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Section 6: Boundary Module

Getting Started: Ansoft

HFSS 8.0


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Synopsis

General Overview Boundary Types, Definitions, and Parameters

Source Types, Definitions, and Parameters

nterface !ayout

"ssi#nin# Boundaries $ace Selection

Precedence

"ssumptions %t&e 'outer( Boundary)

Boundary Setup *+ercise Part 1 Define Boundaries in *+ample

odel Details of Port Definition and .reation

Si/e and Position ode .ount

De#enerate odes

.ali0ration, mpedance, and Polari/ation

Gap Source Ports

Boundary Setup *+ercise Part 2 "dd ports to *+ample odel


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HFSS Boundary List

Perfect * and Perfect 34atural

deal *lectrically or a#netically .onductin# Boundaries

'4atural( denotes Perfect * 'cancellation( 0e&avior

$inite .onductivity

!ossy *lectrically .onductin# Boundary, wit& user-provided conductivity

and permea0ility

mpedance sed for simulatin# 't&in film resistor( materials, wit& user-provided

resistance and reactance in Ω3

6adiation

"n 'a0sor0in# 0oundary condition,( used at t&e perip&ery of a pro7ect in

w&ic& radiation is e+pected suc& as an antenna structure

Symmetry " 0oundary w&ic& ena0les modelin# of only a su0-section of a structure

in w&ic& field symmetry 0e&avior is assured8

9Perfect *: and 9Perfect : su0cate#ories

aster and Slave

'!in;ed( 0oundary conditions for unit-cell studies of infinitely replicatin#

#eometry %e8#8 an antenna array)


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HFSS Boundary Descriptions: Perfect E and

Perfect H/Natural

Parameters: None Perfect E is a perfect electrical conductor=

$orces *-field perpendicular to t&e surface

6epresent metal surfaces, #round planes,

ideal cavity walls, etc8

Perfect H is a perfect ma#netic conductor

$orces -field perpendicular to surface, *-field tan#ential

Does not e+ist in t&e real world, 0ut

represents useful 0oundary constraint for

modelin#

Natural denotes effect of Perfect H applied

on top of some ot&er %e8#8 Perfect *) 0oundary

'Deletes( t&e Perfect E condition, permittin#

0ut not requiring tan#ential electrical fields8

Opens a '&ole( in t&e Perfect E plane

Perfect E Boundary*

Perfect H Boundary

‘Natural’ Boundary

lar perpendicu E

continuous E

parallel E

*NOE: !"en you define a solid o#$ect as a

‘%erf&conductor’ in t"e Material Setu%' a

Perfect E #oundary condition is a%%lied to its

e(terior surfaces))


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HFSS Boundary Descriptions: Finite

Conductivity

Parameters: onducti+ity andPermea#ility $inite .onductivity is a lossy

electrical conductor *-field forced perpendicular, as wit&

Perfect E

owever, surface impedance ta;esinto account resistive and reactive

surface losses

ser inputs conductivity %in

siemens3meter) and relative

permea0ility %unitless)

sed for non-ideal conductor

analysis=

,inite onducti+ity Boundary

g attenuatinlar perpendicu E ,

*NOE: !"en you define a solid o#$ect

as a non-ideal metal .e/g/ co%%er'

aluminum0 in t"e Material Setu% module'

and it is set to ‘Sol+e Surface’' a ,inite

onducti+ity #oundary is automatically

a%%lied to its e(terior faces))


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HFSS Boundary Descriptions: Impedance

Parameters: 1esistance and1eactance' o"ms2square . Ω3 0 3m%edance 0oundary is a direct, user-

defined surface impedance se to represent t"in film resistors

se to represent reacti+e loads 6eactance will NO vary wit&

fre?uency, so does not represent

a lumped 'capacitor( or 'inductor(

over a fre?uency 0and8

.alculate re?uired impedance from

desired lumped value, widt&, and len#t& !en#t& %in direction of current flow) ÷

@idt& A num0er of 's?uares(

mpedance per s?uare A Desired

!umped mpedance ÷ num0er of

s?uares

EXAMPLE: Resistor in Wilkenson Power Divider

6esistor is 85 mils lon# %in direction of flow) and< mils wide8 Desired lumped value is 5 o&ms8

square N

R R

N

lumped

sheet /40875.

