Tutorial: Parallel Plate Waveguide

From openEMS

• Download the latest matlab file using Github: Parallel_Plate_Waveguide.m
• Simulation Time: << 1 min

This tutorial shows the simplest possible simulation setup. We will cover

• the octave script
• visualization of the structure
• openEMS output
• visualization of the result

Refer to the included help inside every octave function to know the meaning of the parameters.

Octave (Matlab) Simulation Script

To start the script within an empty environment, the first lines are:

close all
clear
clc

To specify the FDTD options, we need the FDTD structure:

FDTD = InitFDTD('NrTS',100, 'EndCriteria',0, 'OverSampling',50);
FDTD = SetSinusExcite(FDTD,10e6);
FDTD = SetBoundaryCond(FDTD,{'PMC' 'PMC' 'PEC' 'PEC' 'MUR' 'MUR'});

The first command inititalizes the FDTD data-structure, setting the number of time steps (NrTS) to 100 with an end criteria of 0. The second command specifies a sinusoidal excitation function (in the time domain) with a frequency of 10 MHz. The third command sets the boundary conditions to model a parallel plate (perfect electric conductor at ymin and ymax). The MUR condition absorbs the propagating wave at zmin and zmax.

Next, the CSXCAD geometric library needs to be initialized:

CSX = InitCSX();

To solve for discrete electromagnetic fields, we need to define a mesh. The default units are metres:

mesh.x = -10:10;
mesh.y = -10:10;
mesh.z = -10:30;
CSX = DefineRectGrid(CSX, 1, mesh);

Lets add the source to our parallel plate waveguide (spatial domain):

CSX = AddExcitation(CSX,'excitation',0,[0 1 0]);
CSX = AddBox(CSX,'excitation',0,[-10 -10 0],[10 10 0]);

We need to define what to observe (here a plane where to record the E-field):

CSX = AddDump(CSX,'Et');
CSX = AddBox(CSX,'Et',0,[-10 0 -10],[10 0 30]);

The final task is to write the FDTD and CSX structure into a xml-file:

mkdir('tmp');
WriteOpenEMS('tmp/tmp.xml',FDTD,CSX);

Visualization of the Structure

The defined geometry

To have a look at the geometry we define in the octave script, add:

CSXGeomPlot( 'tmp/tmp.xml' );

After execution of the script, AppCSXCAD will open automatically. The screenshot shows the xy-plane of our computational area. The excitation box (blue) surrounds the area. The dump box is visible as a red line in the center of the screen (it's an xz-plane).

The structure looks good - let's start the simulation.

OpenEMS Simulation

Add

RunOpenEMS('tmp','tmp.xml','');

and start the script again. Close AppCSXCAD and observe the terminal showing the output of openEMS:

 ---------------------------------------------------------------------- 
 | openEMS 64bit -- version v0.0.25-18-gc485f04
 | (C) 2010-2012 Thorsten Liebig <thorsten.liebig@gmx.de>  GPL license
 ---------------------------------------------------------------------- 
	Used external libraries:
		CSXCAD -- Version: v0.2.4-8-g0fb245a
		hdf5   -- Version: 1.8.4
		          compiled against: HDF5 library version: 1.8.4-patch1
		tinyxml -- compiled against: 2.5.3
		fparser
		boost  -- compiled against: 1_46_1
		vtk -- Version: 5.6.1
		       compiled against: 5.6.1
		MPI -- Version: 2.1
		       compiled against: openMPI1.4.3

Create FDTD operator (compressed SSE + multi-threading)
FDTD simulation size: 21x21x41 --> 18081 FDTD cells 
FDTD timestep is: 1.92583e-09 s; Nyquist rate: 25 timesteps @1.03851e+07 Hz
Excitation signal length is: 100 timesteps (1.92583e-07s)
Max. number of timesteps: 100 ( --> 1 * Excitation signal length)
Create FDTD engine (compressed SSE + multi-threading)
Running FDTD engine... this may take a while... grab a cup of coffee?!?
Time for 100 iterations with 18081 cells : 0.21277 sec
Speed: 8.49791 MCells/s 
use Paraview to visualize the FDTD result...

Visualization of the Result

Parallel Plate Waveguide

OpenEMS has created some result files in the tmp folder. Start Paraview to visualize the E-field saved by the dump box definition:

• Choose File/Open and select the "Et_..vtr" file.
• Properties -> Apply
• Object Inspector -> Display -> Color by: E-Field
• Animation -> Play
• Rescale to Data Range occasionally to tune the color mapping
• Hint: You may use paraview-filters to improve the visualisation (e.g. a warp-by-vector filter, be sure to apply this as well).

Animation using a Warp-Filter: parallel_plate_waveguide.mp4

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