The Experts below are selected from a list of 40974 Experts worldwide ranked by ideXlab platform
Roger A. Hitchings - One of the best experts on this subject based on the ideXlab platform.
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Validity of rim area measurements by different Reference Planes.
Journal of glaucoma, 2004Co-Authors: James C. H. Tan, E.t. White, Darmalingum Poinoosawmy, Roger A. HitchingsAbstract:Purpose Reference Plane description of the neuroretinal rim in scanning laser tomography should correctly represent optic nerve morphology. We evaluated how well rim area analysis by different Reference Planes agreed with the appearance of rim area in disc images. Methods Three expert observers subjectively and repeatedly analyzed rim area in Heidelberg Retina Tomograph (HRT) images so that each optic disc was measured six times in 100 eyes, 50 normal and 50 glaucoma. Rim area was evaluated globally and in 30 degree sectors. Agreement between rim appearance, as subjectively analyzed, and objective analysis by an experimental Reference Plane, the standard Reference Plane, and a Reference Plane fixed 320 microm below the Reference ring was assessed in HRT images. Results Subjective analysis of rim area in HRT images was consistent between expert observers. Their analysis of rim appearance agreed more closely with experimental Reference Plane analysis than analysis by the standard or 320-microm Reference Planes; this was true globally and in every region of the nerve (P = 0.000). The experimental Reference Plane yielded higher estimates of rim area than did the standard or 320-microm Reference Planes. Conclusion There was closer correspondence between the appearance of the neuroretinal rim in images and description by the experimental Reference Plane compared with description by the standard and 320-microm Reference Planes.
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Reference Plane definition and reproducibility in optic nerve head images.
Investigative ophthalmology & visual science, 2003Co-Authors: James C. H. Tan, Roger A. HitchingsAbstract:PURPOSE To describe and evaluate a new experimental Reference Plane for measuring rim area in scanning laser tomography. METHODS The experimental Reference Plane was positioned so that (1) it always lay entirely below the margin of the optic nerve head (ONH), (2) it remained at a set z-axis distance below the ONH in images of each eye, and (3) it was at a level where variability in rim area is least. Twenty normal control subjects and 20 patients with glaucoma underwent test-retest scanning laser tomographic imaging by same and different operators during same and separate visits. Control subjects had image series spanning at least 3 years. The effect of the positioning of the Reference Plane on global and regional rim area variability was assessed in intra- and intervisit test-retest images and longitudinal image series and compared with the standard and 320- microm Reference Planes. RESULTS Variability in the experimental Reference Plane was less in test-retest images and longitudinal data (P < 0.05) and more uniform around the ONH than with other Reference Planes. Variability in the former was not appreciably affected by testing involving different operators and visits, or by the presence of glaucoma. CONCLUSIONS Variability in rim area by the experimental Reference Plane was significantly less, more uniform around the ONH, not affected by different operators and visits, and less affected by glaucomatous morphology than other Reference Planes. This difference was pronounced in sequential data and has implications for detecting progression of glaucoma.
Mehmet Ertugrul - One of the best experts on this subject based on the ideXlab platform.
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Reference-Plane-invariant and thickness- and branch-index-independent retrieval of effective parameters of bi-anisotropic metamaterials
AIP Advances, 2015Co-Authors: Ugur Cem Hasar, Joaquim J. Barroso, Tevhit Karacali, Mehmet ErtugrulAbstract:We propose a retrieval method for Reference-Plane-invariant electromagnetic parameter measurements of bi-anisotropic metamaterial slabs without resorting to accurate information of the slab thickness and the branch index. To extract Reference-Plane distances, the slab thickness, and the branch index, we first approximate wave impedances and refractive index away from the slab resonance frequency and then use scattering parameters to calculate the refractive index and the branch index. Once these quantities are determined, they are used as inputs for the retrieval of electromagnetic properties of slabs over the whole band. Different approximations for refractive index and wave impedances are applied to demonstrate the applicability and accuracy of our proposed method. We tested our method for electromagnetic parameter extraction of bi-anisotropic split-ring-resonator and Omega-shaped MM slabs with different number of unit cells. From our analysis, we note that inaccurate information of Reference-Plane distances, the slab length, and the branch index not only changes the amplitude but also shifts the response of the electromagnetic properties. We show that the presented method can be applied for accurate electromagnetic parameter extraction of bi-anisotropic MM slabs.
