scholarly journals Terahertz rectangular waveguides with inserted graphene films biased by light and their quasi-linear electromagnetic modeling

2020 ◽  
Author(s):  
Guennadi A. Kouzaev
Keyword(s):  
Electric Fields ◽  
Iteration Algorithm ◽  
Perturbation Approach ◽  
Current Crowding ◽  
Electromagnetic Modeling ◽  
Graphene Films ◽  
Field Matching ◽  
Rectangular Waveguides ◽  
Sharp Edges ◽  
Conductor Loss

AbstractNovel rectangular waveguides with graphene inserts biased by light are proposed herein. The graphene films short the conductor plates of waveguides and support the localized transverse-electric modes. Their electric fields are parallel to the wide walls of these waveguides, and the eigenmodes have decreased conductor loss. The designs do not involve the conductor and graphene strips with their sharp edges, and the loss associated with the current crowding effect is excluded. The waveguides are treated in the quasi-linear regime using a rigorous field matching method, and the complex dispersion eigenmodal equation is solved using a validated iteration algorithm. At the terahertz frequencies of amplification, where the real part of graphene conductivity is negative, a gain increase is found with the eigenmodal number. This gain can be tuned by the waveguide geometry, dielectric filling, and the level of quasi-Fermi energy. The ideal waveguide theory is corrected using a perturbation approach and the Drude model of surface resistance of waveguide plates.

scholarly journals A parallel finite‐difference approach for 3D transient electromagnetic modeling with galvanic sources

Geophysics ◽  
2004 ◽  
Vol 69 (5) ◽  
pp. 1192-1202 ◽  
Author(s):  
Michael Commer ◽  
Gregory Newman
Keyword(s):  
Magnetic Field ◽  
Finite Difference ◽  
Electric Field ◽  
Electric Fields ◽  
Time Derivative ◽  
Stable Solution ◽  
Parallel Computer ◽  
Staggered Grid ◽  
Electromagnetic Modeling ◽  
Transient Electromagnetic

A parallel finite‐difference algorithm for the solution of diffusive, three‐dimensional (3D) transient electromagnetic field simulations is presented. The purpose of the scheme is the simulation of both electric fields and the time derivative of magnetic fields generated by galvanic sources (grounded wires) over arbitrarily complicated distributions of conductivity and magnetic permeability. Using a staggered grid and a modified DuFort‐Frankel method, the scheme steps Maxwell's equations in time. Electric field initialization is done by a conjugate‐gradient solution of a 3D Poisson problem, as is common in 3D resistivity modeling. Instead of calculating the initial magnetic field directly, its time derivative and curl are employed in order to advance the electric field in time. A divergence‐free condition is enforced for both the magnetic‐field time derivative and the total conduction‐current density, providing accurate results at late times. In order to simulate large realistic earth models, the algorithm has been designed to run on parallel computer platforms. The upward continuation boundary condition for a stable solution in the infinitely resistive air layer involves a two‐dimensional parallel fast Fourier transform. Example simulations are compared with analytical, integral‐equation and spectral Lanczos decomposition solutions and demonstrate the accuracy of the scheme.

A hybrid three‐dimensional electromagnetic modeling scheme

Geophysics ◽  
1981 ◽  
Vol 46 (5) ◽  
pp. 796-805 ◽  
Author(s):  
K. H. Lee ◽  
D. F. Pridmore ◽  
H. F. Morrison
Keyword(s):  
Finite Element ◽  
Electric Fields ◽  
Three Dimensional ◽  
Mathematical Expression ◽  
Finite Element Mesh ◽  
Electromagnetic Modeling ◽  
Variational Integral ◽  
Element Mesh ◽  
Element Technique ◽  
Scattered Fields

