Hasar, Ugur Cem; Kaya, Yunus; Ozturk, Gokhan; Ozturk, Hamdullah; Izginli, Mucahit; Ertugrul, Mehmet

A method has been proposed for accurate characterization of non-reciprocal networks without enforcing the passivity principle. Thanks to the introduced different even and odd coefficients, our method has no singularity-point problem as compared with the conventional method. The proposed method is validated by scattering parameter measurements of a ferrite-loaded waveguide shifter. In addition, it is demonstrated by measurements that our method, as compared with the conventional one, is more resistant to random noise due to post-calibration effects.

AtıfScopus1·WoS1·OpenAlex1

İncele

Hasar, Ugur Cem; Kaya, Yunus; Izginli, Mucahit; Ozturk, Hamdullah; Ertugrul, Mehmet; Ramahi, Omar M.

Metamaterial (MM) slabs in close proximity can couple with one another. This coupling can modify the electromagnetic response of the overall MM structure involving individual MM resonators. The signal flow graph technique along with the ABCD parameters are applied to quantitatively and qualitatively examine this coupling from simulated/measured scattering parameters of cascade connection of closely or largely separated MM slabs. S-parameter measurements of a MM slab constructed by split-ring-resonators were carried out at X-band (8.2-12.4 GHz) to validate our theoretical analysis.

AtıfScopus2·WoS2·OpenAlex2

İncele

Hasar, Ugur Cem; Kaya, Yunus; Ozturk, Gokhan; Ertugrul, Mehmet

We propose a simple method for determination of forward and backward propagation constants of nonreciprocal uniform networks or lines with asymmetric reflections. The wave cascading matrix presentation is used to diagonalize and decompose the line in terms of impedance and amplitude/phase transitions. The proposed method uses scattering parameters of the line/network connection and the thru connection, thus eliminating errors arising from fabrication tolerance and thickness of the second line. Besides, compared with conventional methods which necessitate calibration techniques such as the thru-reflect-line, our method has the advantage that it determines propagation constants without resorting the measurement of any reciprocal reflective standard. Propagation constant measurements of a reciprocal network (different-length X-band waveguide straights) and a nonreciprocal network (microwave phase shifter) were first carried out and then compared with those measured by different methods to validate and monitor the accuracy of our method.

AtıfScopus13·WoS12·OpenAlex11

İncele

Hasar, Ugur Cem; Barroso, Joaquim José; Kaya, Yunus; Karacali, Tehvit; Ertugrul, Mehmet

In this study, we investigate transmitted, reflected, and absorbed powers in forward and backward directions of periodic and aperiodic multilayered structures composed of bi-anisotropic metamaterial (MM) slab and conventional material. Aperiodic multilayered structure is realized by a change in thickness of any bi-anisotropic MM slab or of any conventional material. From this analysis, we note the following key results. First, identical (non-identical) forward and backward transmitted (reflected and absorbed) powers are observed for the analyzed periodic and aperiodic multilayered structures due to reciprocity (reflection-asymmetry) of bi-anisotropic MM slabs. Second, thickness-resonance phenomenon of conventional materials produces some peaks in the transmitted powers of periodic multilayered structures aside from the resonance frequency region of bi-anisotropic MM slabs. Third, each thickness-resonance frequency splits into many frequencies upon increasing the number of sections of periodic multilayered structures (no splitting when number of periods is one). Fourth, while the effect of changing the thickness of any bi-anisotropic MM slab within the aperiodic multilayered structure has no considerable effect around the resonance region of bi-anisotropic MM slabs (resonance of resonating structures such as MM slabs does not change with thickness), the same change in thickness of the conventional material drastically alters forward/backward reflected and absorbed powers aside from the resonance region of bi-anisotropic MM slabs (thickness-resonance totally depends on the value of thickness of conventional materials). The outcomes presented here can be particularly useful for propagation-related applications requiring cascade connection of various MM slabs.

AtıfScopus14·WoS14·OpenAlex15

İncele

Hasar, Ugur C.; Kaya, Yunus; Barroso, Joaquim José; Ertugrul, Mehmet

We propose an effective microwave method for reference-plane-invariant and thickness-independent constitutive parameters measurement of thin materials. A function depending only on the interface reflection coefficient to facilitate fast computations of constitutive parameters is derived. In addition to the extraction of sample thickness, the method can also be applied to unique retrieval of constitutive parameters whose electromagnetic properties are yet unknown. We have performed an uncertainty analysis to examine how the accuracy of the method can be improved. Finally, we have compared the proposed method with other similar methods in the literature using measurements of distilled water and a thinner Plexiglas sample (1 mm). From the comparison, we note that the accuracy of our proposed method is not affected by any inaccurate knowledge of reference-plane positions and the sample length (or both) while those of compared methods are seriously decreased.

