To demonstrate the fact that electric fields (unlike gravitational fields) can be shielded, I have taken to showing the effects of a Faraday cage on radio signals. (I wonder how many more years I'll be able to perform this demonstration this way.) I use a transistor radio as my "field detector" and a metal colander and a metal splatter screen as my blockers.
In serendipitous monkeying around, I noticed that FM signals "behave" better for this demonstration than AM signals do.
The FM seems impervious to being placed on the screen or in the colander. But when encapsulated, it virtually drops to nothing.
The AM signal, on the other hand, is sensitive to being placed in the screen or in the colander. But the signal remains intelligible even when the radio is fully encapsulated.
Take a look.
Faraday Cage AM FM