We present an efficient numerical method for computing electromagnetic (EM) scattering of arbitrary three‐dimensional (3-D) local inhomogeneities buried in a uniform or two‐layered earth. In this scheme the inhomogeneity is enclosed by a volume whose conductivity is discretized by a finite‐element mesh and whose boundary is only a slight distance away from the inhomogeneity. The scheme uses two sets of independent equations. The first is a set of finite‐element equations derived from a variational integral, and the second is a mathematical expression for the fields at the boundany in terms of electric fields inside the boundary. The Green’s function is used to derive the second set of equations. An iterative algorithm has been developed to solve these two sets of equations. The solutions are the electric fields at nodes inside the finite‐element mesh. The scattered fields anywhere may then be obtained by performing volume integrations over the inhomogeneous region. The scheme is used for modeling 3-D inhomogeneities with plane‐wave and magnetic dipole sources. The results agree with earlier model analyses using the finite‐element technique.

scholarly journals Nonlinear model of short-scale electrodynamics in the auroral ionosphere

2000 ◽  
Vol 18 (9) ◽  
pp. 1128-1144 ◽  
Author(s):  
J.-M. A. Noël ◽  
J.-P. St.-Maurice ◽  
P.-L. Blelly
Keyword(s):  
Electric Fields ◽  
Acoustic Waves ◽  
Essential Elements ◽  
Auroral Ionosphere ◽  
Short Scale ◽  
Sharp Edges ◽  
Field Lines ◽  
Electric Fields And Currents ◽  
Auroral Arcs ◽  
Future Work

Abstract. The optical detection of auroral subarcs a few tens of m wide as well as the direct observation of shears several m/s per m over km to sub km scales by rocket instrumentation both indicate that violent and highly localized electrodynamics can occur at times in the auroral ionosphere over scales 100 m or less in width. These observations as well as the detection of unstable ion-acoustic waves observed by incoherent radars along the geomagnetic field lines has motivated us to develop a detailed time-dependent two-dimensional model of short-scale auroral electrodynamics that uses current continuity, Ohm's law, and 8-moment transport equations for the ions and electrons in the presence of large ambient electric fields to describe wide auroral arcs with sharp edges in response to sharp cut-offs in precipitation (even though it may be possible to describe thin arcs and ultra-thin arcs with our model, we have left such a study for future work). We present the essential elements of this new model and illustrate the model's usefulness with a sample run for which the ambient electric field is 100 mV/m away from the arc and for which electron precipitation cuts off over a region 100 m wide. The sample run demonstrates that parallel current densities of the order of several hundred µA m-2 can be triggered in these circumstances, together with shears several m/s per m in magnitude and parallel electric fields of the order of 0.1 mV/m around 130 km altitude. It also illustrates that the local ionospheric properties like densities, temperature and composition can strongly be affected by the violent localized electrodynamics and vice-versa.Key words: Ionosphere (auroral ionosphere, electric fields and currents, ionosphere-magnetosphere interactions)

scholarly journals Investigation of acoustic streaming patterns around oscillating sharp edges

Lab on a Chip ◽  
2014 ◽  
Vol 14 (15) ◽  
pp. 2824-2836 ◽  
Author(s):  
Nitesh Nama ◽  
Po-Hsun Huang ◽  
Tony Jun Huang ◽  
Francesco Costanzo
Keyword(s):  
Acoustic Streaming ◽  
Perturbation Approach ◽  
Sharp Edges

Perturbation approach is utilized to study the acoustic streaming phenomenon induced by the oscillation of sidewall sharp-edges.

scholarly journals Graphene H-Waveguide for Terahertz Lasing Applications: Electromagnetic Quasi-Linear Theory

Nanomaterials ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 2415
Author(s):  
Guennadi A. Kouzaev
Keyword(s):  
Linear Theory ◽  
Linear Method ◽  
Graphene Film ◽  
Current Crowding ◽  
Parallel Plates ◽  
Crowding Effect ◽  
Conductor Loss ◽  
Graphene Plasmons ◽  
Waveguide Design ◽  
Parallel Conductor

