basma1_hfss

7/23/2019 basma1_hfss

http://slidepdf.com/reader/full/basma1hfss 1/58

Finite ElementTutorial in

Electromagnetics #2DRAFT

Sponsored by NSF Grant #05-559: Finite Element MethodExercises for use in Undergraduate Engineering Programs

Specific Absorption Rate

Prepared By: Dr. Vladimir A Labay , Department of Electrical and Computer EngineeringGonzaga University, Spokane, Washington

Estimated time to completeThis tutorial: 60 minutes



2

Outline of Tutorial

1. Introduction

2. Overview of computational electromagnetics (CEM)

– Maxwell’s Equations and their numerical approximation– Full-wave CEM techniques

• The method of moments (MoM)

• The finite difference time domain (FDTD) Method

• The finite element method (FEM)

3. The CEM modeling process– Overview

– Methods of CEM

– Problems and Limitations

4. Finite Element Method (FEM)– Introduction and Overview

– Strengths and Weaknesses

– Weaknesses



3

Outline of Tutorial (con’t)

5. Ansoft’s High Frequency Structure Simulator (HFSS)– Introduction

– Using HFSS to create and improve designs

6. Problem Definition: Specific Absorption Rate (SAR)– What is SAR?

– Health Effects and SAR Limits

– Test Methods

7. Step-by-Step Solution– Launching Ansoft HFSS

– Set up the Design

– Creating a Model

– Set up and Generate Solutions

– Analyze and display results

8. Further Reading and References



4

Tutorial Objectives

• Understand the basis of FE theory for three-dimensional electromagnetic analysis.

(PEO #1)• Understand the fundamental basis of the SAR measurements and radiation field

patterns through the use of Ansoft’s High Frequency Structure Simulator(HFSS)™ three-dimensional finite element software. (PEO #2)

• Be able to construct a correct solid model using the build in 3-D solid modeler and

perform a correct three-dimensional finite element analysis using HFSS solutionengine. (PEO #3)

• Be able to interpret and evaluate finite element solution quality including verifyingconvergence criterion and field plots. (PEO #4)



5

Overview of Computational

Electromagnetics (CEM)• Electromagnetics

– The study of electrical and magnetic fields and their interaction– Governed by Maxwell’s Equations (Faraday’s Law, Ampère’s Circuital Law, and Gauss’ Laws)

• Maxwell’s Equations relate the following Vector and Scalar Fields

E: the Electric Field Intensity Vector (V/M)

H: the Magnetic Field Intensity Vector (A/m)

D: the Displacement Flux Density Vector (C/m2)

B: the Magnetic Flux Density Vector (T)

J: the Current Density Vector (A/m2)

ρ : the Volume Charge Density (C/m3)

μ : is the Permeability of the medium (H/m)

ε : the Permittivity of the medium (F/m)



6

Maxwell’s Equations

ρ =⋅∇ D

DJHt ∂

∂+=×∇

0=⋅∇ B

BEt ∂

∂−=×∇

Faraday’s Law: Ampère’s Circuital Law:

Gauss’ Laws:HB μ = ED ε =

Constitutive Equations:

• Actual solution complex and for realistic problems require approximations

• Numerical approximations of Maxwell’s equations is known as computationalelectromagnetics (CEM)



7

Applications of CEM

• Over the past five decades CEM has been successfully applied to several engineering

areas, including:– Antennas

– Biological electromagnetic (EM) effects

– Medical diagnosis and treatment

– Electronic packaging and high speed circuits

– Superconductivity – Microwave devices and circuits

– Law enforcement

– Environmental issues

– Avionics

– Communications

– Energy generation and conservation

– Surveillance and intelligence gathering

– Homeland Security

– Signal Integrity



8

Full-wave CEM techniques

• Approximations of Maxwell’s equations may be classified into several categories, e.g.,low-frequency, quasi-static, full-wave, lumped element equivalent, etc.

• This tutorial deals with the finite element method a full-wave technique. Full-wavetechniques have the potential to be the most accurate of all numericalapproximations because they incorporate all higher order interactions and do notmake any initial physical approximations

• Examples include:– Finite difference time domain (FDTD) Method– Method of Moments (MoM) Method– Finite Element (FEM) Method– Transmission Line Matrix (TLM) Method

– The Method of Lines (MoL)– The Generalized Multipole Technique (GMT)

The FDTD, MoM and FEM are the most popular today!



9

Full-wave CEM techniques (con’t)

• Central to all methods is the idea of discretizing some unknown electromagneticproperty, for example:

– MoM: the Surface Current– FE: the Electric Field

– FDTD: the Electric and Magnetic Field

• Discretization is also known as meshing that subdivides the geometry in a largenumber of elements

– Two dimensional elements: triangles

– Three dimensional elements: tetrahedral

• Within each element, a simple functional dependence (basis functions) is assumedfor the spatial variation of the unknown

• The amplitude and phase of the unknown quantity is determined by the applicationof the particular CEM



10

Limitations of Full-wave CEM

techniques• CEM is a modeling process and therefore a study in acceptable approximation

• In other words, CEM replaces a real field problem with an approximate one whichcauses limitations and problems that one must keep in mind

• Limitations of the mathematical model and Simplifications in the formulation

– Assumptions are generally made, e.g., assuming an infinite ground plane in an antennastructure. Are the assumption valid?

