Low density artificial microwave magnetic composites

The high frequency permeability of composites made of hollow conducting planes or tubes is derived. It is shown that such composites may exhibit permeability levels significantly different from unity, even for nonmagnetic metal volume fractions lower than 1%. This behavior is related to the skin effect, but it can occur for metal shell thicknesses much lower than the skin depth. The influence of the shape of the hollow inclusion on the permeability is reported. The maximum of the imaginary permeability can be tuned over a wide frequency range by adjusting the conductivity of the metal and the characteristic dimensions of the inclusions. The properties of composites made of hollow ferromagnetic planes are also investigated using experimental values obtained from materials made of ferromagnetic laminations. (C) 1999 American Institute of Physics. [S0021-8979(99)29008-1].