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Diffstat (limited to 'openEMS/matlab/examples/transmission_lines/MSL.m')
-rw-r--r-- | openEMS/matlab/examples/transmission_lines/MSL.m | 185 |
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diff --git a/openEMS/matlab/examples/transmission_lines/MSL.m b/openEMS/matlab/examples/transmission_lines/MSL.m new file mode 100644 index 0000000..b6ec0b3 --- /dev/null +++ b/openEMS/matlab/examples/transmission_lines/MSL.m @@ -0,0 +1,185 @@ +% +% EXAMPLE / microstrip / MSL +% +% Microstrip line on air "substrate" in z-direction. +% +% This example demonstrates: +% - simple microstrip geometry +% - characteristic impedance +% - material grading function +% - geometric priority concept +% +% +% Tested with +% - Matlab 2009b +% - Octave 3.3.52 +% - openEMS v0.0.14 +% +% (C) 2010 Thorsten Liebig <thorsten.liebig@uni-due.de> + +close all +clear +clc + +%% setup the simulation +physical_constants; +unit = 1e-3; % all length in mm + +% geometry +abs_length = 100; % absorber length +length = 600; +width = 400; +height = 200; +MSL_width = 50; +MSL_height = 10; + +%% prepare simulation folder +Sim_Path = 'tmp'; +Sim_CSX = 'msl.xml'; +[status, message, messageid] = rmdir( Sim_Path, 's' ); % clear previous directory +[status, message, messageid] = mkdir( Sim_Path ); % create empty simulation folder + +%% setup FDTD parameter & excitation function %%%%%%%%%%%%%%%%%%%%%%%%%%%%% +max_timesteps = 2000; +min_decrement = 1e-5; % equivalent to -50 dB +f0 = 2e9; % center frequency +fc = 1e9; % 10 dB corner frequency (in this case 1e9 Hz - 3e9 Hz) +FDTD = InitFDTD( max_timesteps, min_decrement ); +FDTD = SetGaussExcite( FDTD, f0, fc ); +BC = {'PMC' 'PMC' 'PEC' 'PMC' 'PEC' 'PEC'}; +FDTD = SetBoundaryCond( FDTD, BC ); + +%% setup CSXCAD geometry & mesh +% very simple mesh +CSX = InitCSX(); +resolution = c0/(f0+fc)/unit /15; % resolution of lambda/15 +mesh.x = SmoothMeshLines( [-width/2, width/2, -MSL_width/2, MSL_width/2], resolution ); % create smooth lines from fixed lines +mesh.y = SmoothMeshLines( [linspace(0,MSL_height,5) MSL_height+1 height], resolution ); +mesh.z = SmoothMeshLines( [0 length], resolution ); +CSX = DefineRectGrid( CSX, unit, mesh ); + +%% create MSL +% attention! the skin effect is not simulated, because the MSL is +% discretized with only one cell! +CSX = AddMaterial( CSX, 'copper' ); +CSX = SetMaterialProperty( CSX, 'copper', 'Kappa', 56e6 ); +start = [-MSL_width/2, MSL_height, 0]; +stop = [ MSL_width/2, MSL_height+1, length]; +priority = 100; % the geometric priority is set to 100 +CSX = AddBox( CSX, 'copper', priority, start, stop ); + +%% add excitation below the strip +start = [-MSL_width/2, 0 , mesh.z(1)]; +stop = [ MSL_width/2, MSL_height, mesh.z(1)]; +CSX = AddExcitation( CSX, 'excite', 0, [0 -1 0] ); +CSX = AddBox( CSX, 'excite', 0, start, stop ); + +%% fake pml +% this "pml" is a normal material with graded losses +% electric and magnetic losses are related to give low reflection +% for normally incident TEM waves +finalKappa = 1/abs_length^2; +finalSigma = finalKappa*MUE0/EPS0; +CSX = AddMaterial( CSX, 'fakepml' ); +CSX = SetMaterialProperty( CSX, 'fakepml', 'Kappa', finalKappa ); +CSX = SetMaterialProperty( CSX, 'fakepml', 'Sigma', finalSigma ); +CSX = SetMaterialWeight( CSX, 'fakepml', 'Kappa', ['pow(z-' num2str(length-abs_length) ',2)'] ); +CSX = SetMaterialWeight( CSX, 'fakepml', 'Sigma', ['pow(z-' num2str(length-abs_length) ',2)'] ); +start = [mesh.x(1) mesh.y(1) length-abs_length]; +stop = [mesh.x(end) mesh.y(end) length]; +% the geometric priority is set to 0, which is lower than the