– Have you made simplifications on the design that are not valid? For example, simplifying athin wire by a current filament.

• Tolerances and Manufacturing deviations

– Tolerances are a part of all manufactured devices. How do small changes in dimensions ormaterial properties affect the performance?

– Do other manufacturing considerations, other that tolerances, affect the performance?

• Finite Discretization– Is the mesh fine enough to properly so that the basis functions can adequately represent the

fields?

• Numerical approximations and Finite machine precision

– Does double precision provide enough accuracy for your problem, especially if it is ill

conditioned?



11

Finite Element Method

Overview • Initially used in structural mechanics and thermodynamics dating back to the 1950’s

• First application in electromagnetics appeared in literature in the late 1960’s but didnot see widespread adoption until the 1980’s

– A problem of “spurious modes” was not solved until the 1980’s through a theoretical breakthrough with edge elements

– Widespread availability of powerful main-frame and personal computers also aided theexpansion

• Starts with the partial differential equation (PDE) form of Maxwell’s Equations

• Solution can be viewed from two main perspectives– Variational analysis

• Finds a variational functional whose minimum corresponds to the solution of the PDE– Weighted residuals

• Introduces a “weighted” residual or error and using Green’s function, shift one of thedifferentials in the PDE to the weighting functions

– In most applications these two viewpoints result in identical equations



12

Finite Element Method (con’t)

• FEM can handle essentially two different types of EM problems

– Eigenanalysis (source-free)

– Deterministic (driven)

• FEM does not include a radiation condition

– Open regions, such as antennas (see below), requires special treatment

• Introduction of a artificial absorbing region within the mesh

• Example Microstrip Patch Antenna

Antenna Patch

Infinite Ground Plane

Substrate Material

Artificial absorbingregion(box surrounding theantenna)



13

Finite Element Method (con’t)

Strengths

• Handles complex geometries and material inhomogeneities easily

• Handles dispersive or frequency-dependent materials easily

• Handles eigenproblems easily

• Has better frequency scaling characteristics that MoM (but usually requires a larger set ofunknowns)

• Easily applicable to “multi-physics” problems by coupling solutions in thermal or mechanical tothe EM solution

Weaknesses

• Inefficient treatment of highly conducting radiators when compared to the MoM

• FEM meshes become very complex for large 3-D structures• More difficult to implement than the FDTD thus limiting their use in commercial software. Little

code development is done by engineers

• Efficient preconditioned iterative solvers are required when higher-order elements are used. Again, restricting the code development by individual engineers



14

Commercial FEM EM Software

Some Companies that market commercial FEM EM software:

• Ansoft Corporation, Inc.– High frequency structure simulator (HFSS)

• Ansys, Inc.– Emag

• Comsol, Inc.– COMSOL Multiphysics with Electromagnetics Module

• SolidWorks Corporation

– COSMOSEMS

H FSS b y An so f t w i l l b e u sed so l el y i n t h i s t u t o r i a l



15

Ansoft HFSS

Overview • HFSS is a high-performance full-wave electromagnetic field simulator for arbitrary

3D volumetric passive device modeling that takes advantage of the familiar Microsoft

Windows graphical user interface. It integrates simulation, visualization, solidmodeling, and automation in an easy-to-learn environment.• HFSS includes:

– A graphical interface to simplify design entry – A field solving engine with accuracy-driven adaptive solutions– Powerful post processor for displaying currents, fields and RF parameters

– Automatic and adaptive mesh generation and refinement and tangential vector finiteelements

– Macro feature allows for users to log sessions of design or simulation to an easy to read file(useful in creating a library of structure based on a nominal structure)

– A comprehensive materials database that contains permittivity-, permeability, electric-,magnetic-loss tangents for common materials.

• Typical HFSS Uses– PCB Board Modeling: Power and Ground Planes, Backplanes– EMC/EMI: Shield Enclosures, Coupling, Near- and Far- Radiation– Antennas/Mobile Communications: Patches, Horns, Radar Cross Section– Connectors: Coaxial (Coax), Transitions– Waveguide: Filters, Resonators, Transitions, Couplers



16

Problem Definition

Specific Absorption Rate (SAR)• The following tutorial is intended to show how to create, simulate, and analyze

simple phantom as described in the IEEE P1528 specification, which is commonly

used to calibrate Specific Absorption Rate test equipment, using the Ansoft HFSSDesign Environment

• This tutorial leads you step-by-step through the design and analysis of a simplephantom. By following the steps in this tutorial you will be able to:

– Draw a 3-D geometric model

– Modify a model’s design parameters– Specify solution settings for a design– Validate a design’s setup– Run a HFSS simulation– Create a 2-D plot of the antenna radiation pattern

– Create a field overlay plot of the results– Animate field plots– Study the mesh created by HFSS for the solution



17

Problem Background

• Introduction– It may seem that everything is going wireless: Wi-Fi, Bluetooth , ZigBee and wireless USB are

all popular today. Along with this rise in the popularity of wireless communications has

come an increased concern for controlling the safety hazards of RF energy—especially forhandheld and wearable transmitters.

