The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
Timor Melamed - One of the best experts on this subject based on the ideXlab platform.
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Time-dependent plane wave spectral analysis of the dyadic Green’s function of a fast moving dielectric-Magnetic Medium
Journal of Electromagnetic Waves and Applications, 2017Co-Authors: Timor Melamed, T. DanovAbstract:AbstractWe investigate the plane wave spectral representations of the time-dependent relativistic electric and Magnetic dyadic Green’s functions (GFs) of an isotropic dielectric-Magnetic Medium that is moving in a constant velocity. We distinguish two speed regimes in which the Medium is moving slower or faster than its wave speed. Using a scalarization process for the EM vectorial problem, the EM dyads are evaluated from scalar GF. The spectral plane wave representations of the dyadic GFss are obtained using the those of the scalar ones according to the appropriate speed regime. We investigate the resulting spectral representations and the associated wave phenomena. Such spectral representations are essentials for solving different canonical scattering problems in which the sources are decomposed into time-dependent (transient) plane waves as part of the boundary problem solutions.
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Relativistic current line Green's function in the presence of a moving planar dielectric-Magnetic Medium
2012 IEEE 27th Convention of Electrical and Electronics Engineers in Israel, 2012Co-Authors: T. Danov, Timor MelamedAbstract:The present contribution is concerned with obtaining the relativistic 2D (3D in relativity jargon) Green's function of a time-harmonic line current that is embedded in a moving dielectric-Magnetic Medium with a planar discontinuity. By applying a plane-wave spectral representation for the relativistic electroMagnetic Green's function of a dielectric-Magnetic Medium that is moving in a uniform velocity, the exact incident and reflected fields are obtained in the form of a spectral integral over plane-waves in the so-called comoving frames. We investigate these spectral representations as well as their asymptotic evaluations and discuss the associated relativistic wave phenomena of direct reflected rays and relativistic head-waves.
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A Simple and Direct Time Domain Derivation of the Dyadic Green's Function for a Uniformly Moving Non-Dispersive Dielectric-Magnetic Medium
IEEE Transactions on Antennas and Propagation, 2012Co-Authors: T. Danov, Timor MelamedAbstract:The present contribution is concerned with deriving the relativistic electric and Magnetic time-dependent dyadic Green's functions of an isotropic dielectric-Magnetic Medium (at the frame-at-rest) that is moving in a uniform relativistic velocity under the framework of the Minkowski constitutive relations. The results presented here correct previous reports in the literature [R. Compton, J. Math. Phys. 7, 2145 (1966)] and [C. Tai, J. Math. Phys. 8, 646 (1967)]. By applying a simple space-time and fields-sources transformation, scalarization of the vectorial problem is obtained. Thus the electroMagnetic dyads are evaluated from the Green's function of the scalar (time-dependent) wave equation in free space. Emphasis is placed on a simple and direct time domain derivation.
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Spectral Analysis of Relativistic Dyadic Green's Function of a Moving Dielectric-Magnetic Medium
IEEE Transactions on Antennas and Propagation, 2011Co-Authors: T. Danov, Timor MelamedAbstract:The present contribution is concerned with obtaining plane-wave spectral representations of the relativistic electric and Magnetic dyadic Green's functions of an isotropic dielectric-Magnetic Medium (at the frame-at-rest) that is moving in a uniform velocity. By applying a simple coordinate transformation, scalarization of the EM vectorial problem is obtained in which the EM dyads are evaluated from Helmholtz's isotropic scalar Green's function. The spectral plane-wave representations of the dyadic Green's functions are obtained by applying the spatial 2D Fourier transform to the scalar Green's function. We investigate these spectral representations in the under and over phase-speed regimes, as well as 2D and 3D formulations and discuss the associated wave phenomena.
