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Section 4: The 3D Modeler

Getting Started: Ansoft HFSS 8.0. Section 4: The 3D Modeler.

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Section 4: The 3D Modeler

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  1. Getting Started: Ansoft HFSS 8.0 Section 4: The 3D Modeler NOTE: The 3D Modeler is the most complex interface in HFSS, and will likely require the most practice for comfort and proficiency. However, students already familiar with the use of a detailed 3D CAD package should find much of the following information can be rapidly assimilated.

  2. Synopsis • 3D Modeler Basics • Modeler Environment • View Selection and Manipulation, Grid and Axis Manipulation • Geometry Classification • Object Types, Attributes, and Vertices • Command Organization and Standards • 3D Modeler “Practice” • Exercise: Draw and manipulate some different objects • Try some basic primitive creations (Box, Cylinder, etc.) • Try some basic drawing operations (Booleans, Sweeps, etc.) • 3D Modeler Lab • Exercise: Construct all geometry necessary for a coax-fed Patch Antenna project • Some Suggestions and Strategies for Geometry Planning

  3. The 3D Modeler: What is it? • The HFSS 3D Modeler, or “Draw” module, is a complete 3D CAD package • Utilizes the ACIS 5 3D toolkit from Spatial Technologies • Same 3D geometry kernel as AutoCAD, many others • Supports object-oriented solid geometry creation from primitives • Construction tools include basic shapes (cylinder, box, planar polygons) • Basic shapes can be modified via revolutions, linear sweeps (‘extrusions’) or sweeps along paths • Split, mirror, and duplicate commands exist • Boolean capabilities permit part subtraction, intersection, and union operations.

  4. HFSS 3D Modeler Environment: The Layout Menu Toolbar The Side Window Coordinate Boxes at top Command Operations appear below. The Drawing Windows Four Views by Default (starting orientation: XY, XZ, YZ, and isometric) All are active drawing windows. All may be rotated, panned, zoomed, and otherwise manipulated. Model units are shown in the Side Window. Units selection is prompted when the 3D Modeler interface is first accessed. (Units can be altered later via the Options menu.) The Command Prompt View or Enter Macro commands (not open by default) The Status Bar Provides help text during drawing operations Displays tool button description if button is ‘held’

  5. HFSS 3D Modeler Environment: View and Location Selection Coordinates displayed as “Absolute” (vs. origin) or “Relative”(for measurements between two locations/vertices) • Window Selection: • One drawing window is active at a time. • Identified by flashing cursor, frame • Shift focus to another window with a single left-click • Shift location within the active window with any subsequent left-click • Location Manipulation: • Moving in 3D or along any combination of axes achieved using coordinate checkboxes in Side Window • Note checkboxes have memory! • Right-clicking accesses movement options as well Coordinate Display/Entry Fields. Checked Components are Active, Unchecked ‘grayed out’ Note: The pointer, as well as the shape of the cursor at the selected location, both reflect the number of components currently ‘active’-- Triangular cursor: one Square cursor: two Diamond cursor: all three Active Frame Shaded, Cursor Flashing

  6. HFSS 3D Modeler Env: View Manipulation • Right-Click Menu also includes View Manipulation Options • Rotate, Pan, Zoom any window (right click again to release) • Hotkeys access manipulation as well: • CTRL-left-mouse-drag: rotate • SHIFT-left-mouse-drag: pan • CTRL-SHIFT-left-mouse-drag: zoom (drag up for ‘in’, down for ‘out’) • Zooming also controlled with Toolbar Icons • Zoom in or out on ‘box’: two left-clicks define opposite corners • “Fit All” tool icon sizes active window to existing geometry • Hotkey “F” performs “Fit All” on all views simultaneously Rotation Shortcut: If you double-click near the appropriate region of the active view menu while in rotate mode, the view will instantly rotate to a specific orientation. For example, double-clicking near the top of a window results in a top down (XY) view, near the left side a left (XZ) view, and near the center a front (YZ) view. Double-clicking in the corners rotates to four different isometric views as well.

