Concept Of Impedance Research Articles

Transmission problems in a thin layer set in the framework of the Hölder spaces: Resolution and impedance concept

We consider a family of singular transmission problems depending on some small positive parameter δ set in the juxtaposition of two rectangular domains. They are written in the form of abstract elliptic equations and the study, here, is given in the Hölder spaces completing in this way the work in Lp cases given in [A. Favini, R. Labbas, K. Lemrabet, S. Maingot, Study of the limit of transmission problems in a thin layer by the sum theory of linear operators, Rev. Mat. Complut. 18 (1) (2005) 143–176]. In this first part, we present a new approach for the resolution of these problems by using the concept of impedance operator. This method is different of the one performing a rescaling in the thin layer, see [A. Favini, R. Labbas, K. Lemrabet, S. Maingot, Study of the limit of transmission problems in a thin layer by the sum theory of linear operators, Rev. Mat. Complut. 18 (1) (2005) 143–176]. It leads to obtain direct and simplified problems. We use the Dunford calculus and some techniques similar to that in [R. Labbas, Problèmes aux limites pour une équation différentielle abstraite de type elliptique, Thèse d'état, Université de Nice, 1987; A. Favini, R. Labbas, S. Maingot, H. Tanabe, A. Yagi, Unified study of elliptic problems in Hölder spaces, C. R. Math. Acad. Sci. Paris 134 (2005); G. Dore, A. Favini, R. Labbas, K. Lemrabet, S. Maingot, A transmission problem in a thin layer, Part I, Sharp estimates, in press], to prove existence, uniqueness, results and some specific estimates on the impedance operator. This study will allow us, in a forthcoming work, to obtain respectively optimal regularities and the limit problem when δ → 0 .

Decentralized harmonic control of sound radiation and transmission by a plate using a virtual impedance approach

The problem under study in this article is the active control of sound transmission and radiation of a panel under a periodic excitation. The control strategy investigated uses independent control loops between an individual polyvinylidene fluoride (PVDF) sensor and an individual lead zirconate titanate (PZT) actuator. The specific approach employed here uses the concept of virtual impedance. The aim is to determine for each frequency the optimal impedance between each PVDF sensor and the corresponding PZT actuator in order to reduce the sound power radiated by the plate. Theoretical predictions are compared to measurements of the sound radiated and transmission loss of a panel mounted with eight PZT-PVDF units. Reductions of up to 20 dB of the acoustic power can be achieved around mechanical resonances of the system, while the control strategy has little effect for off-resonance excitations.

Autonomous adaptive sensorless controller of inverter-based islanded-distributed generation system

A control method for inverter operation in an islanded-distributed generation system is presented. The controller provides sufficient active and reactive power to match the connected load, therein providing high power quality. Control in this mode is based on voltage and frequency droops. Detailed analysis, based on the concept of harmonic impedance, establishes the appropriateness of inductor current feedback against capacitor current feedback, with respect to inverter output power quality. Steepest descent adaptive control is embedded to estimate the output voltage for sensorless operation, which enhances system robustness and performance. To compensate the DSP calculation delay, a modified Kalman filter design is discussed. Simulation and experimental results demonstrate the validity of the proposed control method.

The penetration of sound into an extended reaction ground due to an arbitrarily oriented dipole.

An asymptotic solution is derived for the sound fields below an extended reaction ground due to an arbitrarily oriented dipole placed near the air/ground interface. The derived approximate solutions are compared with accurate numerical schemes based on the fast field formulation and the direct numerical integration of the Fourier integral. It has been shown that the sound field above the ground can be computed accurately by using the concept of effective impedance [K. M. Li et al., J. Acoust. Soc. Am. 104, 679–685 (1998)]. The effective impedance approach is used to derive the asymptotic formula for predicting the penetration of sound into the extended reaction ground. However, there are apparent discrepancies in the predicted sound fields according to the analytical solution and the accurate numerical schemes. A modified analytical formula is then developed that leads to more accurate numerical results. The resulting analytical formula due to an airborne acoustic excitation may be used as a basis for a future study to compute the particle displacements induced by an elastic object buried in a rigid‐frame porous medium.

Impedance Matching and Emission Properties of Nanoantennas in an Optical Nanocircuit

An experimentally realizable prototype optical nanocircuit consisting of a receiving and an emitting nanoantenna connected by a two-wire optical transmission line is studied using finite-difference time- and frequency-domain simulations. To optimize the coupling between optical nanocircuit elements we apply impedance matching concepts in analogy to radio frequency technology. We show that the degree of impedance matching, and in particular the impedance of the emitting nanoantenna, can be inferred from the experimentally accessible standing wave pattern on the transmission line. We demonstrate the possibility of matching the nanoantenna impedance to the transmission line by variations of the antenna length and width realizable by modern microfabrication techniques. The radiation efficiency of the emitting antenna also depends on its geometry but is independent of the degree of impedance matching. The case study presented here provides the basis for experimental realizations of general optical nanocircuits based on readily available gold nanostructures and a large variety of derived novel devices.

