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ANSYS 7.1 TUTORIAL Electrostatic problems Ruben Specogna A.A. 2005/06

ANSYS 7.1 TUTORIAL Electrostatic problems Ruben Specogna A.A. 2005/06. Università di Udine Dipartimento DIEGM Gruppo di Elettrotecnica. Electrostatic problems. The Poisson equation in the plane: Materials, impose boundary conditions Solve for scalar potential V:. Application.

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ANSYS 7.1 TUTORIAL Electrostatic problems Ruben Specogna A.A. 2005/06

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  1. ANSYS 7.1 TUTORIAL Electrostatic problems Ruben Specogna A.A. 2005/06 Università di Udine Dipartimento DIEGM Gruppo di Elettrotecnica Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

  2. Electrostatic problems • The Poisson equation in the plane: • Materials, impose boundary conditions • Solve for scalar potential V: Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

  3. Application • Per-unit-length (PUL) parameters extraction: • Used to simulate multiconductor transmission lines (MTL) (see the course of EMC) • Once you have this parameters you can simulate the transmission line with a circuit solver (like SPICE) and don’t have to care about em-fields anymore… • The capacitance matrix C is the most common PUL parameter: • C can be “extracted” with 2D planar electrostatic problem Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

  4. Parameters extraction Example • Parameters extraction of a microstrip • We solve N electrostatic problems, with N = number of conductors • Every simulation we have to change the boundary conditions • In the example we have amicrostrip with 2 conductorsover a reference plane. C is 2x2. • I need 2 simulations: • 1: V1=1V and V2=0V • 2: V1=0V and V2=1V • For every simulation calculate thecharge for every conductor with the Gauss’s law Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

  5. Numerical Example • Due to planar symmetry we model the line with a planar 2d problem • Due to symmetry we model only half domain • We model the stripline with a line (it’s very thin compared to the Si) • L1 = L4 = 1cm, L2 = L3 = 10cm • r_Si = 10 • For example V1=1.5V and V0=1V (V0) (V1) Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

  6. Element type definition • First part of script “ele_esempio1.inp”: /PREP7!start the preprocessing /TITLE,Microstrip!defining title ET,1,PLANE121!defining element type (ET) !for the simulation !plane121 is a second order quad-triangular element for !electrostatic problems (“help plane121” for other infos) V1=1.5!define some useful constants V0=0.5 MP,PERX,1,1 !assign the material propterties (MP) MP,PERX,2,10!at every material !we have in this example 2 materials: the air and the silicon, !the air is #1 with permeability 1 and the Si is #2 with perm. 10 Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

  7. Modeling !inserting 4 rectangles !syntax: RECTNG, X1, X2, Y1, Y2 RECTNG,0,.5,0,1 RECTNG,.5,5,0,1 RECTNG,0,.5,1,10 RECTNG,.5,5,1,10 !this time all the areas !are non intersecting, so !we can simply glue them AGLUE,ALL !compressing numbering !to avoid hole in the numbering of areas NUMCMP,AREA Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

  8. Defining materials !selecting air areas ASEL,S,,,3,4 !assign material constant 1 !to areas 3 and 4 AATT,1 !selecting Si areas ASEL,S,,,1,2 !assign material constant 2 !to areas 1 and 2 AATT,2 !with the GUI verify the materials: !PlotCtrls -> Numbering -> Elem -> Material Numbers Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

  9. Meshing !we have to select the line that represent the microstrip: !1) with Numbering we can see directly the line number, or better: !2) selection lines having y=1 LSEL,S,LOC,Y,1 !then reselect lines having x=0.25 LSEL,R,LOC,X,.25 !in this second way is more parametric !size of the mesh over the line: !the line will be divided in 8 lines LESIZE,ALL,,,8 !size of the mesh for all domain SMRTSIZE,3 !mesh shape triangular MSHAPE,1 !mesh all areas AMESH,ALL Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

  10. Boundary conditions !select stripline nodes NSEL,S,LOC,Y,1 NSEL,R,LOC,X,0,.5 !attribute voltage V1 to !this lines nodes D,ALL,VOLT,V1 !shield boundary conditions NSEL,S,LOC,Y,0 NSEL,A,LOC,Y,10 NSEL,A,LOC,X,5 D,ALL,VOLT,V0 !if lines are not straight, to select nodes over a line we !can use command NSLL (gives all the nodes over a give line) V2 V1 Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