T. Danov - One of the best experts on this subject based on the ideXlab platform.
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Time-dependent plane wave spectral analysis of the dyadic Green’s function of a fast moving dielectric-Magnetic Medium
Journal of Electromagnetic Waves and Applications, 2017Co-Authors: Timor Melamed, T. DanovAbstract:AbstractWe investigate the plane wave spectral representations of the time-dependent relativistic electric and Magnetic dyadic Green’s functions (GFs) of an isotropic dielectric-Magnetic Medium that is moving in a constant velocity. We distinguish two speed regimes in which the Medium is moving slower or faster than its wave speed. Using a scalarization process for the EM vectorial problem, the EM dyads are evaluated from scalar GF. The spectral plane wave representations of the dyadic GFss are obtained using the those of the scalar ones according to the appropriate speed regime. We investigate the resulting spectral representations and the associated wave phenomena. Such spectral representations are essentials for solving different canonical scattering problems in which the sources are decomposed into time-dependent (transient) plane waves as part of the boundary problem solutions.
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Relativistic current line Green's function in the presence of a moving planar dielectric-Magnetic Medium
2012 IEEE 27th Convention of Electrical and Electronics Engineers in Israel, 2012Co-Authors: T. Danov, Timor MelamedAbstract:The present contribution is concerned with obtaining the relativistic 2D (3D in relativity jargon) Green's function of a time-harmonic line current that is embedded in a moving dielectric-Magnetic Medium with a planar discontinuity. By applying a plane-wave spectral representation for the relativistic electroMagnetic Green's function of a dielectric-Magnetic Medium that is moving in a uniform velocity, the exact incident and reflected fields are obtained in the form of a spectral integral over plane-waves in the so-called comoving frames. We investigate these spectral representations as well as their asymptotic evaluations and discuss the associated relativistic wave phenomena of direct reflected rays and relativistic head-waves.
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A Simple and Direct Time Domain Derivation of the Dyadic Green's Function for a Uniformly Moving Non-Dispersive Dielectric-Magnetic Medium
IEEE Transactions on Antennas and Propagation, 2012Co-Authors: T. Danov, Timor MelamedAbstract:The present contribution is concerned with deriving the relativistic electric and Magnetic time-dependent dyadic Green's functions of an isotropic dielectric-Magnetic Medium (at the frame-at-rest) that is moving in a uniform relativistic velocity under the framework of the Minkowski constitutive relations. The results presented here correct previous reports in the literature [R. Compton, J. Math. Phys. 7, 2145 (1966)] and [C. Tai, J. Math. Phys. 8, 646 (1967)]. By applying a simple space-time and fields-sources transformation, scalarization of the vectorial problem is obtained. Thus the electroMagnetic dyads are evaluated from the Green's function of the scalar (time-dependent) wave equation in free space. Emphasis is placed on a simple and direct time domain derivation.
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Spectral Analysis of Relativistic Dyadic Green's Function of a Moving Dielectric-Magnetic Medium
IEEE Transactions on Antennas and Propagation, 2011Co-Authors: T. Danov, Timor MelamedAbstract:The present contribution is concerned with obtaining plane-wave spectral representations of the relativistic electric and Magnetic dyadic Green's functions of an isotropic dielectric-Magnetic Medium (at the frame-at-rest) that is moving in a uniform velocity. By applying a simple coordinate transformation, scalarization of the EM vectorial problem is obtained in which the EM dyads are evaluated from Helmholtz's isotropic scalar Green's function. The spectral plane-wave representations of the dyadic Green's functions are obtained by applying the spatial 2D Fourier transform to the scalar Green's function. We investigate these spectral representations in the under and over phase-speed regimes, as well as 2D and 3D formulations and discuss the associated wave phenomena.
Akhlesh Lakhtakia - One of the best experts on this subject based on the ideXlab platform.
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Sufficient Conditions for Zero Backscattering by a Uniaxial Dielectric-Magnetic Scatterer Endowed With Magnetoelectric Gyrotropy
IEEE Transactions on Antennas and Propagation, 2020Co-Authors: Hamad M. Alkhoori, Akhlesh Lakhtakia, James K. Breakall, Craig F. BohrenAbstract:As vector wavefunctions are available to represent incident and scattered fields in an isotropic dielectric-Magnetic Medium endowed with magnetoelectric gyrotropy, a transition matrix can be conceptualized to relate the scattered field coefficients to the incident field coefficients for scattering by an arbitrary scatterer composed of a linear Medium. The elements of the transition matrix must satisfy certain conditions for zero backscattering. For a scatterer composed of a uniaxial dielectric-Magnetic Medium endowed with magnetoelectric gyrotropy, the extended boundary condition method (EBCM) can be formulated to determine the transition matrix. The numerical results obtained thereby lead to the formulation of a sufficient set of three zero-backscattering conditions: (i) the scatterer is a body of revolution with the incident plane wave propagating along the axis of revolution; (ii) the impedances of both Mediums are identical; and (iii) the magnetoelectric-gyrotropy vectors of both Mediums are aligned along the axis of revolution, whether or not both magnetoelectric-gyrotropy vectors are co-parallel.
