Frequency Dispersion Effects Research Articles

Dispersion of tsunamis: does it really matter?

Abstract. This article focuses on the effect of dispersion in the field of tsunami modeling. Frequency dispersion in the linear long-wave limit is first briefly discussed from a theoretical point of view. A single parameter, denoted as "dispersion time", for the integrated effect of frequency dispersion is identified. This parameter depends on the wavelength, the water depth during propagation, and the propagation distance or time. Also the role of long-time asymptotes is discussed in this context. The wave generation by the two main tsunami sources, namely earthquakes and landslides, are briefly discussed with formulas for the surface response to the bottom sources. Dispersive effects are then exemplified through a semi-idealized study of a moderate-strength inverse thrust fault. Emphasis is put on the directivity, the role of the "dispersion time", the significance of the Boussinesq model employed (dispersive effect), and the effects of the transfer from bottom sources to initial surface elevation. Finally, the experience from a series of case studies, including earthquake- and landslide-generated tsunamis, is presented. The examples are taken from both historical (e.g. the 2011 Japan tsunami and the 2004 Indian Ocean tsunami) and potential tsunamis (e.g. the tsunami after the potential La Palma volcanic flank collapse). Attention is mainly given to the role of dispersion during propagation in the deep ocean and the way the accumulation of this effect relates to the "dispersion time". It turns out that this parameter is useful as a first indication as to when frequency dispersion is important, even though ambiguity with respect to the definition of the wavelength may be a problem for complex cases. Tsunamis from most landslides and moderate earthquakes tend to display dispersive behavior, at least in some directions. On the other hand, for the mega events of the last decade dispersion during deep water propagation is mostly noticeable for transoceanic propagation.

On the Processes of the Charge Transfer in the Electrical Conducting Polymer Materials

The analysis of charge transfer processes in the electrical conducting solid polymer systems has been carried out. The processes in these systems are divided to two types. The first type is the process of charge transfer between electrodes and particles while the second one - the process of the charge transfer between conductive particles. The description of medium is carried out using Green temperature functions of polarization operators for the molecular medium. It permits taking into account the effects of frequency and space dispersion. The analytical expressions for kinetic parameters of the charge transfer processes from electrodes to particles and between particles in condensed matter have been obtained. The comparison of the general theoretical dependence of the current in electric conducting polymer composites (ECPC) on the average distance between conducting particles with analogical dependence for some real ECPC are presented in the paper.

Dielectric and microwave absorption properties of Ti3SiC2 powders

Ti3SiC2 powders are synthesized via vacuum pressureless sintering method. The dielectric properties of the powders synthesized at different temperature are investigated in the frequency range from 8.2 to 12.4 GHz (X-band), which suggests the remnant TiC has obvious influence on complex permittivity and the pure Ti3SiC2 powders have the highest dielectric loss. The dielectric and microwave absorption properties of Ti3SiC2 powders are studied. Both the real part (ε′) and imaginary part (ε″) increase with Ti3SiC2 concentration but decrease with increasing frequency, which presents the obvious frequency dispersion effect. Furthermore, the effect of thickness on the microwave absorption property of Ti3SiC2/paraffin mixture is analyzed. The mixture with 70 wt% Ti3SiC2 in 2.0 mm thickness presents the optimum microwave absorption property. The effective absorbing bandwidth (below −10 dB) is almost in the whole frequency range and the lowest reflection loss is −33.83 dB. The results show Ti3SiC2 powders are good microwave absorbents in the X-band frequency range.

On the origin of frequency dispersion at the interface between mercury electrode and aqueous solutions of alkali halides

The origin of frequency dispersion of electrochemical impedance is investigated at the interface of mercury and aqueous solutions of single alkali halides. It is found that in the presence of each one of KI, CsI, CsF and CsBr salts, the interface presents certain potential regions where frequency dispersion effects are detected and others where the ideal capacitor behavior is closely approximated. Frequency dispersion effects are contributed by interfacial processes such as anion and cation adsorption, mercury halide film formation and dissolution and charge transfer reactions. The discrimination between frequency dispersion due to charge transfer processes occurring at the Hg/solution interface and that due to reactant adsorption itself is generally difficult and depends on the reaction mechanism, provided that a discrete adsorption step is anticipated.

