ANSYS Tutorial: Capacitance. (GUI Method). Todd Kaiser. Montana State University. EE505 MEMS. Capacitance Modeling Method. • Model Dielectric and Mesh.
ANSYS Tutorial: Capacitance (GUI Method) Todd Kaiser Montana State University EE505 MEMS
Capacitance Modeling Method • Model Dielectric and Mesh • Select nodes on surface of each conductor • Group them into node components and name: cond# • The last conductor is assumed ground • Use CMATRIX command
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Capacitance Matrix C13 3
1
C23
C12 C11
C33
2 C22
c11
c12
c13
C = c21 c22
c23
c31
c33
c32
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Example: Coax Cable – 2D • Inner radius: 1mm • Outer radius: 2mm • Teflon filled: εr = 2.1 C′ =
(
a b
)
2πε 2π (2.1) 8.854 ×10 −12 (F / m ) = 168.5 ×10 −12 (F / m ) = −3 b ( ) × m 2 10 ln ln a 1× 10 −3 (m )
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Start ANSYS
Preferences > Electric
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Select Element • Preprocessor > Element Type > Add/Edit/Delete – Add: Electrostatic: 2D Quad 121
Define Material Properties • Preprocessor > Material Props > Material Models > Electromagnetics > Relative Permittivity > Constant > PERX = 2.1
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Model Structure • Preprocessor > Modeling > Create > Areas > Circle > Annulus – – – –
WP X = 0 WP Y = 0 Rad-1 = 0.001 Rad-2 = 0.002
Mesh the Area • Preprocessor > Meshing > Mesh Tool Æ Smart Size:1 > Mesh Æ Select area > OK
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Select Edge Nodes • Utility Menu > Select > Entities Æ Nodes > Exterior • Utility Menu > Plot > Nodes
Select Inner Conductor Nodes • Utility Menu > Select > Entities > Nodes Æ Reselect Æ Box inner circle of nodes
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Create & Name Component of inner nodes • Utility Menu > Select > Comp/Assembly > Create Component > ‘Cond1’
Select Edge Nodes • Utility Menu > Select > Everything • Utility Menu > Select > Entities Æ Nodes > Exterior • Utility Menu > Plot > Nodes
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Select Outer Conductor Nodes • Utility Menu > Select > Entities > Nodes Æ Reselect Æ Box both circles of nodes Æ unpick Æ Box inner circle of nodes to select only the outer circle of nodes
Create Component of Outer nodes • Utility Menu > Select > Comp/Assembly > Create Component > ‘Cond2’
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Calculate Capacitance Matrix • Type in command window: – cmatrix, 1,’cond’,2,0
• Allow the computer to continue even after it has said solved. • This generates the following results window
Results • • • • • • • • •
*** Ground Capacitance Matrix *** Self Capacitance of conductor 1. = 0.16854E-09 Ground capacitance matrix is stored in 3d array parameter cmatrix ( 1., 1.,1) *** Lumped Capacitance Matrix *** Self Capacitance of conductor 1. = 0.16854E-09 Lumped capacitance matrix is stored in 3d array parameter cmatrix ( 1., 1.,2)
•
Capacitance values are per unit length
•
Capacitance matricies are stored in file cmatrix .txt
• • •
_____________________________________________________________
________________ CMATRIX SOLUTION SUMMARY ___________________
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To look at the potentials and fields • Solution > Analysis Type > New Analysis Æ Steady State
Apply Load to Inner Conductor • Solution > Define Loads > Apply > Electric > Boundary > Voltage > On Lines – Box Æ inner circle – Constant value: 1 (volt)
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Apply Load to Outer Conductor • Solution > Define Loads > Apply > Electric > Boundary > Voltage > On Lines – Box Æ entire structure – Select Unpick: Box Æ inner circle – Constant value: 0 (ground)
Solve • Solution > Solve > Current LS
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PostProcessing • General PostProcessing > Plot Results > Contour Plot > Nodal Solution Æ DOF Solution > Electric Potential
Equipotential Contours
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Modify Legend Scale • Utility Menu > Plot Controls > Style > Contours > Uniform Contours Æ Number of contours = 8
8 levels (defaults to 9)
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Move Legend & Date • Utility Menu > Plot Controls > Style > Multilegend Options > Contour Legend Æ right of window • Utility Menu > Plot Controls > Style > Text > Date Æ left of window
Contour Plot of the Electric Field • General PostProcessing > Plot Results > Contour Plot > Nodal Solution Æ Electric Field > Electric Field Vector Sum
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Vector Plot of Electric Field • General Postprocessing > Plot results > Vector Plot > Predefined Æ Elec Field EF, VRATIO = 0.2
Parallel – 3D (neglect fringing) • Area: 100 microns x 100 microns • Separation 10 microns • Air filled: εr = 1 C=
εA d
=
(8.854 ×10 (F / m))(100 ×10 (m )) −12