  11. Solution task !convert all dimensions in meters ARSCALE,ALL,,,.01,.01,0,,0,1 FINISH !end preprocessing /prep7 /SOLUTION !start solution task SOLVE !solve FINISH !end solution task !see “help plane121” if you have to impose a charge Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

  12. Postprocessing task /POST1 !start postprocessing task PLNSOL,VOLT !plot the electric scalar potential field V !build some tables with the components of electric field E: !syntax: ETABLE, Label, Item, Comp !in our case Item is EF (electrical field) !and components x or y ETABLE,EFX,EF,X ETABLE,EFY,EF,Y !and plot the !vector field E: PLVECT,EFX,EFY Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

  13. Calculate C !We’ll use the energy: We=0.5*C*V^2 (*) !build another table with all the We: !SENE is electrostatic energy ETABLE,SENE,SENE !sum the energy element by summing up rows of the element table SSUM !assign to W the total electrostatic energy *GET,W,SSUM,,ITEM,SENE !calculate C: C=(W*2)/((V1-V0)**2)!use formula (*): C=((C*2)*1E12)!multiply by 2 because of the symmetry *STATUS,C!display the value of C Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

  14. Example 2 All the measures are in micron: a=100 !radius of the conductors d=400 !distance from the conductors ro=800 !radius of the “infinity” Due to the symmetry we model only half of the domain. Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

  15. Preprocessing task /prep7 /title,Calcolo della capacit\`a tra due cilindri a=100 d=400 ro=800 !we’ll use two ET: et,1,plane121 !et1=plane121 et,2,infin110,1,1 !et2=for 2d unbounded field problem !,1,1 are the KEYOPT: !first for PERX=PERY, !second for second order elements. !scaling material parameters to use microns emunit,epzro,8.854e-6 mp,perx,1,1 !setting epsilonr for air Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

  16. Building geometry !drawing 3 cylinders cyl4,d/2,d/2,a, 0 cyl4, 0, 0,ro, 0,,90 cyl4, 0, 0,2*ro,0,,90 !area overlap to find !intersections aovlap,all !compression in the !numbering numcmp,area !Syntax for cyl4: !CYL4, XCENTER, YCENTER, RAD1, THETA1, RAD2, THETA2, DEPTH Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

  17. Meshing smrtsiz,4 mshape,1 !tri mesh amesh,3 !mesh the air !impose only 1 element in !the layer of infinity region lsel,s,loc,x,1.5*ro lsel,a,loc,y,1.5*ro lesize,all,,,1 type,2 !assign material type 2 mshape,0 !quadrangular mesh mshkey,1 !mapped mesh amesh,2 !mesh infinity region !we don’t have to mesh inside the conductors !because they are equipotentials Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

  18. Building all model !we construct all the model: arsymm,x,all !merging the entities nummrg,node nummrg,kpoi !why? Because we want to use a macro called CMATRIX to !calculate the capacitance, but in this case we need both !conductors Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

  19. Boundary conditions !condition for nodes at infinity csys,1!switch to cylindrial system of coordinates nsel,s,loc,x,2*ro!select the nodes sf,all,inf!apply condition !Surface Charge Density/Infinite Surface=CHRGS/INF !conductor nodes: local,11,1,d/2,d/2 !define a cylindrical coordinate system (1), !with center in (d/2,d/2) and label 11. nsel,s,loc,x,a !select surface nodes of first conductor cm,cond1,node !group nodes in a component called “cond1” local,12,1,-d/2,d/2 nsel,s,loc,x,a cm,cond2,node csys,0 !back to Cartesian coordinate system !conducting plate nsel,s,loc,y,0 cm,cond3,node allsel,all !selecting all elements Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

  20. Solution task Finish !finish preprocessing task /solu !start solution task !call macro cmatrix !------------------ !syntax: CMATRIX, SYMFAC, Condname, NUMCOND, GRNDKEY, Capname cmatrix,1,'cond',3,0 Finish !finish solution task Specogna Ruben – ANSYS TutorialLecture 2 – Electrostatic Problems

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