Disorder in coupled-resonator optical waveguides

Disorder in coupled-resonator optical waveguides (CROWs) is modeled by exploiting the concept of the characteristic impedance of a periodic slow-light waveguide. Every imperfection in the CROW structure is modeled as an impedance discontinuity, and the related backreflection is evaluated by using well-known reflection rules. We demonstrate that backreflections induced by disorder scale with the square of the slowing factor and the square of the disorder parameter, both independently of the specific structure. The method is simple and accurate, holds even when the slowing factor of the CROW is modified by disorder, and can be applied to any slow-light structure where the characteristic impedance can be defined. Theoretical and numerical results are supported by an experimental investigation showing the effects of increasing disorder on both frequency and time domain responses of a ring resonator CROW. Pulse envelope distortions due to distributed backreflections along the disordered CROW arise as one of the main limiting factors for applications based on CROWs.

The application of understeer gradient in stability analysis of articulated vehicles

This paper introduces the generalised algebraic formula for understeer gradient (Ku) of articulated vehicles. This formula plays a similar role as that for a single vehicle system. The articulated vehicle is understeer if Ku is positive, neutral steer if it is equal to zero, and oversteer if it is negative. It is not stable in the yaw plane if it is oversteer and driven above the critical speed. The algebraic solutions are validated numerically and compared to experimental data measured from an 18-wheel tractor semi-trailer system. The impedance concept is introduced to facilitate the process of the algebraic analysis of articulated vehicles. This allows Ku and critical speed equations to be expressed in a compact systematic form.

Is an impedance operator necessary causal, and is this an issue of complexity?

An impedance operator describes the mapping of a velocity field across a part of a boundary surface, to the traction field across the same part. Understood to represent the solution of a “direct” problem, i.e., the velocity field describes the problem forcing and the traction field part of the solution, the impedance operator is necessary causal. On the other hand, understood to represent the general solution of an “inverse” problem, i.e., the velocity field is part of the observed solution with the traction field representing the problem forcing, the operator need not be causal. Continuing, a uniqueness theorem that applies to the direct problem assures that the impedance operator thusly defined is unique. The lack of a corresponding theorem for the inverse problem suggests that the impedance operator thusly defined need not be unique. This further suggests requiring causality selects from multiple impedance operators, representing multiple solutions to the inverse problem, the one that is unique. This raises two questions. Is the causality that makes the operator unique a requirement of the governing physics? What impact does this have on the concept of impedance as a tool for addressing complexity in dynamical systems?

Simplified Dynamic Finite-Element Analysis for Three-Dimensional Pile-Grouped-Raft-High-Rise Buildings

Combined with the respective advantages in S-R(Sway-Rocking) impedance concept and finite-element method, a simplified 3D structural dynamic FEM considering composite pile-group-soil effects is presented. The structural members including piles are modeled by spacial beam or shell elements, and raft-base is divided into thick-shell elements with its spring-dashpot boundary coefficient obtained by impedance backcalculated. The mass-spring elements for soil between piles are set to simulate vertical, horizontal pile-group effects by strata-equivalent approach. The soil beside composite body is separated into near-field and far-field parts. The former is modeled by nonlinear spring-dashpot elements based on Winkler’s hypothesis, while the latter is modeled by a series of linear mass-spring-dashpots. With the effects of boundary track forces and energy radiation, the presented model enables researchers to conduct the time-domain nonlinear analysis in a relatively simple manner which avoids sophisticated boundary method and solid-element mesh bringing with tremendous computational cost. The seismic effect on dynamic interaction of pile-soil-complicated structures would be efficiently annotated from two structural engineering and geotechnical engineering aspects and the numerical calculation effort would be drastically decreased too. The complete procedure is mainly performed using the parametric design language assembled in the Finite Element Code Ansys. With the dynamic analysis of foundation and superstructure for a pile-supported 15-storey building, the influence of the participant effect on structural dynamic response will be depicted by various dynamic parameters of pile-soil-raft foundation in detail. Not only do the results have an agreement with some conclusions drawn by the general interaction theory, but also certain of phenomena which would be disagree with that by general analysis is involved. Even with the finite-element meshes for 68 piles, the time-history analysis procedure for PGSS (Pile-Group-Soil-Superstructure) system and the qualitative evaluation with various SSI parameters can be also fulfilled efficiently and rapidly by presented means. These results may be of help to the designers to quickly assess the significance of interaction effect for the high-rise buildings resting on any type or layout of pile-group foundation.

