Tutorial for XFDTD Written by Cynthia Furse Utah State University

XFDTD 3D Finite Difference Time Domain code Written by Remcom, Inc.

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 5 Add path /opt/xfdtd/version5 Multiple user-defined sources Add 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 Factor Where 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=air Material 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 plane or 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 Ez Each 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 Ey Ez

And in the Layer Above it Ex Ey 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 and boxes aren’t lined up 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-cell wires in the z (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 your feedpoint 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 values of interest are available for sine wave source only These are available for pulsed FDTD

Save your geometry

Save FDTD Parameters

Run FDTD

This is what is displayed