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Determination of Reference-Plane Invariant, Thickness-Independent, and Broadband Constitutive Parameters of Thin Materials
IEEE Transactions on Microwave Theory and Techniques, 2015Co-Authors: Ugur Cem Hasar, Joaquim José Barroso, Yunus Kaya, Mehmet ErtugrulAbstract: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.
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Reference-Plane-Invariant Effective Thickness and Electromagnetic Property Determination of Isotropic Metamaterials Involving Boundary Effects
IEEE Journal of Selected Topics in Quantum Electronics, 2015Co-Authors: Ugur Cem Hasar, Musa Bute, Joaquim José Barroso, Yunus Kaya, Tevhit Karacali, Gul Buldu, Mehmet ErtugrulAbstract: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.
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Microwave method for Reference-Plane-invariant and thickness-independent permittivity determination of liquid materials.
The Review of scientific instruments, 2014Co-Authors: Ugur Cem Hasar, Musa Bute, Joaquim José Barroso, Yunus Kaya, Mehmet ErtugrulAbstract: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.
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Reference-Plane invariant transmission-reflection method for measurement of constitutive parameters of liquid materials
Sensors and Actuators A: Physical, 2013Co-Authors: Ugur Cem Hasar, Joaquim José Barroso, Yunus Kaya, Mehmet Ertugrul, Musa ButeAbstract:Abstract 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.
Ugur Cem Hasar - One of the best experts on this subject based on the ideXlab platform.
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Reference-Plane-invariant waveguide method for electromagnetic characterization of bi-axial bianisotropic metamaterials
Sensors and Actuators A: Physical, 2018Co-Authors: Ugur Cem Hasar, Gul Yildiz, Musa Bute, Abdurrahim MuratogluAbstract:Abstract In this paper, we investigate a Reference-Plane invariant (RPI) method for electromagnetic property extraction of bi-axial bianisotropic metamaterial (MM) slabs. In order to obtain unique properties, we applied the frequency varying technique in order to determine the location of the slab within its cell. For validation of the proposed method, we first simulated and then measured scattering parameters of a MM slab constructed by split-ring-resonators, next extracted its electromagnetic properties, and finally compared extracted properties by those retrieved by another method which requires Reference-Plane information. From the comparison, we noted that whereas our proposed method correctly retrieved electromagnetic properties without knowing the value of Reference Plane transformation factors, the accuracy of the tested method was seriously influenced by any inaccurate Reference Plane information.
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Determination of Reference-Plane Invariant, Thickness-Independent, and Broadband Constitutive Parameters of Thin Materials
IEEE Transactions on Microwave Theory and Techniques, 2015Co-Authors: Ugur Cem Hasar, Joaquim José Barroso, Yunus Kaya, Mehmet ErtugrulAbstract: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.
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Reference-Plane-invariant and thickness- and branch-index-independent retrieval of effective parameters of bi-anisotropic metamaterials
AIP Advances, 2015Co-Authors: Ugur Cem Hasar, Joaquim J. Barroso, Tevhit Karacali, Mehmet ErtugrulAbstract:We propose a retrieval method for Reference-Plane-invariant electromagnetic parameter measurements of bi-anisotropic metamaterial slabs without resorting to accurate information of the slab thickness and the branch index. To extract Reference-Plane distances, the slab thickness, and the branch index, we first approximate wave impedances and refractive index away from the slab resonance frequency and then use scattering parameters to calculate the refractive index and the branch index. Once these quantities are determined, they are used as inputs for the retrieval of electromagnetic properties of slabs over the whole band. Different approximations for refractive index and wave impedances are applied to demonstrate the applicability and accuracy of our proposed method. We tested our method for electromagnetic parameter extraction of bi-anisotropic split-ring-resonator and Omega-shaped MM slabs with different number of unit cells. From our analysis, we note that inaccurate information of Reference-Plane distances, the slab length, and the branch index not only changes the amplitude but also shifts the response of the electromagnetic properties. We show that the presented method can be applied for accurate electromagnetic parameter extraction of bi-anisotropic MM slabs.
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Reference-Plane-Invariant Effective Thickness and Electromagnetic Property Determination of Isotropic Metamaterials Involving Boundary Effects
IEEE Journal of Selected Topics in Quantum Electronics, 2015Co-Authors: Ugur Cem Hasar, Musa Bute, Joaquim José Barroso, Yunus Kaya, Tevhit Karacali, Gul Buldu, Mehmet ErtugrulAbstract: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.
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Microwave method for Reference-Plane-invariant and thickness-independent permittivity determination of liquid materials.