  7. HFSS 3D Modeler Env: Axis Manipulation • The HFSS Modeler Coordinate System is malleable • Several Axis Display Options • Origin can be moved, axes rotated • Axis changes required for some drawing commands! • Multiple Local coordinate systems can be saved • Starting coordinate system automatically saved as Global • Coordinates menu contains axis manipulation commands • Select new origin location before choosing Move Origin • Select new intercept before choosing Rotate (X, Y, or Z) • Two Toolbar Icons also provided Axis Display Toggle (left) Switches between large and small, one and two-sided axis display modes Move Origin Icon (right) Same as Menu Pick for Move Origin from Coordinates menu.

  8. HFSS 3D Modeler Env: Grid Options • The Grid also has multiple options • Grid Settings available under View Menu, some via Toolbar icons • Can pre-set to open with custom preferences using Options Menu • Save Module Preferences under View Menu • Sizing may be automatic or fixed • Auto Adjust grid changes with zoom depth • Fixed can be set to desired size (point-to-point spacing) • Grid can be rotated to each plane • Toolbar Icon or View Menu • Grid normal identified by dashed axis, projection lines • Influences active coordinates, right-click menu operations • Polar Grid also Available Grid Display Toggle (left) Turns Grid visibility on or off Rotate Grid Icon (right) Toggles grid between different coordinate planes. Same operation as selection in View menu.

  9. HFSS 3D Modeler Geometry: Object Classification and Attributes Note: The Visibility Icon also allows direct access to the visibility attribute of each object; useful in complex models to temporarily ‘hide’ objects so that others may be more easily viewed or manipulated • HFSS Models have three types of objects: • Solids: have volume and surfaces (3D) • Sheets: have only surface area (2 or 3D) • Polylines: have only length (1, 2, or 3D) • Only solids and sheets get used in the FEM solution process • Volumes (within solids) can have material characteristics defined • Surfaces (on sheets or solids) can have boundary characteristics applied • Polylines can be used in post-processing, but are ignored in solutions • All HFSS objects have Attributes • Type, name, and color most important • Visibility, ‘Model’, and Wireframe attributes also available • View/Edit Attributes via the View menu or highlighted toolbar icon

  10. HFSS 3D Modeler Geometry: Vertices and Snap Options • All objects are defined by vertices • Even true-curved objects have at least two wireframe vertices • Many drawing commands require definition of a base vertex from which you create or manipulate objects • Different snap options allow selection of existing object vertices or features • Grid snap selects a point on (or parallel to) the drawing grid • Vertex snap selects an existing object’s vertex. • ‘Other’ options allow snapping to different object features • Midpoint of object edges and center of object faces most often used • The cursor is enlarged to indicate vertex or ‘other’ snap selection Snap options are on side window with coordinate fields. The correct snap choice can make location selection for geometry creation very easy.

  11. HFSS 3D Modeler Geometry: Complex Object Construction • Basic objects are created as primitives • Polylines: point, polyline (open or closed), arc • Sheets: closed polyline, rectangle, circle • Solids: Box, Cylinder • More complex objects are generated by manipulation of primitives • Sweeping a line around an axis or along a vector creates a sheet • Sweeping a sheet around an axis, along a vector, or along a path creates a solid • Boolean Operations Permit object unions, intersections, and subtractions • Remember the solid overlap issue? Boolean subtraction is one way to handle it. • Most Booleans result in primitive deletion; use clipboard to preserve if necessary! • The resulting object will have the name of the starting construction object From a simple rectangular or circular cross-section, detailed figures of revolution, extrusions, or helices can be formed.

  12. HFSS 3D Modeler Commands: Drawing Command Organization The Solids menu contains commands to create solid objects, and all Boolean operations The Surfaces menu contains commands which act upon or create sheet objects. The Lines menu contains commands which create or modify polyline objects. Closed polyline objects (rectangles, circles) which can become sheets are also generated here. The Arrange menu permits manipulation of existing objects, including rotation, movement, and mirroring. All menu items in Arrange require at least one object be selected to be available. The Edit menu permits object selection, copying and pasting to the clipboard, as well as duplication of selected objects along lines, around axis, or thru mirror planes

