotentialAmplitude to 1V.

3. Repeat the same procedure for Sphere2, this time choosing −1V asthe amplitude.

Note that the spheres count as sources when using the low frequencysolver, so we don’t have to set up any other sources.

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1.2 EM-Simulation 1 TWO METALLIC SPHERES

Figure 2: Simulation Settings

Figure 3: Solid Regions

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1.2 EM-Simulation 1 TWO METALLIC SPHERES

1.2.3 Boundaries

Figure 4: Boundaries

1. Now switch to Boundaries. We want to use Dirichlet.

2. Select X low and choose Dirichlet from the drop down box. Rightclick on X low and copy and paste it to all other boundaries.

We don’t need to set up the sensors as SEMCAD implements an OverallField Sensor by default.

1.2.4 Grid

Now we have two metallic spheres, each with a different potential. Nextwe have to set up the grid that SEMCAD uses to break down its calculationsto finite parts.

1. Click on Grid, select Sphere 1 and set the Mode to Geometrical. Thiswill tell SEMCAD to better refine the grid on the object. Select Sphere1 and check Gang Axes. Set the Curvature Resolution to 0.5.

2. Repeat for Sphere 2.

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1.3 Extracting and Interpreting the Results1 TWO METALLIC SPHERES

3. Right click on Voxels and select Make Voxels. The Grid will now becalculated.

Figure 5: Grid Settings

4. Start the simulation by clicking on the green start button in the toolbar.

1.3 Extracting and Interpreting the Results

Once the simulation has finished, you can view the results in a lot ofdifferent ways. Here we will provide one example on how to view thoseresults.

1.3.1 Extracting

1. Click on Results in the EM Tab, choose Overall Sensors and E(x, y, z)and select Slice Field View.

2. Click Next on the appearing screens.

3. Switch to the Viewers tab (if SEMCAD didn’t do so automatically).Here you will be able to manipulate at which coordinate the modelis sliced and a lot of other options that can’t be explained in detailhere, but should be self-explaining.

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1.3 Extracting and Interpreting the Results1 TWO METALLIC SPHERES

Figure 6: Extracting Results

4. If you right click on Simulation 1 in the viewer tab you get severaloptions to view the simulation data differently, e.g. Surface FieldView.

Figure 7: Viewing the Results

1.3.2 Interpreting the results

You are free to try different settings for the amplitude, the size of thespheres and the distance. Note that in order to change parameters like the

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1.3 Extracting and Interpreting the Results1 TWO METALLIC SPHERES

distance done in the modeling tab you have to delete any results and gridalready calculated.

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2 CAPACITOR

2 Capacitor

In this exercise we will create a model of a parallel-plate capacitor andcalculate its charge with the help of SEMCAD.

2.1 Creating the model

1. Create a new SEMCAD project.

2. Set the Model Unit to cm.

3. Create Brick 1 using the Brick icon in the modeling toolbar, use theorigin as the first corner, set the second corner to (15,15,0).

Figure 8: Parallel-Plate Capacitor

4. Right click on Brick 1, select copy and then paste the first brick.

5. Change the name of the copied brick to Brick 2. Set Translation Z to3cm.

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2.2 EM-Simulations 2 CAPACITOR

2.2 EM-Simulations

1. Switch from the Model tab to the EM-Simulations tab to enter thesimulation settings.

2. Delete the default simulation, then right click and choose New Sim-ulation→ Low Frequency to create a new low frequency simulation.

3. The default settings of the new simulation are Low Frequency Solverwith Solver Type set to Electro Static solver.

4. In Solid Regions select Brick 1, change the Type to PEC/Metal andset the Potential Amplitude to 1V to assign a potential to the plate.

