Effective Transmission Coefficient Research Articles

Gate-controlled near-surface Josephson junctions

Gate-tunable Josephson junctions are interesting for quantum technology applications, such as gatemon qubits and topological Majorana-based qubits. Furthermore, high-frequency compatible geometries can be utilized for implementing electrically pumped parametric amplifiers. In this paper, we combine processing, measurements, and modeling of near-surface InGaAs Josephson field-effect transistors in order to facilitate circuit simulations of actual non-ideal devices. We developed a compact model using Verilog-A and confirmed the validity of our model by accurately reproducing our measured data by circuit simulations in Advanced Design System. From the circuit simulations, an effective gate-dependent transmission coefficient, with a peak value of ∼ 3.5%, was extracted, mainly limited by contact transparency.

A Damped Double Dipole Antenna for UHF RFID Sensing in the Frequency Domain

Ultrahigh frequency (UHF) radio frequency identification (RFID) tags provide an inexpensive framework for distributed sensing, yet for the most cost-effective implementation, it is necessary to consider antenna design in concert with the capabilities of responsive materials that can be coupled to the tag response. Materials, such as functionalized carbon nanotubes (CNTs), have been engineered to change in resistance when exposed to a variety of analytes and have been incorporated in RFID tags to create low-cost sensors that work at a fixed reader–tag separation distance. This article presents a damped double dipole antenna design enabling UHF RFID tags that are able to sense changes in resistance of a sensing element (with a conductivity similar to that of printed CNT networks) regardless of reader–tag distance within the far-field read range. Simulations of the proposed design show two methods of operation, either by comparing the damping between two resonant peaks or by shifting the resonant frequency of the RFID tag. The first method is validated experimentally with surface mount resistors, showing a relative change in the effective antenna transmission coefficient, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\tau _{e}$ </tex-math></inline-formula> , of 0.2 for a 35% change in resistance of the sensing element.

Wireless Performance Evaluation of Building Materials Integrated With Antenna Arrays

To avoid negative visual and weight impact of antenna arrays in indoor multiple-input multiple-output (MIMO) systems, the antenna arrays can be integrated in building materials. In this letter, we model building materials integrated with antenna arrays and develop an approach that can characterize and evaluate their wireless performance using a ray-tracing model that incorporates multipath propagation from line-of-sight (LOS), reflected, and other paths. The approach comprises the following: 1) Using the effective transmission coefficient to characterize the electromagnetic (EM) coupling between the antenna array and the building material with which it is integrated; 2) Taking the spatially averaged capacity as a performance metric to quantify wireless performance of integrated materials; 3) Optimizing integrated materials&#x2019; wireless performance by tuning their conductivity, permittivity, thickness and integration depth; and 4) Comparing wireless performance between optimized and unoptimized integrated materials. Our numerical results show that the spatially averaged capacity varies with different material property settings, indicating that integrated materials should be carefully designed to enhance their wireless performance.

Effect of interfacial roughness on thermal boundary conductance: An elastic wave model using the Kirchhoff approximation

Interfacial roughness plays an important role in nanoscale thermal transport, while this issue still lacks a theoretical description due to the difficulty in quantifying the phonon scattering at the disordered interface. We report an elastic wave model (EWM) that describes the phonon–interface interaction by the interface elasticity. The transmissivity calculation based on the interfacial displacement and stress continuity incorporates the mode conversion and nonlinear vibration spectra of phonon waves, and the resulting cut-off frequency. Compared with the acoustic mismatch model that also assumes specular scattering of phonons waves, the applicable range of EWM is extended to room temperature and shows better accuracy. Based on this model, we use a statistical method with the Kirchhoff approximation and introduce the tangent plane slope distribution to determine the phonon scattering at a Gaussian-distributed rough interface. And the effective transmission coefficient is calculated by integrating the contributions of all points to the energy transmission. Calculated thermal boundary conductance (TBC) by a Landauer formula agrees well with the experiments of Al/SiO2/Si and Au/SiO2/Si rough interfaces. And the results show that the TBC of interface with sub-nanometer RMS roughness (10−10 m) is close to that of the smooth interface. After this transition, the increasing σ can significantly impact the interfacial heat transfer. Compared with existing models, the EWM can quantitatively estimate the effect of roughness on TBC and give a transmission image of wave-like phonons at the interface. This work contributes to an in-depth understanding of phonon wave effects in nanostructures.