35

875.04

5.3

Ω===

==


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HFSS Boundary Descriptions: adiation

Parameters: None " 1adiation 0oundary is an a#sor#ing#oundary condition, used to mimic continued

propa#ation 0eyond t&e 0oundary plane

"0sorption is ac&ieved via a second-

order im%edance calculation

Boundary s&ould 0e constructed correctly for

proper a0sorption

Distance $or stron# radiators %e8#8

antennas) no closer t&an λ3< to any

structure8 $or wea; radiators %e8#8 a

0ent circuit trace) no closer t&an λ31C to

any structure

Orientation T&e radiation 0oundarya0sor0s 0est w&en incident ener#y flow

is normal to its surface

S&ape T&e 0oundary must 0e

conca+e to all incident fields from wit&in

t&e modeled space

Note #oundary does not

follo4 ‘#rea5’ at tail end

of "orn/ oing so

4ould result in a con+e(

surface to interior

radiation/

Boundary is λ3< away from

&orn aperture in all directions8


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HFSS Boundary Descriptions: adiation!

cont"

6adiation 0oundary a0sorption profile

vs8 incidence an#le is s&own at left 4ote t&at a0sorption falls off

si#nificantly as incidence e+ceeds


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HFSS Boundary Descriptions: Symmetry

Parameters: y%e .Perfect E or Perfect H0 Symmetry 0oundaries permit modelin# of

only a fraction of t&e entire structure under

analysis

Two Symmetry Options

Perfect E : *-fields are perpendicular to t&esymmetry surface

Perfect H : *-fields are tan#ential to t&e

symmetry surface

Symmetry 0oundaries also &ave furt&er

implications to t&e Boundary ana#er and

$ields Post Processin# *+istence of a Symmetry Boundary will

prompt 'Port mpedance ultiplier( verification

*+istence of a symmetry 0oundary allows for

near- and far-field calculation of t&e 'entire(

structure

.onductive ed#es, < sides

"is rectangular 4a+eguide contains a

symmetric %ro%agating mode' 4"ic" could

#e modeled using "alf t"e +olume

+ertically////

Perfect * Symmetry %top)

888or &ori/ontally8

Perfect Symmetry

%left side)


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HFSS Boundary Descriptions: Symmetry!

cont"

Geometric symmetry does not

necessarily imply field symmetry

for &i#&er-order modes

Symmetry 0oundaries can act as

mode filters

"s s&own at left, t&e ne+t &i#&erpropa#atin# wave#uide mode is

not symmetric a0out t&e vertical

center plane of t&e wave#uide

T&erefore one symmetry case is

valid, w&ile t&e ot&er is notE

mplication 7se caution 4"enusing symmetry to assure t"at real

#e"a+ior in t"e de+ice is not filtered

out #y your #oundary conditions))

Perfect E Symmetry .to%0

Perfect H Symmetry

.rig"t side0

T*2C ode in @6FC

Properly represented wit&

Perfect * Symmetry

ode can not occur properly

wit& Perfect Symmetry


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HFSS Boundary Descriptions: #aster/Slave

Boundaries

Parameters: oordinate system'master2sla+e %airing' and %"asing Master and Sla+e 0oundaries are used

to model a unit cell of a repeatin#

structure

"lso referred to as lin5ed #oundaries aster and Slave 0oundaries are

always %aired one master to one slave

T&e fields on t&e slave surface are

constrained to 0e identical to t&ose on

t&e master surface, wit& a p&ase s&ift8

onstraints T&e master and slave surfaces must 0e

of identical s&apes and si/es

" coordinate system must 0e identified

on t&e master and slave 0oundary to

identify point-to-point correspondence7nit ell Model of End-,ire !a+eguide 9rray

@G Port

%0ottom) Ground Plane

Perfectly atc&ed !ayer

%top)

Slave Boundaryaster Boundary

Origin


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HFSS Source List

Port ost .ommonly sed Source8 ts use results in S-parameter output

from $SS8

Two Su0cate#ories 'Standard( Ports and 'Gap Source( Ports

"pply to Surface%s) of solids or to s&eet o07ects

ncident @ave

sed for 6.S or Propa#ation Studies %e8#8 $re?uency-SelectiveSurfaces)

