Nicolson-Ross-Weir Method Research Articles

An improved NRW method to extract electromagnetic parameters of metamaterials

ABSTRACTIn this article, an improved Nicolson–Ross–Weir (NRW) method has been developed to accurately retrieve electromagnetic parameters of metamaterials. By solving roots of higher degree for transmission term and applying first‐order approximation of Taylor's series to the resultant term, the accuracy of the proposed NRW method can be greatly improved. Combined with Kramers–Kronig (K‐K) relationship, the developed method can correctly solve the branch of the refractive index caused by complex exponential function and thus the proposed method is free from the limitation of the electric thickness of the measured materials. Numerical results including a single slab of fishnet structure and three slabs of wires and split‐ring resonators are given to show accuracy and efficiency of the proposed method. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:647–652, 2016

Enhanced electromagnetic shielding behavior of multi-walled carbon nanotube entrenched poly (3,4-ethylenedioxythiophene) nanocomposites

Exceptionally high electromagnetic shielding behavior shown by composites of poly (3,4-ethylenedioxythiophene)/multi-walled carbon nanotube (PCNT) which showed maximum shielding attenuation of 58 dB in the Ku-band. The electron micrographs confirm the wrapping of poly (3,4-ethylenedioxthiophene) (PEDOT) over multiwalled carbon nanotubes (MWCNTs) resulting in strong interfacial, electronic and space charge polarizations. The EMI shielding results showed that shielding by PCNT composites are mainly due to shielding effectiveness by absorption rather than shielding attenuation by reflection. Complex permittivity and permeability of composites have been calculated using scattering parameters (S11 and S21) based on theoretical calculations given in the Nicolson–Ross–Weir method. The composites were further characterized by Raman spectroscopy, TGA, XRD, and FTIR.

Impact of ZnO substitution on magnetic response and microwave absorption capability of strontium-natural nanoferrites

Ferrite being a compound derived from iron oxides including magnetite and hematite possesses similar properties as ceramics which are hard and brittle. Certainly, the mounting demand for electronics has been a major factor driving the exponential growth of ferrite based materials. ZnO doped strontium-natural nanoferrites of composition (80−x)Fe2O3:xZnO:20SrCO3, where x=0, 10, 20mol% are synthesized and sintered via the solid state reaction scheme. Samples are characterized by SEM, XRD, VSM, and VNA measurements to determine the impact of ZnO contents’ variation on the surface morphology, structure, magnetic and microwave absorption properties. The Nicolson–Ross–Weir method is applied to evaluate samples’ reflection loss. The average grain size of the strontium ferrite is found to reduce with the increase in ZnO concentration. Materials sintered at 1100°C without ZnO incorporation are composed of hexagonal SrFe12O19. Meanwhile, the addition of ZnO produces cubic ZnFe2O4 and SrFeO2 phases. Insertion of ZnO results in reduction of magnetic parameters and reflection loss. Furthermore, the anisotropy magnetic field of strontium natural ferrites displays a rapid drop from 350kA/m to 79.6kA/m with the increase in ZnO. Strontium ferrite containing 20mol% of ZnO exhibits superior microwave absorption with reflection loss within −45dB to −55.94dB in the frequency range of 7–13GHz. This facilely synthesized a new class of materials which is believed to be economically promising for microwave absorption applications in the GHz range.

Retrieval of Effective Parameters of Subwavelength Periodic Photonic Structures

We revisit the standard Nicolson–Ross–Weir method of effective permittivity and permeability restoration of photonic structures for the case of subwavelength metal-dielectric multilayers. We show that the direct application of the standard method yields a false zero-epsilon point and an associated spurious permeability resonance. We show how this artifact can be worked around by the use of the cycle shift operator to the periodic multilayer in question.

Simple procedure for robust and accurate complex permittivity measurements of low-loss materials over a broad frequency band

In this research paper, we propose a simple procedure for accurate, stable and broadband measurements of complex permittivity of low-loss dielectric samples with considerable lengths. We identify and demonstrate by numerical and analytical analyses the main ill-behaved factor that gives rise to inaccurate peaks for measurements of electrical properties of low-loss samples in the well-known Nicolson–Ross–Weir method. Without using this factor in the expressions and combining better features of the methods available in the literature, the proposed procedure allows highly accurate permittivity measurements over a broad band. We have validated the proposed method by permittivity measurements of a low-loss sample by different methods.

13-28GHz 대역에서 다양한 매질의 유전율 측정

Abstract This paper presents the results of permittivities of various materials by measurements of the dielectric properties for the materials in millimeter-wave band. Since the advantages of millimeter wave band include the miniaturization, weight reduction of component and a lot of information transfer, its study has received increasing attention of researches. Also, because of the characteristics of the band have the superior straightness and the small diffractive, in the band, the analysis for the reflection and transmission characteristics of the materials will be very important. Moreover, a low interference is one of characteristics of the band due to the fact that the millimeter wave is absorbed in the materials. Therefore, in this paper, the reflection and transmission characteristics of materials are measured in the band by using the free space method. Based on the presented result, the permittivities of the materials are derived by the calculation of Nicolson-Ross Weir method.

Effective Electromagnetic Parameters of Metamaterial Transmission Line Loaded With Asymmetric Unit Cells

In this paper, we propose the generalized extraction procedure for retrieval of the effective constitutive parameters for a metamaterial transmission line loaded with asymmetric unit cells. The asymmetric unit cell is replaced with a transmission line immersed in equivalent bianisotropic medium described by effective parameters e, μ, and Zc, and bianisotropic parameters u and η. The proposed retrieval procedure is applied to novel dual-band unit cells and compared with the standard Nicolson-Ross-Weir (NRW) method that is originally developed for the symmetric unit cell and then extended to the asymmetric one using the averaged value of reflection coefficients. It has been shown that, in case of pronounced asymmetry, the NRW method gives only the exact value of refraction, but effective permittivity and permeability are considerably different from the exact values since they are calculated by means of the approximate value of characteristic impedance.

Composite material made of plasmonic nanoshells with quantum dot cores: loss-compensation and ε-near-zero physical properties

A theoretical investigation of loss-compensation capabilities in composite materials made of plasmonic nanoshells is carried out by considering quantum dots (QDs) as the nanoshells’ cores. The QD and metal permittivities are modeled according to published experimental data. We determine the modes with real or complex wavenumber able to propagate in a 3D periodic lattice of nanoshells. Mode analysis is also used to assess that only one propagating mode is dominant in the composite material whose optical properties can hence be described via homogenization theory. Therefore, the material effective permittivity is found by comparing different techniques: (i) the mentioned mode analysis, (ii) Maxwell Garnett mixing rule and (iii) the Nicolson–Ross–Weir method based on transmission and reflection when considering a metamaterial of finite thickness. The three methods are in excellent agreement, because the nanoshells considered in this paper are very subwavelength, thus justifying the parameter homogenization. We show that QDs are able to provide loss-compensated ε-near-zero metamaterials and also loss-compensated metamaterials with large negative values of permittivity. Besides compensating for losses, the strong gain via QD can provide optical amplification with particular choices of the nanoshell and lattice dimensions.