Effect of internal structure on dynamically coupled heat and moisture transfer in closed-cell thermal insulation

Closed-cell thermal insulation is a common insulation material with low thermal conductivity. When temperature and humidity gradients are present, moisture penetration, condensation, and accumulation might occur in the material, thereby affecting the system's thermal performance. In traditional methods used for analyzing coupled heat and moisture transfer, it is difficult to quantify the effective transmission coefficient and isolate the impact of the related structures. A multi-scale model to predict the effect of the internal structure of closed-cell thermal insulation (phenolic) on the process of dynamic heat and moisture transfer is presented in this paper. Based on a reconstructed geometry that describes the internal structure of closed-cell thermal insulation, the relationships between the multiple structure parameters and effective transmission coefficients are analyzed using the lattice Boltzmann method. From the simulation data, a database is derived. A neural network algorithm is then used to predict the effective transmission coefficients at the mesoscopic scale. Furthermore, a multi-scale model was developed by combining the mesoscopic effective transmission coefficients with the macroscopic dynamically coupled heat and moisture model. The effects of the internal structure on the process of dynamic heat and moisture transfer are analyzed using the multi-scale model. Based on the simulation results, the optimal structures of the phenolic thermal insulation for minimum heat loss and low moisture ingress are selected and discussed.

Application of heuristic UTD formulation for describing scattering by a thin and multilayer anisotropic slab

The previously developed heuristic uniform theory of diffraction (UTD) corner and wedge diffraction coefficients for a thin lossless anisotropic slab are generalized and applied for predicting electromagnetic scattering by a thin and multilayer anisotropic slab with complex permittivity and permeability tensors. The effective reflection and transmission coefficients of a thin and multilayer slab are used in the heuristic formulation to determine the scattered fields. Numerical results are provided for various scattering problems that demonstrate the application of the heuristic formulations for a thin and multilayer structure.

A High-Frequency Solution for Scattering by a Multilayer Anisotropic Slab

The previously developed heuristic uniform theory of diffraction corner and wedge diffraction coefficients for a thin lossless anisotropic slab are generalized and applied for predicting electromagnetic scattering by a lossy/lossless multilayer anisotropic slab. The effective reflection and transmission coefficients of a multilayer slab are used in the heuristic formulation to determine the scattered fields. The heuristic coefficients derived for a thin slab are applied to a multilayer slab with a finite thickness. Numerical results are provided for various scattering problems that demonstrate the validity of the heuristic formulations for a multilayer structure.

Controllable quantum interference from two-photon scattershot sources

We describe a multi-mode passive linear optical network which emulates the two-photon number statistics of a beam splitter, irrespective on where the two photons enter the network. This is done by firstly defining general properties that the generator of the network matrix must fulfil. We then show that the network's effective transmission coefficient can be freely set to replicate either the absence of coincidence counts (i.e. the Hong-Ou-Mandel dip), or a 100% coincidence rate, as well as all possible two-photon beam splitter statistics between these two extremal points. Finally, we demonstrate that this network, in comparison to simpler systems, provides a better sampling rate and other resource advantages.

Methodology for Evaluation of District Heating Network Efficiency

The definition of overall district heating network performance indicators is under-investigated in the literature. This study reviews existing methods of performance estimation and develops a convenient methodology for an array of district heating networks applied to a Danish case study. Performances of the networks with state-of-art pipe transmission coefficients are compared to older traditional pipes using an effective average approach. The reported efficiencies and analysis of contributing factors show, that a single parameter is not sufficient to compare large-scale district heating systems and a multiparametric analysis must be employed. The effective average total heat transmission coefficient is evaluated based on the Technical Evaluation Factor and a multivariate regression is performed on typical sets of network parameters: pipe type, pipe series, pipe age, and operational temperature. The developed methodology is applied to testing an array of geographically independent district heating networks, pointing to possible performance bottlenecks, and discussing potential remedies.