Assessment of 50%-Propagation-Delay for Cascaded PCB Non-Linear Interconnect Lines for the High-Rate Signal Integrity Analysis

This paper presents an enlarged study about the 50-% propagation-time assessment of cascaded transmission lines (TLs). First and foremost, the accurate modeling and measurement technique of signal integrity (SI) for high-rate microelectronic interconnection is recalled. This model is based on the reduced transfer function extracted from the electromagnetic (EM) behavior of the interconnect line RLCG-parameters. So, the transfer function established takes into account both the frequency dispersion effects and the different propagation modes. In addition, the transfer function includes also the load and source impedance effects. Then, the SI analysis is proposed for high-speed digital signals through the developed model. To validate the model understudy, a prototype of microstrip interconnection with w = 500 µm and length d = 33 mm was designed, simulated, fabricated and tested. Then, comparisons between the frequency and time domain results from the model and from measurements are performed. As expected, good agreement between the S-parameters form measurements and the model proposed is obtained from DC to 8 GHz. Furthermore, a de-embedding method enabling to cancel out the connectors and the probe effects are also presented. In addition, an innovative time-domain characterization is proposed in order to validate the concept with a 2.38 Gbit/s-input data signal. Afterwards, the 50-% propagation-time assessment problem is clearly exposed. Consequently an extracting theory of this propagation-time with first order RC-circuits is presented. Finally, to show the relevance of this calculation, propagation-time simulations and an application to signal integrity issues are offered.

Computation of static and frequency-dependent line parameters of multilayer CPW using static SDA and single layer reduction method

We reformulate the quasi-static SDA applicable to a lossy multilayer CPW that also incorporates two-layer model of a conductor thickness and the concept of effective permeability due to magnetic field penetration in an imperfect conductor. The present static SDA formulation accounts for the effect of conductor thickness and low frequency dispersion on computation of quasi-static effective relative permittivity and characteristic impedance. The paper also presents the single layer reduction (SLR) formulation and circuit model to compute frequency dependent line parameters of a lossy multilayer CPW. The accuracy of formulation is comparable to that of HFSS and CST, without using complex and time consuming full-wave methods. The results of CST for εeff, Z0, αd, αc of multilayer CPW, in the frequency range 1–100 GHz, deviate from results of HFSS up to 1.26%, 2.78%, 11.75%, and 18.7%, respectively; whereas corresponding deviations of present formulation are up to 1.56%, 2.4%, 3.04%, and 7%. The results of the present formulation and HFSS are also compared against the available experimental results. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:18–29, 2014.

Theoretical study of heavy-atom tuning of nonlinear optical properties in group 15 derivatives of N,N,N-trimethylglycine (betaine)

Nitrogen is a common structural element in the acceptor moieties of organic donor-acceptor nonlinear optical (NLO) chromophores. In order to assess the effect of substitution with heavier group 15 elements, computational studies of the nonlinear optical properties of betaine derivatives, (CH(3))(3)X(+)CH(2)CO(2)(-) (X = N, P, As, Sb, Bi), have been performed. First hyperpolarisabilities, β(HRS)(-2ω; ω, ω), corresponding to hyper-Rayleigh scattering susceptibilities have been estimated for this series using TDDFT quadratic response calculations including polarisable-continuum method water solvation and show a five-fold increase on going from N to Bi. Differential frequency dispersion effects lead to a gradual increase in this ratio as the wavelength of the incident radiation is increased from 1907 nm to 800 nm. The depolarisation ratio of the NLO response indicates that the change in β is accompanied by a change in the type of chromophore from octupolar (X = N) to a linear donor-acceptor type (X = Bi). The observed increase of the NLO response correlates with the changing electronic configurations of the group 15 elements and alterations in the character of the frontier molecular orbitals. Relativistic effects are found to play an important part in enhancement of the NLO response in the Sb and Bi betaine derivatives. These results suggest that derivatisation of organic molecules that otherwise display small β values with heavy group 15 elements is a useful method for creating enhanced NLO chromophores.

Extrinsic and Intrinsic Frequency Dispersion of High-k Materials in Capacitance-Voltage Measurements.

