Incident electric field attenuation near a metallic plate

[Bobymayor]

Hello everybody,

I was visualizing the electric field radiation pattern of an antenna in a 3D EM simulation software (CST), and to see it with my eyes made me realize something I probably heard during my studies but forgot. What is the phenomenon behind what you can see below, which is the E-field attenuation when it is near a metallic plate (in the middle, side view), while the E-field is propagating from right to left ?

I believe it is related to charges inside the metal that radiates an E-field all around the surface, opposite to incident E-field ?

Thanks !

 

[tech99]

That is correct. The metal is a conductor, so there can be no E-field at its surface. This means that all the energy is reflected and the phase of the reflected E-field is opposing the incident field. Another way to look at is that the electrons at the surface of the metal move in response to the incident E-field and, as per Newton, exert a force of reaction against it. The incident E-field does work against this force. The force is created by the static E-field lines of the electrons being bent due to the acceleration, and the direction of the radiated, tangential component is opposite to the incident field.
Notice that if the plate is smaller than half a wavelength, its effect on the incident field is very small.

 

[Bobymayor]

Thank you for your answer ! I will continue to dig into this, I only found courses introducing this behavior but for electrostatic case, which I guess is necessary to understand the dynamic case.