Phase relations in superconductor–normal metal–superconductor tunnel junctions

The phase difference $\phi$, between the superconducting terminals in superconductor-normal metal-superconductor tunnel junctions (SINIS), incorporates the phase differences $\chi_{1,2}$ across thin interfaces of constituent $SIN$ junctions and the phase incursion $\varphi$ between the side faces of the central electrode of length $L$. It is demonstrated here that $\chi_{1,2}$ pass through over their proximity-reduced domain twice, there and back, while $\phi$ changes over the single period. Two corresponding solutions, that describe the double-valued order-parameter dependence on $\chi_{1,2}$, jointly form the single-valued dependence on $\phi$, operating in two adjoining regions of $\phi$. The phase incursion $\varphi$ plays a crucial role in creating such a behavior. The current-phase relation $j(\phi,L)$ is composed of the two solutions and, at a fixed small $L$, is characterized by the phase-dependent effective transmission coefficient.

Non-symmetrized quantum noise in a Kondo quantum dot

The fluctuations of electrical current provide information on the dynamics of electrons in quantum devices. Understanding the nature of these fluctuations in a quantum dot is thus a crucial step insofar as this system is the elementary brick of quantum circuits. In this context, we develop a theory for calculating the quantum noise at finite frequency in a quantum dot connected to two reservoirs in the presence of interactions and for any symmetry of the couplings to the reservoirs. This theory is developed in the framework of the Keldysh non-equilibrium Green function technique. We establish an analytical expression for the quantum noise in terms of the various transmission amplitudes between the reservoirs and of some effective transmission coefficient which we define. We then study the noise as a function of the dot energy level and the bias voltage. The effects of both Coulomb interactions in the dot and asymmetric couplings with the reservoirs are characterized.

Anomalous zero-temperature magnetopolaronic blockade of resonant electron tunneling in Majorana-resonant-level single-electron transistor

The magnetopolaronic generalization of a Majorana-resonant-level (MRL) model is considered for a single-level vibrating quantum dot coupled to two half-infinite $g=1/2$ Tomonaga-Luttinger liquid (TLL) leads. A qualitatively new non-trivial formula for the effective transmission coefficient and differential conductance for resonant magnetopolaron-assisted tunneling is obtained under the assumption about a fermion-boson factorization of corresponding averages. This approach is valid for the case of weak magnetopolaronic coupling in a system. Surprisingly, it is found that despite a supposed weakness of interaction between fermionic and bosonic subsystems in that case, a strongly correlated electron transport in the system reveals features of strong (and, hence, anomalous) magnetopolaronic blockade at zero temperature if the energy of a vibrational quantum is the smallest (but nonzero) energy parameter in the system. Such an effect should be referred to as magnetic phase-coherent magnetopolaron-assisted resonant tunneling of Andreev type, that originates from a special, Majorana-like, symmetry of magnetopolaron-coupled tunnel Hamiltonian. The effect predicted in this paper can be used as an experimental fingerprint of Majorana-resonant level situation in single-electron transistors as well as for detection of ultra-slow zero-point oscillations of suspended carbon nanotubes in the Majorana-resonant level regime of electron tunneling through corresponding single-electron transistors.

Analysis of coupled micro rings resonators and coupled Fabry–Pérot resonators with a single physical view

Coupled micro ring resonators gained a lot of interest in recent years in the field of silicon photonics. Although it is well recognized that coupled ring resonators and coupled Fabry–Pérot resonators operate with similar physical principles, their analysis in the literature is artificially separated, often each resonator type is analysed with different physical arguments, techniques and nomenclature. As a result, coupled rings resonators and coupled Fabry–Pérot resonators appear as two different problems, and the similarity in the physical principles that govern their operation is blurred. What is more unfortunate is that the established physical intuition, familiar from Fabry–Pérot analysis, is lost in notation when dealing with coupled micro rings. Here, we argue how a lossless boundary between two dielectrics and a lossless waveguide-coupler can be viewed as a single entity: an abstract ‘boundary’ that transmits and reflects optical fields according to Stokes relations. Using this view, Fabry–Pérot and micro rings become a single type of resonator. Accordingly, we calculate effective reflection and transmission coefficients of several configurations of coupled Fabry–Pérot and rings resonators. We calculate these coefficient by the intuitive method of summing reflected fields and by the method of transfer matrix. We illustrate that the effective reflection and transmission coefficients of a coupled ring resonator is similar to 3 layers Fabry–Pérot resonator and discuss the subtle difference. It is hoped that the common nomenclature and analysis used for both types of coupled resonators will give the reader a clear and basic understanding of both types of resonators.

