Dependence Of Transmission Coefficient Research Articles

Study of birefringence inside nanocrystalline Zinc Oxide thin films using terahertz spectroscopy

We present experimental characterizations of nanocrystalline Zinc Oxide (ZnO) thin films in far-infrared (terahertz) frequency region using terahertz time-domain spectroscopy. A time dependent profile, frequency dependent transmission coefficient, refractive index, absorption coefficient and optical density of ZnO thin films are measured in the terahertz regime. A birefringence is observed as a result of TO–LO phonon splitting took place in the ZnO deposited at 400 °C substrate temperature, while at low substrate temperature of 200 °C there is no sign of birefringence. Thus, it can be clearly evidenced that the presence of birefringence in ZnO is correlated with crystallinity exists inside of the thin films. Absorption behaviour of ZnO nano-crystalline thin films shows the potential use of it for future THz photonics devices. RF magnetron sputtering is the key for the deposition of nanocrystalline ZnO thin films on Si (100) substrate at different temperatures. The X-ray diffraction pattern of ZnO thin films were confirmed the formation of wurtzite hexagonal structure and nanocrystalline nature of the deposited ZnO thin films.

Room temperature high Giant Magnetoresistance graphene based spin valve and its application for realization of logic gates

In this study we carried out first principle calculations for spin dependent electronic transport in our proposed spintronic device consisting of graphene nanoribbon as scattering region with cobalt electrodes and magnesium oxide as tunneling barrier. The I–V Characteristics are calculated by using Non-Equilibrium Green's Function formalism in combination with Semi-Empirical (SE) Extended Huckel Theory (EHT) using Atomistic Tool Kit software at room temperature. The high value of GMR (Giant Magnetoresistance) is recommended for spintronic devices. The results reveal that the device shows a very high GMR ratio of 5.16×104%. The device also shows very low off state current, therefore negligible off state power consumption. The investigation of spin dependent non equilibrium transport is done by examining bias dependent transmission coefficients. Furthermore, some basic logic gates, like NOT, AND and NOR have been realized from the modeled device. The device may also find applications in data storage, magnetic field sensors etc.

Electromagnetic-wave propagation through an array of superconducting qubits: Manifestations of nonequilibrium steady states of qubits

We report a theoretical study of the electromagnetic waves (EWs) propagation through an array of superconducting qubits, i.e. coherent two-level systems, embedded in a low-dissipative transmission line. We focus on the near-resonant case as the frequency of EWs $\omega \simeq \omega_q$, where $\omega_q$ is the qubit frequency. In this limit we derive the effective dynamic nonlinear wave equation allowing one to obtain the frequency dependent transmission coefficient of EWs, $D(\omega)$. In the linear regime and a relatively wide frequency region we obtain a strong resonant suppression of $D(\omega)$ in both cases of a single qubit and chains composed of a large number of densely arranged qubits. However, in narrow frequency regions a chain of qubits allows the resonant transmission of EWs with greatly enhanced $D(\omega)$. In the nonlinear regime realized for a moderate power of applied microwave radiation, we predict and analyze various transitions between states characterized by high and low values of $D(\omega)$. These transitions are manifestations of nonequilibrium steady states of an array of qubits achieved in this regime.

All-Pass Negative Group Delay Function With Transmission Line Feedback Topology

A novel circuit theory of all-pass Negative group delay (NGD) function is investigated. The NGD function is implemented with unity direct chain feedback (UDCF) system. The active circuit is built with an operational amplifier in feedback with a lossy transmission line (TL). The UDCF topology S-parameter model is established versus TL parameters. The NGD analysis is elaborated from the frequency dependent transmission coefficient. The NGD behavior characterization is developed. The synthesis method allowing to determine the UDCF topology parameters in function of the targeted NGD values, gain and reflection coefficient is formulated. The all-pass NGD function is validated with a proof-of-concept (POC) design. Frequency and time domain simulations confirm the feasibility of the innovative all-pass NGD function. With S-parameter analysis, it was shown that the UDCF circuit exhibits NGD up to -7-ns with gain more than 0-dB and reflection coefficient -20-dB. More importantly, time-domain analysis illustrates how the transient tested voltage outputs can be in advance compared to the input.

