Musa Bute

Microwave method for reference-plane-invariant and thickness-independent permittivity determination of liquid materials.

An attractive transmission-reflection method based on reference-plane invariant and thickness-independent expressions has been proposed for accurate and unique retrieval of complex permittivity of dielectric liquid samples. The method uses both branch-index-independent expressions and a restricted solution set for determining unique and fast complex permittivities. A 2D graphical method has been applied to demonstrate the operation and validation of the proposed method. A uncertainty analysis has been performed to monitor how the accuracy of the proposed method can be improved by a correct selection of sample holder properties. Scattering parameter measurements of two tested reference liquids (distilled water and methanol) have been carried out for comparison of various techniques with the proposed one when the reference-planes and sample thickness are not precisely known. We note from the comparison that whereas other techniques are seriously affected by imprecise knowledge of both reference-planes and sample thickness, the proposed method removes this restriction.

Power analysis of multilayer structures composed of conventional materials and bi-anisotropic metamaterial slabs

In this paper, we analyze wave propagation properties (transmitted, reflected, and absorbed powers) of composite multilayer structures consisting of bi-anisotropic metamaterial (MM) slabs and conventional isotropic materials. We also separately investigate the propagation properties of bi-anisotropic MM slabs and conventional materials to better interpret the results. We consider two different bi-anisotropic MM slab structures composed of only split-ring-resonators (SRRs) and composing SRRs and a rod. In the analysis, we apply the well-known transfer matrix method to obtain transmitted, reflected, and absorbed powers of the composite structures. From the analysis, we note the following three important results. First, while the transmitted powers from forward and backward directions of the multilayer structure are identical (reciprocal feature), reflected (and absorbed) powers from forward and backward directions of the multilayer structure are different. This difference arises from reflection asymmetric nature of the bi-anisotropic MM slabs. Second, whereas the conventional material loss influences propagation characteristics aside resonance frequencies of bi-anisotropic MM slabs, bi-anisotropic MM loss worsens propagation properties of the multilayer structure at resonance frequencies of these slabs. Third, variations in (or determination of) electromagnetic properties of low-loss thin conventional materials in between two bi-anisotropic MM slabs can be realized at frequencies in which conventional materials demonstrate thickness-resonance effect.

Reference-Plane-Invariant Effective Thickness and Electromagnetic Property Determination of Isotropic Metamaterials Involving Boundary Effects

It is well recognized that near-field effects become dominant when the metamaterial (MM) is in resonance. In addition, any inaccurate information of the location of reference planes, and the effective length can seriously affect the accuracy of retrieved electromagnetic properties of MMs. By considering all these issues, in this research paper, we propose a retrieval method for reference-plane invariant and thickness-independent determination of electromagnetic parameters of MM slabs involving boundary effects. Our method first accomplishes determination of effective length of MMs and calibration-plane factors using scattering parameter measurements, aside the resonance region, of two identical MMs with different lengths. Our method then incorporates near-field effects in accurate retrieval of electromagnetic properties of MMs. The method is verified by scattering parameters simulated for a homogeneous conventional material and a weakly or negligibly coupled inhomogeneous MM slab made by two metallic concentric split-ring-resonators. Consequences of an inaccurate information of reference-plane transformation factors and the value of effective lengths and of noninclusion of near field effects on the retrieved electromagnetic properties are thoroughly discussed by way of few examples to substantiate the accuracy of the proposed method.

Determination of constitutive parameters of homogeneous metamaterial slabs by a novel calibration-independent method

A calibration-independent line-line method for broadband and simultaneous constitutive parameters determination of homogeneous metamaterial (MM) slabs is proposed. It is shown that the sufficient condition for parameters retrieval by the proposed method is to measure uncalibrated (raw) complex scattering parameters of measurement cells (different air regions in free-space) which are completely and partially loaded by the two identical metamaterial slabs. The stability of derived equations for different measurement uncertainty cases is analyzed. We have validated the proposed method by using simulated scattering parameters of a MM slab with split-ring-resonators and then by comparing the extracted electromagnetic parameters with those of a general method used in the literature in the cases with and without a small offset in reference-plane positions (as well as other measurement errors). From this comparison, we note that while the general method does not eliminate those errors, the proposed method not onl...