– To catch up to this new technology, new safety standards and test methods have beenrecently been approved by the Institute of Electrical and Electronics Engineers (IEEE),namely, the IEEE C95.7 “Recommended Practice for Radio Frequency Safety Programs,3kHz to 300 GHz”, and the IEEE 1528 “Recommended Practice for Determining the Peak

Spatial-Average Specific Absorption Rate (SAR) in the Human Head from WirelessCommunications Devices”

• Health Effects– EM waves entering the human body cause the biological tissue or organ to heat. This is

generally counteracted by thermoregulation (blood flow through the heated tissue or organ)to dissipate the heat produced by the EM wave. However, the eyes and male testes are

particularly susceptible to RF heating because these organs have no direct blood supply and,hence, no way of dissipating heat. The heating effects in human tissue are a function offrequency. In general, higher the frequency, the greater the heating effect. However, also ingeneral the EM penetration in the human body is less. With the recent explosion of wirelessdevices, particularly, cellular phones, most safety concerns have focused on EM absorption by the head.



18

Problem Background (con’t)

• FCC Guidelines for exposure to EM energy at the RF frequencies

– Maximum Permissible Exposure (MPE)

– Specific Absorption Rate (SAR)

• Maximum Permissible Exposure (MPE)

– Sets limits on the radiated far fields to which people may be exposed

– Limits vary with frequency and for controlled or uncontrolled exposure situations

Maximum permissible exposure (MPE)as a function of frequency



19


• The SAR Index

– Sets limits of exposure under near-field conditions

– SAR is an index that quantifies the rate of energy absorption in biological tissue and is

expressed in watts per kilogram (W/kg) of biological tissue. SAR is generally averaged over a volume corresponding to either 1 g or 10 g of body tissue. The SAR of a wireless product can be measured in two ways:

• measured directly using body phantoms, robot arms, and associated test equipment.

• mathematically modeled (this tutorial)

– The limits for SAR are defined for the exposure of the whole body or a partial body (e.g., headand trunk), or hands, feet, wrists, and ankles. SAR limits are based on whole-body are 0.08 W/kg with limits are less stringent for exposure to hands, wrists, feet, and ankles.

– For the head, the United States has set the limit to be 1.6 W/kg for 1-g volume-averagedSAR.



20


• SAR Data– In the United States, the Cellular Telecommunication Industry Association (CTIA) requires

that any mobile phone it certifies be sold with explanatory information. This informationmust confirm that the phone has passed FCC safety standards. Manufacturers must alsoinclude applicable SAR data for that phone and an explanation of how the SAR testing was

done.– The Mobile Manufacturers Forum (including Alcatel, Ericsson, Mitsubishi Electric,

Motorola, Nokia, Panasonic, Philips, Siemens, and Sony) reports SAR values on its Web site(www.mmfai.org).

Test facilities use a specificanthropomorphic mannequin(SAM) phantom for SARmeasurements



21


• SAR data (con’t)

Table 1: SAR data from the IEEE P1528 standard

Frequency

(MHz)1g SAR 10G SAR

Local SAR atsurface (above

feedpoint)

Local SAR atsurface

(y=2 cm offsetfrom feedpoint)

300 3.0 2.0 4.4 2.1

450 4.9 3.3 7.2 3.28

835 9.5 6.2 14.1 4.9

900 10.8 6.9 16.4 5.4

1450 29.0 16.0 50.2 6.5

1800 38.1 19.8 69.5 6.8

1900 39.7 20.5 72.1 6.6

2450 52.4 24.0 104.2 7.7

3000 63.8 25.7 140.2 9.5



22

Conventions used in this Tutorial

• Main Procedures are presented in Bold. Detailed procedures and indicated by anumbered list after the main procedure. Notes are in italics.

• Bold type is used for the following:– Keyboard entries that should be typed in their entirety exactly as shown. For example,

“Inf_GND” means to type the Inf followed by a underscore then type GND– Om screen prompts and messages, names of options and text boxes, and menu commands.

For example, click Edit>Select>By name

– Labeled keys on the computer keyboard. For example, “Press Enter”

• Italic type is used for the following:– Emphasis– Keyboard entries when a name or variable muse be typed in place of words in italics. For

example, “copy file name” means to type the word copy, to type a space, and then to type a

file name.