Bias dependent transport property of defective hydrogen passivated tilted black phosphorene nanoribbon

Using the density functional theory and non-equilibrium Green's function method, we investigated the bias dependent transport property of point defective hydrogen passivated tilted phosphorene nanoribbons. Here, we calculated the I-V curve by changing the defect position. Here, three different defect sites were considered; edge, central defect, and mid-point defect between edge and central region. It was found that the I-V characteristic was substantially sensitive to the defect position because the onset bias voltage and the increment in the current with bias were different from each other. Besides, unlike the conventional belief, we obtained that the magnitude of the current due to the point defect was four to five times enhanced compared with that in the defect-free pristine nanoribbon structure. We found that the simple analysis based on the Fermi level shifting at finite bias was not enough to explain the I-V curve. Instead, we realized that it was necessary to consider both bias dependent transmission coefficient and density of states in the scattering region to explain the I-V curve.

Aspects of electron transport in zigzag graphene nanoribbons

In this paper, we investigate the aspects of electron transport in the zigzag graphene nanoribbons (ZGNRs) using the nonequilibrium Green’s function (NEGF) formalism. The latter is an esoteric tool in mesoscopic physics. It is used to perform an analysis of ZGNRs by considering potential well. Within this potential, the dependence of transmission coefficient, local density of states (LDOS) and electron transport properties on number of atoms per unit cell is discussed. It is observed that there is an increment in electron and thermal conductance with increasing number of atoms. In addition to these properties, the dependence of same is also studied in figure of merit. The results infer that the contribution of electrons to enhance the figure of merit is important above the crossover temperature.

Modeling wave propagation through the skull for ultrasonic transcranial Doppler

One problem associated with transcranial Doppler ultrasound (TCD) is the relatively low energy penetrating inside the brain through the skull, seriously limiting the image quality. This may be due to the impedance mismatch at the bone interface and to the bone frequency dependent attenuation. The objective of this paper is to model ultrasonic wave propagation through the skull. To do so, an analytical model was developed based on the estimation of the transmission coefficients inside the brain, leading to frequency dependent overall transmission coefficient for a given skin and bone thickness. Moreover, a finite element model was developed taking into account absorption phenomena. Both methods were validated experimentally by comparing the numerical and analytical results with results obtained from a phantom mimicking the skull having an attenuation coefficient equal to 30 dB/cm at 2.25 MHz and a thickness of 4.4 mm. A 2 mm layer of water mimicked the skin. The difference between the maximum amplitude of normalized received US signals obtained analytically and experimentally was 1%. The average relative difference between them was 0.3%. Thus, a working model is designed which can predict the energy inside the brain. Furthermore, the results show that impedance mismatch plays a major role in transmission loss rather than frequency dependent attenuation

MICROWAVE PROPAGATION IN TOOTH AND DENTAL DEFECT

INTRODUCTION:The most common method of conventional dental diagnosisinvolves X-rays, such as Radio Tomography (RT) or Computer Tomography (CT). Such methods are used for diagnosing pores in dental material that can lead to premature failure of dental material. Diagnosis by X-ray provides an objective analysis. However, repeated radiation from X-rays can cause biological damage to human tissues. From this point of view, there is a significant need to progress to quantitative non-invasive and non-destructive testing (NDT) methods to measure dental material and improve treatment options. This article focuses on applying microwave technology to characterize teeth and teeth replacements. Knowledge of microwave propagation in biomaterial with no defects, using a defined microwave frequency range, and subsequently comparing the result with defective material could provide a means of dental diagnosis without the risk of radiation for the patient, i.e. without X-ray. OBJECTIVES: The primary objective of this study was to examine microwave technology in the field of dental medical diagnosis as a new NDT method. METHODS: The basic concept of applying microwave technology to characterize teeth in dental diagnosis was examined using a basic algorithm designed in the MATLAB programming language. Tests used dielectric properties of tooth and tooth decay and propagated electromagnetic (EM) waves to show different characteristics of chosen materials.RESULTS: The analyses of frequency dependent reflection and transmission coefficients of the chosen material, specificallyteeth, atfrequency range 0 GHz to 30 GHz, computed differences between healthy and defective dental material.CONCLUSION: Thus, this could be used in providing a dental diagnosis without exposing patients to radiation, i.e. without X-ray. The next stage will involve creating a complete model of a jaw with teeth, and designing a sensor for crack detection for comparisons using this basic algorithm.

