| In order to approach a shield effect?low reflection and high absorption. At the first, the paper systematically studied the influencing rules of component, granularity and frequency on permeability (μ′, μ″), permitivity (ε′,ε″), impedance (η) and attenuation constant (α) of Ni series and Fe series composites when f<1GHz. Secondly, made an objective evaluation about shielding performance of composites that contained electric materials, ferrite or polymer. A SFGM (Shielding Functionally Gradient Materials) design of shielding materials aiming to low reflection and high absorption was made when f<1GHz, and bright forward a dual-impedance-gradient-layer design modal of SFGM for the first time. This design modal can decrease the reflection and increase the absorption more effectively than that of single-impedance-gradient-layer design. For the dual-impedance-gradient-layer design, the more perfect the impedance gradient materials became, the less reflection there was, and that, the reflection would be zero eventually. The dual-impedance-gradient-layer design gave a new method for solving the question about low reflection and high absorption. When f<1GHz, "Component?shielding performance"dual-direction CAD of shielding materials was put forward and completed in the paper. This CAD method could overcome the shortage of "electromagnetic parameter?shielding performance"CAD method, and be used to evaluate the material's shield effect and guide the design of shielding materials. At the last, we exploringly put forward a method for qualitative evaluation of materials'reflection when f<1GHz, and the result that dual-impedance-gradient-layer design can decrease reflection effectively was validated by experiments.
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