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The Huygens principle for a uniaxial dielectric-Magnetic Medium with gyrotropic-like magnetoelectric properties
arXiv: Optics, 2008Co-Authors: Tom G. Mackay, Akhlesh LakhtakiaAbstract:The dyadic Green functions for a uniaxial dielectric-Magnetic Medium, together with a reversible field transformation, were implemented to derive a formulation of the Huygens principle appropriate to a uniaxial dielectric-Magnetic Medium with gyrotropic-like magnetoelectric properties.
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Simple derivation of dyadic Green functions of a simply moving, isotropic, dielectric-Magnetic Medium
arXiv: Optics, 2005Co-Authors: Akhlesh Lakhtakia, Tom G. MackayAbstract:Dyadic Green functions for time-harmonic fields in a homogeneous, isotropic, dielectric-Magnetic Medium, moving with constant velocity, are derived by first implementing a simple transformation and then using the dyadic Green functions available for uniaxial dielectric-Magnetic Mediums.
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negative phase velocity in a uniformly moving homogeneous isotropic dielectric Magnetic Medium
Journal of Physics A, 2004Co-Authors: Tom G. Mackay, Akhlesh LakhtakiaAbstract:Homogeneous, isotropic Mediums characterized by relative permittivity scalars and relative permeability scalars are well known to support the propagation of plane waves with negative phase velocity (NPV), provided that both R 0 and μR > 0), can support NPV propagation when they are viewed in a reference frame which is uniformly translated at a sufficiently high velocity. Representative numerical examples are used to explore the constitutive parameter regimes which support NPV propagation under the uniform-velocity condition.
R. Tourbot - One of the best experts on this subject based on the ideXlab platform.
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Nuclear and Magnetic Medium range order in amorphous Tb67Zr33 containing hydrogen
Journal of Non-crystalline Solids, 1993Co-Authors: Qi Chen, R. Tourbot, B BoucherAbstract:Abstract Small angle neutron scattering (SANS) measurements have been carried out on amorphous Tb 67 Zr 33 containing hydrogen. A zero-field cooled sample is studied at room temperature in the paraMagnetic state and at low temperature in the Magnetically ordered state. Nuclear Medium range order (MRO) is observed and is consistent with a variation of sample composition and a local variation of the amount of hydrogen trapped in the sample. Magnetic MRO correlated with nuclear MRO displays weak variations over large distances (∼10 2 nm) and a strong local variation (∼2 nm). A comparison is made between the SANS results and the characteristic Magnetic temperatures as obtained from classical Magnetic measurements for Tb 67 Zr 33 and Tb 65 Cu 35 amorphous alloys.
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Nuclear and Magnetic Medium-range order in TbxSi1-x amorphous alloys (x=0.59, 0.87) containing hydrogen
Journal of Physics: Condensed Matter, 1992Co-Authors: B Boucher, R. TourbotAbstract:Small-angle neutron scattering measurements were carried out on (Tb0.59Si0.41)H0.15 and (Tb0.87Si0.13)H0.15 amorphous alloys above and below the Magnetic ordering temperature for zero field cooled (ZFC) and field cooled (FC) samples. From the measurements the authors have determined the spatial variation of the nuclear and Magnetic scattering length per unit volume and describe the nuclear and Magnetic Medium-range order (MRO) for ZFC and FC samples. The existence of large nuclear and Magnetic domains (or of nuclear and Magnetic fluctuations) extending over a few hundred Angstroms coexisting with less extended (a few tens of Angstroms) fluctuations is shown. Moreover some small nuclear or Magnetic inhomogeneities are found to exist and they seem to contain most of the 15 atomic per cent of hydrogen which have been detected in the sample composition. An applied Magnetic field tends to align the local magnetization, but does not increase the spatial extension of fluctuations or domains, locked by the nuclear MRO, although their contrast is found to decrease. The comparison with the amorphous alloy Tb65Cu35 shows the generality of these results but does not allow one to understand the difference in the macroscopic Magnetic properties, in particular the difference between the hysteresis loops.
