Formula For Impedance Research Articles

Effective impedance modeling of metamaterial structures.

We present methods for retrieving the effective impedance of metamaterials from the Fresnel reflection coefficients at the interface between two semi-infinite media. The derivation involves the projection of rigorous modal expansions onto the dominant modes of the two semi-infinite media. It is shown that the effective impedance can also be written as a ratio of averaged field quantities. Thus, a number of effective impedance formulas, previously obtained by field averaging techniques, can also be derived from the scattering-based formalism by an appropriate choice of projection. Within the effective medium limit, it is observed that a simple semianalytic modeling technique based on the effective impedance can be used to reliably compute the reflection coefficients of metamaterials over a wide range of incidence angles. We use this technique to model planar metamaterial waveguides or surface modes.

Interpretation of electrochemical impedance spectroscopy (EIS) circuit model for soils

Based on three different kinds of conductive paths in microstructure of soil and theory of electrochemical impedance spectroscopy (EIS), an integrated equivalent circuit model and impedance formula for soils were proposed, which contain 6 meaningful resistance and reactance parameters. Considering the conductive properties of soils and dispersion effects, mathematical equations for impedance under various circuit models were deduced and studied. The mathematical expression presents two semicircles for theoretical EIS Nyquist spectrum, in which the center of one semicircle is degraded to simply the equivalent model. Based on the measured parameters of EIS Nyquist spectrum, meaningful soil parameters can easily be determined. Additionally, EIS was used to investigate the soil properties with different water contents along with the mathematical relationships and mechanism between the physical parameters and water content. Magnitude of the impedance decreases with the increase of testing frequency and water content for Bode graphs. The proposed model would help us to better understand the soil microstructure and properties and offer more reasonable explanations for EIS spectra.

Creatine Supplementation Increases Total Body Water in Soccer Players: a Deuterium Oxide Dilution Study

This study aimed to evaluate changes in total body water (TBW) in soccer athletes using a deuterium oxide dilution method and bioelectrical impedance (BIA) formulas after 7 days of creatine supplementation. In a double-blind controlled manner, 13 healthy (under-20) soccer players were divided randomly in 2 supplementation groups: Placebo (Pla, n=6) and creatine supplementation (CR, n=7). Before and after the supplementation period (0.3 g/kg/d during 7 days), TBW was determined by deuterium oxide dilution and BIA methods. 7 days of creatine supplementation lead to a large increase in TBW (2.3±1.0 L) determined by deuterium oxide dilution, and a small but significant increase in total body weight (1.0±0.4 kg) in Cr group compared to Pla. The Pla group did not experience any significant changes in TBW or body weight. Although 5 of 6 BIA equations were sensitive to determine TBW changes induced by creatine supplementation, the Kushner et al. 16 method presented the best concordance levels when compared to deuterium dilution method. In conclusion, 7-days of creatine supplementation increased TBW determined by deuterium oxide dilution or BIA formulas. BIA can be useful to determine TBW changes promoted by creatine supplementation in soccer athletes, with special concern for formula choice.

Simulation computation and analytic modification of characteristic impedance of parallel-plate transmission line

Based on time domain reflection theory, a novel way to calculate the characteristic impedance of a parallel-plate transmission line is proposed. With CST microwave studio, a simulation model is established to calculate the accurate value of the characteristic impedance of the parallel-plate transmission line. Based on the results, the analytic formula for the characteristic impedance of the parallel-plate transmission line is modified. Furthermore, the effect of broadening of the bottom plate of parallel-plate transmission line on its characteristic impedance is researched. Considering the effect of broadening of bottom plate, a new formula for the characteristic impedance of the parallel-plate transmission line is proposed. The final formula could be applied to the calculation of the characteristic impedance of bounded-wave simulators and other electromagnetic pulse simulators with similar structure.

Estimation of elastic parameters using two-term fatti elastic impedance inversion

Elastic impedance (EI) inversion has been widely used in industry to estimate kinds of elastic parameters to distinguish lithology or even fluid. However, it is found that conventional three-term elastic impedance formula is unstable even with slight random noise in seismic data, due to the ill-conditioned coefficient matrix of elastic parameters. We presented two-term Fatti elastic impedance inversion method, which is more robust and accurate than conventional three-term elastic impedance inversion. In our method, density is ignored to increase the robustness of inversion matrix. Besides, P-impedance and S-impedance, which are less sensitive to random noise, are inverted instead of V P and V S in conventional three-term elastic impedance. To make the inversion more stable, we defined the range of K value as a constraint. Synthetic tests claim that this method can obtain promising results with low SNR (signal noise ratio) seismic data. With the application of the method in a 2D line data, we achieved λρ, μρ and V P/V S sections, which matched the drilled well perfectly, indicating the potential of the method in reservoir prediction.