Accurate Physical Modeling of Discretization Error in 1-D Perfectly Matched Layers Using Finite-Difference Time-Domain Method

In this paper we present an accurate physical model of discretization error in a 1-D perfectly matched layer (PML) using the finite-difference time-domain method. The model is based on the concept of the discrete wave impedance of the PML. This concept implies that the wave impedance in the discretized space changes, with respect to the continuous value, when absorption occurs. These changes depend on the absorption per unit length, as well as on the discretization step. In the discretized space, both, the magnitude and phase of wave impedance are modified. We employ numerical simulations obtained using a 1-D code to test the proposed model. We then compare the results with those obtained from coaxial wave guide geometry using a commercial 3-D software package. One important consequence of this modeling scheme is the feasibility of the PML without return losses due to discretization error. In practice, numerical results show that by correctly adjusting the electromagnetic parameters of the PML (electric permittivity and magnetic permeability), a significant improvement in the reflection characteristics is obtained. In some cases, it could be as much as 78 dB. The remaining return losses are successfully explained as second-order effects related to the discontinuity of electromagnetic parameters at the interface between the simulation space and PML.

FEM simulation of a sono-reactor accounting for vibrations of the boundaries

The chemical effects of acoustic cavitation are obtained in sono-reactors built-up from a vessel and an ultrasonic source. In this paper, simulations of an existing sono-reactor are carried out, using a linear acoustics model, accounting for the vibrations of the solid walls. The available frequency range of the generator (19–21 kHz) is systematically scanned. Global quantities are plotted as a function of frequency in order to obtain response curves, exhibiting several resonance peaks. In absence of the precise knowledge of the bubbles size distribution and spatial location, the attenuation coefficient of the wave is taken as a variable, but spatially uniform parameter, and its influence is studied. The concepts of acoustic energy, intensity, active power, and source impedance are recalled, along with the general balance equation for acoustic energy, which is used as a convergence check of the simulations. It is shown that the interface between the liquid and the solid walls cannot be correctly represented by the simple approximations of either infinitely soft, or infinitely hard boundaries. Moreover, the liquid–solid coupling allows the cooling jacket to receive a noticeable part of the input power, although it is not in direct contact with the sonotrode. It may therefore undergo cavitation and this feature opens the perspective to design sono-reactors which avoid direct contact between the working liquid and the sonotrode. Besides, the possibility to shift the main pressure antinode far from the sonotrode area by exciting a resonance of the system is examined.

Input Impedance, Nanocircuit Loading, and Radiation Tuning of Optical Nanoantennas

Here we explore the radiation features of optical nanoantennas, analyzing the concepts of optical input impedance, optical radiation resistance, impedance matching, and loading of plasmonic nanodipoles. We discuss how the concept of antenna impedance may be applied to optical frequencies and how its quantity may be properly defined and evaluated. We exploit these concepts in the optimization of nanoantenna loading by optical nanocircuit elements, extending classic concepts of radio-frequency antenna theory to the visible regime for the proper design and matching of plasmonic nanoantennas.

Assessment of compliance in pulmonary arterial hypertension

The main mechanical feature of the pulmonary circulation is the ability to sustain low pressure levels even in the presence of high flow,1 thus being defined as a low resistance/high compliance system. Pulmonary hypertension is a multifactorial clinical condition mainly characterized by vascular remodelling that increases right ventricular afterload, eventually leading to ventricular dysfunction.2 Most of the clinical presentation and haemodynamic behaviour is directly related to the development and progression of right heart failure. Usually, this increase in afterload is described as the increase in pulmonary vascular resistance (PVR); indeed, PVR is one of the components of the right ventricular afterload. However, the total afterload is determined by three different vascular characteristics: resistance, compliance, and impedance.3 Whilst the concept of impedance is a little more difficult to transpose to the clinical setting, once it accounts the inertial properties of blood flow, resistance and compliance can be easily assimilated, even though, in the setting of pulmonary hypertension, most of the attention has been paid to the former only. … *Corresponding author. Tel: +331 46453135, Fax: +331 46453135, Email: rgrsz{at}uol.com.br

Calculation of Energy-Related Quantities of Conductors Using Surface Impedance Concept

This paper focuses on the application of surface impedance concept in a post-processing stage for the calculation of such characteristics of conductors such as energy stored in the conductor's skin layer, power losses, inductance, and resistance per unit length. Derivations are performed in terms of - and - formalisms. Numerical examples are included to illustrate the method and validate the results.