6esults must 0e post-processed in $ields odule no S-parameters

can 0e provided

"pplies to entire +olume of modeled space

Holta#e Drop or .urrent Source 'deal( volta#e or current e+citations

"pply to Surface%s) of solids or to s&eet o07ects

a#netic Bias nternal $ield Bias for nonreciprocal %ferrite) material pro0lems

"pplies to entire solid o#$ect representin# ferrite material


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HFSS Source Descriptions: Port

Parameters: Mode ount' ali#ration'3m%edance' Polari=ation' 3m%/ Multi%lier " %ort is an aperture t&rou#& w&ic&

#uided electroma#netic field ener#y is

in7ected into a D $SS model8 T&ere

are two types

Standard Ports T&e aperture is solvedusin# a 2D ei#ensolution w&ic& locates

all re?uested propa#atin# modes

.&aracteristic impedance is

calculated from t&e 2D solution

mpedance and .ali0ration !ines

provide furt&er control >a% Source Ports "ppro+imated field

e+citation is placed on t&e #ap source

port surface

.&aracteristic impedance is

provided 0y t&e user durin# setup

EXAMPLE STANDARD PORTS

EXAMPLE GAP-SOURCE PORTS


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HFSS Source Descriptions: Incident $ave

Parameters: Poynting


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HFSS Source Descriptions: %olta&e Drop and

Current Source

*+ample Holta#e

Drop %0etween

trace and #round)

*+ample .urrent

Source %alon# trace

or across #ap)

Parameters: irection and Magnitude

" +oltage dro% would 0e used toe+cite a volta#e 0etween two metal

structures %e8#8 a trace and a #round)

" current source would 0e used to

e+cite a current alon# a trace, or

across a #ap %e8#8 across a slotantenna)

Bot& are 'ideal( source e+citations,

wit&out impedance definitions 4o S-Parameter Output

ser applies condition to a 2D or D

o07ect created in t&e #eometry Hector identifyin# t&e direction of t&e

volta#e drop or t&e direction of t&e

current flow is also re?uired


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HFSS Source Descriptions: #a&netic Bias

Parameters: Magnitude and

irection or E(ternally Pro+ided T&e magnetic #ias source is used

only to provide internal 0iasin# -

field values for models containin#

nonreciprocal %ferrite) materials8

Bias may 0e uniform field %enterparameters directly in $SS)888

Parameters are direction and

ma#nitude of t&e field

888or 0ias may 0e non-uniform

%imported from e+ternal

a#netostatic solution pac;a#e) "nsoft(s D * $ield

Simulator provides t&is

analysis and output

"pply source to selected D solid

o07ect %e8#8 ferrite puc;)


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Sources/Boundaries and Ei&enmode

Solutions

"n Eigenmode solution is a direct solution of t&e resonant

modes of a closed structure

"s a result, some of t&e sources and 0oundaries discussed so

far are not availa0le for an *i#enmode pro7ect8 T&ese are "ll *+citation Sources

Ports

Holta#e Drop and .urrent Sources

a#netic Bias

ncident @aves

T&e only unavaila0le 0oundary type is 6adiation Boundary

" Perfectly Matc"ed 8ayer construction is possi0le as a

replacement


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'(e HFSS Source/Boundary Setup Interface

Side Window

oordinate ,ields and

Sna% O%tions

Source/Boundary Li!

S"o4s all sources and

#oundaries currently

assigned to t"e %ro$ect

and t"eir status? allo4sselection for +ie4ing'

editing' and deletion

Source/Boundary Con!ro"

9llo4s Naming' contains e(ecution

controls .9ssign' lear' 7nits///0

Boundary A!!ri#u!e $ie"d

1egion 8ayout c"anges to %ro+ide

entry fields for selected source or #oundary

c"aracteristics and o%tions/

Source/Boundary Dro%-Down

8ists all source or #oundary ty%es'

#ased on radio #utton selected

Gra%&ica" 'iew Window

S"o4s geometry' %ermits

%oint-and-clic5 selection'

+ector definition' and

assignment/

Source/Boundary Se"ec!ion Bu!!on

Menu and Too"#ar

Pic( O%!ion ontrols selection o%tions

in gra%"ical 4indo4


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Boundary #ana&er: )*+ect/Face Selection

T&e >ra%"ical Pic5 options %1) control

t&e result of clic;in# in t&e #rap&icalview window8

O#$ect : mouse-clic5 selects

e(terior of entire o#$ect

,ace: mouse-clic5 selects

closest face of o#$ect

Boundary : mouse-clic5 selectsclosest e(isting #oundary

condition .if any0

To s&ift your focus to an o07ect or face

deeper into t&e model, use t&e ri#&t

mouse menu %2) c&oice Ne(t Be"ind ,

or t&e &ot;ey 94:

Selected faces will &i#&li#&t in a #rid

pattern selected o07ects will &ave

t&eir wireframe &i#&li#&ted

ultiple faces may 0e selected

simultaneously a second clic;

deselects already-selected faces

18

28

NOE: "e same gra%"ical +ie4 mani%ulation

s"ortcuts for rotation' %anning' and =ooming found

in t"e ra4 module also 4or5 "ere? t"e +isi#ility

icon also assists o#$ect2face selection #y ‘"iding’

e(terior o#$ects/


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Boundary #ana&er: )*+ect/Face Selection!

cont"

T&e *dit menu %) provides furt&er

Select options, includin# ,aces3ntersection

,aces intersection opens a list

0o+ containin# all o07ects in

t&e model

Selectin# two touc&in# o07ects

from t&e list will prompt t&einterface to automatically find

all intersectin# faces

Note: only e(terior faces in

intersection are selected' not

faces of one o#$ect 4"ic" are

inside t"e )o"u*e of t"e ot"er T&e *dit menu Select option By

Name %


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Boundary ,ssi&nment: -eneral Procedure

Select Source orBoundary radio 0utton,

and desired type from

t&e drop-down listin#

Select t&e face or faces

on w&ic& you wis& to

apply t&e

source30oundary

condition

%"0ove 2 steps

interc&an#ea0le)

$ill in any necessary

parameters for t&e

source30oundary 4ame t&e

source30oundary, and

press t&e 9ssign 0utton

18 Select source or 0oundary and type

28 Select face%s)

8 $ill in Parameters as necessary


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Boundary ,ssi&nment: Precedence

Boundary assi#nments are

order de%endent : Boundaries assi#ned later

supercede t&ose

assi#ned earlier over any

s&ared surfaces

Ports are t&e e+ception

t&ey always supercede

any earlier or later

assi#nments

Ports will sort to t&e

0ottom of t&e

0oundary list to

reflect t&is fact Boundaries can 0e

re-prioriti/ed usin#

t&e odel menu

3n t"e %ictured e(am%le' t"e ‘radiation’

#oundary o+erlays t"e orange rectangle.on t"e #ac5 face0 4"ic" 4as earlier

assigned as t"e %ort/ Ports' "o4e+er'

al4ays ta5e %recedence' and s"o4 at t"e

#ottom of t"e #oundary listing/


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Boundary ,ssi&nment: Default Boundary

"ny e(terior face of t&e

modeled #eometry not #iven

a user-defined 0oundary

condition is assumed to 0e

a Perfect E Default 0oundary called

outer

ma#ine entire model

0uried in solid metal

unless you instruct

ot&erwise

To view 0oundaries and see

if you missed an

assi#nment, use t&e

Boundary is%lay pic; from

t&e Model menu Grap&ical window s&ows

0ot& user and auto-

assi#ned 0oundaries


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Boundary Setup E.ercise Part

@e will practice 0y

assi#nin# 0oundaries to a.oa+ to icrostrip

transformer model

T&is e+ercise is only Part @

of t&e entire operation

e+citation assi#nment will0e covered after a detailed

description of $SS

sources and port

assi#nment

n t&e a+well Pro$ect

Manager , find t&e pro7ectentitled A #nd&e(er and

O%en it

Once open, proceed to

Setu% Boundaries2Sources

NOE: "e model for t"is e(ercise is nearly

identical to t"at used in t"e Material Setu%

e(ercise' #ut "as #een s%lit in "alf along t"e a(is

of t"e microstri% and coa( feed to demonstrate

symmetry #oundary a%%lication as 4ell/


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Boundary Setup E.ercise: 'race #etali0ation

NOE: Since solid Material %arameters are already

a%%lied' t"ere is already a #oundary on t"e e(terior of t"emetal o#$ects A%in' A%in@' and A%inC/ !e only need to

a%%ly t"e surface metali=ation for t"e actual microstri%

trace line' and define outer radiation' ground %lane' and

symmetry #oundaries/

18 Select t&e Boundary radio Button8

28 $rom t&e list of availa0le 0oundaries, select Perfect E /

8 Set t&e Grap&ical Pic; option to ,ace/

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