scispace - formally typeset
Search or ask a question
Topic

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.


Papers
More filters
Patent
03 Dec 1993
TL;DR: In this paper, an automatic circuit measures electrosurgical generator output and controls in accord with impedance between activated movable bipolar electrodes able to contact tissue, and assesses changes in impedance between the electrodes.
Abstract: An automatic circuit measures electrosurgical generator output and controls in accord with impedance between activated movable bipolar electrodes able to contact tissue. Voltage monitor in parallel and current monitor in series with the electrodes measure instantaneous variations and generate proportional signals. First and second calculators receive the signals and find respectively, by dividing the voltage by current, short circuit impedances and impedances other than short circuit impedances between the electrodes. First and second comparators receive the respective outputs from the first and second calculators and assess them against respective first and second references providing signs of short conditions and assessments of changes in impedance between the electrodes. A logic analyzer receives the signs and assessments and evaluates them to permit the instantaneous starting, operating or stopping of the electrosurgical generator. The electrodes include an instrument and a set of cables with a preselected combined impedance so the maximum instantaneous impedance between the electrodes is less than the preselected combined impedance. The second reference is user adjustable. Switches, associated with each of the voltage monitor and the current monitor, choose the gain applied to the proportional signals respectively therefrom. First and second calculator gain changers receive the signals for setting the range across which those respective signals are used. Methods have steps of monitoring voltage and current, generating signals, dividing the voltage signal by current signal to find short circuit impedance between the electrodes and the instantaneous changes in impedance for other than the short circuit impedance, assessing those findings against references and permitting the starting, operating, or stopping of the electrosurgical generator.

687 citations

Journal ArticleDOI
TL;DR: In this paper, an artificial impedance surface that is implemented as an array of sub-wavelength metallic patches on a grounded dielectric substrate is designed to scatter a known input wave into a desired output wave.
Abstract: We have developed a method for controlling electromagnetic surface wave propagation and radiation from complex metallic shapes. The object is covered with an artificial impedance surface that is implemented as an array of sub-wavelength metallic patches on a grounded dielectric substrate. We pattern the effective impedance over the surface by varying the size of the metallic patches. Using a holographic technique, we design the surface to scatter a known input wave into a desired output wave. Furthermore, by varying the shape of the patches we can create anisotropic surfaces with tensor impedance properties that provide control over polarization. As an example, we demonstrate a tensor impedance surface that produces circularly polarized radiation from a linearly polarized source.

682 citations

Journal ArticleDOI
TL;DR: In this article, the authors proposed a reactive impedance surface (RIS) as a substrate for planar antennas that can miniaturize the size and significantly enhance both the bandwidth and the radiation characteristics of an antenna.
Abstract: The concept of a novel reactive impedance surface (RIS) as a substrate for planar antennas, that can miniaturize the size and significantly enhance both the bandwidth and the radiation characteristics of an antenna is introduced. Using the exact image formulation for the fields of elementary sources above impedance surfaces, it is shown that a purely reactive impedance plane with a specific surface reactance can minimize the interaction between the elementary source and its image in the RIS substrate. An RIS can be tuned anywhere between perfectly electric and magnetic conductor (PEC and PMC) surfaces offering a property to achieve the optimal bandwidth and miniaturization factor. It is demonstrated that RIS can provide performance superior to PMC when used as substrate for antennas. The RIS substrate is designed utilizing two-dimensional periodic printed metallic patches on a metal-backed high dielectric material. A simplified circuit model describing the physical phenomenon of the periodic surface is developed for simple analysis and design of the RIS substrate. Also a finite-difference time-domain (FDTD) full-wave analysis in conjunction with periodic boundary conditions and perfectly matched layer walls is applied to provide comprehensive study and analysis of complex antennas on such substrates. Examples of different planar antennas including dipole and patch antennas on RIS are considered, and their characteristics are compared with those obtained from the same antennas over PEC and PMC. The simulations compare very well with measured results obtained from a prototype /spl lambda//10 miniaturized patch antenna fabricated on an RIS substrate. This antenna shows measured relative bandwidth, gain, and radiation efficiency of BW=6.7, G=4.5 dBi, and e/sub r/=90, respectively, which constitutes the highest bandwidth, gain, and efficiency for such a small size thin planar antenna.

653 citations

Journal ArticleDOI
TL;DR: In this article, a direct three-dimensional finite-difference time-domain (FDTD) method is applied to the full-wave analysis of various microstrip structures and antennas.
Abstract: A direct three-dimensional finite-difference time-domain (FDTD) method is applied to the full-wave analysis of various microstrip structures. The method is shown to be an efficient tool for modeling complicated microstrip circuit components and microstrip antennas. From the time-domain results the input impedance of a line-fed rectangular patch antenna and the frequency-dependent scattering parameters of a low-pass filter and a branch-line coupler are calculated. These circuits were fabricated and the measurements made on them are compared with the FDTD results and shown to be in good agreement. >

646 citations

Journal ArticleDOI
TL;DR: In this paper, simple analytical formulas are introduced for the grid impedance of electrically dense arrays of square patches and for the surface impedance of high-impedance surfaces based on the dense array of metal strips or square patches over ground planes.
Abstract: Simple analytical formulas are introduced for the grid impedance of electrically dense arrays of square patches and for the surface impedance of high-impedance surfaces based on the dense arrays of metal strips or square patches over ground planes. Emphasis is on the oblique-incidence excitation. The approach is based on the known analytical models for strip grids combined with the approximate Babinet principle for planar grids located at a dielectric interface. Analytical expressions for the surface impedance and reflection coefficient resulting from our analysis are thoroughly verified by full-wave simulations and compared with available data in open literature for particular cases. The results can be used in the design of various antennas and microwave or millimeter wave devices which use artificial impedance surfaces and artificial magnetic conductors (reflect-array antennas, tunable phase shifters, etc.), as well as for the derivation of accurate higher-order impedance boundary conditions for artificial (high-) impedance surfaces. As an example, the propagation properties of surface waves along the high-impedance surfaces are studied.

636 citations


Network Information
Related Topics (5)
Voltage
296.3K papers, 1.7M citations
87% related
Capacitor
166.6K papers, 1.4M citations
85% related
Amplifier
163.9K papers, 1.3M citations
85% related
Dielectric
169.7K papers, 2.7M citations
81% related
Electromagnetic coil
187.8K papers, 1.1M citations
80% related
Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,514
20223,479
20211,009
20201,579
20191,924
20181,809