Monte Carlo simulations of heterogeneous electron transfer: New challenges

We report results of MC simulations of electron transfer across a metal electrode/electrolyte solution interface. The model presumes the Landau–Zener theory and a random walk on a two-dimensional lattice formed by crossing parabolic reaction free energy surfaces along the solvent coordinate. Emphasis is put on investigating the activationless discharge regime; the bridge-assisted electron transfer is also partially addressed. We have calculated effective electronic transmission coefficient as a function of the electrode overpotential and temperature in a wide range of orbital overlap. The dependence of the transmission coefficient on the electronic density of states is analyzed as well.

An Accurate Current Model for III–V Field Effect Transistors Using a Novel Concept of Effective Transmission Coefficient

In this work, we investigate the transport phenomena in compound semiconductor material based buried channel Quantum Well MOSFET with a view to developing a simple and effective model for the device current. Device simulation has been performed in quantum ballistic regime using non-equilibrium Greens function (NEGF) formalism. The simulated current voltage characteristics using a novel concept of effective transmission coefficient has been found to define the reported experimental data with high accuracy. The proposed model has also been effective to capture the transport characteristics reported for other compound semiconductor material based field effect transistors. The concept of the proposed effective transmission coefficient and hence the model lends itself to be a simple and powerful device analysis tool which can be extensively used to predict the performance of a wide variety of compound semiconductor devices in the pre fabrication stage. It has also demonstrated consistency with device characteristics for doping concentration and channel length scaling. Thus the model can help the device or process engineers to tune the devices for the best possible performance.

Evaluation of stress wave propagation through rock mass using a modified dominate frequency method

This paper presents an evaluation of stress wave propagation through rock mass using a modified dominate frequency method. The effective velocity and transmission coefficient of stress wave propagation through rock mass with different joint stiffnesses are investigated. The results are validated by the theoretical method and the effects of incident frequency on the calculation accuracy are discussed. The results show that the modified dominate frequency method can be used to predict the effective velocity when the frequency of stress waves is within the low frequency range or high frequency range. However, the error cannot be ignored when the frequency is in the transitional frequency range. On the other hand, the modified dominate frequency method can be used to predict the transmission coefficient when the frequency of stress wave is within the low frequency range or optimal frequency range. However, the error cannot be ignored when the wave is within the high frequency range, which approaches 40% when the frequency is sufficiently large. Finally, the optimal stiffness–frequency relationship for the maximum calculation errors of effective velocity and the minimum calculation errors of transmission coefficient are proposed.

Experimental investigation of the radiation shielding efficiency of a MCP detector in the radiation environment near Jupiter’s moon Europa

Neutral Ion Mass spectrometer (NIM) is one of the instruments in the Particle Environmental Package (PEP) designed for the JUICE mission of ESA to the Jupiter system. NIM, equipped with a sensitive MCP ion detector, will conduct detailed measurements of the chemical composition of Jovian icy moons exospheres. To achieve high sensitivity of the instrument, radiation effects due to the high radiation background (high-energy electrons and protons) around Jupiter have to be minimised. We investigate the performance of an Al–Ta–Al composite stack as a potential shielding against high-energy electrons. Experiments were performed at the PiM1 beam line of the High Intensity Proton Accelerator Facilities located at the Paul Scherrer Institute, Villigen, Switzerland. The facility delivers a particle beam containing e−, μ− and π− with momentum from 17.5 to 345MeV/c (Hajdas et al., 2014). The measurements of the radiation environment generated during the interaction of primary particles with the Al–Ta–Al material were conducted with dedicated beam diagnostic methods and with the NIM MCP detector. In parallel, modelling studies using GEANT4 and GRAS suites were performed to identify products of the interaction and predict ultimate fluxes and particle rates at the MCP detector. Combination of experiment and modelling studies yields detailed characterisation of the radiation fields produced by the interaction of the incident e− with the shielding material in the range of the beam momentum from 17.5 to 345MeV/c. We derived the effective MCP detection efficiency to primary and secondary radiation and effective shielding transmission coefficients to incident high-energy electron beam in the range of applied beam momenta. This study shows that the applied shielding attenuates efficiently high-energy electrons. Nevertheless, owing to nearly linear increase of the bremsstrahlung production rate with incident beam energy, above 130MeV their detection rates measured by the MCP detector compares to the MCP rate of the incident electron beam. We define key performance parameters for the shielding and show direction of its improvements by introducing additional layer of material to attenuate γ-rays and reduce the MCP sensitivity to the penetrating radiation. The experiments also verify the predictions by modelling tools used currently for optimisation of shielding against high-energy particles.

