Showing papers on "Transmission coefficient published in 2002"

Sharp asymmetric line shapes in side-coupled waveguide-cavity systems

Abstract: We show that, for an optical microcavity side coupled with a waveguide, sharp, and asymmetric line shapes can be created in the response function by placing two partially reflecting elements into the waveguides. In such a system, the transmission coefficient varies from 0% to 100% in a frequency range narrower than the full width of the resonance itself. We numerically demonstrate this effect by simulating the propagation of electromagnetic waves in a photonic crystal.

Floquet scattering theory of quantum pumps

Abstract: We develop the Floquet scattering theory for quantum-mechanical pumping in mesoscopic conductors. The nonequilibrium distribution function, the dc charge, and heat currents are investigated at arbitrary pumping amplitude and frequency. For mesoscopic samples with a discrete spectrum we predict a sign reversal of the pumped current when the pump frequency is equal to the level spacing in the sample. This effect allows us to measure the phase of the transmission coefficient through the mesoscopic sample. We discuss the necessary symmetry conditions (both spatial and temporal) for pumping.

Phonon wave-packet dynamics at semiconductor interfaces by molecular-dynamics simulation

Abstract: We directly observe phonon wave packets of well-defined frequency and polarization scattering at a coherent semiconductor interface using molecular-dynamics simulations. We find that in the low-frequency limit the transmission coefficients of both longitudinal and transverse acoustic phonons agree well with those predicted by the continuum-level based acoustic mismatch model. However, the transmission coefficients rapidly decrease close to the cutoff frequency, a result that can be understood within a simple one-dimensional discrete atomic-chain model. We also find that the transmission coefficient for transverse acoustic phonons depends strongly on the relative orientation of the polarization and the Si-Si bonds in the diamond lattice structure.

Ultrasound tunneling through 3D phononic crystals.

Abstract: We report the study of ultrasound tunneling in 3D phononic crystals, consisting of fcc arrays of close-packed tungsten carbide beads in water. The transmission coefficient, phase velocity, and group velocity were measured along the [111] direction, allowing us to systematically investigate the tunneling of ultrasound at frequencies in the lowest band gap. Our experimental data are interpreted using multiple scattering theory, which provides a good explanation of our results. The effect of absorption and the difference between the tunneling of classical waves and quantum waves are discussed.

The Woods-Saxon potential in the Dirac equation

Abstract: The two-component approach to the one-dimensional Dirac equation is applied to the Woods?Saxon potential. The scattering and bound state solutions are derived and the conditions for a transmission resonance (when the transmission coefficient is unity) and supercriticality (when the particle bound state is at E = ?m) are then derived. The square potential limit is discussed. The recent result that a finite-range symmetric potential barrier will have a transmission resonance of zero momentum when the corresponding well supports a half-bound state at E = ?m is demonstrated.

Numerical studies of left handed metamaterials

Abstract: We use the three dimensional Finite Difference Time Domain (FDTD) technique to study metamaterials exhibiting both negative permittivity and permeability in certain frequency bands. The structure under study is the well-known periodic arrangement of rods and split-ring resonators, previously used in experimental setups. The three parameters we study are the transmission coefficient of a slab, the phase variation of the propagating fields within the metamaterial, and the refraction of a wave through a prism. To our knowledge, this is the first time that the last two parameters are studied rigorously using a numerical method. The results of this work show that fields propagating inside the metamaterial with a forward power direction exhibit a backward phase velocity and negative index of refraction.

A ray-tracing approach for indoor/outdoor propagation through window structures

Abstract: A ray-tracing approach for indoor/outdoor propagation through windows is proposed. Using both the finite-difference time-domain (FDTD) method and a ray-tracing algorithm, several cases of indoor/outdoor propagation through windows were investigated. It is shown that wave transmission through windows cannot generally be accounted for through a single transmission coefficient parameter. Instead, a full diffraction pattern needs to be accounted for and multiple-ray representation is therefore required. It is also shown that a single window model may be used to calculate transmission through set of windows in a typical building structure as a building block. Results from the implementation of a multiple-ray representation and FDTD simulations showed good agreement. Results were validated for both normal and oblique incident cases. The developed ray-tracing approach, therefore, facilitates the use of the developed window model in available ray-tracing algorithms often used for propagation characterization of urban environments. Simulation results were further validated by conducting measurements on scaled models at 30 GHz. The experimental results agreed well with the simulation data, thus validating the accuracy of the developed ray-tracing model for transmission through windows.

