Tutorial for XFDTD

Written by Cynthia Furse

Utah State University

XFDTD

• 3D Finite Difference Time Domain code

• Written by Remcom, Inc.

• http://www.remcom.com

To start XFDTD at USU

• Edit your .cshrc file. Add the path/opt/xfdtd

• Type “source .cshrc” to run this file (otherwise you would have to log out/in)

Other versions of XFDTD available:

• Version 5Add path /opt/xfdtd/version5

• Multiple user-defined sourcesAdd path /opt/xfdtd/quicksign

This is what the XFDTD Window Looks Like

To Create an FDTD Grid Space:

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.

Orientation.You are viewing the xy-plane.Slice #Zoom FactorWhere in the plane...

Location of your cursor

To change the plane you are viewing:

Edit the Menu of Electrical Material Parameters

Edit Electrical Properties of the Materials to be in your model

Material 0=airMaterial 1 = PEC (metal)Here Material 2 will be teflon.

r

Display the Edit Panel to Draw or Edit your Model

Here are Several Model Elements

Choose Material

Draw one planeor more simultaneously.

Types of Single-Cell Models

Wire Plate Cube

The Library has Other Elements

Let’s Start with a Single-Cell “Wire” made of Material 2

Ex

Ey

EzEach Cell has Ex, Ey, Ez components

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)

Ez is in Material 2

Ey is in Material 2

See How a Cube of Material is Defined in this layer:

Ex

ExEyEy

Ez

Ez

Ez

Ez

And in the Layer Above it

Ex

Ex

EyEy

No Ez’s

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

And Another

Slice 27

The Top is Slice 28

But we want the top of the patch antenna to be metal, so choose the plate element

and change it to Material 1 (PEC)

Add a plate to the bottom, too.

Slice 24

(Checking the coordinates of the teflon box in layer 25 and repeating them on layer 24 helped draw this plate)

Look at this “sandwich” in the yz and xz planes

If the plates andboxes aren’t linedup correctly, fix them

We want to add a feedpoint to the center. Use the cursor to find

where this is.

(24,28)

Look at the feed location

X=24

View-YZplane

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

3 single-cellwires in thez (vertical)direction

gap

Find the Location of the Feed Point Gap with the Cursor

(24,28,27)

Open Voltage Sources Panel

Choose a Source and “Add Feed to List”. You may have several

sources.

This is yourfeedpoint location

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

Other valuesof interest areavailable forsine wave sourceonly

These areavailable forpulsed FDTD

Save your geometry

Save FDTD Parameters

Run FDTD

This is what is displayed