Wave Propagation in 1D EBGs: Periodic Multilayer Films Consisting of Two Different Materials [This Issue's Contribution

This paper presents the fundamental concept of wave propagation in periodic multilayer films consisting of two different materials, so-called one-dimensional electromagnetic bandgap (EBG) materials. To this end, Floquet's theorem is first presented. Next, the transmission-line analogy is used to simplify the concept of wave propagation in one dimension. The Bloch impedance concept is then presented, and its usefulness is illustrated in the applications of truncated periodic structures. Through a few case studies, it is shown that the ripples usually appearing in the pass band of the EBGs are due to the mismatch of the transmission-line ports. When the EBG structures are terminated to appropriate Bloch impedances, the ripples disappear. The material can be used in undergraduate or graduate Microwave or Advanced Engineering Electromagnetics courses. The students need to know about the ABCD matrix in advance. The material helps students in better understanding of microwave filters, and shows the importance of matching the terminal ports and number of unit cells. Students can use software packages such as MATLAB to obtain the Bloch impedances, and such as Ansoft HFSS to reproduce the scattering parameters presented in this paper. The materials in this paper are consistent with those in [3, 7, 8, 9] and, in some cases, are summarized from these references to improve the clarity.

Predicted attenuation of sound in a rigid-porous ground from an airborne source

An approximate analytical formula has been derived for the prediction of sound fields in a semi-infinite rigid-porous ground due to an airborne source. The method starts by expressing the sound fields in an integral form, which can subsequently be evaluated by the method of steepest descents. The concept of effective impedance has been introduced by using a physically plausible assumption. The integral can then be simplified and evaluated analytically. The analytical solution can be expressed in a closed form analogous to the classical Weyl-Van der Pol formula that has been used for predicting sound fields above a rigid-porous ground. Extensive comparisons with the wave-based numerical solutions according to the fast field formulation and the direct evaluation of the integral have been conducted. It has been demonstrated that the analytical formula is sufficiently accurate to predict the penetration of sound into a wide range of outdoor ground surfaces.

On the Concept of Electrical Impedance for an Electrolytic Cell

The analysis of the electrical impedance of an electrolytic cell in the shape of a slab is performed. We have solved, numerically, the differential equations governing the phenomenon of the redistribution of the ions in the presence of an external electric field, and compared the results with the ones obtained by solving the linear approximation of these equations. The control parameters in our study are the amplitude and the frequency of the applied voltage, assumed a simple harmonic function of the time. We show that for the large amplitudes of the applied voltage, the actual current is no longer harmonic at low frequencies. From this result it follows that the concept of electrical impedance of a cell is a useful quantity only in the case where the linear approximation of the fundamental equations of problem work well.

Improved Power Sharing Scheme for a Microgrid with Multiple Distributed Generators

This paper explores the active and reactive power sharing scheme for the parallel operation of inverter interfaced distributed generators (DGs) in a microgrid system. Applicability of conventional wireless control technique, based on P-f and Q-V droop regulations, is also investigated for the load sharing among the DGs with the help of small signal analysis. The conventional droop technique is found to be ineffective in a distribution system with resistive dominated line. In particular, the reactive power becomes highly uncontrolled with large circulating VAR in the presence of high R/X. The virtual impedance concept proposed in the paper intends to address this problem. The so-called virtual impedance is self-regulated variable aiming to reduce the impedance mismatch thereby eliminating the circulating VAR. Consequently, the scheme provides effective active and reactive power sharing among the DGs by adjusting the magnitude and frequency of the voltage at steady-state. Simulation results presented for the two-DGs microgrid system, confirms the validity of the proposed scheme.

Longwave Phonon Tunnelling Using an Impedance Concept

In this paper we study numerically the transmission, re∞ection and dwell times of phonons propagating through semiconductor multilayer structures. The tunnelling of optical and acoustic phonon at normal incidence on multiple layers systems is analyzed. We adopt the continuum model valid for long-wavelength oscillations. The isomorphism between acoustical and optical propagation in heterostructures, and electromagnetic waves in transmission lines, is analyzed. We use an impedance concept similar to the quantum-mechanical one introduced by Khondker to calculate the transmission and re∞ection coe-cients. This study could also be useful for the design of phonons fllters.

A Fractional Derivative Operator for Surface Impedance TLM Modeling

A new and straightforward implementation of metallic losses in a time-domain field computation namely, the transmission line matrix (TLM) is presented. The approach is based on the description of the skin surface impedance concept directly in time-domain by means of a digital filter representing a fractional derivative operator. Numerical implementation based on recent advances in signal processing is shown. Finally, the new approach is tested and compared to usual TLM implementation showing the stability and accuracy of the scheme.