The Review of scientific instruments, 2014Co-Authors: Ugur Cem Hasar, Musa Bute, Joaquim José Barroso, Yunus Kaya, Mehmet ErtugrulAbstract: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.
James C. H. Tan - One of the best experts on this subject based on the ideXlab platform.
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Validity of rim area measurements by different Reference Planes.
Journal of glaucoma, 2004Co-Authors: James C. H. Tan, E.t. White, Darmalingum Poinoosawmy, Roger A. HitchingsAbstract:Purpose Reference Plane description of the neuroretinal rim in scanning laser tomography should correctly represent optic nerve morphology. We evaluated how well rim area analysis by different Reference Planes agreed with the appearance of rim area in disc images. Methods Three expert observers subjectively and repeatedly analyzed rim area in Heidelberg Retina Tomograph (HRT) images so that each optic disc was measured six times in 100 eyes, 50 normal and 50 glaucoma. Rim area was evaluated globally and in 30 degree sectors. Agreement between rim appearance, as subjectively analyzed, and objective analysis by an experimental Reference Plane, the standard Reference Plane, and a Reference Plane fixed 320 microm below the Reference ring was assessed in HRT images. Results Subjective analysis of rim area in HRT images was consistent between expert observers. Their analysis of rim appearance agreed more closely with experimental Reference Plane analysis than analysis by the standard or 320-microm Reference Planes; this was true globally and in every region of the nerve (P = 0.000). The experimental Reference Plane yielded higher estimates of rim area than did the standard or 320-microm Reference Planes. Conclusion There was closer correspondence between the appearance of the neuroretinal rim in images and description by the experimental Reference Plane compared with description by the standard and 320-microm Reference Planes.
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Reference Plane definition and reproducibility in optic nerve head images.
Investigative ophthalmology & visual science, 2003Co-Authors: James C. H. Tan, Roger A. HitchingsAbstract:PURPOSE To describe and evaluate a new experimental Reference Plane for measuring rim area in scanning laser tomography. METHODS The experimental Reference Plane was positioned so that (1) it always lay entirely below the margin of the optic nerve head (ONH), (2) it remained at a set z-axis distance below the ONH in images of each eye, and (3) it was at a level where variability in rim area is least. Twenty normal control subjects and 20 patients with glaucoma underwent test-retest scanning laser tomographic imaging by same and different operators during same and separate visits. Control subjects had image series spanning at least 3 years. The effect of the positioning of the Reference Plane on global and regional rim area variability was assessed in intra- and intervisit test-retest images and longitudinal image series and compared with the standard and 320- microm Reference Planes. RESULTS Variability in the experimental Reference Plane was less in test-retest images and longitudinal data (P < 0.05) and more uniform around the ONH than with other Reference Planes. Variability in the former was not appreciably affected by testing involving different operators and visits, or by the presence of glaucoma. CONCLUSIONS Variability in rim area by the experimental Reference Plane was significantly less, more uniform around the ONH, not affected by different operators and visits, and less affected by glaucomatous morphology than other Reference Planes. This difference was pronounced in sequential data and has implications for detecting progression of glaucoma.
Yunus Kaya - One of the best experts on this subject based on the ideXlab platform.
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Reference-Plane-Invariant Effective Thickness and Electromagnetic Property Determination of Isotropic Metamaterials Involving Boundary Effects
IEEE Journal of Selected Topics in Quantum Electronics, 2015Co-Authors: Ugur Cem Hasar, Musa Bute, Joaquim José Barroso, Yunus Kaya, Tevhit Karacali, Gul Buldu, Mehmet ErtugrulAbstract: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.
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Determination of Reference-Plane Invariant, Thickness-Independent, and Broadband Constitutive Parameters of Thin Materials
IEEE Transactions on Microwave Theory and Techniques, 2015Co-Authors: Ugur Cem Hasar, Joaquim José Barroso, Yunus Kaya, Mehmet ErtugrulAbstract: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.
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Microwave method for Reference-Plane-invariant and thickness-independent permittivity determination of liquid materials.
The Review of scientific instruments, 2014Co-Authors: Ugur Cem Hasar, Musa Bute, Joaquim José Barroso, Yunus Kaya, Mehmet ErtugrulAbstract: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.
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Reference-Plane invariant transmission-reflection method for measurement of constitutive parameters of liquid materials
Sensors and Actuators A: Physical, 2013Co-Authors: Ugur Cem Hasar, Joaquim José Barroso, Yunus Kaya, Mehmet Ertugrul, Musa ButeAbstract:Abstract 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.