Fluctuating-bias controlled electron transport in molecular junctions

We consider the problem of transport through a multiterminal molecular junction in the presence of a stochastic bias, which can also be used to describe transport through fluctuating molecular energy levels. To describe these effects, we first make a simple extension of our previous work [Phys. Rev. B 91, 125433 (2015)] to show that the problem of tunneling through noisy energy levels can be mapped onto the problem of a noisy driving bias, which appears in the Kadanoff-Baym equations for this system in an analogous manner to the driving term in the Langevin equation for a classical circuit. This formalism uses the nonequilibrium Green's function method to obtain analytically closed formulas for transport quantities within the wide-band limit approximation for an arbitrary time-dependent bias and it is automatically partition free. We obtain exact closed formulas for both the colored and white noise-averaged current at all times. In the long-time limit, these formulas possess a Landauer-B\uttiker--type structure which enables the extraction of an effective transmission coefficient for the transport. Expanding the Fermi function into a series of simple poles, we find an exact formal relation between the parameters which characterize the bias fluctuations and the poles of the Fermi function. This enables us to describe the effect of the temperature and the strength of the fluctuations on the averaged current which we interpret as a quantum analog to the classical fluctuation-dissipation theorem. We use these results to convincingly refute some recent results on the multistability of the current through a fluctuating level, simultaneously verifying that our formalism satisfies some well-known theorems on the asymptotic current. Finally, we present numerical results for the current through a molecular chain which demonstrate a transition from nonlinear to linear $I\text{\ensuremath{-}}V$ characteristics as the strength of fluctuations is increased, as well as a stochastic resonance effect in the conductance of this system.

Characterization of anisotropic acoustic metamaterial slabs

In an anisotropic acoustic metamaterial, the off-diagonal components of its effective mass density tensor should be considered in order to describe the anisotropic behavior produced by arbitrarily shaped inclusions. However, few studies have been carried out to characterize anisotropic acoustic metamaterials. In this paper, we propose a method that uses the non-diagonal effective mass density tensor to determine the behavior of anisotropic acoustic metamaterials. Our method accurately evaluates the effective properties of anisotropic acoustic metamaterials by separately dealing with slabs made of single and multiple unit cells along the thickness direction. To determine the effective properties, the reflection and transmission coefficients of an acoustic metamaterial slab are calculated, and then the wave vectors inside of the slab are determined using these coefficients. The effective material properties are finally determined by utilizing the spatial dispersion relation of the anisotropic acoustic metamaterial. Since the dispersion relation of an anisotropic acoustic metamaterial is explicitly used, its effective properties can be easily determined by only using a limited number of normal and oblique plane wave incidences into a metamaterial slab, unlike existing approaches requiring a large number of wave incidences. The validity of the proposed method is verified by conducting wave simulations for anisotropic acoustic metamaterial slabs with Z-shaped elastic inclusions of tilted principal material axes.

Anomalous barrier escaping in an externally modulated environment of system-reservoir coupling

The time-dependent barrier passage of an activated rate process is studied where the heat bath in the system-reservoir coupling environment is modulated by an external fluctuation. For a thorough inspection on the barrier recrossing dynamics, the Kramers rate and effective transmission coefficient are calculated of the reactive flux method. In the particular case of a δ-correlated noise activated Ornstein–Uhlenbeck process, it is found that, the external modulation can in some cases result in an maximum effective transmission coefficient. This reveals a maximum net flux and can be obtained from the minimum barrier recrossing resulted from appropriate external modulation.