I've seen that sometimes frequency selective surfaces are used to load a certain impedance to a certain antenna (for instance for input matching purposes).
These surfaces act like a filter on the equivalent transmission line that describes the radiated wave propagation in the space surrounding the antenna.
In this article an incident electromagnetic plane wave on a frequency selective surface made of a periodic sequence of square metal rings is considered.
The authors say:
When the transverse magnetic field faces the vertical strips, it induces current in the loop. This current leads to a secondary magnetic field around the strips, within which magnetic energy is stored. Thus, the vertical strips have an inductive effect.
Well, there are some things I don't understand:
- How can a time - varying magnetic field induce current in vertical strips and so in the loops? I have always been using the Faraday law in this way: time - varying magnetic flux across a surface => Induced current along the loop that defines that surface.
In this case, the magnetic field does not enter the surfaces of the loops.
Can we say that it's the Electric field of the wave that moves electrons in the vertical strips and causes current to flow?
Next, the article says that the magnetic field surrounds two adjacent vertical strips, like in the following picture:
Is it the magnetic field created by induced currents in the loops?