Figure 9: Solid Regions

5. Select Brick 2, change the Type to PEC/Metal and set the PotentialAmplitude to −1V.

6. It is not necessary to apply any settings to the sources as the Solidregions act as such.

7. The Overall Field Sensor is used to record the field distribution. Thissensor is always used by default.

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2.2 EM-Simulations 2 CAPACITOR

8. The Boundaries are automatically configured to Dirichlet.

9. Click on Grid to generate a default grid.

10. In Global Settings change the Padding Low and High for the Z-Axisto 0.7m. The Padding adds extra space outside of the model so thatthe Boundary conditions can be met.

11. Select Brick 1, check Gang Axes and set the Refine on Lower andUpper Boundary to 0.6. Apply the same settings to Brick 2.

12. The resulting grid should have 0.964467 MCells.

Figure 10: Grid Settings

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2.2 EM-Simulations 2 CAPACITOR

13. Make Voxels.

14. Start the simulation.

15. View the results.

16. Copy Simulation 1, rename it to Simulation 3 and insert a dielectricumbetween the two plates. This can be done by changing the epsilon ofthe background. Click on File→Materials..., copy Water(distilled)and paste it on the Background.

17. Make Voxels.

18. Start the simulation.

19. View the results.

20. Now create a new project.Create the same parallel plate capacitor asbefore, but this time set the distance between the plates to 3mm.

21. Calculate a fine grid.

22. Start the simulation and view the results.

Figure 11: Viewing the results

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2.3 Extracting and Interpreting the Results 2 CAPACITOR

2.3 Extracting and Interpreting the Results

Calculate the theoretical values of Q for all settings ( ε0 = 8.8542 ·10−12F/m).Given that |D| = Q/A for a parallel plate capacitor, calculate the value

of Q by using SEMCAD’s numeric results for D. Extract D(x, y, z, f 0).You can extract the results of SEMCAD by using a provided script on

the website. The script is called QDA.py. Open it by clicking on SEMCADX Script→Open Script and press F5. Why are the results of the numericaland theoretical calculations different?

Calculate the theoretical value of E = U/d. Compare this with themaximum of the numerically calculated E.

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3 PLANE WAVE

3 Plane wave

This exercise will deal with a plane wave. SEMCAD provides easy waysto model plane waves in 3D and analyzing those models for differentfrequencies.

3.1 Modeling and Simulating

1. Choose the Plane Wave Source icon. Enter the points (-150, -150,-150) and (150, 150,150) for the First and Second Corner respectively.

2. Click Done: Plane Wave Source 1 is added to the model.

3. Set the Frequency to 3000 MHz for the harmonic simulation.

4. Select the Plane Wave Source 1: the E, H, and k orientation and thesignal Scope is shown. For this simulation the k vector of the PlaneWave will be oriented in positive Z-direction, so it is not necessary tochange phi, theta or psi.

5. Make Voxels and Simulate.

6. Save the project under a different name, excluding the results.

7. Insert a dielectricum, a cube of a size smaller than the cube you’vecreated in the beginning. As with the plate capacitor, get the param-eters of distilled water from the material list and paste those settingsto the small cube.

8. Make Voxels and Simulate. You’ll have to change the grid size bychanging the scale factors. Be sure to stay under 1 Mio. Voxels.

9. Extract the E-Field and look at the results of both simulations.

3.2 Questions

How would you explain the differences in the 2 simulations?

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3.2 Questions 3 PLANE WAVE

Figure 12: Plane Wave

Figure 13: Plane Wave with dielectricum inserted

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4 TELEPHONE AND HEAD

4 Telephone and Head

In this exercise we will create a model of a phone, import a 3D model ofa head, assign parameters to the materials and extract results from thissimulation setting.

Figure 14: Head and phone model

4.1 Modeling the Case of the Phone

1. Create a Group by clicking on the Group icon and rename this groupphone.

2. Create two points p1(20, -16, -130) and p2(-20, 0, 10) by clicking onthe point icon.

3. Click on the brick icon and select p1 and p2 to build the brick. Renamethe brick Case.

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4.2 Modeling of the Monopole Antenna 4 TELEPHONE AND HEAD

Figure 15: 2 Points

Figure 16: Phone Case

4.2 Modeling of the Monopole Antenna

A 1mm gap is left between the phone case and the antenna where anedge source can be placed. The antenna is to be modeled as a 79mm long

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4.3 Adding the Source and the Sensors 4 TELEPHONE AND HEAD

cylinder with a radius of 1.25 mm.