  13. HFSS 3D Modeler Commands: Drawing Command Cheat-Sheet 2D Primitive Generation(Rectangle, Circle) 1. Start from a base or beginning vertex. 2. Define a Normal Axis, size, and (for circle) vertex count. 3. Specify covered (sheet) or not (polyline). 4. Provide name and color. 3D Primitive Generation(Box, Cylinder) 1. Start from a base vertex (corner for box, end center for cyl) 2. Define XYZ size (box) or Axis, radius, height, and # of facets (cyl) 3. Provide name and color. Arrange Operations(Move, Mirror, Rotate, etc.) 1. Select object(s) to operate upon before going to Arrange 2. Define vector, axis and rotation angle, or mirror plane for operation. 3. Object attributes (name and color) unchanged. Sweep Operations(Along line, around axis, etc.) 1. Select Sweep mode (along vector, etc.) 2. Select profile (cross-section) to be swept (may be polyline or sheet) 3. Define vector, axis of rotation, or path polyline, depending on type of sweep 4. Resulting solid/sheet has same name as profile used. Duplication Operations(Along line, around axis, etc.) 1. Select object(s) to operate upon before selecting Duplicate 2. Define vector, axis and rotation angle, or mirror plane for operation 3. Define desired total quantity (including original) 3. Object duplicates created with increments of original name (e.g. ‘box1’, ‘box2’, ...) Polyline Generation(polylines and arcs) 1. Define starting point and subsequent vertices 2. Can be edited, including insertion, deletion, and movement of pre-created vertices. 3. If planar and closed, can be covered (sheet). 4. Require name and color.

  14. HFSS 3D Modeler Commands: Boolean Operation Cheat-Sheet UNION 1. Select all objects to be united at once. 2. Result of union maintains name and color of first object selected. ...If you want to keep an object used in the union available after the union is completed, first select that object and copy it to the clipboard! STITCH (under Surfaces) Identical to union, but valid for 2D sheet objects only SUBTRACTION 1. Select all objects to be subtracted from (the operands, or ‘stock’) 2. Select all objects to subtract (the operators, or ‘tools’) 3. Result of subtraction is the objects selected in 1., less any volume which intersected objects selected in 2. Objects selected in 2. above are thrown away! ...If you want to keep an object to be used as a ‘tool’ in a subtraction operation, first select that object and copy it to the clipboard! INTERSECTION 1. Select all objects to be intersected at once. 2. Result of intersection maintains name and color of first object selected. 3. All other objects are discarded ...If you want to keep an object to be used in an intersection, first select that object and copy it to the clipboard!

  15. HFSS 3D Modeler Commands: Other Drawing Commands SOLIDS-->SPLIT 1. Define any necessary coordinate system translation and rotation before selecting Split command 2. Split command allows ‘splitting’ of objects along XY, YZ, or XZ planes. 3. Options allow keeping the positive, negative, or both halves (with respect to the Normal of the split plane) 4. You do not need to select objects first. 5. Parts retain name/color attributes of original. SURFACES-->SECTION 1. Define coordinate system translation before beginning Section command 2. Section allows creation of a 2D cross-section of any 3D object, along the XY, XZ, or YZ planes 3. Sections created will be uncovered (polyline) objects, and must be covered to make them sheets again. 4. You do not need to select objects first. 5. Objects created will be named “slice”, “slice1”.... Rename using Attributes if desired. OTHER COMMANDS: 1. Surfaces-->Cover Lines creates sheets from closed polylines 2. Surfaces-->Uncover Faces reverses this process 3. Surfaces-->Detach Faces creates sheet objects from the faces of solids 4. Surfaces-->Connect creates a sheet connection between two polylines 4. Solids-->Helix creates a helix from a provided sheet cross-section profile 5. Solids-->Cover surfaces creates a solid from a 3D closed polyline or sheet UNDO AND REDO: The Edit menu also contains Undo... and Redo... commands. On the toolbar, these are represented by the counterclockwise arrow (undo) and clockwise arrow.

  16. HFSS 3D Modeler Practice: Rectangle Your instructor should walk you through opening a new HFSS temporary project, and entering the Draw Module. 1. From the Lines menu, select Rectangle 2. Side window prompts for first point. Type (2, 2, 0) into the coordinate boxes. Enter button confirms starting point. 3. Side window prompts for rectangle plane, size, name, and color. A. Select XY plane B. Leave ‘Covered’ checked. This results in a sheet rather than a hollow outline. C. Enter x=10, y=15 D. Leave default name “rect1” E. Pick a color (user option) 4. Enter button finishes object creation; cursor is left at opposite corner from the starting vertex. Note: Rectangle dimensions will be ‘roughed out’ during entry of X and Y sizes; this feature provides visual feedback before the object creation is finalized. 1. 2. (not shown) 3. 4.