The use of a non-linear model for a more realistic calculation of the “[formula omitted] effect” in magnetoelastic ribbons

In the current paper an exact analytic expression in a closed form is given for the impedance Z of a finite size coil having as a core a magnetoelastic thin ribbon along its axis. From the impedance formula, the resonance and anti-resonance frequencies fR and fA are calculated and their ratio is related to the “ΔE effect” of the magnetoelastic materials. This is of great importance for these materials because the “ΔE effect” reveals information about their internal structure and also the resonance and anti-resonance frequencies are relatively easy to measure. Our analysis is more realistic than previous attempts to do similar calculations which overestimate the anti-resonance frequency because a) a more accurate non-linear model is used in the current work to describe the magnetic behavior of the magnetoelastic thin ribbon, and b) finite size coils are assumed as is the case in real experiments. The results show that even though fR depends on the “ΔE effect” and ribbon properties (material and geometry), fA depends additionally on the geometry of the excitation coil.

An Improved Formula for the Transfer Impedance of Two-Layer Braided Cable Shields

In this letter, we propose a formula for evaluating the transfer impedance of two-layer braided cable shields. The proposed formula results from the combination of the model proposed by Vance for the evaluation of the equivalent transfer impedance of a two-layer braided shield and the improved Kley model for the transfer impedance of single-layer braided shields.

Novel Compact Microstrip Stepped-Impedance Resonator Using Computational Approach and Application to Dual-Band Bandpass Filters

This paper discusses a novel multi-stub-loaded stepped-impedance resonator (MSLSIR) with a specific feeding structure. The fundamental and higher order modes of resonant frequencies of the stepped-impedance resonator are key parameters involved in the design of a dual-band bandpass filter (DBPF). However, since resonant frequencies are dependent on each other, the overall structure is not compact. The proposed MSLSIR has the advantage of flexible control over one resonant frequency while the other frequency is fixed. Furthermore, the utilization of isosceles right-angled triangular (IRT) and short-circuited stubs as loaded elements improves size miniaturization of DBPF when a low permittivity substrate is used. The analysis of the IRT stub is based on the coupling impedance formulas derived by integration of the associated Green`s function. As an application, a DBPF is presented, which operates at 3.5 and 5.2 GHz, corresponding to the WiMAX and WLAN applications, respectively. In addition, a good stopband rejection, up to $$3\hbox {f}_{1}$$3f1, is obtained using the defected ground structure technique. An overall good agreement between the calculated, simulated and measured results is observed, thereby confirming the effectiveness of the proposed method.

Analytic modeling, simulation and interpretation of broadband beam coupling impedance bench measurements

First, a generalized theoretical approach towards beam coupling impedances and stretched-wire measurements is introduced. Applied to a circular symmetric setup, this approach allows to compare beam and wire impedances. The conversion formulas for TEM scattering parameters from measurements to impedances are thoroughly analyzed and compared to the analytical beam impedance solution. A proof of validity for the distributed impedance formula is given. The interaction of the beam or the TEM wave with dispersive material such as ferrite is discussed. The dependence of the obtained beam impedance on the relativistic velocity β is investigated and found as material property dependent.Second, numerical simulations of wakefields and scattering parameters are compared. The applicability of scattering parameter conversion formulas for finite device length is investigated. Laboratory measurement results for a circularly symmetric test setup, i.e. a ferrite ring, are shown and compared to analytic and numeric models. The optimization of the measurement process and error reduction strategies are discussed.

High-Accurate Numerical Computation of Internal Impedance of Cylindrical Conductors for Complex Arguments of Arbitrary Magnitude

In this paper, a numerical model is proposed for computing the per-unit-length internal impedance of tubular cylindrical conductors for complex arguments of arbitrary magnitudes. The proposed model either numerically solves the exact formula for internal impedance consisting of modified Bessel functions or utilizes asymptotic approximations of modified Bessel functions when applicable. It is shown that the results obtained by the proposed model are highly accurate and numerically stable. The proposed model is also applicable for solid cylindrical conductors.

Dynamic flow resistivity based model for sound absorption of multi-layer sintered fibrous metals

The sound absorbing performance of the sintered fibrous metallic materials is investigated by employing a dynamic flow resistivity based model, in which the porous material is modeled as randomly distributed parallel fibers specified by two basic physical parameters: fiber diameter and porosity. A self-consistent Brinkman approach is applied to the calculation of the dynamic resistivity of flow perpendicular to the cylindrical fibers. Based on the solved flow resistivity, the sound absorption of single layer fibrous material can be obtained by adopting the available empirical equations. Moreover, the recursion formulas of surface impedance are applied to the calculation of the sound absorption coefficient of multi-layer fibrous materials. Experimental measurements are conducted to validate the proposed model, with good agreement achieved between model predictions and tested data. Numerical calculations with the proposed model are subsequently performed to quantify the influences of fiber diameter, porosity and backed air gap on sound absorption of uniform (single-layer) fibrous materials. Results show that the sound absorption increases with porosity at higher frequencies but decreases with porosity at lower frequencies. The sound absorption also decreases with fiber diameter at higher frequencies but increases at lower frequencies. The sound absorption resonance is shifted to lower frequencies with air gap. For multi-layer fibrous materials, gradient distributions of both fiber diameter and porosity are introduced and their effects on sound absorption are assessed. It is found that increasing the porosity and fiber diameter variation improves sound absorption in the low frequency range. The model provides the possibility to tailor the sound absorption capability of the sintered fibrous materials by optimizing the gradient distributions of key physical parameters.