1. Create three points p3(-12, -8, 11), p4(-12, -6.75, 11) and p5(-12, -8,90), and click on the Arc icon to create a circle. Select p3 as the centerand p4 as the start and end point on the circle.

2. Click on the Extrude icon and select the previously created circle (Arc1) as the profile to extrude. Select the points p3 and p5 to create thecylindrically swept body. Rename it Antenna.

3. Create the point p6(0, 0, 0) and rename it Speaker Point. This pointwill be used later.

4.3 Adding the Source and the Sensors

1. Create the point p7(-12, -8, 10), which is the intersection of the axis ofthe antenna with the top of the case.

2. Create the Edge Source by clicking on the corresponding icon andselect p3 and p7 as the termination points.

Figure 17: Complete Phone with Edge Source

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4.4 Importing the SAM phantom model 4 TELEPHONE AND HEAD

Note that it is not necessary to add any sensors, as the necessary sensorsare added by default, the Sensor of Edge Source, Overall Field Sensor,and Far Field Sensor.

4.4 Importing the SAM phantom model

1. Select the root (Model) in the modeling tree, generate a new modelinggroup for the phantom and activate it.

2. Import the SAM Phantom model via the File → Import Model →ACIS SAT File menu command. The zipfile containing the phantommodel (SAM Head.zip) is located in the directory in which the tutorialprojects are installed. If there are no tutorials installed on your ma-chine download the model from http://www.semcad.com/sup down-loads.html. This model contains the three predefined reference pointsat the openings of the left and right auditory canals and at the mouthof the phantom.

Figure 18: Head Model

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4.4 Importing the SAM phantom model 4 TELEPHONE AND HEAD

4.4.1 Moving and Rotating the head

You need to move the phantom near the generic phone such that the leftear reference point of the phantom coincides with the Speaker Point of thephone. In order to do so, select the modeling group which contains thephantom. Selecting a modeling group instead of a single item will applyany operation, such as moving, to all items contained in that group. Clickon Movein the modeling toolbar and then on the left ear reference point ofthe phantom to designate it as the starting point of the translation vector.The end point will be the origin by default, where the speaker of the phoneis located. You can complete the move operation by clicking on the Donebutton.

Figure 19: Translation of head phantom

In order to move the phantom and the phone into the desired positions,the head will be rotated instead of the phone. This is to avoid staircasingerrors at the case and at the antenna of the phone, since in this way theywill remain aligned with the axes of the coordinate system.

1. Select the model group which contains the phantom and click onRotate in order to rotate it. In the Rotate Selected Parts dialog

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4.5 EM-Simulations 4 TELEPHONE AND HEAD

window you are required to select two points for the rotation axis.Here, you can either choose the two reference points at the phantom’sears, or, alternatively, enter two arbitrary points on the y-axis (seeFigure 20). Finally, enter an angle of -61◦ in the dialog window andclick on Done to finalize the operation.

2. Rotate the phantom around the z-axis (e.g. (0, 0, 0) and (0, 0, 100)) byan angle of −3.9◦. Proceed in the same way as in the previous step.Be sure that the profile of the phantom’s ear is aligned with the caseof the phone.

3. Now, bring the phantom into ”touch position”. Select two points onthe x-axis (e.g. (0, 0, 0) and (100, 0, 0)) and rotate the phantom by −4◦.