First-principles study of spin transport in BN doped CrO2–graphene–CrO2 magnetic tunnel junction

We investigate the spin-dependent electronic transport properties of Magnetic tunnel junction (MTJ) consisting of Boron (B) and Nitrogen (N) doped graphene nanosheet sandwiched between two CrO2 half-metallic–ferromagnet (HMF) electrodes. A large value of tunnel magnetoresistance (TMR) and perfect spin filtration was obtained as compared to un-doped graphene MTJ structures reported in past. The use of HMF electrodes further raises the TMR and improves the spin filtration in comparison to MTJs with metallic and ferromagnetic (FM) electrodes, which suggest HMF electrodes as a suitable candidate over metallic and FM electrodes for implementing graphene sheet based MTJs. A high value of TMR ∼100% is obtained at zero bias voltage, which remains constantly high at higher bias voltages in the range of 0 V to 1 V. The higher value of TMR and better (near perfect) spin filtration abilities suggest its usefulness in spin-valves and other spintronics based applications. The spin-dependent non-equilibrium transport is also investigated by analyzing the bias dependent transmission coefficients.

Investigation of Anisotropic Cylindrical Semiconductor-Dielectric Waveguides

The use of semiconductor-dielectric waveguides is low at the moment due to disadvantage of high attenuation of electromagnetic microwaves. The attenuation depends on structures and materials of semiconductor-dielectric waveguides. Dependences of transmission coefficient on the frequency of semiconductor-dielectric waveguides and on different densities of electrons in semiconductors are studied in this paper. As well as the influence of periodicity on transmission of electromagnetic microwaves in semiconductor-dielectric waveguides is discussed. It is shown that frequency dependences of transmission coefficient of periodical semiconductor-dielectric waveguides obtain the properties of the band pass filter. Also it is shown that the choice of semiconductor and dielectric materials have a significant impact on the nature of the transmission and attenuation of electromagnetic microwaves. DOI: http://dx.doi.org/10.5755/j01.eee.21.5.13327

IJIREEICE - Electrical, Electronics, Instrumentation and Control

2 Abstract: In this paper we analyzed the behavior of the Electromagnetic waves on some of the human tissues. As Electromagnetic waves propagate from one homogeneous medium to another, they experience a change of the wave impedance in the interface. The impedance mismatch generally leads to the reflection, absorption, and transmission of Electromagnetic waves. In the case of non homogeneous media like a human body, it is complex to analyze the behavior of Electromagnetic waves. The reflection and transmission coefficients vary from tissue to tissue and they are dependent on permittivity, conductivity, conductivity and frequency. Moreover, these fundamental parameters are also dependent on frequency. The frequency dependent reflection and transmission coefficients of some human tissues, especially bone tissues are computed at frequency range 0 to 10 GHZ using MATLAB.

Thermal resistance at constrictions in 2D mesoscopic ribbons at low temperatures

Phonon transport in junctions formed between suspended membranes of the same material is studied using Monte Carlo method. The investigation is conducted at 1K for systematically chosen ratios of (d/D) where d is the junction width and D the membrane length. The influence of surface roughness is taken into account. The dependency of the constriction thermal resistance (in μmK/W) is established: RJ ≈ [2.4 + 2.0 × (d /D)−1/2] × 109. The average and frequency dependent transmission coefficients are determined as a function of (d/D). These structural configurations are inherent in thermoelectric; and graphene and silicene related applications.

