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Spin excitations in laser-molecular-beam epitaxy grown nanosized YIG films: towards low relaxation and desirable magnetization profile
摘要： We describe synthesis of nanosized Y3Fe5O12 (YIG) films grown by laser-molecular-beam epitaxy on Gd3Ga5O12 (GGG) and Nd3Ga5O12 (NdGG) substrates with (111) orientation and present results of ferromagnetic resonance (FMR) and spin wave propagation studies in these heterostructures. It is found that magnetic parameters of YIG films grown on NdGG and GGG substrates are considerably different. FMR spectra of YIG/NdGG structures are characterized by a large number of narrow peaks, while FMR spectra of YIG/GGG structures consist of a small number of peaks or one peak. The effective magnetization of YIG films grown on NdGG substrates is less than that of YIG films grown on GGG and is more sensitive to the growth conditions. A lateral inhomogeneity of YIG/NdGG structures is observed in spin wave propagation experiments. For YIG/NdGG and YIG/GGG structures the FMR linewidth ?H of a single peak sharply increases with temperature decrease from 298 to 67 K. The observed increase of ?H is explained by typical relaxation processes caused by the presence of Fe2+ ions. From the spin-wave propagation study it is also found that relaxation of spin-waves explains only a minor part of the FMR single peak linewidth in YIG/NdGG structures. On the basis of obtained results, YIG/GGG/semiconductor- and YIG/NdGG/semiconductor-heterostructures with expected low spin-wave relaxation and desirable effective magnetization profile are proposed.
关键词： magnetization profile,ferromagnetic resonance,spin wave propagation,laser-molecular-beam epitaxy,YIG films
更新于2025-09-19 17:13:59
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Nose-Cone Conformal Substrate-Integrated Waveguide Slot Array Antenna for X-Band Radar Applications
摘要： This paper presents the design of nose-cone conformal substrate-integrated waveguide (SIW) slot array antenna for modern radar applications. Firstly, the wave propagation characteristics have been investigated in doubly curved SIW, and it has been observed that they are non-uniform along the longitudinal direction of nose-cone conformal SIW. To ensure the constant wave propagation along the length of conformal SIW, the conventional design of SIW is reformulated for nose-cone conformal SIW and circuit model modification has been demonstrated. Secondly, the procedure for designing a SIW-based array on curved surfaces has been developed. In the proposed design, rectangular waveguide (RWG) to SIW feeding structure has been used to avoid spurious radiations. Finally, 1 × 6 element-based nose-cone conformal slotted array has been designed and compared with planar and cylindrical conformal arrays. It has been observed from the results that the nose-cone conformal slot array offers low sidelobe levels (SLLs) and high gain. For the validation of the proposed design, the conformal slotted array has been fabricated and measured, which exhibited a reasonable agreement between the measured and the simulated data.
关键词： substrate-integrated waveguide,high gain,X-band radar,nose-cone conformal,wave propagation,sidelobe levels,slot array antenna
更新于2025-09-19 17:13:59
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Electron holography for vortex beams
摘要： A combined technology of vortex beam technique and electron holography has been developed. A range of about 10 times the diameter of the grating opening was irradiated and electron holography, electron vortex beam, orbital angular momentum, helical wavefront, wave propagation two-wave interference between a Bragg diffraction wave as a vortex beam and transmitted wave from and around a fork-shaped grating was recorded as a hologram. Reconstruction by using the Fourier transform method has been simultaneously performed for amplitude and phase distributions. Furthermore, by using a wave aberration function, amplitude and phase distributions at various propagation positions were reconstructed numerically, resulting in confirmation of vortex beam twists.
关键词： helical wavefront,electron holography,electron vortex beam,orbital angular momentum,wave propagation
更新于2025-09-19 17:13:59
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A laser pulse impactful on a half-space using the modified TPL Ga??N models
摘要： this article aims to investigate the wave propagation of generalized thermoelastic half-plane under the effect of thermal loading due to laser pulse with and without energy dissipation. The normal mode method is proposed to solve the problem and get numerical results for the field quantities. The outcomes of the physical quantities have been illustrated graphically and reported to compare the simple Green–Naghdi II and III and their modified single-, dual-, and three-phase-lag models. The graphical outcomes indicate that the different types of Green–Naghdi models with thermal relaxations have great effects on the temperature, displacements, dilatation and stresses.
关键词： laser pulse,Green–Naghdi models,thermal loading,wave propagation,thermoelasticity
更新于2025-09-19 17:13:59
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Wave Scattering and Power Flow in Straight-Helical-Straight Waveguide Structure
摘要： The knowledge of wave scattering and power flow in waveguide structures is important for many engineering applications. In this paper, power flow and scattering in a straight-helical-straight waveguide structure are investigated using the wave and finite element (WFE) method. For simple (straight or helical) waveguides, wave scattering (and subsequently the power flow and scattering) can be resolved analytically. This is not the case for complex waveguides such as laminated or sandwiched waveguides or waveguides with noncanonical cross-sections. In such cases, the WFE method is used to model the wave behavior in each waveguide in the structure. The power flow is then studied by considering how waves reflect and transmit at the boundaries that join the straight waveguides with the helical waveguide. We present three numerical examples but analytical solutions can be obtained for the first example only; for the second and third examples, the WFE is used in earnest since the wave behavior and subsequently the power flow would at best be extremely difficult to formulate analytically.
