Articles you may be interested inUsing multi-walled carbon nanotubes in spark plasma sintered Pb(Zr0.47Ti0.53)O3 ceramics for tailoring dielectric and tunability properties

The dielectric properties of xNiFe2O4-(1−x)Pb0.988(Zr0.52Ti0.48)0.976Nb0.024O3 ceramic composites with different volume filling factors (x = 2, 5, 10, 20, 30, 40, 50, 60, 70 wt. %) prepared by sol-gel method have been investigated in the frequency range (106 ÷ 109) Hz. A reducing effective permittivity with increasing the ferrite amount was observed as result of the “sum property.” The experimental results have been compared with the effective permittivity values predicted by effective medium approximation (EMA) models and finite element method (FEM) calculations. The comparison was aimed to evaluate the appropriateness of the results of the two approaches in describing the effective dielectric properties of the composite with contrasting permittivities and to understand the role of microstructural characteristics on the dielectric response in a broad filling factor range. The best description of the experimental data in overall filling factor range is given by the results of FEM calculations which used realistic microstructures and among the EMA models, by the Lichtenecker's formula.

Experimental evidence of left-handed properties of the Fe-, CoFe-, and Co-based glass-covered amorphous microwires in free standing systems is demonstrated. A new broadband frequency shielding metastructure with selective transmission frequency in the microwave range is presented. The X-band microwave-guide and the free-space methods were used as experimental techniques in the frequency range from 1 to 12 GHz. The X-band experimental results show that the mixed metastructure presents left-handed behavior between 8.5 and 10.5 GHz. The mixed metastructure for large areas presents broadband frequency domains, with left-handed properties between 6.5 and 10.5 GHz (the sum of intrinsic ferromagnetic and antiferromagnetic resonance frequencies domains of individual microwires) and a transmission window between 7.6 and 10.5 GHz. Double negative characteristics of the metastructures are in agreement with the computed results calculated based on Landau–Lifshitz–Gilbert equations and Nicolson-Ross-Weir analytical method.

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Motivated by the spate of recent experimental and theoretical interest in effective dielectric properties of composite materials, we consider randomised scalable checkerboard geometries. Earlier calculations of their effective permittivity are subject to various numerical difficulties which give rise to significant errors, especially for high permittivity contrast ratio between the phases. We describe a numerical protocol for estimating the permittivity with attention to its application in the analysis of randomization of phases and scaling. We apply this protocol to different N × N checkerboard geometries and provide explicit calculations of the effective permittivity and field average. We also discuss, in detail, the influence that topological defects, i.e., phase contacts at corners, have on the effective dielectric properties. The associated statistics of the permittivity for the half-filling case is Gaussian for small permittivity ratios. Our results support the suggestion that the deviation function for the half filling case obeys a power-law scaling with N due to finite-size effects as we let the length scale of the stochastic inhomogeneities approach zero. We show how these results are generic for two-color random checkerboards. We argue that the effect of spatial fluctuations of permittivity is weak as N is increased. We also discuss the potential, the challenges, and the limitations of these calculations.