  Ni coated SiO2 and SiO2 coated Ni composite particles with core-shell
structures were designed, prepared and their microwave absorption properties
were characterized. The comparison study of the shell effect on the effective
electromagnetic parameters reveals that the effective permittivity/permeability
was crucially determined by the percent and the intrinsic electromagnetic
parameters of the component materials regardless of various core/shell
structures. Both of the composite core-shell structures could have good
microwave absorption properties. Investigation of the input impedance indicates
that, good microwave absorption performances are a consequence of proper
electromagnetic impedance matches when the effective electromagnetic parameters
were modulated.