Computational studies of water exchange around aqueous Li+ with polarizable potential models

To enhance our understanding of the mechanism of water-exchange around aqueous Li(+), we carried out a systematic study on this system using molecular dynamics simulations with polarizable potential models. The mechanistic properties associated with the water-exchange process, such as potentials of mean force, time dependent transmission coefficients, and the corresponding rate constants, were examined using transition rate theory, the reactive flux method, and Grote-Hynes treatments of the dynamic response of the solvent. We compared the computed rate theory results with results from previous corresponding studies in which classical non-polarizable force fields were used. Our computed barrier heights for water exchange are significantly larger than those obtained using classical non-polarizable force fields. We also studied the effect of pressure on water-exchange rates and the corresponding activation volume. Our computed rate results for water exchange increase with pressure; therefore, a small negative activation volume is observed.

Nonlinear thermoelectric transport: A class of nanodevices for high efficiency and large power output

Molecular junctions and similar devices described by an energy dependent transmission coefficient can have a high linear response thermoelectric figure of merit. Since such devices are inherently non-linear, the full thermodynamic efficiency valid for any temperature and chemical potential difference across the leads is calculated. The general features in the energy dependence of the tranmission function that lead to high efficiency and also high power output are determined. It is shown that the device with the highest efficiency does not necessarily lead to large power output. To illustrate this, we use a model called the t-stub model representing tunneling through an energy level connected to another energy level. Within this model both high efficiency and high power output are achievable. Futhermore, by connecting many nanodevices it is shown to be possible to scale up the power output without compromising efficiency in an (exactly solvable) n-channel model even with tunneling between the devices.

Transmission of massless Dirac fermions through an array of random scatterers in terms of Fabry-Perot resonances: a Green’s function approach

Transmission properties of massless Dirac fermions that are charge carriers in graphene through a double potential barrier can be completely understood in terms of resonances in Fabry-Perrot cavity. Using a Green’s function based approach we generalize this analysis to the case of transmission through an array of short range random scatterers modeled as delta function. The method helps to understand such disordered transport in terms of well-known optical phenomena such as Fabry-Perot resonances. Using this optical analogy we particularly provide a microscopic understanding of the interplay between disorder-induced localisation that is the hallmark of a non-relativistic system and two important properties of such massless Dirac fermions, namely, complete transmission at normal incidence and periodic dependence of transmission coefficient on the strength of the barrier that leads to a periodic resonant transmission. Within this framework we show that this leads to two different types of conductance behaviour as a function of the system size at the resonant and the off-resonance strengths of the delta function potential.

Modeling the acoustic scattering from large fish schools using the Bloch-Floquet theorem

Scattering from large fish schools can significantly contribute to volume reverberation in the open ocean measured by mid-frequency long-range SONAR systems (1–10 kHz). This can potentially cause large false-alarms, especially if the resonance frequencies of the fish’ air-filled swim bladder is excited. Hence, to ultimately improve the detection performance of long-range SONAR systems, we seek an efficient modeling technique for the acoustic scattering created by large school of fish, which readily accounts for the fish bio-acoustic properties, school’s spatial configuration and multiple scattering effects. We exploit here a key observation to simplify our problem: fish in larger schools tend to swim in a periodic arrangement whereby we approximate the large school as an infinite system with a periodic collection of fish’ air filled swimbladders. Thus, the Bloch-Floquet theorem, governing waves in periodic media, allows predictions of the acoustic field in an infinite media by simply modeling the dynamic response of a single unit cell only (containing one fish). This approach allows one to rapidly predict the frequency dependent reflection and transmission coefficient on a semi-infinite fish school for various incident waves. Good agreement was found with the results obtained from finite element modeling of realistic, finite sized fish schools.