Boundary Effects on the Determination of Electromagnetic Properties of Bianisotropic Metamaterials From Scattering Parameters

A retrieval method is proposed for determination of electromagnetic properties of bianisotropic metamaterial (MM) slabs involving boundary effects from electric and magnetic surface susceptibilities. To achieve this, we derived two characteristic functions for wave impedances by the application of generalized sheet transition conditions from which electromagnetic constitutive parameters are determined using scattering (S-) parameters of a pair of slabs with different lengths. We applied our method for extraction of electromagnetic parameters of an Ω-shaped MM slab. From our analysis, we noted the following main results. First, when compared with other methods that do not consider boundary effects, we noted that our method retrieves reference-plane-invariant and thickness-independent electromagnetic properties provided that higher order wave interactions at interfaces are negligible when considering two separate pairs of MM slabs differing by the same length and when the accuracy of simulations (meshing size) is improved. Second, extracted constitutive parameters are in good agreement with the locality conditions over which our model is constructed. Third, extracted electric surface susceptibilities at interfaces are correspondingly greater than magnetic surface susceptibilities due to strong electric resonance of the Ω-shaped MM slab.

Constitutive parameters determination of bi-anisotropic metamaterials using a waveguide method

A retrieval method is proposed for determination of electromagnetic properties of bi-anisotropic metamaterial (MM) slabs inserted in a waveguide. For this goal, forward and backward reflection and transmission scattering (S-) parameters of a configuration where the slab is positioned into a waveguide are first derived and then a procedure for extraction of electromagnetic properties of this slab is presented. We performed full-wave electromagnetic simulations on the bi-anisotropic MM slab with split-ring-resonators to validate the proposed method.

Calibration-free extraction of constitutive parameters of magnetically coupled anisotropic metamaterials using waveguide measurements

A calibration-free method for extraction of electromagnetic properties of magnetically coupled anisotropic biaxial metamaterial (MM) slabs from waveguide measurements is proposed. It relies on three measurement steps (thru, empty line, and the same line arbitrarily loaded by the MM slab) to extract electromagnetic properties. It is evaluated against another calibration-dependent method for retrieval of electromagnetic properties of a MM slab constructed by C-shaped resonators. From evaluation analysis, we note that our method, as compared to the calibration-dependent method, not only accurately extracts electromagnetic properties without requiring the use of expensive calibration standards but also is reference-invariant.

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.

New approaches for enhancements on transmission of electromagnetic signals

In this study, frequently encountered unwanted parasitic or noise signals during the transmission of electromagnetic signals are tried to be reduced by a new approach is proposed. By this method, the mentioned noise effect between the near transmitter-receiver or two reciprocal antennas, is aimed to be eliminated. In this context, to provide more healthier data transfer between the transmitter and receiver, metamaterial absorber has been designed to eliminate this noise signals and also designs were supported by the CST which is a powerful simulation program.

Retrieval parameters of chiral metamaterials with proposed crescent shaped split ring resonators

We propose a new uniaxial chiral metamaterial which is composed of four crescent shaped split-ring resonators mutually twisted by 90° and patterned on opposite sides of a dielectric substrate. It illustrates a strong optical activity and circular dichroism in the range from 5 GHz to 10 GHz. The presented design can be fabricated more easily due to its efficient metallic structures. Furthermore, chirality value of this proposed chiral metamaterial is large enough the optical applications. This study also shows that the proposed crescent shaped chiral metamaterials have good responses when compared with other studied samples in literature. All validations are performed by computer simulation program CST Microwave Studio in the 5–10 GHz frequency range.