|Third Example—Wave normal to reflector, 1 mm wide gap, transverse polarization|
In this example, the plane wave, polarized with the E field in the x direction, enters from top vertical, and strikes the reflecting surface at normal incidence, but in this case the surface has a gap which is 1mm wide in the x direction and infinitely long in the y direction (out of the page), and infinitely deep in the z direction. The magnitude of the E field is shown. Note that some of the wave incident on the gap excites a TE01 mode in the gap, which carries power downwards in the -z direction. Considered as a waveguide, the gap is infinitely wide in the y direction, and so the cutoff frequency is zero and the wavelength of the TE01 mode in the gap is the same as the free-space wavelength. Not all of the wave incident on the gap can excite this mode, however, and that power is back scattered nearly isotropically. The rms field strength of the incoming wave is 1 V/m.