priority +% of the MSL, thus the MSL (copper) has precendence +priority = 0; +CSX = AddBox( CSX, 'fakepml', priority, start, stop ); + +%% define dump boxes +start = [mesh.x(1), MSL_height/2, mesh.z(1)]; +stop = [mesh.x(end), MSL_height/2, mesh.z(end)]; +CSX = AddDump( CSX, 'Et_', 'DumpMode', 2 ); % cell interpolated +CSX = AddBox( CSX, 'Et_', 0, start, stop ); +CSX = AddDump( CSX, 'Ht_', 'DumpType', 1, 'DumpMode', 2 ); % cell interpolated +CSX = AddBox( CSX, 'Ht_', 0, start, stop ); + +%% define voltage calc box +% voltage calc boxes will automatically snap to the next mesh-line +CSX = AddProbe( CSX, 'ut1', 0 ); +zidx = interp1( mesh.z, 1:numel(mesh.z), length/2, 'nearest' ); +start = [0 MSL_height mesh.z(zidx)]; +stop = [0 0 mesh.z(zidx)]; +CSX = AddBox( CSX, 'ut1', 0, start, stop ); +% add a second voltage probe to compensate space offset between voltage and +% current +CSX = AddProbe( CSX, 'ut2', 0 ); +start = [0 MSL_height mesh.z(zidx+1)]; +stop = [0 0 mesh.z(zidx+1)]; +CSX = AddBox( CSX, 'ut2', 0, start, stop ); + +%% define current calc box +% current calc boxes will automatically snap to the next dual mesh-line +CSX = AddProbe( CSX, 'it1', 1 ); +xidx1 = interp1( mesh.x, 1:numel(mesh.x), -MSL_width/2, 'nearest' ); +xidx2 = interp1( mesh.x, 1:numel(mesh.x), MSL_width/2, 'nearest' ); +xdelta = diff(mesh.x); +yidx1 = interp1( mesh.y, 1:numel(mesh.y), MSL_height, 'nearest' ); +yidx2 = interp1( mesh.y, 1:numel(mesh.y), MSL_height+1, 'nearest' ); +ydelta = diff(mesh.y); +zdelta = diff(mesh.z); +start = [mesh.x(xidx1)-xdelta(xidx1-1)/2, mesh.y(yidx1)-ydelta(yidx1-1)/2, mesh.z(zidx)+zdelta(zidx)/2]; +stop = [mesh.x(xidx2)+xdelta(xidx2)/2, mesh.y(yidx2)+ydelta(yidx2)/2, mesh.z(zidx)+zdelta(zidx)/2]; +CSX = AddBox( CSX, 'it1', 0, start, stop ); + +%% write openEMS compatible xml-file +WriteOpenEMS( [Sim_Path '/' Sim_CSX], FDTD, CSX ); + +%% show the structure +CSXGeomPlot( [Sim_Path '/' Sim_CSX] ); + +%% run openEMS +openEMS_opts = ''; +openEMS_opts = [openEMS_opts ' --engine=fastest']; +% openEMS_opts = [openEMS_opts ' --debug-material']; +% openEMS_opts = [openEMS_opts ' --debug-boxes']; +RunOpenEMS( Sim_Path, Sim_CSX, openEMS_opts ); + +%% postprocess +freq = linspace( f0-fc, f0+fc, 501 ); +U = ReadUI( {'ut1','ut2','et'}, 'tmp/', freq ); % time domain/freq domain voltage +I = ReadUI( 'it1', 'tmp/', freq ); % time domain/freq domain current (half time step offset is corrected) + +% plot time domain voltage +figure +[ax,h1,h2] = plotyy( U.TD{1}.t/1e-9, U.TD{1}.val, U.TD{3}.t/1e-9, U.TD{3}.val ); +set( h1, 'Linewidth', 2 ); +set( h1, 'Color', [1 0 0] ); +set( h2, 'Linewidth', 2 ); +set( h2, 'Color', [0 0 0] ); +grid on +title( 'time domain voltage' ); +xlabel( 'time t / ns' ); +ylabel( ax(1), 'voltage ut1 / V' ); +ylabel( ax(2), 'voltage et / V' ); +% now make the y-axis symmetric to y=0 (align zeros of y1 and y2) +y1 = ylim(ax(1)); +y2 = ylim(ax(2)); +ylim( ax(1), [-max(abs(y1)) max(abs(y1))] ); +ylim( ax(2), [-max(abs(y2)) max(abs(y2))] ); + +% calculate characteristic impedance +% arithmetic mean of ut1 and ut2 -> voltage in the middle of ut1 and ut2 +U = (U.FD{1}.val + U.FD{2}.val) / 2; +Z = U ./ I.FD{1}.val; + +% plot characteristic impedance +figure +plot( freq/1e6, real(Z), 'k-', 'Linewidth', 2 ); +hold on +grid on +plot( freq/1e6, imag(Z), 'r--', 'Linewidth', 2 ); +title( 'characteristic impedance of MSL' ); +xlabel( 'frequency f / MHz' ); +ylabel( 'characteristic impedance Z / Ohm' ); +legend( 'real', 'imag' ); + +%% visualize electric and magnetic fields +% you will find vtk dump files in the simulation folder (tmp/) +% use paraview to visualize them |