Transcript xfdtd

Tutorial for
XFDTD
Written by Cynthia Furse
University of Utah
XFDTD
• 3D Finite Difference Time Domain code
• Written by Remcom, Inc.
• http://www.remcom.com
To start XFDTD in the CADE Lab
• type 'xfdtd53' in a shell.
* Suggestion: First open the folder where you want your XFDTD file in.
Geometry File
XFDTD uses two file types for any simulation. The Geometry file contains information about grid
spacing and size, material types, and the location of objects in the grid. Its
extension is ".id". The other file type is the fdtd file. This file contains all simulation
paramenters, including the location of sources, number of timesteps, and data to be saved
during the simulation.
To run a simulation, a Geometry file has to be created. After the Geometry file has been
saved, an fdtd file needs to be created. The fdtd file automatically references the geometry
file that was open when it is created. After the fdtd file is created and saved, calcfdtd
can be run. The data will be stored in the directory that xfdtd was opened in. After the
simulation run is complete, the fdtd file needs to be reloaded into xfdtd for data to be
viewed and plotted.
This is what the XFDTD Window
Looks Like
To Create an New Geometry:
Define the FDTD Grid
Cell Size
Total Space (model
plus surrounding air)
This means you
will be defining the
materials at the
locations of the E
field components
View the Grid.
This will show you the grid.
So far it contains only air.
Location of your cursor
Orientation.
You are
viewing the
xy-plane.
Zoom Factor
Where in the
plane.(layer#)
To change the plane you are
viewing:
ZY plane
XY plane
ZX plane
3D view
Edit the Menu of Electrical
Material Parameters
Add Electrical Materials
Double select ADD
Then, choose Next
Available or
Choose Color
* Disabled “Num Lock” in your computer keyboard, if double click cannot process.
Edit Electrical Properties of the
Materials to be in your model
s
Enter your material e r
Material 0=air
Material 1 =
PEC (metal)
Lookup the material
properties for your
material.
Only needed when computing SAR
Edit the Color for Your Material
If you click Choose Color instead of Next Available:
Display the Edit Panel to Draw or
Edit your Model
Here are Several Model Elements
Choose Material
Blocks of Plate and Cube
Types of SingleCell Models
Wire Plate Cube
Build Layers above or below
Start to Define Your Geometry
Choose Material
The Library has Other Elements
Let’s Start with a Single-Cell “Wire” made of
Material 2, What I Named Substrate
Electric Grid Lines Represent
Each Ex,Ey,Ez Component…
(The Grid has also been Zoomed)
This means the
Ex component
is “in” material
2 (but the Ey,Ez
components are
in material
0=air)
Each Cell has
Ex, Ey, Ez
components
Ez is in
Material 2
Ey is in
Material 2
Ey
Ez Ex
See How a Cube of Material is
Defined in this layer:
Ez
Ex
Ey
Ey
Ez
Ez
Ex
Ez
And in the Layer Above it
No Ez’s
Ex
Ey
Ey
Ex
* To erase or undo, use Free Space in Electrical Materials to cover.
Draw the Teflon Box for Patch
Antenna on Slice 25
Alternatively we
could have used
rectangular box
in the library.
Hold Middle
Mouse Button
to Drag, Click
Left Button to
Build.
Add Another Layer
Slice 26
* Or in Geometry Editing Tools, add number of layers in Additional Layers for above or below levels.
And Another Layer
Slice27
The Top is Slice 28
But we want the top of the patch antenna
to be metal, so choose the plate element
PEC
Add a plate to the bottom, too.
Slice 25
(We used the plate
instead the cube to
draw layers of PEC,
therefore, it’s on the
same layer with
Taflon)
Look at this “sandwich” in the yz
and xz planes
If the plates and
boxes aren’t lined
up correctly, fix
them
We want to add a feedpoint to the center
of the patch. Use the cursor to find
where this is.
(27,23,28)
Look at the feed location
(Make sure that’s your
feedpoint when you put
your cursor at your feed
Location)
View-XZplane
Y=23
Use Single Cell Wire (PEC) from
Edit Panel
Use these wires to connect top to
bottom plate, leaving one cell gap
for voltage feed source
2 single-cell
wires in the
z (vertical)
direction
gap
Find the Location of the Feed
Point Gap with the Cursor
The location
to put your
source need to
be one grid
below the
feedpoint
because the
source take
one grid
space. We put
our cursor at
the gap.
(27,23,27)
Save Your Geometry
• Now you have
created your
geometry file
• You have
found where to
put your
source
• Save your
geometry as
~.id file
Types of Simulations
Steady State
Steady state simulations use the sinusoid source found in the FDTD - Run
Paramenters - Voltage Source menu. This is very useful to determine exact parameters of an
object at the specified input frequency. This includes SAR values, efficiency, radiation
patterns, and input impedance. Many of these values can be found by simply looking at the
Steady State Option in the Plot menu.
Transient
Transient simulations are excellent for determining the general paramaters of an antenna over
a range of frequencies. Transient simulations use a gaussian pulse, or one of its variations
as a source. By running a transient simulation. One can easily determine the input
impedance over a large frequency range. This allows you to find the resonant frequency
of an antenna, and gives you the information needed to make changes to your design.
Transient Simulation:
Open Voltage Sources Panel
Choose a Source and “Add Port
to List”. You may have several
They Can be
sources.
edit in “Set
Waveform”
This is your
feedpoint
location
If you want to
S-paramters
results
A note on # of Time Steps
For steady state simulations, enough time steps must be included
to reach steady state conditions. Otherwise, the results will be
invalid. To determine if convergence has been reached. Store
near zone values. Look at the near zone values to determine if
Steady State has been reached.
For transient simulation, more time steps will allow larger FFT
transforms. This will give plots more data points, giving smoother
graphs.
Close the Source Window, and Reopen It to
see the source location on your grid.
The source
location will
only show
when the
source
window is
open.
Define what you want FDTD to
save after calculation
These are
available for
pulsed FDTD
Other values
of interest are
available for
sine wave source
only
Save your geometry again
Save FDTD Parameters as a .fdtd
file
Run FDTD
This is what is displayed
Start simulation
If you want to see EM fields,
select yes, and you will be impressed
Simulation Starts
XY Plane of EM Field
You can
change the
Plane and view
fields in
Different
direction
Display Results
•When Simulation is Finished, Reopen the
.fdtd file again, then display the result.
Simulation S-parameters Results
Then Click
First Click
You can edit your plot parameters here
S11 Response
You can see the resonance frequency of
this antenna is around 1.1GHz
Impedance Measurements
Real Impedance Response
Steady State Simulation
*
First to find out what frequency your antenna operates at, then add the source.
Steady State Simulation
Edit by clicking
“Set Waveform”
Radiation Pattern (E-field) Set Up
Run FDTD
Display Steady State Data
Steady State Data
Radiation Pattern
Radiation Plot Setup
Display Plot
Plot Setup
Change to Polar Plot Format
Change to Polar Plot Format
Radiation Pattern
End of Tutorial