• The plus (+) sign is used between keyboard keys to indicate that you should press thekeys at the same time. For example, “Press ctrl+u” means to press the ctrl key andthe u key at the same time.



23

Overview of Ansoft HFSS

• There are numerous ways to perform most tasks. This tutorial will show you one way.Keep in mind that with experience you will learn the other ways.

• There is no required sequence of events when creating a design. Design steps can beperformed in any logical order.

• You can quickly modify design properties at any time. For example, you can changedimensions through the Properties window.

• You can easily track modifications to your design in the history tree and the projecttree.

• You can modify the model view at any time.

• You can save time by parameterizing design properties.

• You can use HFSS’s extensive post-processing features to evaluate solution results.



24

Overview of Ansoft HFSS (con’t)

• The Ansoft HFSS window

– A Project Manager contains the design tree which outlines the structure of the project

– A Message Manager the allows you to view errors or warning

– A Property Window that displays and allows you to change model parameters

– A Progress Window that displays solution progress

– A 3-D Modeler Window which contains the model and model tree for the active design

ProjectDesign

Design

AutomationDesign Results

Design Setup

}

}

Other Designs

The Project Window A project is a collection of one or moredesigns saved in a single *.hfss file. Anew project is automatically created when HFSS is launched. A new project is listed in the project

tree in the Project Manager windowand is named Projectn by default.Project definitions, such as materialassignments, are stored under theproject name.



25


Menu Bar

ProjectManager with ProjectTree

MessageManager

Properties Window

3-D Modeler Window

Toolbars

Progress Window

Coordinate Entry Fields (not highlighted)Status Bar



26


• Solution Types in HFSS

– Driven Modal-

• This solution calculates the modal-based S-Parameters. The Scattering Matrix or S-matrix solutions will be expressed in terms of the incident and reflected powers of waveguide modes

– Driven Terminal

• This solution calculates the terminal-based S-parameters of multi-conductor transmission line ports.The Scattering or S-matrix solutions will be expressed in terms of terminal voltages and currents

– Eigenmode• This solution calculates the eigenmodes, or resonances, of a structure. The eigenmode solver finds the

resonant frequencies of the structure and the fields at those resonant frequencies

• Convergence criterion for various solution types

– Driven Modal

• Delta S for the modal S-parameters– Driven Terminal

• Delta S for the single-ended or differential nodal S-parameters

– Eigenmode

• Delta F where F is the frequency



27


• Changing the View in the 3-D Modeler Window

At any time during the creation of the 3-D Model you can change the view by using:

– Under the menu item View

• Rotate – The structure will be rotated around the coordinate system

• Pan – The structure will be translated in the graphical area

• Dynamic Zoom – Moving the mouse upwards will increase the zoom facto whilemoving the mouse

• Zoom In/Out – In this mode a rubber band rectangle will be defined by dragging themouse. After releasing the mouse the zoom factor will be applied

• Fit All – This will zoom the defined structure to a point where it fits in the drawingarea

• Fit Selection – This fits only the selected objects into the drawing area

• Spin – Drag the mouse and release the mouse button to start the object spinning. Thespeed of the dragging prior to releasing the mouse controls the speed of the spin.

• Animate – Create or display the animation of parametric geometry

– Feel free to discover any one of these commands during the tutorial. Remember, Ctrl-D gets you back to the original size and holding down the A lt key and clicking the upper right handcorner of the 3-D Modeler window get you back to the normal perspective.

Si l ti St b St



28

Simulation: Step-by-Step

ProcedureOutline of Simulation1. Set up the Design

– Launch Ansoft HFSS, Set the Tool Option, Rename the open a New Project, Set SolutionType, Set the Units

2. Create the 3-D model– Create the Dipole Antenna– Create a bowl to represent the phantom head– Assign boundary conditions– Fill the bowl with brain fluild

– Create Lumped ports and Excitations– Set up the Radiation Boundary

3. Set up and Generate Solutions– Add a solution setup to the Design– Validate the Design– Analyze the Design

4. Compare Solutions– Create a Rectangular Plot of the Reflection Coefficient– Create a Radiation Pattern and Field Plot of the structure



29

Set up the Design

Launch Ansoft HFSS1. To access Ansoft HFSS, click the Microsoft Start button, select Programs, and select the

Ansoft>HFSS 10 program group. Click HFSS 10.

Setting Tool Options1. Select the menu item Tools>Options>HFSS Options2. HFSS Options Window:

a. Click the General Tab

• Use wizards for data entry when creating new boundaries: Checked• Duplicate boundaries with geometry: Checked

b. Click the OK button

3. Select the menu item Tools>Options>3D Modeler Options4. 3D Modeler Options Window

a. Click the Operation tab

• Automatically cover closed polylines: Checked b. Click the Drawing tab• Edit property of new primitives: Checked

c. Click the OK button



30

Set up the Design (con’t)

Save a New Project1. Click File>Save As

2. Use the file browser to locate the folder in which you want to save the project and thendouble click the folder’s name3. Type SAR and File Name text box and then click Save.4. Do not forget to save your design periodically throughout the tutorial.