Figure 20: Rotation of head phantom

4.5 EM-Simulations

1. Keep the Excitation Mode as Harmonic.

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4.5 EM-Simulations 4 TELEPHONE AND HEAD

2. Keep the Frequency of the simulation at 900MHz and the SimulationTime at 10 periods.

3. Select the case of the phone and change the Type in the Materialswindow to PEC.

4. Select the antenna of the phone and set it to PEC.

5. Select the SAM Liquid, and set the Rel. Permittivity to 41.5 and theElectrical Conductivity to 0.97S/m.

6. Select the SAM Shell, and set the Rel. Permittivity to 3.7. Repeat forthe Reference Points by either manually entering the value, or usingthe Copy command on the SAM Shell and then the Paste commandon the Reference Points.

7. Set the Absorption Strength of the X low boundary to Low.

8. Right-click on the X low boundary, choose Copy, then multi-selectthe remaining boundaries and Paste the settings.

9. Select Grid: the grid is automatically calculated. To obtain an accu-rate representation of e.g. the impedance it is necessary to refine thegrid slightly.

10. Select the Antenna either by selecting it directly in the Grid RegionsList or using the Picker and clicking on it in the 3D modeling window.For the local grid settings set the Refinement on Lower and UpperBoundary to 0.06 for the Z-Axis.

11. Select the Case, check Gang Axes and set the Refinement on Lowerand Upper Boundary to 0.15.

12. Select the SAM Liquid either by selecting it directly in the GridRegions List or using the Picker and clicking on it in the 3D modelingwindow. Change the Mode to Bounding Box. This will introduceBaselines, resulting in a finer grid in the region the maximum SAR

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4.5 EM-Simulations 4 TELEPHONE AND HEAD

(a) Antenna (b) Case

Figure 21: Grid Settings for phone

is expected in, giving a more accurate result. The total grid shouldnow have 0.84048 MCells.

Figure 22: Grid Settings Head Phantom

13. Copy and Paste Harmonic Simulation 1.

14. Rename the copied simulation Harmonic Simulation 2.

15. Change the frequency to 2000MHz.

16. Click on Grid. There will be too many voxels now, the light versionof SEMCAD can only handle 1Mio. Voxels. So change the OverallScale Factor to 2. This should result in a voxel count slightly below 1Mio..

17. Make Voxels for both simulations.

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4.6 Extracting and Interpreting Results 4 TELEPHONE AND HEAD

18. Click on Run Batch and choose both simulations.

19. Lean back and wait for the simulation to end.

4.6 Extracting and Interpreting Results

4.6.1 Defining SAR

The ”Specific absorption rate” (SAR) is a measure of the rate at whichradio frequency (RF) energy is absorbed by the body when exposed toradio-frequency electromagnetic field. It is defined as the power absorbedper mass of tissue and has units of watts per kilogram. SAR is usuallyaveraged either over the whole body, or over a small sample volume(typically 1g or 10g of tissue). The value cited is then the maximum levelmeasured in the body part studied over the stated volume or mass. It canbe calculated from the electric field within the tissue as:

SAR =σ|E|2

2ρ(1)

In Europe, the limit for a cell phone is 2 W/kg, averaged over a volumeof 10 grams of tissue.1

4.6.2 Calculating SAR

In order to calculate the average SAR follow these steps.

1. Start with Harmonic Simulation 1.

2. Right click on the Spatial Peak SAR[IEEE-1529] icon of the OverallField sensor results in the project tree and select the Slice Field Viewer.

3. The SAR distribution can be averaged over an arbitrary mass accord-ing to IEEE 1529, set it to 10g.

4. Select the solids to be considered for the SAR computation. SelectSAM Liquid. Click Next to start the computation.

1Source: Wikipedia

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4.6 Extracting and Interpreting Results 4 TELEPHONE AND HEAD

Figure 23: Spatial Peak SAR

5. Choose view details. This will show you the Averaged SAR basedon IEEE-1529. The value should be 0.0139817 W/kg

6. Now switch to Harmonic Simulation 2 and extract the results in thesame way. Compare the Average SAR. How would you explain theresults?

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