In capacitance-voltage (C-V) measurements, frequency dispersion in high-k dielectrics is often observed. The frequency dependence of the dielectric constant (k-value), that is the intrinsic frequency dispersion, could not be assessed before suppressing the effects of extrinsic frequency dispersion, such as the effects of the lossy interfacial layer (between the high-k thin film and silicon substrate) and the parasitic effects. The effect of the lossy interfacial layer on frequency dispersion was investigated and modeled based on a dual frequency technique. The significance of parasitic effects (including series resistance and the back metal contact of the metal-oxide-semiconductor (MOS) capacitor) on frequency dispersion was also studied. The effect of surface roughness on frequency dispersion is also discussed. After taking extrinsic frequency dispersion into account, the relaxation behavior can be modeled using the Curie-von Schweidler (CS) law, the Kohlrausch-Williams-Watts (KWW) relationship and the Havriliak-Negami (HN) relationship. Dielectric relaxation mechanisms are also discussed.

Low leakage current in metal-insulator-metal capacitors of structural Al2O3/TiO2/Al2O3 dielectrics

Metal–insulator–metal (MIM) capacitors with Al2O3/TiO2/Al2O3 (ATA) dielectrics were fabricated and investigated. At 0 V and frequencies of 100 kHz and 1 MHz, the MIM capacitors with ATA (3/20/3 nm) and ATA (6/20/6 nm) thin films had low leakage current densities of approximately 5.2 × 10−13 and 1.5 × 10−13 A/cm2, respectively, and high capacitance densities of ∼19.48 and ∼20.13 fF/μm2, respectively. The frequency dispersion effect for these MIM capacitors was very small. The electrical transport mechanism, which is the device conduction mechanism, was determined for the varying structures of MIM capacitors.

A nested-grid Boussinesq-type approach to modelling dispersive propagation and runup of landslide-generated tsunamis

Abstract. A tsunami generated by large-volume landslide can propagate across the ocean and flood communities around the basin. The evolution of landslide-generated tsunamis is affected by the effects of frequency dispersion and involves processes of different temporal and spacial scales. In this paper, we develop a numerical approach employing the weakly nonlinear and fully nonlinear Boussinesq-type theories and nested computational grids. The propagation in a large domain is simulated with the weakly nonlinear model in a geographical reference frame. The nearshore wave evolution and runup are computed with the fully nonlinear model. Nested grids are employed to zoom simulations from larger to smaller domains at successively increasing resolutions. The models and the nesting scheme are validated for theoretical analysis, laboratory experiments and a historical tsunami event. By applying this approach, we also investigate the potential tsunami impact on the US east coast due to the possible landslide on La Palma Island. The scenario employed in this study represents an event of extremely low probability.

Multicarrier Communications Based on the Affine Fourier Transform in Doubly-Dispersive Channels

The affine Fourier transform (AFT), a general formulation of chirp transforms, has been recently proposed for use in multicarrier communications. The AFT-basedmulticarrier (AFT-MC) systemcan be considered as a generalization of the orthogonal frequency division multiplexing (OFDM), frequently used in modern wireless communications. AFT-MC keeps all important properties of OFDM and, in addition, gives a new degree of freedom in suppressing interference caused by Doppler spreading in time-varying multipath channels. We present a general interference analysis of the AFT-MC system that models both time and frequency dispersion effects. Upper and lower bounds on interference power are given, followed by interference power approximation that significantly simplifies interference analysis. The optimal parameters are obtained in the closed form followed by the analysis of the effects of synchronization errors and the optimal symbol period. A detailed interference analysis and optimal parameters are given for different aeronautical and land-mobile satellite (LMS) channel scenarios. It is shown that the AFT-MC system is able to match changes in these channels and efficiently reduce interference with high-spectral efficiency.

Homogenization of time harmonic Maxwell equations and the frequency dispersion effect

We perform homogenization of the time-harmonic Maxwell equations in order to determine the effective dielectric permittivity ε h and effective electric conductivity σ h . We prove that ε h and σ h depend on the pulsation ω; this phenomenon is known as the frequency dispersion effect. Moreover, the macroscopic Maxwell equations also depend on ω; they are different for small and large values of ω.

