Electrical impedance

About: Electrical impedance is a research topic. Over the lifetime, 36015 publications have been published within this topic receiving 371891 citations. The topic is also known as: electrical impedance & complex impedance.

Microstrip lines for microwave integrated circuits

Abstract: Microstrips, transmission lines of metallic layers deposited on a dielectric substrate, are very useful for the microwave and millimeter wave hybrid integrated circuits required for solid-state radio systems because of their simplicity and planar structure. To design hybrid integrated circuits with microstrips requires computation or measurement of the impedance, the attenuation, the guide wavelength, and the unloaded Q of the line. These parameters can be obtained from the effective dielectric constant and the characteristic impedance of the corresponding air line. This paper gives the exact design data for all line parameters for the most important cases. We report the impedance and attenuation measurements performed on microstrips. Satisfactory agreement is obtained with theoretical results based on conformal mapping with logarithmic derivatives of theta functions and expressions involving the partial derivatives of the impedance with respect to independent line parameters.

Plasma simulation by artificial dielectrics and parallel-plate media

Abstract: A plasma in the absence of dc magnetic fields is representable, from the electromagnetic viewpoint, as a lossy dielectric with a complex index of refraction whose real part is less than one. Its electrical properties, such as propagation constant and intrinsic impedance, can be simulated by microwave structures, such as artificial dielectrics of lossy metallic rods, and by H - plane parallel-plate guides. Design techniques are presented for application to the modeling of plasma media. Examples include problems of radiation from antennas on a plasma-coated ground plane, with magnetic line sources and electric aperture radiators simulated by parallel-plate guides and rodded media, respectively. Radiation patterns of these models show good agreement with established theory. Waveguide measurements on the rodded media also confirm the expected propagation and impedance characteristics.

Deconvolution of electrochemical impedance spectra for the identification of electrode reaction mechanisms in solid oxide fuel cells

Abstract: The polarization processes occurring at the electrode–electrolyte interfaces of solid oxide fuel cells (SOFC) were investigated by electrochemical impedance spectra measured at single cells under realistic operating conditions. The approach presented is based on distributions of relaxation times which are the basic quantity of interest in electrochemical impedance data analysis. A deconvolution method was developed and implemented that yields these characteristic distribution patterns directly from the impedance spectra. In contrast to nonlinear least squares curve fit of equivalent circuit models, no a priori circuit choice has to be made. Even more importantly, the excellent resolving capacity allows the untangling of the impedance contributions of up to three physically distinct processes within one frequency decade. With the method, processes with the highest polarization losses can be identified and targeted to improve cell performance. Based on the distributions, a general strategy for the identification of the reaction mechanisms is given. The evaluation of the distributions in terms of peak parameters is illustrated by a physical model for oxygen reduction at the SOFC cathode–electrolyte interface. The method is expected to find many applications in electrochemistry beyond the field of solid oxide fuel cell development.

Virtual-Impedance-Based Control for Voltage-Source and Current-Source Converters

Abstract: The virtual impedance concept is increasingly used for the control of power electronic systems. Generally, the virtual impedance loop can either be embedded as an additional degree of freedom for active stabilization and disturbance rejection, or be employed as a command reference generator for the converters to provide ancillary services. This paper presents an overview of the virtual-impedance-based control strategies for voltage-source and current-source converters. The control output impedance shaping attained by the virtual impedances is generalized first using the impedance-based models. Different virtual impedances and their implementation issues are then discussed. A number of practical examples are demonstrated to illustrate the feasibility of virtual impedances. Emerging applications and future trends of virtual impedances in power electronic systems conclude this paper.

Synthesis of a finite two-terminal network whose driving-point impedance is a prescribed function of frequency

Abstract: Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering, 1931