3 Dimensional representation of effect on cavity resonance fields by introduction of absorber

 

Above is a representation of the resonant H fields in an empty cavity.  Cavity dimensions are 3"x5"x0.8".  Note that the field strength is spread throughout the cavity
(image developed using CST Microwave Studio www.cst.com)

This is a representation of the field strength within a cavity with a thin sheet of high permittivity-high permeability absorbent material added along one wall.  Note how the energy resides primarily in the material rather than interfering with circuitry in the cavity.
(image developed using CST Microwave Studio www.cst.com)