关键词： wave propagation,power flow,Wave and finite element,power scattering,helical waveguides
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Sozopol, Bulgaria (2019.9.6-2019.9.8)] 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Spontaneous bremsstrahlung of ultrarelativistic electrons within the resonant conditions in the field of a nucleus and external electromagnetic field
摘要： We have developed small-sized terahertz free-electron lasers by using low-cost and compact microtrons combining with magnetrons as high-power RF sources. We could stabilize the bunch repetition rate by optimizing a modulator for the magnetron and by coupling the magnetron with an accelerating cavity in the microtron. By developing high-performance undulators and low-loss waveguide-mode resonators having small cross-sectional areas, we could strengthen the interaction between the electron beam and the THz wave inside the FEL resonators to achieve lasing even with low-current electron beams from the microtron. We used a parallel-plate waveguide in a planar electromagnet undulator for our ?rst THz FEL. We try to reduce the size of the FEL resonator by combining a dielectric-coated circular waveguide and a variable-period helical undulator to realize a table-top THz FEL for applying it to the security inspection on airports.
关键词： submillimeter wave technology,free electron lasers,submillimeter wave propagation,electron beams,undulators,Electromagnetic radiation
更新于2025-09-16 10:30:52
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Derivation and Experimental Verification of the near-field 2D and 3D optical intensities from a finite-size light emitting diode (LED)
摘要： We derive the near-field light intensity distributions of an inorganic LED on its surface and in volumetric space. Our closed-form solution for 3D intensity distribution for a finite-size LED is consistent with Lambert’s Cosine Law, which provides the 3D intensity distribution for an infinitesimal, flat light source. We also derive the formula for the 2D intensity distribution on a diode surface showing its similarity to a Gaussian function, which is typically used to approximate the surface light intensity profile for an LED and a laser diode. Our 2D intensity distribution function produces light propagation similar to the Gaussian beam propagation in space. However, unlike the Gaussian approximation, our formula invariably produces this behavior without assuming the refractive index inside the diode follows a quadratic function of the transverse spatial domains. Our 2D and 3D spatial intensity formulas in near-field for LEDs offer a unique way to calculate the peak intensity that occurs at the center of the flat LED source. We demonstrate, as expected, that the peak intensity increases with the size of the LED source as well as the brightness of each radiative electron-hole pair, which is a function of the drive current and quantum efficiency of the LED.
关键词： Near-field Photometry,Optical Waveguides,Display,Optical Wave Propagation,Closed-Form Solutions,and Lighting.,Lasers,Light Emitting Diodes,Mathematical Physics
更新于2025-09-16 10:30:52
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Problem of Coupled Electromagnetic TE-TE Wave Propagation in a Layer Filled with Nonlinear Medium with Saturation
摘要： Propagation of coupled electromagnetic TE-TE wave in a nonlinear plane layer is considered. The layer is located between two half-spaces with constant permittivities. The permittivity in the layer is described by nonlinearity with saturation. The physical problem is reduced to a nonlinear two-parameter eigenvalue problem for a system of (nonlinear) ordinary differential equations. Existence and uniqueness of solution to the two-parameter eigenvalue problem is proved. Iteration method for solving given problem is presented. Convergence theorem of the iteration method is proved.
关键词： wave propagation,perturbation method,saturated nonlinearity,plane nonlinear waveguide,Maxwell’s equations
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Epitaxial GaAs Lift Off via III-VI Layered Compounds
摘要： The global bandwidth shortage facing wireless carriers has motivated the exploration of the underutilized millimeter wave (mm-wave) frequency spectrum for future broadband cellular communication networks. There is, however, little knowledge about cellular mm-wave propagation in densely populated indoor and outdoor environments. Obtaining this information is vital for the design and operation of future fifth generation cellular networks that use the mm-wave spectrum. In this paper, we present the motivation for new mm-wave cellular systems, methodology, and hardware for measurements and offer a variety of measurement results that show 28 and 38 GHz frequencies can be used when employing steerable directional antennas at base stations and mobile devices.
关键词： 5G,cellular,MIMO,millimeter wave propagation measurements,28GHz,directional antennas,38GHz,channel models,mobile communications
更新于2025-09-16 10:30:52
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Nonlinear Fiber Optics || Pulse propagation in fibers
摘要： For an understanding of the nonlinear phenomena in optical ?bers, it is necessary to consider the theory of electromagnetic wave propagation in dispersive nonlinear media. The objective of this chapter is to obtain a basic equation that governs propagation of optical pulses in single-mode ?bers. Section 2.1 introduces Maxwell’s equations and important concepts such as the linear and nonlinear parts of the induced polarization and the frequency-dependent dielectric constant. The concept of ?ber modes is introduced in Section 2.2 where the single-mode condition is also discussed. Section 2.3 considers the theory of pulse propagation in nonlinear dispersive media in the slowly varying envelope approximation with the assumption that the spectral width of the pulse is much smaller than the frequency of the incident radiation. The numerical methods used to solve the resulting propagation equation are discussed in Section 2.4.
关键词： electromagnetic wave propagation,dispersive nonlinear media,numerical methods,nonlinear phenomena,optical fibers,single-mode fibers,fiber modes,pulse propagation,dielectric constant,induced polarization,Maxwell’s equations
更新于2025-09-12 10:27:22