Signal IntegritySoftware name: Ansoft HFSS 91What is HFSSHigh Frequency Structure SimulatorUses Finite Element Method to solve EM problemsFrequency Domain SolutionFull wave Solver23Different Methods in Electromagnetic AnalysisMOM4What is Finite Element Method (FEM) Software?FEM software is a design tool for engineers and physicists, utilizing rapid computations to solve large problems insoluble by analytical, closed-form expressionsThe “Finite Element Method” involves subdividing a large problem into individually simple constituent units which are each soluble via direct analytical methods, then reassembling the solution for the entire problem space as a matrix of simultaneous equationsFEM software can solve mechanical (stress, strain, vibration), aerodynamic or fluid flow, thermal, or electromagnetic problems5FEM Problem ConstraintsGeometry can be arbitrary and 3-dimensionalModel subdivision is generally accomplished by use of tetrahedral or hexahedral (brick) elements which are defined to fill any arbitrary 3D volumeBoundary Conditions (internal and external) can be varied to account for different characteristics, symmetry planes, etc.Size constraints are predominantly set by available memory and disk space for storage and solution of the problem matrixSolution is created in the frequency domain, assuming steady-state behavior6Example of Adaptive meshingWaveguide Filter at right (symmetry along top face) shows effect of mesh adaptation. The region between posts has a denser mesh, due to the superposition of reflected energy found in the solution process.PostPost7When is an FEM solver appropriate for Electromagnetic Problems (Lower Bound)? /100/1000Use a Quasi-Static Solver Use a FEM Full-Wave SolverProblem ScaleExample: Finding Signal Integrity impacts of a Via in the signal path /10/10(OVERLAP)Example: Coax to WG TransformerWhen the Electrical Length (in wavelengths) requires phase consideration/10 is a guideline; there are exceptionsWhen radiation from the device must be consideredWhen S-Parameters are the desired outputWhen lossy dielectric materials have significant effects8Some Typical High-Frequency Electromagnetic ApplicationsWaveguide ComponentsAntennaRF Integrated CircuitsEMC9Example 1: Eigenmode ProblemFind the resonant frequencies of a perfect metal box filled with “glass”. The box size is 3x2x2 inch.Draw the electric field inside the box at those resonant frequencies.10Ansoft HFSS Project FlowConfigurationDrawingBoundarySource ExcitationSolution SetupSolvingAnalyzeDataPlot11ConfigurationClick HFSS 9 to start the problemClick: File - Save As - filenameClick: Project - Insert HFSS DesignNow, HFSS design interface has 6 sub-windows: project window, property window, drawing window, history window, message window and execution window1213Configuration cont.Click: HFSS - Solution type, Pop up window shows three typesPick the Eigenmode 14ConfigurationClick: Tool - Option - General OptionOption window pop up.Select Default Units tabChange the length to: “inch”15ConfigurationClick: View - Grid SettingGrid setting screen pops upSelect grid size as 1 inch16Structure DrawingClick: Draw - Box ( You can also click on the draw box toolbar)On Drawing window, first click will set the start point, second click will set the base end point, and the third click will set the height of box. ( draw a 3 inch x 2 inch x 2 inch box)The property window will pop up. In the command tap, make sure the Position is at 0, 0, 0. The x-size, y-size and z-size is what you wanted.In the Attribute tab, change the material to “glass”. Change the Transparency to be “0.8”17DrawingHere is the picture of what you get.You can always change the item properties by clicking the item, and modifying them at property window18HintHold the keyboard “Shift” and drag the mouse, you can PAN the drawingHold the keyboard “ALT” and drag the mouse, you can rotate the drawingHold the “Shift” and “ALT” and drag the mouse, you can zoom the drawing19BoundaryClick Selection toolbar. See picture. Change the Selection from Object to FaceNow, click the face of box. Hold down the CTRL key and click face to add all 6 faces as selected. You may need to rotate the BOX so you can select all 6 faces.In menu, click HFSS - Boundaries - Assign - Perfect E. This assigns perfect Electric conductor on all 6 faces of box20HintYou can also set the selection box as “Object”, and select the whole box to assign the boundary. In that case, the software will assign same type of boundary on every surface of this objectiveYou can also select one face assigned as “Perfect E” and another face assigned as “Radiation” or any other type of boundary.21QuestionIf the object is already a metal, you dont need to assign the boundary on that face. Why?For Eigenmode solution, you must assign Perfect E or Finite conductor on all face. Why?22Source ExcitationFor eigenmode solution, you dont need to add source excitation. The software will automatically add the EM excitation inside the boundary. For driven modal or driven terminal projects, you DO need to add source excitation. And, it is very important you do it right. ( more on later.)23Solution SetupThe structure is ready to simulate. Click: HFSS - Validation check to see if theres any mistakes in drawing or boundary assignments. Click: HFSS- Analysis Setup - Add Solution Setup24Solution SetupThe Solution setup window pops up.Change Minimum Frequency to: 1GHzChange Number of Modes to 5. ( find first 5 resonant frequencies)Change Maximum Number of Passes to 5Click OK25Solution Setup 2You can enter multiple solution setups. This is useful and convenient when you are seeking for multiple answers.Go to Solution setup menu again, this time enter (1) Minimum Freq. 1GHz, (2) Number of Modes: 1, (3) Number of pass to 5.Now, you have two solutions in the project. If you check the project manager window, they are called setup1 and setup2 under Analysis tab.26Run SimulationClick: HFSS - AnalyzeRelax and wait. This project takes less than a couple minutes to simulate. Large projects will take more than 24 hours to simulate.Watch the “execute window” or “message window” for any errors or warnings. 27Solution DataClick: HFSS - Results - Solution Data Click Eigenmode Data tab. It shows the results of first 5 modesQuestion: What is first resonant frequency? What is 2nd Freq? What is the 3rd ?28EM PlotClick the BOX1 on drawing windowPlot the Electric field inside the box by clicking: HFSS - Fields - Plot Fields - Mag_E Field plot window will pop up. 29EM plot cont.Select Solution Setup2 Last AdaptiveOnly plot the first resonant frequencySelect “BOX1” at In Volume sub-window.Select “Mag_E” at Quantity sub-window.Click: Done30E Field Plots31Plot AnimationClick: HFSS - Field - AnimateSelect: 18 frames (steps)Click: OK324th Resonant Plot334th Resonant, Vector Plot34HomeworkDesign a cylinder cavityBase Radius = 2 inchHeight = 5 inchInside material = FR4_eposyFind: first 5 resonant frequenciesPlot: Mag_E field for 5th resonant 35