Sarcopenia, sarcopenic obesity and mortality in older adults: results from the National Health and Nutrition Examination Survey III.

Sarcopenia is defined as the loss of skeletal muscle mass and quality, which accelerates with aging and is associated with functional decline. Rising obesity prevalence has led to a high-risk group with both disorders. We assessed mortality risk associated with sarcopenia and sarcopenic obesity in elders. A subsample of 4652 subjects ≥60 years of age was identified from the National Health and Nutrition Examination Survey III (1988-1994), a cross-sectional survey of non-institutionalized adults. National Death Index data were linked to this data set. Sarcopenia was defined using a bioelectrical impedance formula validated using magnetic resonance imaging-measured skeletal mass by Janssen et al. Cutoffs for total skeletal muscle mass adjusted for height(2) were sex-specific (men: ≤5.75 kg/m(2); females ≤10.75 kg/m(2)). Obesity was based on % body fat (males: ≥27%, females: ≥38%). Modeling assessed mortality adjusting for age, sex, ethnicity (model 1), comorbidities (hypertension, diabetes, congestive heart failure, osteoporosis, cancer, coronary artery disease and arthritis), smoking, physical activity, self-reported health (model 2) and mobility limitations (model 3). Mean age was 70.6±0.2 years and 57.2% were female. Median follow-up was 14.3 years (interquartile range: 12.5-16.1). Overall prevalence of sarcopenia was 35.4% in women and 75.5% in men, which increased with age. Prevalence of obesity was 60.8% in women and 54.4% in men. Sarcopenic obesity prevalence was 18.1% in women and 42.9% in men. There were 2782 (61.7%) deaths, of which 39.0% were cardiovascular. Women with sarcopenia and sarcopenic obesity had a higher mortality risk than those without sarcopenia or obesity after adjustment (model 2, hazard ratio (HR): 1.35 (1.05-1.74) and 1.29 (1.03-1.60)). After adjusting for mobility limitations (model 3), sarcopenia alone (HR: 1.32 ((1.04-1.69) but not sarcopenia with obesity (HR: 1.25 (0.99-1.58)) was associated with mortality. For men, the risk of death with sarcopenia and sarcopenic obesity was nonsignificant in both model-2 (HR: 0.98 (0.77-1.25), and HR: 0.99 (0.79-1.23)) and model 3 (HR: 0.98 (0.77-1.24) and HR: 0.98 (0.79-1.22)). Older women with sarcopenia have an increased all-cause mortality risk independent of obesity.

Theory and Simulation of Arbitrarily Shaped Groove Staggered Double Grating Array Waveguide

A theoretical model for the arbitrarily shaped groove staggered double grating array waveguide (SDGAW) slow-wave structure is proposed in this paper. The boundary of the groove was approximately replaced by a series of steps and the formulas of dispersion and interaction impedance were obtained utilizing the field matching method combined with the continuity of transverse admittance. Considering the traditional single mode approximation (SMA) model is not so accurate for describing the high frequency (HF) characteristics, a multiple modes approximation (MMA) model is established, which takes account for the higher order terms in the grooves, thus greatly improves the accuracy of the numerical calculations. As an example, the HF characteristics of a cosine groove SDGAW for a 0.22-THz traveling wave tube were calculated utilizing the SMA model, the MMA model, and HFSS code, the results were compared and discussed. Comparison of the HF characteristics among several kinds of groove shaped SDGAWs has been made by numerical calculation.