A novel graphene H-waveguide is proposed for active terahertz components. A graphene film illuminated by strong pumping light shorts the parallel conductor plates. The terahertz modes propagating along this film are amplified at certain conditions. A rigorous electromagnetic (EM) quasi-linear method of analytical calculations of TEy and TMy eigenmodes is used in this paper to select these conditions. Among them is the use of bound TEy modes interacting with graphene plasmons at frequencies of negative graphene resistance, minimizing conductor loss associated with parallel plates, and excluding the current-crowding effect from the waveguide design. The limitations of the used theory are considered, and the applications of this waveguide are proposed.

scholarly journals АВТОМАТИЗАЦІЯ ФІНІШНОГО ОБРОБЛЕННЯ ПРЯМОКУТНИХ КУТОВИХ ХВИЛЕВОДІВ S-ДІАПАЗОНУ

2020 ◽  
pp. 45-53
Author(s):  
Павло Романович Тришин ◽  
Наталя Вікторівна Гончар ◽  
Кирило Олександрович Терещенко
Keyword(s):  
Machining Accuracy ◽  
Cnc Milling ◽  
Special Equipment ◽  
Welding Seam ◽  
Extrusion Processing ◽  
Cnc Milling Machine ◽  
Surface Damages ◽  
Rectangular Waveguides ◽  
Sharp Edges ◽  
Grinding Machines

Finishing of waveguides (sharp edges blunting, burrs removal, polishing of welding or soldering of the duct and flanges) is carried out in order to eliminate all surface damages that are formed from previous operations and give it the necessary roughness, which affects the amount of active power loss. In most cases of complex spatial shape rectangular waveguides with angled welded transitions, the finishing of the duct is performed manually or by means of small mechanization. An alternative to the finishing of waveguide duct is anode-abrasive vibration honing, abrasive-extrusion processing, processing on special grinding machines, hydro-abrasive pumping. These methods are low productivity, require complex equipment, washing treated surfaces, and are applied only to straight waveguides or those that have a smooth flexion. Preliminary researches of polishing the waveguide duct with a polymer-abrasive brush have shown good results in terms of roughness, performance and electrical parameters.To automate finishing of the waveguides that have simple form or one simple rectangular flexion, it was proposed to perform it on a horizontal CNC milling machine. For processing of waveguides two types of polymer-abrasive brushes of Osborne firm were consistently applied: internal and end brushes. Processing involved polishing duct in welding seam spots and a flange, burrs removal immediately after processing on the same machine on which milling of flanges of waveguides was carried out.Also for mechanization of finishing the complex designed waveguides (more than one flexion) it is offered to replace operation of consecutive manual polishing by small mechanization of polishing on special equipment. The trajectory of the tool was provided by a copier.This device also provides the preset tightness automatically and ability to adjust it as the tool wears out. As a result of the improvement in finishing, the manual polishing of the waveguide was completely removed, and the geometry and roughness of the duct were significantly improved. The development of special equipment has significantly (3…5 times) reduced time and human impact on machining accuracy.

Control of Metal Alloy Oxidation with Electric Fields

1973 ◽  
Vol 31 ◽  
pp. 164-165
Author(s):  
R. R. Dils ◽  
P. S. Follansbee
Keyword(s):  
Electric Fields ◽  
Oxidation Process ◽  
Base Alloy ◽  
Oxide Surface ◽  
Platinum Electrodes ◽  
Insulating Layer ◽  
Iron Base Alloy ◽  
Alloy Oxidation ◽  
Aluminum Oxide Layer ◽  
And Control

Electric fields have been applied across oxides growing on a high temperature alloy and control of the oxidation of the material has been demonstrated. At present, three-fold increases in the oxidation rate have been measured in accelerating fields and the oxidation process has been completely stopped in a retarding field.The experiments have been conducted with an iron-base alloy, Pe 25Cr 5A1 0.1Y, although, in principle, any alloy capable of forming an adherent aluminum oxide layer during oxidation can be used. A specimen is polished and oxidized to produce a thin, uniform insulating layer on one surface. Three platinum electrodes are sputtered on the oxide surface and the specimen is reoxidized.

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