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Conventional single-port strip-line techniques to measure permeability of thin films are based on the quasistationary approximation. In this paper, wave phenomena in the measurement cell are taken into account. Particularly, the dielectric response of the sample may be accounted for and removed by the consideration of the geometry of the cell and the sample. An additional measurement with a reference sample with known constitutive parameters allows the directivity error and the frequency response error to be removed from the experimental reflectivity data; accounting for the field inhomogeneity inside the strip cell is also introduced. A proper selection of the reference sample is shown to be critical for the measurement accuracy. The measurement results may also be affected by the demagnetization of the sample. With these corrections introduced, the operating frequency range of the technique is extended up to 8GHz. The measurement results are validated by the data obtained with either standard materials or by conventional techniques.

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The mixing rules for the permittivity and permeability of composites are known to depend greatly on the microscopic structure of the composite. This dependence can be quantified in terms of Bergman’s spectral function. In this paper, the spectral function of actual magnetic composites is reconstructed from their measured microwave constitutive parameters. The samples under study are composed of carbonyl iron or Fe–Cr–Al alloy powders embedded in a paraffin wax matrix. The permittivity and permeability of the samples is measured in the 0.1–10 GHz frequency band. The proposed approach to process the measured data allows the spectral function of the composite and frequency dependence of intrinsic permeability of inclusions to be derived. The obtained results are in agreement with available tabulated data.

Intrinsic permeability of sendust alloys is determined from the measured microwave permittivity and permeability of composites filled with either spherical or flaky sendust powders. The permittivity and permeability measurements are performed applying the coaxial reflection-transmission technique in the 0.05 to 18 GHz frequency range. The effects of the filling factor, inclusion shape, and size on composite constitutive parameters are discussed. The permeability of metal inclusion is retrieved from the measured permeability of composites using a generalized Maxwell Garnett equation that accounts for the percolation threshold. The equation parameters are found by fitting the measured dependence of composite permittivity and permeability on frequency and filling. The inclusion dimensions calculated from the found parameters agree with the results of grain-size analyses. The alloy intrinsic permeability is retrieved from inclusion permeability with the account for skinning. The fitted frequency and damping factor of ferromagnetic resonance depend on the inclusion shape. The calculated reflectivity map of the flake-filled composite shows that sendust powders are promising fillers for interference suppressors and microwave absorbers at frequencies close to 1 GHz.

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