This java applet demonstrates electromagnetic waves in a 3-d rectangular waveguide.

At the top of the applet on the left you will see the waveguide with a wave moving in the positive z direction. The color green means that an electric field component is present and is pointing in the positive or negative y direction.

The guide is being driven with a single driving frequency, but various normal modes may be present. Each one is operating at the same frequency, but the phase velocity will generally be different for different modes. Below the guide you will see two grids showing each normal mode's contribution to the wave pattern in the guide. The TE modes (transverse electric modes; modes with the electric field vector perpendicular to the z axis) are shown on top and TM modes (transverse magnetic modes; modes with the magnetic field vector perpendicular to the z axis) are shown on the bottom. Move the mouse over a grid square to see what mode it represents.

Each element of the grid has a color which indicates the presence or absence of that mode. Black means the mode is not present; green means the mode is present with a positive coefficient, and red means it is present with a negative coefficient. In addition, each mode may have a phase shift, which indicates that its oscillatory cycle leads or lags others with the same phase velocity. This is indicated by a vertical blue line.

A phase shift is normally hard to detect. If the applet is stopped, then by altering the phase of a mode you can see the mode oscillate. If the applet is running it is harder to tell, unless the mode is combined with some other mode; in that case, the phase will affect the interference pattern between the two modes.

Also, some modes may be crossed out with a diagonal line. This means the driving frequency is not high enough to drive that mode. Adjusting the Driving Frequency slider will allow that mode to be activated.

You can add or remove a mode by clicking on it. If you click and drag up and down you can fine-tune the magnitude of the mode. If you drag left and right you can alter the phase shift.

Double-clicking on a mode will clear all other modes and just set that one.

For performance reasons, only 10 modes can be active at a time.

The Show Electric Field popup will let you select which field is shown: the electric field, the magnetic field, or both. You can also view the currents or charge in the walls.

The Show Field popup controls how the field is displayed. The choices are:

• Show Field (tri-color) shows the x component of the field as red, y as green, and z as blue. The sign of the field component isn't indicated.
• Show Field X shows the x component of the field as green if it's positive and red if it's negative. The other components aren't shown. If the field has no x component then the display is blank.
• Show Field Y shows the y component of the field as green if it's positive and red if it's negative.
• Show Field Z shows the z component of the field as green if it's positive and red if it's negative.
• Show Field Magnitude shows the magnitude of the field vector in green. The direction of the field is not indicated.
• Show Field Vectors shows little field vectors indicating the magnitude and direction of the field. As the field gets stronger, the vectors turn from black (weakest) to green to white (strongest). The number of vectors shown can be controlled with the Vector Density slider.
• Show Particles on Field Lines shows a bunch of particles moving in the direction of the field lines. They move faster where the field is stronger. Note that the particles are only a educational device intended to show the shape of the field lines; in real life, particles would not move in this manner.

The Show Field popup also controls how you can view the current; in that case, think "current vector" when you see "field" in the above directions. There is only one way to view the charge, however; green means positive charge and red means negative.

The Slice popup allows you to look at planar slices of the guide rather than looking at the contents of the entire guide. If the popup is set to No Slicing, you view the entire guide. Otherwise you will see the guide sliced in one of three directions. The location of the slice can be adjusted by dragging the line running along the sides of guide near the slice.

The Mouse popup controls what happens when you click on the guide. If you set it to Adjust Angle or Adjust Zoom, you can adjust the orientation or size of the 3-d view by clicking and dragging on the guide.

The Stopped checkbox can be used to stop the applet for a moment.

The Stop Oscillation checkbox can be used to stop the oscillation for a moment; this is useful when "Show Particles" is selected. The particles keep moving, to illustrate the field lines, but the oscillation of the electric and magnetic fields stops so the field lines are easier to follow.

The Show Sides checkbox shows the field on the sides of the guide rather than inside.

The Alternate Rendering checkbox is used to speed up rendering, but it actually slows things down on some machines. Also for large windows and low resolutions it is usually slower. (Internally, it uses the MemoryImageSource class instead of drawing a bunch of rectangles.)

The Oscillation Speed slider controls the speed of oscillation.

The Particle Speed slider controls the speed of the particles.

The Number of Particles slider controls the number of particles.

The Brightness slider can be used just like the brightness on a TV, to brighten dim areas of the guide.

The Image Resolution slider can be used to generate a higher quality image. If you move it to the right, it will increase the resolution of the image, but it will also slow things down, so be careful.

The Width and Height sliders will adjust the width or height of the guide. This changes the phase velocities and cutoff frequencies of each mode.

The Clear button clears all modes.

The Reset Particles button resets the particle positions to some random state.