10 × 10
−6
−6
(m )
2
= 8.854 × 10 −15 (F )
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Start ANSYS
Preferences > Electric
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Select Element • Preprocessor > Element Type > Add/Edit/Delete – Add: Electrostatic: 3D Quad 123
Define Material Properties • Preprocessor > Material Props > Material Models > Electromagnetics > Relative Permittivity > Constant > PERX = 1
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Define Units (microns) • Preprocessor > Material Properties > Electromag Units > User Defined Æ Specify Free space Permittivity = 8.854e-6 • Capacitance will be in pF
Model Structure • Preprocessor > Modeling > Create Volume > Block > By Dimensions Æ – X = 50,-50 – Y = 50, -50 – Z = 5, -5
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Plot Views • Utility Menu > PlotCtrls • Æ Pan – Zoom – Rotate – Iso
Mesh the Volume • Preprocessor > Meshing > Mesh Tool Æ Smart Size:6 > Mesh Æ Select Volume > OK
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Select Top Area • Utility Menu > Select > Entities > Areas – by Num/Pick
Plot Selected Area • Utility Menu > Plot > Areas
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Select nodes attached to area • Utility Menu > Select Æ Nodes attached to areas, all
Create Conductor Component 1 • Utility Menu > Select > Comp/Assembly > Create Component Æ ‘cond1’
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Select Bottom Area • • •
Utility Menu > Select > Everything Utility Menu > Plot > Elements Utility Menu > Select > Entities > Areas – by Num/Pick
Select nodes attached to area • Utility Menu > Select Æ Nodes attached to areas, all
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Create Conductor Component 2 • Utility Menu > Select > Comp/Assembly > Create Component Æ ‘cond2’
Calculate Capacitance Matrix • Type in command window: – cmatrix, 1,’cond’,2,0
• Allow the computer to continue even after it has said solved. • This generates the following results window
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Results • • • • • • • • • • • • •
________________ CMATRIX SOLUTION SUMMARY ___________________ *** Ground Capacitance Matrix *** Self Capacitance of conductor 1. = 0.88540E-02 Ground capacitance matrix is stored in 3d array parameter cmatrix ( 1., 1.,1) *** Lumped Capacitance Matrix *** Self Capacitance of conductor 1. = 0.88540E-02 Lumped capacitance matrix is stored in 3d array parameter cmatrix ( 1., 1.,2) Capacitance matricies are stored in file cmatrix .txt
_____________________________________________________________
More Complex Geometries • Import or draw geometry (2D) • Extrude to metal thickness • Create block of air between metal structures • Group nodes on metal into conductor assemblies • Ground plane is the highest number assembly • Use Cmatrix command
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GUI to Batch • Utilities Menu > File > Write DB log File
/BATCH ! /COM,ANSYS RELEASE 11.0 UP20070125 15:07:18 07/30/2008 /input,start110,ans,'C:\Program Files\ANSYS Inc\v110\ANSYS\apdl\',,,,,,,,,,,,,,,,1 !* /NOPR /PMETH,OFF,0 KEYW,PR_SET,1 KEYW,PR_STRUC,1 KEYW,PR_THERM,0 KEYW,PR_FLUID,0 KEYW,PR_ELMAG,0 KEYW,MAGNOD,0 KEYW,MAGEDG,0 KEYW,MAGHFE,0 KEYW,MAGELC,0 KEYW,PR_MULTI,0 KEYW,PR_CFD,0 /GO !* ! /COM, ! /COM,Preferences for GUI filtering have been set to display: ! /COM, Structural !* !* /NOPR /PMETH,OFF,1 KEYW,PR_SET,1 KEYW,PR_STRUC,1 KEYW,PR_THERM,0 KEYW,PR_FLUID,0 KEYW,PR_ELMAG,1 KEYW,MAGNOD,0 KEYW,MAGEDG,0 KEYW,MAGHFE,0 KEYW,MAGELC,1 KEYW,PR_MULTI,1 KEYW,PR_CFD,0 /GO !* ! /COM, ! /COM,Preferences for GUI filtering have been set to display: ! /COM, Structural ! /COM, Electric !* /PREP7 !* !* /NOPR /PMETH,OFF,1 KEYW,PR_SET,1 KEYW,PR_STRUC,0 KEYW,PR_THERM,0 KEYW,PR_FLUID,0 KEYW,PR_ELMAG,1 KEYW,MAGNOD,0
KEYW,MAGEDG,0 KEYW,MAGHFE,0 KEYW,MAGELC,1 KEYW,PR_MULTI,0 KEYW,PR_CFD,0 /GO !* ! /COM, ! /COM,Preferences for GUI filtering have been set to display: ! /COM, Electric !* !* ET,1,SOLID123 !* !* !* EMUNIT,MUZRO,0.125663706144E-05 EMUNIT,EPZRO,0.885399999845E-05 !* !* MPTEMP,,,,,,,, MPTEMP,1,0 MPDATA,PERX,1,,1 BLOCK,-50,50,-50,50,-5,5, ! VPLOT ! /VIEW, 1 ,1,1,1 ! /ANG, 1 ! /REP,FAST SMRT,6 MSHAPE,1,3D MSHKEY,0 !* CM,_Y,VOLU VSEL, , , , 1 CM,_Y1,VOLU CHKMSH,'VOLU' CMSEL,S,_Y !* VMESH,_Y1 !* CMDELE,_Y CMDELE,_Y1 CMDELE,_Y2 !* ! EPLOT ASEL,S, , , 2 NSLA,S,1 ! NPLOT ! /VIEW, 1 ,-1 ! /ANG, 1 ! /REP,FAST ! /VIEW, 1 ,,,1 ! /ANG, 1 ! /REP,FAST ! /VIEW, 1 ,1,1,1
! /ANG, 1 ! /REP,FAST ! /VIEW, 1 ,-1 ! /ANG, 1 ! /REP,FAST ! /VIEW, 1 ,,,1 ! /ANG, 1 ! /REP,FAST CM,cond1,NODE ALLSEL,ALL ! /VIEW, 1 ,1,1,1 ! /ANG, 1 ! /REP,FAST ! EPLOT ASEL,S, , , 1 NSLA,S,1 ! NPLOT ! /VIEW, 1 ,1 ! /ANG, 1 ! /REP,FAST CM,cond2,NODE cmatrix,1,'cond',2,0 ! /COM,ANSYS RELEASE 11.0 UP20070125 15:11:22 07/30/2008 ! LGWRITE,'captutorial','lgw','C:\DOCUME~1\tjkai ser\Desktop\',COMMENT
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