A numerical comparison of the Westervelt equation with viscous attenuation and a causal propagation operator

The Westervelt wave equation can be used to describe non-linear propagation of finite amplitude sound. If one assumes that the medium can be treated as a thermoviscous fluid, a loss mechanism can be incorporated, but such a loss mechanism is not adequate if the medium is dispersive. In order to accurately describe pulse propagation in a dispersive medium the Westervelt equation must incorporate attenuation and dispersion correctly. Szabo has shown that the effects of frequency dependent attenuation and dispersion can be included by the use of a causal time-domain propagation factor (TDPF) which is obtained from a corresponding time domain convolution operator. In previous work the TDPF has been successfully employed in the linear wave equation for both isotropic and non-isotropic media, and the authors recently carried out a comparison of numerical solutions, in one dimension, to the Westervelt equation using the TDPF with those obtained using a traditional loss mechanism for a themoviscous fluid. These computations showed that the TDPF correctly incorporated the full dispersive characteristics of the media, and that the results may differ significantly from those obtained using the traditional loss term. In this work the problem of propagation of ultrasonic acoustic energy through human tissue in two dimensions is solved numerically using the Westervelt equation with the TDPF, and comparisons are made with computations treating the human tissue as a thermoviscous fluid. The equations are solved using the method of finite differences.

Frequency dispersion effect and parameters extraction method for novel HfO2 as gate dielectric

The electric characteristic of MOS capacitor with HfO2/SiO2/p-Si grown by ALCVD (atom layer chemical vapor deposition) is investigated. The C-V curves show that the accumulation capacitances take on the frequency dispersion at high frequency. For MOS capacitor with ultra thin HfO2/SiO2 gate stack, different fabrication processes and measurement equipment will cause parasitic effect. Here an equivalent circuit model that can eliminate the frequency dispersion effect is proposed. The C-V characteristics curve at high frequency shows some distortion because of the bulk defects and the interface states. This paper discusses the distortion of the high frequency MOS C-V characteristic curve. A data processing method is advanced and interface trap density distribution in the band gap is presented. By comparing the ideal C-V curve with the experimental C-V curve, the typical electrical parameters of MOS capacitor are extracted, including the shift of flat-band voltage, the oxide charges and the density of interface traps at the SiO2/Si interface.

The problem of preparing entangled pairs of polarization qubits in the frequency-nondegenerate regime

The problems associated with practical implementation of the scheme proposed for preparation of arbitrary states of polarization ququarts based on biphotons are discussed. The influence of frequency dispersion effects are considered, and the necessity of group velocities dispersion compensation in the frequency non-degenerate case even for continuous pumping is demonstrated. A method for this compensation is proposed and implemented experimentally. Physical restrictions on the quality of prepared two-photon states are revealed.

A kinetic model for optically pumped cesium vapor laser

The solvent-dependent and frequency-dependent nonlinear optical （NLO） properties of one-dimensional charge transfer （1DCT） molecule, p-nitroaniline （pNA） and two-dimensional charge transfer （2DCT） molecule, 1,3-diamino-4,6- dinitrobenzen （DADB） have been studied by using the density functional theory （DFT） and time-dependent coupled perturbed Hartree-Fork （TDHF） method, respectively. The reasons of the influence of the solvent polarity and incident light frequency on the NLO properties for 1DCT and 2DCT molecules were also discussed. Theoretical results demonstrate that the first hyperpolarizability β and ultraviolet spectra strongly depend on the dielectric constant ε of solvent, but solvent polarity has little effect on the anisotropy ratio η and depolarization ratio D due to the linear relationship between ︱βxxy︱ and ︱βyyy︱ with the increase of the solvent dielectric constant ε. In addition, the incident frequency has a great influence on β,η and D . It is found that the solvent effect and the frequency dispersion effect should be considered in calculations for obtaining accurate results.

Theoretical study of the second-order nonlinear optical properties of one- and two-dimensional charge transfer molecules in solvents

The solvent-dependent and frequency-dependent nonlinear optical （NLO） properties of one-dimensional charge transfer （1DCT） molecule, p-nitroaniline （pNA） and two-dimensional charge transfer （2DCT） molecule, 1,3-diamino-4,6- dinitrobenzen （DADB） have been studied by using the density functional theory （DFT） and time-dependent coupled perturbed Hartree-Fork （TDHF） method, respectively. The reasons of the influence of the solvent polarity and incident light frequency on the NLO properties for 1DCT and 2DCT molecules were also discussed. Theoretical results demonstrate that the first hyperpolarizability β and ultraviolet spectra strongly depend on the dielectric constant ε of solvent, but solvent polarity has little effect on the anisotropy ratio η and depolarization ratio D due to the linear relationship between ︱βxxy︱ and ︱βyyy︱ with the increase of the solvent dielectric constant ε. In addition, the incident frequency has a great influence on β,η and D . It is found that the solvent effect and the frequency dispersion effect should be considered in calculations for obtaining accurate results.

