TAILORING THE MICROWAVE PERMITTIVITY AND PERMEABILITY OF COMPOSITE-MATERIALS

The microwave permittivity (epsilon(r)) and permeability (mu(r)) of co mposite materials are tailored by adding various loading agents to a h ost plastic and are subsequently modeled using the Maxwell Garnett the ory and second order polynomials. With the addition of manganese zinc ferrite, strontium ferrite, nickel zinc ferrite, barium tetratitanate and graphite powders, materials with values of epsilon', e '', mu', mu '' as high as 22, 5, 2.5 and 1.7 have been obtained. Permittivity and permeability data are calculated at 2.0245 GHz from reflection and tr ansmission measurements performed in a 7 mm coaxial test line. The Max well Garnett (MG) theory successfully models epsilon(r) if the filling factor is less than 0.30 and ratio /epsilon(1)/ (host)/ /epsilon(2)/ (powder) is greater than 0.04. As this ratio decreases, the MG theory is shown to be independent of epsilon(2) and second order polynomials are used to effectively model the dielectric constant. Polynomials are also used for the ferrite composites because it was determined that t he MG theory was unable to model mu(r). This deficiency is attributed to the difference of domain structures that exist in powdered and sint ered ferrites.