Rename the Design

1. The design is already listed in the project tree when HFSS opens. It is named HFSSDesignn by default. The 3-D Modeler window appears to the right of the ProjectManager. To rename the design: Right-click HFSSDesignn in the project tree, and thenclick Rename on the shortcut menu.

2. Type PhantomHead and then press Enter.

Select the Solution Type1. As you set up the design for analysis, available settings depend on the solution type. For

this design, you will choose Driven Model as the solution type. To specify the designsolution type, click HFSS>Solution Type

2. In the Solution Type dialog box, select Driven Modal and then click OK .



31

Create the Model

Set the Drawing Units1. To set the units of measurement for drawing the geometric model. Click 3D

Model>Units2. Select mm for the Select units pull-down list and then click OK

Create the 3-D Model of the Phantom HeadThe Phantom Head is made of two main structures

1. The Antenna providing the EM radiation

2. The Phantom Head adsorbing the EM raditionYou will create each geometry separately and assign material properties to each.

Create an Offset Coordinate System1. To create an offset coordinate system, select the menu item 3-D Modeler>Coordinate

System>Create>Relative CS>Offset2. Using the coordinate entry fields (at the bottom of the screen), enter the box position:

X: 0.0, Y: 0.0, Z: -6.8, Press the Enter Key



32

Create the Model (con’t)

Create Dipole Antenna Arm 1

1. To set the grid plane, select the menu item 3D Modeler>Grid Plane>XZ

2. To create the dipole antenna, select the menu item Draw>Cylinder

3. Using the coordinate entry fields, enter the cylinder position:

X: 0.0, Y: -84.0, Z: 0.0, Press the Enter Key

4. Using the coordinate entry fields, enter the radius:

dX: 1.8, dY: 0.0, dZ: 0.0, Press the Enter Key

5. Using the coordinate entry fields, enter the height:


4. To set the name, select the Attribute tab from the Properties window (see next slide)

5. For the Value of Name type: Dipole

6. To set the material, click the vacuum button that is in the value of the Material row.

7. Type pec in the Search by name field and select pec from the list and then click OK (Note: By default, the material to the box is “vacuum”)

8. Click the Edit box in the Transparent row.

9. Move the slider to your preferred transparency level (about 0.6) and then click OK .

10. Click the OK button to close the Properties dialog.



33


To fit the view of the model

1. Select the menu item View>Fit All>Active View or press Ctrl+D.

The Properties window appears, with the Command tab selected, enabling you to Modify the dimensions and position

of the box. While the Properties window is open, you will use it to assign a name to the box, confirm its materialassignment, an make it more or less transparent, depending on your preferences. You will notice the Properties box

remains on the left hand of the screen.

Material

Name



34


Create Dipole Antenna Arm 21. To create arm 2, select the menu item Edit>Select All Visible (or Ctrl+A)

2. Select the menu item, Edit>Duplicate>Mirror3. Using the coordinate entry fields, enter the anchor point of the mirror plane :X: 0.0, Y: 0.0, Z: 0.0, Press the Enter key

4. Using the coordinate entry fields, enter the target point of the vector normal to mirrorplane:

dX: 0.0, dY: 1.0, dZ: 0.0, Press the Enter key

5. Select the Attribute tab in the Properties dialog.6. For the Value of Name type: Dipole27. Click the OK button to close the Properties window.

Group the Dipole Antenna Arms1. To group the dipole arms, select the menu item Edit>Select All Visible (or Ctrl+A)

2. Select the menu item 3D Modeler>Boolean>Unite

Set Grid Plane1. To set the grid plane, select the menu item 3D Modeler>Grid Plane>XY



35


Create Source1. To create the source, select the menu item Draw>Rectangle

2. Using the coordinate entry fields, enter the center position:X: -1.8, Y: -0.5, Z: 0.0, Press the Enter Key

3. Using the coordinate entry fields, enter the radius:dX: 3.6, dY: 1.0, dZ: 0.0, Press the Enter Key

4. Select the Attribute tab in the Properties dialog.5. For the Value of Name type: Source

6. Click the OK button to close the Properties window.7. Click Crtl-D to see the entire object



36


Assign Excitation to the Source

1. To select the trace, select the menu item Edit>Select>By Name

2. With the Select Object dialog open, select the object named Source and click the OK

button ( Note: You can also select the object from the model tree)3. To assign a lumped port excitation, select the menu item

HFSS>Excitations>Assign>Lumped Port

4. In Lumped Port: General,

a. For Name: p1

b. For Resistance: 50c. For Reactance: 0

d. Click the Next button

5. In Lumped Port: Modes,

a. Number of Modes: 1

b. For Mode 1, click the None column and select New Line

c. Using the coordinate entry fields, enter the vector position

X: 0.0, Y: -0.5, Z: 0.0, Press the Enter key

d. Using the coordinate entry fields, enter the vertex

dX: 0.0, dY: 1.0, dZ: 0.0, Press the Enter key

e. Click the Next button

( ’ )



37


Assign Excitation to the Source (con’t)

1. In Lumped Port: Post Processing

a. For Port Renormalization: Renormalize All Mode

b. For Full Port Impedance: 50 ohms2. Click the Finish button

3. To zoom in on the source, hold down on the Alt+Shift and left click of the 3-D modeler window. Move you mouse in the upward direction.