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Magnetic Medium-range order in amorphous TbxSi1−x (x = 0.59; 0.87)
Journal of Magnetism and Magnetic Materials, 1992Co-Authors: B Boucher, R. TourbotAbstract:Abstract The Magnetic Medium-range order has been determined by small-angle neutron scattering for two TbxSi1−x amorphous alloys (x = 0.59; 0.87). There is coexistence of small spatial fluctuations of the magnetization over long distances and bigger spatial fluctuations over small distances. We also observe some aggregates which are either Magnetic or nonMagnetic. The latter allow us to obtain the magnetization of the amorphous sample. The measurements for field cooled and zero-field cooled samples evidence different Magnetic behaviour of the part showing spatial fluctuations and aggregates.
Jen-yuan Chang - One of the best experts on this subject based on the ideXlab platform.
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A hybrid flattening method for roller-leveling of flexible Magnetic Medium
Microsystem Technologies, 2018Co-Authors: Brian Chen, Jen-yuan ChangAbstract:Mechanics modeling of roller leveling process is presented in this work with aim placed on the manufacturing of flexible Magnetic Medium in linear Magnetic encoders. Roller leveling process is a complex forming process that utilizes bending moments to achieve flattening of the process material. In the manufacturing of Magnetic encoding Medium, the release of residual stress is a crucial step since it is directly related to the mechanical flatness of the Medium, which will significantly affect the performance of the Magnetic encoder. In this paper, mechatronics integration of a roller leveler is developed for flattening of Magnetic Medium. A hybrid modeling of Magnetic Medium flattening method is established through analytical model to predict and analyze its residual curvature and stress with given design parameters. The relationship between leveling roller indentation and curvature of Magnetic Medium are investigated, followed by validation which is carried out using the proposed model, the Magnetic Medium and the roller leveler. The presented work can be implemented toward flattening and forming of common media.
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Investigation of Flexible Magnetic Medium Microstructure Behavior Under Implementation of Roller Leveling Process
ASME-JSME 2018 Joint International Conference on Information Storage and Processing Systems and Micromechatronics for Information and Precision Equipm, 2018Co-Authors: Brian Chen, Jen-yuan ChangAbstract:The aim of this paper is to investigate the effect of roller leveling process on the behavior of microstructure in flexible Magnetic Medium. Linear Magnetic encoder is a highly precise measuring device that required accurate quality control during manufacturing. Previous studies have demonstrated the feasibility of roller leveling application to enhance the manufacturing of flexible Magnetic Medium. Mechanical shape defects in Magnetic Medium occurred during manufacturing due to environmental conditions can be eliminated through roller leveling process. In this paper, further steps were taken to understand the effect of roller leveling process in the microstructural level. From experimental results, it demonstrates that roller leveling process, a type of cyclic loading process, would not encourage crack growth if cracks were not initiated prior to leveling process. In addition to removing mechanical shape defects, understanding roller leveling process in Magnetic Medium application through investigating microstructure behavior has implications toward the fabrication quality of flexible Magnetic Medium.
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Magnetic Characteristic Analysis of Linear Magnetic Medium Installation for Improving Recording Accuracy
2018 Asia-Pacific Magnetic Recording Conference (APMRC), 2018Co-Authors: Brian Chen, Jen-yuan ChangAbstract:In the installation of linear Magnetic system, any curved or uneven surfaces of the Magnetic Medium would result in significant fluctuations in final recording accuracy. This work investigates effect of Medium curvature on recording accuracy. Preliminary experimental results suggest that significant recording accuracy can be affected by Medium Magnetic flux distribution resulted from Medium curvature This also suggests that should the Medium can be flattened, the recording accuracy can be improved.