Electron transfer through a molecular wire: Consideration of electron-vibrational coupling within the Liouville space pathway technique

Abstract: To fully account for electron-vibrational coupling and vibrational relaxation in the course of electron motion through a molecular wire a density operator approach is utilized. If combined with a particular projection operator technique a generalized master equation can be derived which governs the populations of the electronic wire states. The respective memory kernels are determined beyond any perturbation theory with respect to the electron-vibrational coupling and can be classified via so-called Liouville space pathways. An ordering of the different contributions to the current-voltage characteristics becomes possible by introducing an electron transmission coefficient which describes ballistic as well as inelastic electron transport through the wire. The general derivations are illustrated by numerical calculations which demonstrate the drastic influence of the electron-vibrational coupling on the wire transmission coefficient as well as on the current-voltage characteristics.

An estimate of the error caused by the plane-wave approximation in free-space dielectric measurement systems

Abstract: In a free-space measurement system, the electrical constitutive parameters of a plane sheet of material are determined using incident, transmitted and reflected electromagnetic beams. The electrical parameters are almost always obtained from the measured transmission and reflection coefficients using a procedure that approximates each beam as a single plane wave whose wavefront is parallel to the surfaces of the sheet (the plane-wave approximation). A theoretical model is constructed to investigate, in a very general way, the limitations of the plane-wave approximation. The field of the incident beam is taken to be a Gaussian function at the center of the sheet and analytic expressions are obtained for the transmitted and reflected beams using the plane-wave spectrum technique. Power transmission and reflection coefficients are calculated and series expansions of these coefficients are used to determine under what conditions the plane-wave approximation applies. Graphical results are presented to show how the error associated with the plane-wave approximation depends on the various parameters for the problem: electrical size of the beam waist, electrical thickness of the sheet etc.

Low momentum scattering in the Dirac equation

Abstract: It is shown that the amplitude for reflection of a Dirac particle with arbitrarily low momentum incident on a potential of finite range is −1 and hence the transmission coefficient T = 0 in general. If, however, the potential supports a half-bound state at momentum k = 0 this result does not hold. In the case of an asymmetric potential the transmission coefficient T will be nonzero whilst for a symmetric potential T = 1. Therefore in some circumstances a Dirac particle of arbitrarily small momentum can tunnel without reflection through a potential barrier.

Determination of thickness, refractive index, and thickness irregularity for semiconductor thin films from transmission spectra

Abstract: A simplified theoretical model has been proposed to predict optical parameters such as thickness, thickness irregularity, refractive index, and extinction coefficient from transmission spectra. The proposed formula has been solved for thickness and thickness irregularity in the transparent region, and then the refractive index is calculated for the entire spectral region by use of the interference fringes order. The extinction coefficient is then calculated with the exact formula in the transparent region, and an appropriate model for the refractive index is used to solve for the extinction coefficient in the absorption region (where the interference fringes disappear). The proposed model is tested with the theoretical predicted data as well as experimental data. The calculation shows that the approximations used for solving a multiparameter nonlinear equation result in no significant errors.

Scattering on a Compact Domain with Few Semi-Infinite Wires Attached: Resonance Case

Abstract: A Scattering problem is studied for Neumann Laplacian with a continuous potential on a domain with a smooth boundary and few semi-infinite wires attached to it at the points of contact on the boundary. In resonance case when the frequency of the incoming waves in the wires coincides with some resonance frequency of the domain the approximate formula for the transmission coefficient from one wire to another is derived: in the case of weak interaction between the domain and the wires the transmission coefficient is proportional to the product of values of the corresponding resonance eigenfunction of inner problem at the corresponding points of contact.