4. In the Project Window, expand the Excitations and select p1. You should now see a

close-up of the source.

Lumped Port(similar to wave ports but internal

to the structure)

Integration Line(defined by the vector)

h d l ( ’ )



38


More on Excitations

– In the previous step, you defined a lumped port. Ports and a unique type of boundarycondition that allow energy to flow into and out of a structure. In HFSS, you can assign aport to an 2-D or 3-D object face. Before the full 3-D EM field inside a structure can be

calculated, it is necessary to determine the excitation field at each port. HFSS uses anarbitrary port solver to calculate the natural field patterns or modes that can exist inside atransmission structure with the same cross section as the port. The resulting 2-D fieldpatterns serve as boundary conditions for the full 3-D problem.

– The port solver assumes that the Lumped Port you have defined is connected to a semi-

infinitely long transmission line (coaxial in this case) with the same cross-section andmaterial properties.

– The field pattern of the traveling wave inside the Lumped Port is calculated using Maxwell'sequations.

– It is necessary to calibrate the port, with a calibration line, a line explicitly defines the up orpositive direction. At any Lumped Port, the direction of the field atωt=0 can be in at leastone of two directions. At some ports, such as circular ports, there can be more than twodirections. If you do not define an integration line, there solution may be out-of-phase to what you were expecting.

– The polarity reference for the line is established by the arrow head (+) to the base (-) of theterminal line.

h d l ( ’ )



39


Add a New Material1. To add a new material, using the 3D Modeler Materials pull down menu (shown

below), choose Select2. From the Select Definition Window, click the Add Material button

3. On the View/Edit Material Window a. For the Material Name type: Head b. For the Value of Relative Permittivity type: 4.6c. Click the OK button

4. Click the OK button

3D Modeler Materials pull down menu

C h M d l ( ’t)



40


Set the Working Coordinate System

1. To set the working coordinate system, select the menu item 3D Modeler>CoordinateSystem>Set Working CS

2. In the Select Coordinate System window, select Global and click the Select button

Create the bowl

1. To create the bowl, select the menu item, Draw>Sphere

2. Using the coordinate entry fields, enter the center position:

X: 0.0, Y: 0.0, Z: 111.5, Press the Enter Key

3. Using the coordinate entry fields, enter the radius:


4. To set the name, select the Attribute tab from the Properties window

5. For the Value of Name type: Bowl6. To set the material, click the vacuum button that is in the value of the Material row.



9. Click the OK button to close the Properties dialog.

C h M d l ( ’t)



41


Create an Offset Coordinate System

1. To create an offset coordinate system, select the menu item 3D Modeler>CoordinateSystem>Create>Relative CS>Offset

2. Using the coordinate entry fields, enter the origin:X: 0.0, Y: 0.0, Z: 164.0, Press the Enter Key

Create an opening in the Bowl

1. To select the object Bowl, select the menu item Edit>Select>By Name

2. In the Select Object dialog, select the object named Bowl and click the OK button

3. To split the bowl object, select the menu item 3D Modeler>Boolean>Split

4. In the Split window:

1. For the Split Plane: XY

2. For Keep Fragments: Negative Side

3. For Split Objects: Split entire selection


C t th M d l (con’t)



42


Add a New Material

1. To add a new material, using the 3D Modeler Materials pull down menu, choose Select

2. From the Select Definition Window, click the Add Material button

3. On the View/Edit Material Window a. For the Material Name type: Brain_Fluid

b. For the Value of Relative Permittivity type: 42.9

c. For the Value of the Bulk Conductivity type: 0.9

d. Click the OK button


Set Working Coordinate System

1. To set the working coordinate system, select the menu item 3D Modeler>Coordinate

System>Set Working CS2. In the Select Coordinate System window, select Global and click the Select button




43

Create the Model (con t)

Create Brain Fluid

1. To create the brain fluid, select the menu item Draw>Sphere

2. Using the coordinate entry fields, enter the center position:

X: 0.0, Y: 0.0, Z: 111.5, Press the Enter Key 3. Using the coordinate entry fields, enter the radius:



5. For the Value of Name type: BrainFluid



8. Click the OK button to close the Properties dialog

Side View




44


Create the Shell of the Bowl

1. To select the objects Bowl and BrainFluid, select the menu item Edit>Select>ByName

2. In the Select Object dialog, select the objects named Bowl and BrainFluid3. Click the OK button

4. To complete the bowl, select the menu item 3D Modeler>Boolean>Subtract

5. In the Subtract window

a. For Blank Parts: Bowl

b. For Tool Parts: BrainFluidc. For Clone tool objects before subtracting: Checked


Create an Offset Coordinate System

1. To create an offset coordinate system, select the menu item 3D Modeler>CoordinateSystem>Create>Relative CS>Offset

2. Using the coordinate entry fields, enter the origin:

X: 0.0, Y: 0.0, Z: 134.0, Press the Enter Key




45


Set the Fluid Level

1. To select the object BrainFluid, select the menu item Edit>Select>By Name

2. In the Select Object dialog, select the object named BrainFluid and click the OK button

3. To split the bowl object, select the menu item 3D Modeler>Boolean>Split4. In the Split window:

a. For the Split Plane: XY

b. For Keep Fragments: Negative Side

c. For Split Objects: Split entire selection


Side view




46


Create a SAR Calculation Line

1. To create a line, select the menu item Draw>Line

2. Using the coordinate entry fields, enter the vertex point:

X: 0.0, Y: 0.0, Z: -129.0, Press the Enter Key

3. Using the coordinate entry fields, enter the vertex point :



5. For the Value of Name type: SAR_line


Set Working Coordinate System

1. To set the working coordinate system, select the menu item 3D Modeler>Coordinate

System>Set Working CS2. In the Select Coordinate System window, select RelativeCS1 and click the Select

button




47


Set the Default Material

1. To set the default material, using the 3D Modeler Materials pull down menu choosevacuum

Create Air Box

1. Select the menu item Draw>Box

2. Using the coordinate entry fields, enter the box position:

X: -155.0, Y: -155.0, Z: -44.0, Press the Enter Key

3. Using the coordinate entry fields, enter the opposite corner of the box:



5. For the Value of Name type: Air

6. Make sure the material is set at vacuum in the value of the Material row.7. Click the Edit box in the Transparent row.

8. Move the slider to transparency level to 1 and then click OK .

9. Click the OK button to close the Properties dialog

10. Select the menu item View>Fit All>Active View to fit the view




48


Create Radiation Boundary

1. To select the object Air, select the menu item Edit>Select>By Name

2. In the Select Object dialog, select the objects named Air and click the OK button

3. To create a radiation boundary, select the item HFSS>Boundaries>Assign>Radiation4. In the Radiation Boundary window, enter the name Rad1 and click the OK button

Create a Radiation Setup

1. To define a radiation setup, select the menu item HFSS>Radiation>Insert Far FieldSetup>Infinite Sphere

2. In the Far Field Radiation Sphere Setup dialog, make the following settings:

Name: ff_2d

Phi: Start: 0, Stop: 90, Step Size: 90

Theta: Start: -180, Stop: 180, Step Size: 23. Click the OK button to close the dialog

Analyze the Model



49

Analyze the Model

Analysis Setup1. To create an analysis setup, select the menu item HFSS>Analysis Setup> Add Solution

Setup2. In the Solution Setup window, click the General tab and enter

Solution Frequency: 835 MHzMaximum Number of Passes: 20Maximum Delta S per Pass: 0.02

3. Click the OK button4. If you haven’t done so in a while, save the project

Model Validation1. To validate the model, select the menu item HFSS>Validation Check 2. Click the Close button (To view any errors or warning messages, use the message manager

at the bottom of the screen)

Analyze1. Congratulations you are ready to analyze. To start the solution process, select the menu itemHFSS>Analyze

View the Solution Data



50

View the Solution Data

Solution Data1. To view the Solution Data, select the menu item HFSS>Results>Solution Data2. Click the Profile tab to view the solution profile

(elapsed time, mesh generation statistics, etc.)3. Click the Convergence tab

to view solution convergence asa function of pass number and thenumber of tetrahedra used.

Note the total number of passes.Click Plot.4. Click the Matrix Data

tab to view the data.5. Click the Close button

Create Reports



51

Create Reports

Create a report that plots the input return loss vs. Adaptive Pass1. To create this report, select the menu item HFSS>Results>Create Report2. In the Create Report Window, select:

Report Type: Modal Solution DataDisplay Type: Rectangular Plot

3. Click the OK button4. In the Traces window, select the following:

Solution: Setup1: Adaptive_1

5. Click the Y tab and select:Category: S ParameterQuantity: S(p1,p1)Function: dB

6. Click the Add trace button7. Click the Done button8. Double Click on the x-axis, the

X-Axis Properties dialog appears9. Select the Scaling Tab10. Uncheck the Autoscale box11. Set Max to your maximum number of passes12. Click the OK button

Create Reports (con’t)



52

Create Reports (con t)

Create a SAR Report1. To create a SAR report, select the menu item HFSS>Results>Create Report2. In the Create Report window, select:

Report Type: Fields

Display Type: Rectangular3. Click the OK button4. In the Traces window, set the following:

Solution: Setup1:LastAdaptiveGeometry: SAR_Line

5. In the Y tab, select

Category: Calculator ExpressionsQuantity: Local_SAR, Average_SAR (use the Shift key to make multiple selections)Function: <none>

1. Click the Add Trace button2. Click the Done button

Create a Mesh Plot



53

Create a Mesh Plot

Create a Mesh Plot on the in the Brain Fluid

1. To create a Magnetic Field Plot, return to the 3-D Modeler Window by selectingHFSS>3D Model Editor. Note: This step is only necessary if you have a Plot window

open.2. To select the object BrainFluid, select the menu item Edit>Select>By Name

3. In the Select Object dialog, select the objects named BrainFluid and click the OK button.

4. To open the Create Field Plot window, click HFSS>Fields>Plot Mesh

5. Select Setup1:LastAdaptive as the solution to plot in Solution pull-down list6. Accept the default settings by clicking Done.

7. Rotate the object to see other perspectives of the plot

8. After viewing the mesh, delete the plot by left clicking

MeshPlots on the Project Tree and select Delete

9. Hold down the Alt key and click the upper righthand corner of the 3D Modeler window to

return to the normal view.

Create Field Plot



54

Create Field Plot

Create a 2-D plot of the field distribution in the head1. Return to the 3D Modeler window by selecting HFSS>3D Model Editor2. To select the Global YZ plane for your plot, using the Model Tree, expand Planes3. Select Global: YZ

4. Select the menu item HFSS>Fields>Fields>E>Mag_E5. In the Create Field Plot window, select:

Solution: Setup1: LastAdaptiveQuantity: Mag_EIn Volume: BrainFluid

6. Click the Done button

7. To modify the attributes of a field plot, select the menu item HFSS>Fields>Modify Plot Attributes

8. In the Select Plot Folder dialog,select E Field and click the OK button

9. Click the Scale tabSelect: Use limits

Min: 2Max: 200Scale: Log

10. Click the Close button

Create Field Plot (con’t)



55

Create Field Plot ( )

Animate the Field Overlay Plot

An animated plot is a series of frames that displays a field, mesh, or geometry at varying

values. You specify the values of the plot that you want to include, called a frame.

1. Right-click Mag_E1 in the Project Tree, and then click Animate2. In the Setup Animation window, click the Swept Variable tab:

Name: AnimationE

Swept Variable: Phase

Start: 0deg

Stop: 180degSteps: 6


4. After viewing the animation, click the stop button in the Animation dialog that hasappeared in the upper left hand corner

Create Field Plot (con’t)



56

Create Field Plot

Create a 2-D plot of the far field pattern

1. To create a 2-D polar far field plot, select the menu item HFSS>Results>CreateReport

2. In the Create Report Window, select:Report Type: Far Fields

Display Type: Radiation Pattern


4. In the Traces window, set the following:

Solution: Setup1:Sweep1Geometry: ff_2d

5. In the Sweeps tab, make sure Theta is the primary sweep. Select Phi under the Namecolumn, and on the drop list, select Theta if it is not.

6. In the Mag tab,select:

Category: GainQuantity: GainL3Y

Function: dB

7. Click the Add Trace button

8. Click the Done button

Exercises



57

Exercises

1. Create another solution setup and analyze the phantom head at differentfrequency. Choose a frequency listed in Table 1: SAR data from the IEEE P1528standard. You will recall that the previous tutorial analyzed the structure at 835

MHz. Does you finite element analysis agree with measurements?2. Create a 3-D radiation plot of the Electric Field in the Brain Fluid. You may need

to modify your solution setup to include complete sweeps in both the Theta andPhi directions.

Further Reading and References



58

Further Reading and References

• SAR

– Standard IEEE P1528, “Recommended Practice for Determining the Peak Spatial-AverageSpecific Absorption Rate (SAR) in the Human Body Due to Wireless CommunicationDevices: Experimental Techniques,” Institute of Electrical and Electronics Engineers, New York, NY, 2005

– EN 50361, “Basic Standard for Measurement of Specific Absorption Rate Related toExposure to Electromagnetic Fields for Mobile Phones (300 MHz-3GHz),” EuropeanCommittee for Electrical Standardization (CENELEC), Brussels, 2001

• Electromagnetics

– N.N. Rao, Elements of Engineering Electromagnetics, Pearson Prentice Hall, Upper SaddleRiver, NJ, 2004

– W.H. Hayt and J.A. Buck, Engineering Electromagnetics, McGraw-Hill, New York, NY,2006

• Computational Electromagnetics– J.Jin, The Finite Element Method in Electromagnetics, 2nd edition, Wiley, New York, NY,2002

– P.P Silvester and R.L. Ferrari, Finite Elements for Electrical Engineers, 3rd edition,Cambridge University Press, Cambridge, 1996

Documents

basma1_hfss