  17. HFSS 3D Modeler Practice: Cylinder 1. 1. From the Solids menu, select Cylinder 2. Side window prompts for axis and base vertex. Select Z axis. Type (7, 9.5, 0) into the coordinate boxes. Enter button confirms starting point. 3. Side window prompts for cylinder radius, height, and vertex count. A. Select Z axis B. Enter radius=5, height=10 C. Leave ‘Num segments’ checked. This results in a faceted cylinder. Change the value to “16”. D. Leave name as “cyl1” E. Pick a color (user option) 4. Enter button finishes object creation, leaving cursor at the far end of the cylinder from the base vertex, on the radius. Note: Again, solid object will be ‘sketched’ to provide visual feedback before command is completed. Number of vertices are not reflected in ‘sketch’ 2. (not shown) 3. 4.

  18. HFSS 3D Modeler Practice: Polyline (open) 1. From the Lines menu, select Polyline 2. Side Window prompts for name of polyline to create/edit. (‘rect1’ will show in this list.) Press ‘OK’ button at bottom to accept default polyline name of ‘pline1’. 3. Side window changes to polyline draw mode. Beneath object name and color selection, the top button defines the action to occur each time ‘Enter’ is pressed (add vertex, delete vertex, insert vertex...). The bottom button defines the type of segment that will be created between the prior and current vertex (straight, arc, spline). A. Move coordinates to (2, 2, 0) and click “Enter”. An ‘X’ marks first vertex. B. Move coordinates to (2, 2, 8) and click “Enter”. (Note: you may wish to use the YZ view!) A ‘+’ shows subsequent vertices. C. Repeat, placing coordinates at (2, -2, 12) and (2, -16, 12). D. If we wanted to close the polyline at the first point, we could press “Close”. Instead, press “Done” to leave open. 4. Side window exits polyline mode; line is created.

  19. HFSS 3D Modeler Practice: Sweep 1. From the Solids menu, select Sweep... Along Vector 2. Side Window prompts for name of profile to sweep. Select ‘rect1’ and press ‘Enter’ 3. Side window prompts for vector values. Enter X=5, Y=5, Z=10 (in vector) boxes and press ‘Enter’. A canted solid parallelogram is created. 4. From the Edit menu, select “UndoSweepvec”. 5. From the Solids menu, select Sweep... Along Path 6. Side Window prompts for name of profile to sweep. Select ‘rect1’ and press ‘Enter’ 7. Side Window prompts for name of path to sweep along. Select ‘pline1’ and press ‘Enter’. 8. Side Window prompts for Draft Angle (growth of profile as it sweeps). Leave at zero and press ‘Enter’. An extrusion of the rectangle along the open polyline is created. Step 3 Step 8

  20. HFSS 3D Modeler Practice: Duplicate/Mirror 3. 1. Use the Visibility tool icon to ‘hide’ all geometry but the sweep object from the prior page (‘rect1’). 2. From the Edit menu, pick Select..., or use the Selection tool icon (outlined at left) to select the object ‘rect1’. Press ‘Enter’ to confirm your selection is finished. 3. From the Edit menu, pick Duplicate...Mirror. The side window will now prompt you for a point on the mirror plane. Select the origin and press ‘Enter’. 4. The Side Window will now prompt you for a point on the normal to the mirror plane. Select the point (2,2,0) by entering the coordinate or ‘snapping’ to the appropriate vertex on the ‘rect1’ object. 5. You should end up with a duplicate of the original swept part, positioned such that it is ‘mirrored’ 90 degrees from the original in the same position from the origin. 6. Note that in this case the same operation could also have been performed using Duplicate...Around Axis. 2. 1. 4. (not shown) The Duplicate...Mirror command can utilize any plane of reflection in the model, and is therefore not tied to the existing coordinate axes. The reflection plane is defined by its normal vector, with the tail on the plane and the head orthogonal to the plane. The normal vector need not be of ‘unit’ length.