Velocity-direction dependent transmission coefficient of electron through potential barrier grown on anisotropic semiconductor

In contrast to the usual wavevector dependent transition coefficients, the velocity-direction dependent transition coefficients of an incident electron are calculated. Through a potential barrier grown on anisotropic semiconductors, the transition coefficients of an incident electron are calculated in all valleys and incident-directions. In the anisotropic semiconductor, the mathematical expressions of the electron wavevector are also derived in the framework of the incident-angle and incident-energy parameters.

Energy distribution and quantum yield for photoemission from air-contaminated gold surfaces under ultraviolet illumination close to the threshold

The kinetic energy distributions of photo-electrons emitted from gold surfaces under illumination by UV-light close to the threshold (photon energy in the order of the material work function) are measured and analyzed. Samples are prepared as chemically clean through Ar-ion sputtering and then exposed to atmosphere for variable durations before quantum yield measurements are performed after evacuation. During measurements, the bias voltage applied to the sample is varied and the resulting emission current measured. Taking the derivative of the current-voltage curve yields the energy distribution which is found to closely resemble the distribution of total energies derived by DuBridge for emission from a free electron gas. We investigate the dependence of distribution shape and width on electrode geometry and contaminant substances adsorbed from the atmosphere, in particular, to water and hydro-carbons. Emission efficiency increases initially during air exposure before diminishing to zero on a timescale of several hours, whilst subsequent annealing of the sample restores emissivity. A model fit function, in good quantitative agreement with the measured data, is introduced which accounts for the experiment-specific electrode geometry and an energy dependent transmission coefficient. The impact of large patch potential fields from contact potential drops between sample and sample holder is investigated. The total quantum yield is split into bulk and surface contributions which are tested for their sensitivity to light incidence angle and polarization. Our results are directly applicable to model parameters for the contact-free discharge system onboard the Laser Interferometer Space Antenna (LISA) Pathfinder spacecraft.

Photonic Band Characteristics in a Metallic Waveguide

We study the transmission coefficient and photonic band characteristics in an inhomogeneous metallic circular waveguide with perfect conducting walls and having periodic variation of dielectric constant along the axial direction by the transfer matrix method. The propagation ceases below the waveguide cutoff and above that band characteristics are found to set in for different waveguide modes. In order to avoid multiple waveguide mode scattering by the superlattice, the dimension of the guide is chosen in such a manner that at the operating frequency, only the lowest mode can occur. We investigate the number of unit cells (N) dependent transmission coefficient of the structure and also when acting as single or double electromagnetic barrier. Specifically, we demonstrate the existence of super narrow transmission band and a gap region for experimentally realizable structures. Photonic crystals have important applications in optical filtering with super narrow transmission band. For the guiding structure of infinite transverse extent, the analysis is found to agree well with that of wave propagation normal to the superlattice planes. Bloch's theorem which dramatically simplifies the periodic problem does not apply. The finitely periodic case can be solved analytically for arbitrary N using the transfer matrix approach. This paper is concerned with a theory of PBS in an inhomogeneous metallic waveguide with perfect conducting walls and having periodic variation of dielectric constant along the axial direction only. In fact, the behaviour of the electromagnetic field in the optical waveguide with a stratified medium inside is analyzed. The 1D stratified medium of infinite transverse extent has been studied extensively. Here, we consider 1D finite PC which is of finite transverse extent. We develop the general theory for the guiding structure. The formulation of the problem is done so that we get scalar wave equation for the longitudinal component of the electric and magnetic fields. The component Hz satisfies the Helmholtz equation whose solution has been obtained through the transfer matrix formulation. mn mn mn m n m z     

Structural and electrical investigation of (Ag3AsS3)x(As2S3)1−x superionic glasses

Abstract Structural studies of (Ag3AsS3)x (As2S3)1−x chalcogenide superionic glasses in the compositional range x = 0.3–0.9 were performed by scanning electron microscopy. Temperature and compositional dependences of transmission coefficient, electrical conductivity, and activation energy were investigated