Modeling of GaN-based resonant tunneling diodes: Influence of polarization fields

Abstract: Resonant tunneling diodes (RTD) based on GaN/AlGaN heterojunctions should in principle show high values of peak/valley ratio due to the large conduction band discontinuities between GaN and AlGaN. Moreover, such structures have been studied to be used in quantum cascade lasers for near infrared emission. However, polarization fields can mask such benefits and make the design of RTD quite complicated. In this work, we have applied an atomistic point of view to describe current flowing in GaN-based RTD and investigate polarization issues. We used the sp3d5s* tight-binding (TB) model and a transfer matrix approach to describe the proper scattering states of the RTD system. The TB model allows us to describe the whole Brillouin zone of the semiconductors and relax all the envelope function approximations usually made for treating tunneling problems in RTDs. We observe that the effect of the polarization fields is to shift the transmission coefficient peaks while keeping a very high PVR.

Capacitively Loaded Loop as Basic Element of Negative Permeability Meta-material

Abstract: A simple one-dimensional meta-material which exhibits negative permeability within a finite frequency band is proposed in this paper. Instead of recently introduced split-ring resonators, this structure comprises an array of the capacitively loaded small loop antennas. Due to resonant behaviour of the antenna current, intensity of the magnetic field of the incoming plane wave may be locally decreased yielding a stop-band with negative effective permeability. Theoretical analysis was verified by measurements of the transmission coefficient of experimental structures in free space and in rectangular waveguide, in 10 GHz frequency band. The developed structure was also combined with previously reported negative permittivity wire structure and left-handed (backward wave) properties were observed.

Proton Transfer from Photoacid to Solvent

Abstract: We calculated the proton-transfer rate constant from a super photoacid, 5,8-dicyano-2-naphthol (DCN2), to a protic solvent as a function of temperature. Previously, we found that the temperature dependence of the proton-transfer rate constant is explained as a continuous transition from nonadiabatic to solvent-controlled limits. The model we used to calculate the proton-transfer rate constant is based on a diffusive propagation of the solvent configuration along a generalized solvent coordinate from the reactant potential surface toward the crossing point with the product potential surface. The proton transfer occurs at the crossing point, and the rate is calculated by a sink term placed at the crossing point. The sink term includes the solvent velocity and the Landau−Zener transmission coefficient. Both the diffusion constant and the Landau−Zener transmission coefficient depend on the dielectric relaxation of the solvent. The calculations are compared with the experimental data and an interpolation expre...

The Open Sea Tests of the Offshore Floating Type Wave Power Device “Mighty Whale”: Performance of the Prototype

Abstract: This paper presents the characteristics of wave conditions, wave energy absorption, response of hull-motion and wave height dissipation based on the results of the open sea tests. 0.5–1.0m of significant wave height and 6–7 seconds of significant wave period appear the most predominant, and average wave energy is estimated 4.88kW/m around the test site. Average power output for the test is approximately 6kWh and the maximum total energy efficiency is around 15% that is ranging from 6–7 seconds of significant wave period. Slow drift oscillation of hull was observed motion in surge, sway and yaw and the value of its amplitude almost equal to estimated values in design stage. Then the mean value of transmission coefficient is about 0.8 under 8.0 seconds of significant wave period. We are considering that the results of the tests should be useful for optimum design of an offshore floating type wave power device.Copyright © 2002 by ASME

Electromagnetic modeling of finite length wires buried in a lossy half-space

Abstract: The horizontal buried wire of a finite length is analyzed by using the scattering theory. The current distribution along the wire due to an external electromagnetic interference (EMI) source is governed by the half-space Pocklington integral equation. The effect of the lower half-space is taken into account via the transmission coefficient (TC) appearing within the integral equation kernel. The principal advantage of the TC approach vs rigorous Sommerfeld integral approach is the formulation simplicity and reduced computational cost. The variational boundary element procedure is used for solving the Pocklington integral equation and the current induced along the buried wire due to the transmitted plane wave or current source excitation is obtained.