  21. HFSS 3D Modeler Practice: Unite and Split 1. 1. From the Solids menu, pick Unite. The Side Window will prompt you for the names of all available objects that can be united. Select ‘rect1’ and ‘rect2’, in that order, and press ‘Enter’. The two overlapping solids will be united into one. 2. Now pick the indicated vertex on the top face of the object by snapping to it, or entering coordinate (12, -12, 27). From the Coordinates menu, pick Set Current CS...Move Origin. The origin will move here. 3. Be sure your grid plane is displayed with Z as the normal, using the appropriate icon. 4. Pick the opposite concave corner on the top face of the united object as shown. From the Coordinates menu, pick Set Current CS...Rotate Y. The coordinate axes will rotate so that this point becomes a Y intercept. 5. From the Solids menu, pick Split. The side window will now prompt for the split axes and which parts to keep. Select “YZ” and “Above plane” and press ‘Enter’. The Side Window will now list all objects available for splitting: Select ‘rect1’ and press ‘Enter’. The part will be cut diagonally along the YZ plane as shown. Step 2 Step 4 3. (hidden by menu) 5.

  22. HFSS 3D Modeler Practice Concluded • This concludes the introductory 3D Modeler practice session. Please select Exit from the File menu (do not save changes when prompted). • When you are returned to the HFSS Executive window, click Exit. • We will now walk through the complete geometry construction for a Coax-fed Patch antenna problem. We will only build the geometry for this problem; not solve it.

  23. HFSS 3D Modeler Exercise: Patch Antenna • This is a coaxial-probe fed rectangular patch antenna designed to operate near 2 GHz. The patch itself is 3 x 4 cm in size. • It is constructed on a 0.32 cm thick substrate, 10 x 10 cm in size, with ground plane cladding on the bottom surface except where the coax penetrates. • The coaxial probe has an inner diameter of 0.2 cm and an outer diameter of 0.46 cm • The entire model will be placed in an air volume 18 x 18 x 10 cm in size • When instructed, create a New project in the Project Manager called “patch” and open the Draw Module. Drawing Objects Needed: Boxes: Substrate, Air volumeCylinders: Coax inner and outer sections, port ‘cap’Rectangle: Patch Drawing operations needed: Split (to prevent coax inner conductor overlap)

  24. HFSS 3D Modeler Exercise: Macro Interface As an introductory illustration of the time saving features of the Ansoft Macro Language, we will record our drawing operations as we construct the patch antenna problem. 1. From the View menu, pick “Command Prompt”. This will open the direct macro text interface across the bottom of the modeler window. Although not necessary for recording, this will allow you to see visible feedback as individual commands are enabled thru the graphical interface. 2. From the File menu, pick Macro...Start Recording. The interface will prompt you for a macro name to record to, pre-assuming the name “mod3.mac” to be saved in the current project’s directory. Accept this default filename and proceed to the next page. From here onward, all commands performed will be recorded into this file. Step 2 Step 1

  25. Patch Exercise: Create Substrate Solid 1. We want to create our model centered at the origin of the coordinate system with the top of the substrate (the plane of the patch antenna) at Z=0. For an antenna model, due to the post-processing coordinate system used, we want the antenna’s peak gain at zenith to be directed along the Z axis. Therefore we want our substrate to extend in the XY plane, centered at the origin. (ALL UNITS FOLLOW IN CM) 1. From the Solids menu, pick Box. Set your starting vertex to (-5, -5, 0), and press the ‘Enter’ button to confim. 2. The Side Window now prompts for the box size. Enter a size of X=Y=10, Z= -0.32 . Note that using a negative Z ‘size’ builds in the negative Z direction from the starting point at Z=0. 3. Name the object ‘substrate’, select a color, and press ‘Enter’ to complete object creation. 4. If the object appears small, you may zoom or Fit your view. 2. 3.

  26. Patch Exercise: Create Patch Rectangle If we assume that the metalization thickness of the patch is insignificant compared to its dimensions, we can model its geometry as a 2D sheet object with very accurate results. (The same is true for much microstrip and stripline circuitry, where edge-to-edge coupling is not important.) 1. From the Lines menu, select Rectangle. Define our starting coordinate as (-1.5, -2, 0) and confirm. 2. Set the rectangle to exist in the XY plane, with the dimensions X=3, Y=4. The rectangle will be ‘sketched’ in as the size values are entered. 3. Give the rectangle the name “patch” and choose a color. Press ‘Enter’ to complete the drawing command. 1. 2. 3.

