USC Signal Integrity Lab Course1 Ansoft High Frequency Structure Simulator HFSS

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USC Signal Integrity Lab Course1Ansoft High
Frequency Structure Simulator (HFSS)

• ELCT 762
• USC

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Acknowledgement

• Thanks to Ansoft for
• providing free EMS packages to USC / Intel Signal
  Integrity Lab
• providing free software to APOGEE students
• allowing us to use some of their training
  materials

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Signal Integrity Lab

• Located at Engineering building, 3D22
• Software name Ansoft HFSS 9
• APOGEE students can get free software from Ansoft
• Contact hao1.li_at_intel.com if you dont know how

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What is HFSS

• High Frequency Structure Simulator
• Uses Finite Element Method to solve EM problems
• Frequency Domain Solution
• Full wave Solver

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Different Methods of Electromagnetic Analysis
MOM
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What 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 expressions
• The 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 equations
• FEM software can solve mechanical (stress,
  strain, vibration), aerodynamic or fluid flow,
  thermal, or electromagnetic problems
• Suggested course ELCT 891H, computational
  electromagnetic.

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FEM Problem Constraints

• Geometry can be arbitrary and 3-dimensional
• Model subdivision is generally accomplished by
  use of tetrahedral or hexahedral (brick) elements
  which are defined to fill any arbitrary 3D volume
• Boundary 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 matrix
• Solution is created in the frequency domain,
  assuming steady-state behavior

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Example of Adaptive meshing
Waveguide 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.
Post
Post
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When is an FEM solver appropriate for
Electromagnetic Problems (Lower Bound)?
Example Finding Signal Integrity impacts of a
Via in the signal path
Example Coax to WG Transformer
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?/100
?/10
Problem Scale
Use a Quasi-Static Solver
Use a FEM
Full-Wave Solver
(OVERLAP)

• When the Electrical Length (in wavelengths)
  requires phase consideration
• ?/10 is a guideline there are exceptions
• When radiation from the device must be considered
• When S-Parameters are the desired output
• When lossy dielectric materials have significant
  effects

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Some Typical High-Frequency Electromagnetic
Applications
Antenna
Waveguide Components
RF Integrated Circuits
EMC
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Example 1 Eigenmode Problem

• Find 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.

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Ansoft HFSS Project Flow
Configuration
Source Excitation
Solving
Drawing
Solution Setup
Boundary
Analyze Data Plot
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Configuration

• Click HFSS 9 to start the problem
• Click File -gt Save As -gt filename
• Click Project -gt Insert HFSS Design
• Now, HFSS design interface has 6 sub-windows
  project window, property window, drawing window,
  history window, message window and execution
  window

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Configuration cont.

• Click HFSS -gt Solution type,
• Pop up window shows three types
• Pick the Eigenmode

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Configuration

• Click Tool -gt Option -gt General Option
• Option window pop up.
• Select Default Units tab
• Change the length to inch

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Configuration

• Click View -gt Grid Setting
• Grid setting screen pops up
• Select grid size as 1 inch

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Structure Drawing

• Click Draw -gt 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

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Drawing

• Here is the picture of what you get.
• You can always change the item properties by
  clicking the item, and modifying them at property
  window

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Hint

• Hold the keyboard Shift and drag the mouse, you
  can PAN the drawing
• Hold the keyboard ALT and drag the mouse, you
  can rotate the drawing
• Hold the Shift and ALT and drag the mouse,
  you can zoom the drawing

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Boundary

• Click Selection toolbar. See picture. Change the
  Selection from Object to Face
• Now, 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 -gt Boundaries -gt Assign -gt
  Perfect E. This assigns perfect Electric
  conductor on all 6 faces of box

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Hint

• You 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 objective
• You can also select one face assigned as Perfect
  E and another face assigned as Radiation or
  any other type of boundary.

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Question

• If 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?

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Source Excitation

• For 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..)

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Solution Setup

• The structure is ready to simulate. Click HFSS
  -gt Validation check to see if theres any
  mistakes in drawing or boundary assignments.
• Click HFSS-gt Analysis Setup -gt Add Solution
  Setup

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Solution Setup

• The Solution setup window pops up.
• Change Minimum Frequency to 1Ghz
• Change Number of Modes to 5. ( find first 5
  resonant frequencies)
• Change Maximum Number of Passes to 5
• Click OK

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Solution Setup 2

• You 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.

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Run Simulation

• Click HFSS -gt Analyze
• Relax 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.

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Solution Data

• Click HFSS -gt Results -gt Solution Data
• Click Eigenmode Data tab. It shows the results of
  first 5 modes
• Question What is first resonant frequency? What
  is 2nd Freq? What is the 3rd ?

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EM Plot

• Click the BOX1 on drawing window
• Plot the Electric field inside the box by
  clicking HFSS -gt Fields -gt Plot Fields -gt
  Mag_E
• Field plot window will pop up.

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EM plot cont.

• Select Solution Setup2 Last Adaptive
• Only plot the first resonant frequency
• Select BOX1 at In Volume sub-window.
• Select Mag_E at Quantity sub-window.
• Click Done

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E Field Plots
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Plot Animation

• Click HFSS -gt Field -gt Animate
• Select 18 frames (steps)
• Click OK

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4th Resonant Plot
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4th Resonant, Vector Plot
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Homework

• Design a cylinder cavity
• Base Radius 2 inch
• Height 5 inch
• Inside material FR4_eposy
• Find first 5 resonant frequencies
• Plot Mag_E field for 5th resonant