Probability density function of polarization dependent loss (PDL) in optical transmission system composed of passive devices and connecting fibers

Abstract: This paper presents a probability density function formula for predicting the polarization dependent loss (PDL) in an optical transmission system composed of passive devices and connecting fibers. A new calculation technique, which enables the probability density function formula to be obtained theoretically, is used instead of the most complicated part of the Muller-matrix or Jones-matrix calculations, which has been thought to be necessary for analyzing PDL. This technique involves calculation of the transmission coefficients of the transmission system and its devices from their PDLs. In the theoretical development, the central limit theorem is used as the sole approximation. A Monte Carlo numerical simulation was done to verify the validity of the analytical theory. Very good agreement between simulation and analytical theory is obtained when the number of devices having PDL is four or more. An experiment also demonstrated the validity of the analytical theory. The theory can also explain some phenomena that occur in systems composed of optical amplifiers, even though it had originally been developed to explain PDL-related phenomena in systems composed of passive devices only.

Wave Transmission at Detached Breakwaters for Shoreline Response Modeling

Abstract: : The Coastal and Hydraulics Engineering Technical Note (CHETN) herein evaluates selected available formulas for predicting wave transmission at reef breakwaters and more conventional multilayer structures, leading to recommendations for the most appropriate formulas for shoreline-response modeling. The GENESIS shoreline response numerical model is modified to allow for automated time-dependent calculation of the wave transmission coefficient, and a case study is presented to illustrate the new predictive capability.

Electronic transport properties of Sierpinski lattices in a magnetic field

Abstract: We have studied the electronic transport properties of open Sierpinski gasket systems in the presence of a magnetic field. The real-space renormalization-group scheme combined with the generalized eigenfunction method is used to calculate the transmission and reflection coefficients. Three kinds of electronic exits are investigated upto the thirtieth generation Sierpinski lattice. Some resonant-transmission features and the symmetry of the transmission coefficient T to the magnetic flux Φ are observed and discussed.

Method of optical proximity correction

Abstract: A method of optical proximity correction is disclosed, which is suitable for use in the microlithography process of high numerical aperture, wherein the exposure light source contains a P-polarized light and an S-polarized light, which are mutually perpendicular, and the transmission coefficient of the P-polarized light is larger than that of the S-polarized light. This method is applied to each pattern with different pattern directions for proceeding correction using different optical proximity correction models respectively, wherein when any pattern is corrected, the ratio of the transmission coefficient between the P-polarized light and S-polarized light, and the angle between the pattern direction and P-polarized light/S-polarized light of this pattern are taken into account.

Magnonic spectral gaps and discrete transmission in serial loop structures

Abstract: In the frame of the long-wavelength Heisenberg model, the magnonic bandgaps and the selective transmission in a serial loop structure, made of loops pasted together with segments of finite length, are investigated theoretically. The loops and the segments are assumed to be one-dimensional ferromagnetic materials. Using a Green function method, we obtained closed-form expressions for the band structure and the transmission coefficients for an arbitrary value of the number N of loops in the serial loop structure. It was found that the gaps originated from the periodicity of the system. The width of these forbidden bands depends on the structural and compositional parameters. We also present analytical and numerical results for the transmission coefficient through a defective geometry where the length of one finite branch has been modified. It was demonstrated that the presence of this defect in the structure can give rise to localized states inside the gaps. We show especially that these localized states are very sensitive to the size of the loops and to the periodicity as well as to the length and the location of the defect branch.

Tunneling time of spin-polarized electrons in ferromagnet/insulator (semiconductor) double junctions under an applied electric field

Abstract: Based on the group velocity concept and the two-band model, we investigated tunneling properties of spin-polarized electrons traversing ferromagnetic/insulator (semiconductor) double junctions under the influence of an external electric field. The tunneling time and the transmission coefficient, as well as the spin polarization, were calculated and examined. Effects of the electric field and quantum size are also considered. The results indicate that the tunneling time strongly depends on the spin orientation of tunneling electrons. In a wide range of incident energy, spin-down electrons spend a longer time tunneling through the structure than spin-up ones, and the difference of the tunneling time Δτ between electrons with opposite spin orientation is very sensitive to the incident energy in the lower energy region. Moreover, the variation of Δτ with the increasing of the incident energy shows pronounced oscillations for certain applied bias and structural size. The results also indicate that spin polariz...