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This paper presents a class of ultrathin metamaterial screens for microwave reflectivity reduction from metallic surfaces. The screens consist of a highly conductive sheet with periodic patterns on top of a thin grounded lossy substrate. The periodic patterns of the screens are composed of nonuniform patches. It is found that the considered screens exhibit about 60% larger working bandwidth than those with uniform patches. A simple analytical equivalent circuit is also derived for mechanism understanding and quick design for the screens. [ABSTRACT FROM AUTHOR]

Simultaneously high permeability and permittivity results in a pronounced dimensional effect in Mn-Zn ferrite cores, which makes the measured complex permeability differ for cores with different dimensions. This paper provides a succinct method to solve an inverse problem of tracing dimension-independent or intrinsic complex permeability and permittivity for Mn-Zn ferrites using two toroidal and rectangular-cross-sectioned cores with different dimensions. The apparent complex permeability of ferrite cores with other dimensions can then be predicted from the traced intrinsic values, so will the effective impedance of common-mode chokes made of such cores. The traced intrinsic permeability is in good agreement with the measured apparent complex permeability of a very small toroidal ferrite core, in which dimensional effect can be ignored. The apparent complex permeabilities of ferrite cores with other dimensions are measured experimentally, and are also calculated from the determined intrinsic values. A very good agreement between the measured and calculated values is found. [ABSTRACT FROM AUTHOR]

Analysis of the principle of the published lumped circuit methods for determination of the intrinsic complex permeability and permittivity of the Mn-Zn ferrites reveals that as long as the electric and the magnetic field distributions in the core(s) in two measurements are different, the two intrinsic values can be determined. Using this principle, we developed a set of general lumped circuit methods based on a toroidal Mn-Zn ferrite core as the measurement sample. We examined two possible different excitation modes: magnetic field excitation and electric field excitation. The two different excitation modes result in significantly different field distributions in the sample. Thus, high accuracy can be guaranteed in principle. For the magnetic field excitation, we present in this paper a general finite-difference method to solve the fields in the core and the impedance of the ferrite core inductor. To avoid the stray capacitance among the coils of the ferrite core winding inductor in the measurement, we made a set of short-ended coaxial test fixtures. We performed experiments to determine the intrinsic complex permeability and permittivity of a Mn-Zn ferrite core up to 10 MHz by using the two general methods and validated the measured intrinsic values experimentally. [ABSTRACT FROM AUTHOR]