  27. Patch Exercise: Create Coaxial Probe Feed 3. The coaxial probe should contact the patch, penetrating the substrate. We will construct this as a faceted cylinder at the origin. 1. In the Side Window, check the box next to ‘Other...’ in the ‘Snap To:’ options. A dialog will open with further options. Check ‘Face center’ and press the ‘OK’ button to confirm. Graphical clicking operations will now snap us to the center of any object faces. 2. Click in the graphical window anywhere in the vicinity of the top face of the ‘substrate’ box or of the ‘patch’ rectangle. Your cursor should snap immediately to the origin. (0, 0, 0) 3. From the Solids menu, pick Cylinder. The Side Window prompts for an axis (pick Z) and a base vertex. Press ‘Enter’ to confirm (0, 0, 0) is the base center. 4. Set the cylinder radius to 0.1, height to -0.82, number of facets to 8. Give the cylinder the name ‘probe’, select a color different than the default if desired, and press ‘Enter’. 2. 1. 4. Why only 8 facets? Since the coaxial feed and probe of the patch antenna are very narrow and do not need high detail to properly excite the patch, use fewer facets to save on overall tetrahedra in the model!

  28. Patch Exercise: Create Coaxial Dielectric 1. The coaxial dielectric will lie beneath the substrate, concentric with the probe extending beneath the bottom of the substrate. We will assume the outer conductor is of zero thickness, as it will not influence the antenna fields. 2. Note that following the prior command, you should have been left at vertex location (0.1, 0, -.82) on the radius at the bottom of the ‘probe’ cylinder. Re-set the X coordinate to ‘0’ using the Side Window, and from the Solids menu pick Cylinder. 3. The Side Window prompts for an axis (pick Z) and a base vertex. Press ‘Enter’ to confirm (0, 0, -.82) is the base center. 5. Set the cylinder radius to 0.23, height to 0.5, number of facets to 8. Give the cylinder the name ‘outer’, select a color different than the default if desired, and press ‘Enter’. Your drawing should look similar to the one at left upon completion. (Drawing at left inverted from black background to better show geometry).)

  29. Patch Exercise: Create Coaxial Port ‘Cap’ 2. 1. Use the rotation hotkey (CTRL-left-mouse-drag) or double-clicks to orient a view window so that your are looking up at the bottom surface of the ‘substrate’ and ‘outer’ objects. (You may also wish to zoom in.) If your ‘Other’ Snap mode is still on, a single mouse-click on the bottom face of the ‘outer’ cylinder should snap to the coordinate (0, 0, -.82). 2. Again from the Solids menu, pick Cylinder. The Side Window will prompt you for an axis (pick Z) and a base vertex. Confirm (0, 0, -.82) is the starting point by pressing ‘Enter’. 3. Configure the cylinder to have a radius of 0.23, a height of -0.25, and 8 facets using the fields in the Side Window. Give the cylinder the name ‘cap’, select a color, and press ‘Enter’ to complete the geometry creation. 3. What is a port ‘cap’?Since we will need to surround the antenna with an air volume for the fields to radiate into, we cannot leave the back end of the coaxial cable ‘open’ to that air. We need to provide a cap object to assure that our model excitation can flow only up the coaxial cable we have created. We will do this by placing a solid cylinder the same size as the ‘outer’ cylinder on its bottom face. Although this may look like a ‘short’, it permits the port to behave properly. (Further discussion in Boundaries)

  30. Patch Exercise: Create Air Volume 1. The final object we need to create is the air volume for the structure to radiate into. Since the antenna is intended to operate near 2 GHz, and the substrate is 10 x 10 cm, we will construct an air volume of 18 x 18 x 10 cm in size. (Sizing of radiation volumes will be discussed in the Boundaries presentation.) 1. From the Solids menu, pick Box. The Side Window will prompt you for a starting vertex. Set the cursor to the coordinate (-9, -9, 5) using the fields in the Side Window, and press ‘Enter’ to confirm. 2. Set the size of the box to X=Y=18, Z= -10. The interface should sketch in a box which completely surrounds our geometry created thus far. (You may wish to zoom out to see it better.) 3. Give the box the name ‘airvol’, select a color, and press ‘Enter’ to complete its creation. 2. 3.