Análisis de formulaciones aproximadas de impedancia interna para el estudio de transitorios de alta frecuencia en cables subterráneos de alta tensión

En este artículo se presenta un análisis de las formulaciones aproximadas de impedancia interna para el estudio de transitorios de alta frecuencia en cables subterráneos de alta tensión. El análisis se desarrolla en el dominio de la frecuencia y la conversión al dominio del tiempo se realiza utilizando la transformada rápida de Fourier. El cable se modela como una línea de transmisión multiconductora, utilizando análisis modal y la teoría de redes de dos puertos. Las formulaciones aproximadas de impedancia interna que se analizan son las propuestas por Gary y Wedepohl-Wilcox, las cuales son utilizadas en el modelado de líneas de transmisión aérea y subterránea, respectivamente. Para efectuar el análisis se realiza una comparación de las formulaciones aproximadas con el modelo exacto de impedancia interna y se determina el error relativo de cada formulación para los valores reales como para los valores imaginarios. Los resultados muestran que la formulación aproximada propuesta por Gary para el modelado de líneas de transmisión aéreas se puede utilizar en cables subterráneos para analizar fenómenos transitorios electromagnéticos de alta frecuencia con resultados aceptables. Para realizar el estudio comparativo de las formulas aproximadas de impedancia interna se propone una serie de casos de estudios en los cuales se determina la magnitud del voltaje transitorio, el tiempo de viaje y la atenuación de la onda en líneas monofásicas subterráneas utilizando diferentes longitudes.

Analysis of high frequency characteristics of the sine waveguide

A theoretical analysis of the high frequency characteristics for an all-metal slow-wave system (SWS), i.e., a sine waveguide, is performed in this paper. The continuous profile of the cosine groove is approximated by a series of connected rectangular steps, and the SWS is divided into several regions reasonably, then the expressions of the field in all the regions are given. The dispersion equation and coupling impedance formula of the SWS are obtained by using the field matching theory combined with the matching of the admittance. The high frequency characteristics for a sine waveguide used in a 220 GHz TWT are discussed, and the calculation results are in good agreement with those obtained from three-dimensional electromagnetic simulation software CST-MWS. The effects of the geometrical parameters on high frequency characteristic of the sine waveguide are also investigated in detail.

An Improvement of Closed-Form Formula for Mutual Impedance Computation

In this paper, we present an improvement of a closed-form formula for mutual impedance computation. Depending on the center-to-center spacing between two rectangular microstrip patch antennas, the mutual impedance formula is separated into two parts. The formula based on synthetic asymptote and variable separation is utilized for spacings of more than 0.5 λ0. When the spacing is less than 0.5 λ0, an approximate formula is proposed to improve the computation for closely spaced elements. Simulation results are compared to computational results of mutual impedances and mutual coupling coefficients as functions of normalized center-to-center spacing in both E- and H-plane coupling configurations. A good agreement between simulation and computation is achieved.

Characteristic impedance of a microstrip line with a dielectric overlay

Purpose – The purpose of this paper is to present an analytical expression for the characteristic impedance of a microstrip line in presence of a dielectric cover. Design/methodology/approach – Assuming a quasi-TEM propagation mode, a rigorous conformal mapping based on the Schwarz-Christoffel transformation is employed to derive the equivalent capacitance model, which can then be applied to derive a closed analytical expression for the effective permittivity and the characteristic impedance of the line. Findings – Such a formulation is not limited to the case of a single cover layer, but an arbitrary number of electric overlays can be considered as well. Comparisons with published numerical results and full-wave simulations in the case of a single cover layer have been also performed to test the validity of the proposed approach. Originality/value – The new analytical formula for the characteristic impedance of a microstrip line with a single dielectric cover shows better performances compared to the one of closed formulas already presented in the literature.

Symbolic Analysis of Input Impedance of CMOS Floating Active Inductors with Application in Fully Differential Bandpass Amplifier

This paper proposes a study of input impedance of 2 types of CMOS active inductors. It derives 2 input impedance formulas. The first formula is the input impedance of the grounded active inductor. The second formula is the input impedance of the floating active inductor. After that, these formulas can be used to simulate magnitude and phase response of input impedance as a function of current consumption with MATLAB. Common mode rejection ratio (CMRR) of the fully differential bandpass amplifier is derived based on superposition principle. CMRR as a function of input frequency is plotted as a function of current consumption.

Resonance properties of low-energy electron beams radiation in a two-layer waveguide

We obtain an approximating formula for the low-energy impedance of a two-layer cylindrical waveguide, which allows constructing explicit expressions for the space-time functions that characterize the radiation of a charged particle in a waveguide. The general laws of the evolution of impedance and wake potentials with increasing particle energy and with the change of geometric and electrodynamical parameters of the waveguide are obtained. The settings of waveguides convenient for experimental research and having resonance properties at energies of about 20 MeV are revealed.

Exact Solution of Pollaczek's Integral for Evaluation of Earth-Return Impedance for Underground Conductors

Calculation of earth-return impedance for underground conductors is based on the efficient evaluation of Pollaczek's integral. So far, the established practice involved either approximate expressions or numerical integration algorithms. Apart from extensive comments on the latter, this paper presents for the first time three exact solutions in the form of converging series. One of the series guarantees a specific relative accuracy for any parameter range with a specific number of terms and can be regarded as the definite solution that will hopefully settle the issue of computing Pollaczek's integral both rapidly and accurately. The exact solution provides the means to assess the validity of the impedance formula.