AtıfScopus53·WoS52·OpenAlex52

İncele

Hasar, Ugur Cem; Barroso, Joaquim José; Buldu, Gul; Bute, Musa; Kaya, Yunus; Karacali, Tevhit; Ertugrul, Mehmet

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.

AtıfScopus15·WoS15·OpenAlex15

İncele

Hasar, Ugur Cem; Barroso, Joaquim José; Kaya, Yunus; Ertugrul, Mehmet; Bute, Musa; Catalá-Civera, José M.

A two-step measurement procedure has been proposed for measurement of complex permittivity of dielectric materials using one-port reflection measurements. In the procedure, as a first step, a graphical method is applied to analyze on the complex reflection-coefficient plane the general pattern of dielectric behavior of the sample. Then, as a second step, optimization algorithms are utilized for retrieving electrical properties of samples. The procedure requires measurement of complex reflection scattering parameters of at least two samples with different lengths. It has been validated by X-band measurements of three polyvinyl chloride samples with lengths 5, 10, and 20 mm.

AtıfScopus14·WoS13·OpenAlex15

İncele

Hasar, Ugur Cem; Barroso, Joaquim José; Bute, Musa; Kaya, Yunus; Kocadagistan, Mustafa Engin; Ertugrul, Mehmet

We propose a non-resonant-type method for reference-plane invariant and thickness-independent permittivity measurement of solid dielectric materials when there is no information from permittivity. To achieve this, we derive a branch-index-independent function and verify that it determines the sample thickness and permittivity without resorting to finding the correct branch index value for three different measurement scenarios: (a) measurements at closely separated frequencies of non-dispersive samples, (b) measurements at largely separated frequencies of non-dispersive samples, and (c) measurements at largely separated frequencies of dispersive samples. Via a differential uncertainty analysis, the effect of inaccurate sample thickness on permittivity determination is also presented for demonstration of the improvement achieved by our method. For validation, we measured the permittivity of an approximately 20 mm PTFE sample using the presented method and compared its result with those from other similar methods. From the comparison, we note that the accuracy of tested methods from literature drastically decreases when accurate information of sample thickness is not known (in addition to a further decrease in accuracy when correct transformation factors from reference-planes are not known a priori), while the accuracy of our method is not influenced.

AtıfScopus25·WoS22·OpenAlex25

İncele

Hasar, Ugur Cem; Bute, Musa; Barroso, Joaquim J.; Sabah, Cumali; Kaya, Yunus; Ertugrul, Mehmet

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-anisotropicMMslabs and conventional materials to better interpret the results. We consider two different bi-anisotropic MM slab structures composed of only splitring- 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.

AtıfScopus11·WoS11·OpenAlex13

İncele

Hasar, Ugur Cem; Barroso, Joaquim José; Kaya, Yunus; Ertugrul, Mehmet; Bute, Musa

We propose a new transmission-reflection method for measuring constitutive parameters of liquid samples inside an asymmetric measurement cell (a sample over a low-loss holder in vertical position inside an empty waveguide section). We derived reference-plane invariant expressions for constitutive parameters measurement of liquid samples from reference-plane dependent scattering parameters. In addition, we also applied a simple approach for unique determination of transformation factor and reference-plane distances. After, we also investigated how the performance of the proposed method could be improved by performing a differential uncertainty analysis. From this analysis, we found the following key results: (a) the accuracy of the proposed method could be enhanced for low-loss liquid samples by using thicker samples, and (b) the effect of constitutive parameters and the length of the (low-loss) sample holder on constitutive parameters measurements of liquid samples by the proposed method is a key parameter in increasing the accuracy of the measurements. Finally, we performed constitutive parameter measurements of distilled water and methanol to validate the proposed method and compared the proposed method with similar methods in the literature. From the measurements, we note that our method is especially useful for liquid sample measurements when the reference-plane transformation factors are not known a priori and/or if the measurements are carried out over a high frequency range.

AtıfScopus20·WoS19·OpenAlex22

İncele