  31. Patch Exercise: Split Probe!! 1.  1. From the Options menu, pick Check Overlap. The modeler will check for overlapping geometry, and should warn you that some does exist by selecting two objects. Recall that we created our coaxial probe to penetrate the substrate, yet extend beyond its bottom. Therefore the ‘probe’ object is in illegal overlap with both ‘substrate’ and ‘outer’. This must be corrected before the problem can be modeled. 2. Zoom in in the vicinity of the coaxial ‘probe’ and ‘outer’ objects. Using the vertex Snap features, snap the cursor to any vertex at the Z= -.32 plane (the bottom of the substrate, or the top of the ‘outer’ cylinder. 3. From the Coordinates menu, select Set Current CS...Move Origin. 4. From the Solids menu, select Split. The Side Window will prompt you for the Split Plane (pick XY) and Keep Fragments options (pick Both). Press ‘Enter’. 5. The Side Window will give you a list of objects you may split. Select ‘probe’ and click ‘OK’ to confirm selection. 3. 2. 4. 5. (illustration shows probe object after being split) Remember, objects which intersect one another such that one is not entirely enclosed by the other will have shared volumes that the software will not know how to assign conditions to later on. Splitting the probe into a section inside the ‘substrate’ and a section inside the ‘outer’ objects will prevent this ambiguity.

  32. Patch Exercise: Macro Completion 1. From the File menu, pick Macro...Stop Recording. This will result in a message informing you the macro file has been saved. 2. Now from the File menu, pick Macro...Edit Macro. The macro we’ve created is automatically opened in a macro editor interface, as shown at left. 3. If you wish, highlight one of the drawing lines (like ‘Box’ or ‘Cyl’) by clicking on it. The right side panel contains the alterable arguments for that command. It should be easy to see how the macro could be edited to change the dimensions of some of the objects we created. The macro could then be re-run in another fresh HFSS session to create the entire geometry, with any changes made. 4. Exit the Macro Editor from the File menu. Exit the 3D Modeler from the File menu. You will be prompted to save your geometry, choose ‘Yes’. This completes the 3D Modeler Lab. This page of the presentation is offered as an example of macro recording and access; full macro use and construction is covered in Advanced HFSS Training.

  33. Geometry Modeling Suggestions • Consider how you want your geometry oriented and located before beginning • For antenna problems, a +Z antenna zenith has advantages in post-processing patterns • For many problems, centering at the origin aids geometry construction, including split operations for symmetry utilization

  34. Geometry Modeling Suggestions, cont. • Don’tOverspecify: Use only those details necessary for the electromagnetic behavior of the model at the frequencies you intend to analyze it. • This is especially important when importing geometry from other CAD packages. Often tiny fillet radii or miniscule screw hole penetrations exist in the original data which are unnecessary for the analysis at hand. • Don’t overdo facetization on cylindrical or revolution objects. In many cases, 12-16 facets is sufficient Thin metal plates connected by vias look like a solid metal path to lower frequencies. Each vertex in a problem must be used by the mesher...are all these facets necessary for a mesh at your frequency?

  35. Geometry Modeling Suggestions, cont. • Use symmetry wherever possible to reduce your model volume. • Remember however that geometric symmetry does not always imply field symmetry if higher order mode propagation is involved!!! • (The “Boundary Module” presentation will describe symmetry planes and their use.) • For models with port excitations, don’t overdo the port extension length. • Extensions on the order of the port aspect ratio are sufficient for higher-order mode decay • (The “Boundary Module” presentation will go into more discussion regarding the port extension and why it is used.) This model may be split by a perfect_h symmetry plane. Port extensions need not be large fractions of wavelength.

  36. Geometry Modeling Suggestions, cont. Edge Coupling will be significant • Use trace thickness in planar circuitry only where necessary • Thickness is necessary when: • ...it is a significant portion (>15% or so) of the metal trace width • ...edge-to-edge coupling is a major contributor to the device behavior • ...thickness approaches skin depth (within a factor of 2 to 3), requiring meshing interior to metal volumes to capture true field penetration effects • If you determine thickness must be considered, use virtual objects or extra plane breaks to prevent extreme aspect ratios which can prevent clean meshing • A virtual object is an object that will be given the same material assignment as its surroundings, making it a ‘tool’ to provide additional mesh vertices only. Edge coupling insignificant The octagonal virtual solid surrounding the spiral inductor trace (which has metal thickness included) helps transition the mesh out to the surrounding air volume.

  37. The limitation of the modeler

  38. Virtual Object

  39. Compensating for the Aspect Ratio

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