Dispersion, High-Frequency and Power Characteristics of AlN/GaN Metal Insulator Semiconductor Field Effect Transistors with in-situ MOCVD Deposited Si3N4

The paper presents a systematic study of in-situ passivated AlN/GaN Metal Insulator Semiconductor Field Effect Transistors (MISFETs) with submicron gates. DC, high frequency small signal, large signal and low frequency dispersion effects are reported. The DC characteristics are analyzed in conjunction with the power performance of the device at high frequencies. Studies of the low frequency characteristics are presented and the results are compared with those of AlGaN/GaN High Electron Mobility Transistors (HEMTs). Small signal measurements showed a current gain cutoff frequency and maximum oscillation frequency of 49.9GHz and 102.3GHz respectively. The overall characteristics of the device include a peak current density of 335mA/mm, peak extrinsic transconductance of 130mS/mm, a maximum output power density of 533mW/mm with peak power added efficiency (P.A.E.) of 41.3% and linear gain of 17dB. The maximum frequency dispersion of transconductance and output resistance of the fabricated MISFETs is 20% and 21% respectively.

Microstructure and Dielectric Properties of Chopping SiCf/LAS Composites

Abstract The chopping SiC f /LAS composites were prepared by the hot-pressing method. The effects of hot-pressing time and pressures on the microstructures and the dielectric properties of the composites were researched. Compared with the LAS matrix and the SiC fibre, the results of dielectric constant testing in the range of 8-12 GHz indicate that the dielectric constant real part, imaginary part and dielectric dissipation of all samples increase by 1-3 orders of magnitude, and show obvious frequency dispersion effect. Their real parts increase while their imaginary parts and dielectric dissipations decline with the increase of the hot-pressing time or pressures. The SEM fractographs show that the composite interfacial films between the fibre and the matrix are thickened with the increase of the hot-pressing time or pressures.

Effects of dielectric permittivities on skin heating due to millimeter wave exposure.

BackgroundBecause the possibility of millimeter wave (MMW) exposure has increased, public concern about the health issues due to electromagnetic radiation has also increased. While many studies have been conducted for MMW exposure, the effect of dielectric permittivities on skin heating in multilayer/heterogeneous human-body models have not been adequately investigated. This is partly due to the fact that a detailed investigation of skin heating in a multilayer model by computational methods is difficult since many parameters are involved. In the present study, therefore, theoretical analyses were conducted to investigate the relationship between dielectric permittivities and MMW-induced skin heating in a one-dimensional three-layer model (skin, fat, and muscle).MethodsApproximate expressions were derived for the temperature elevation and temperature difference in the skin due to MMW exposure from analytical solutions for the temperature distribution. First, the power absorption distribution was approximated from the analytical solution for a one-layer model (skin only). Then, the analytical expression of the temperature in the three-layer model was simplified on the basis of the proposal in our previous study. By examining the approximate expressions, the dominant term influencing skin heating was clarified to identify the effects of the dielectric permittivities. Finally, the effects of dielectric permittivities were clarified by applying partial differentiation to the derived dominant term.ResultsSkin heating can be characterized by the parameters associated with the dielectric permittivities, independently of morphological and thermal parameters. With the derived expressions, it was first clarified that skin heating correlates with the total power absorbed in the skin rather than the specific absorption rate (SAR) at the skin surface or the incident power density. Using Debye-type expression we next investigated the effect of frequency dispersion on the complex relative permittivity of tissue. The parametric study on the total power absorbed in the skin showed that skin heating increases as the static permittivity and static conductivity decrease. In addition, the maximum temperature elevation on the body surface was approximately 1.6 times that of the minimum case. This difference is smaller than the difference caused by the thermal and morphological parameters reported in our previous study.ConclusionThis paper analytically clarified the effects of dielectric permittivities on the thermally steady state temperature elevation and the temperature difference in the skin of a one-dimensional three-layer model due to MMW exposure.