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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
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Journal ArticleDOI
TL;DR: In this article, the complex Poynting theorem has been used to show that the antenna is essentially equivalent to a one port lossy network, where the Foster reactance theorem holds for antennas.
Abstract: The calculation of antenna Q has been an interesting and a controversial topic for years. We first give a rigorous study of antenna Q by introducing a complete description of the complex power balance relation for an antenna system. Using the complex Poynting theorem, we have shown that the antenna is essentially equivalent to a one port lossy network. The Foster reactance theorem is usually stated for a lossless network. The main purpose of this paper is to determine whether the Foster reactance theorem holds for antennas. By making use of a complex frequency domain version of the Poynting theorem, we have shown that the Foster reactance theorem is valid for an antenna. Finally, the Foster reactance theorem for the antenna has been applied to demonstrate the widely held assumption Q/spl ap/1/B, provided Q/spl Gt/1, where B stands for the fractional bandwidth of an arbitrary antenna.

135 citations

Journal ArticleDOI
TL;DR: In this article, a method to estimate the magnet temperature in surface permanent-magnet machines using high-frequency carrier signal injection is proposed. But the method is limited to the case of a single rotor.
Abstract: This paper proposes a method to estimate the magnet temperature in surface permanent-magnet machines using high-frequency carrier signal injection. The injection of a high-frequency signal, superimposed on the fundamental excitation, allows the estimation of the stator high-frequency impedance, which is a function of both the stator and rotor impedances. The temperature of the magnets is shown to have a significant weight on the overall stator high-frequency impedance, from which it can be estimated. The high-frequency carrier signal is injected intermittently in order to minimize potential adverse effects on the normal operation of the machine. This paper first explains the physics behind the magnet temperature dependence. Then, the principles of the method, as well as its practical implementation, are discussed. Experimental verification of the method is provided.

134 citations

Patent
21 Dec 1994
TL;DR: In this paper, a remote switching module has two signal terminals connected by just two conductors to the signal terminals of a local decoding module, which can detect the different impedance levels by sensing the current flow on the conductors.
Abstract: A communication system comprises a remote switching module having two signal terminals connected by just two conductors to the signal terminals of a local decoding module. Power is directly provided only to the local decoding module, which applies DC voltage of a first level across the conductors. The remote switching module has a voltage regulator which provides power of a second voltage level lower than the first level for operating a control unit in the switching module. The control unit controls a variable impedance having higher and lower impedance levels and which is connected across the switching module's signal terminals. The decoding module can detect the different impedance levels by sensing the current flow on the conductors. The switching module communicates with the decoding module by modulating the time intervals between changes in impedance levels. The system has particular utility for retrofitting cooling to a heating systems where preexisting thermostat wiring has only two conductors, say when an air conditioning function is added to a previously heat only system. The system is also useful when installing electronic thermostats on heating and cooling systems originally controlled by a mechanical thermostat.

134 citations

Patent
21 Jan 2003
TL;DR: In this article, an amplitude modulation circuit provides modulated supply current (IPA) possibly in combination with modulated input voltage (VPA) to a radio frequency power amplifier (48) and includes a detection circuit (66) responsive to changes in the ratio of VPA to the AM modulation impedance.
Abstract: An amplitude modulation circuit provides modulated supply current (IPA) possibly in combination with modulated supply voltage (VPA) to a radio frequency power amplifier (48) and includes a detection circuit (66) responsive to changes in the ratio of that voltage (VPA) to the modulated supply current (IPA), described herin as its AM modulation impedance. Such impedance (resistance) changes commonly arise from changing coupling characteristics at the antenna assembly (54) driven by the power amplifier (48). A gain control circuit may be associated with the detection circuit (66), and made responsive thereto, thus allowing adjustment of modulation gain control responsive to changes in AM modulation impendance.

134 citations

Patent
11 May 2009
TL;DR: In this article, the authors present methods and systems for calibration of RFID sensors used in manufacturing and monitoring systems, which include measuring impedance of an RFID sensor antenna, relating the measurement of impedance to one or more parameters (such as physical, chemical and biological properties), computing one ormore analytical fit coefficients, and storing the one OR more analytical fit coefficient on a memory chip of the RFID Sensor.
Abstract: Methods and systems for calibration of RFID sensors used in manufacturing and monitoring systems are provided. The methods include measuring impedance of an RFID sensor antenna, relating the measurement of impedance to one or more parameters (such as physical, chemical and biological properties), computing one or more analytical fit coefficients, and storing the one or more analytical fit coefficients on a memory chip of the RFID sensor. Measuring impedance of the RFID sensor may comprise measuring complex impedance which involves measuring complex impedance spectrum, phase angle and magnitude of the impedance, at least one of frequency of the maximum of the real part of the complex impedance, magnitude of the real part of the complex impedance, zero-reactance frequency, resonant frequency of the imaginary part of the complex impedance, and antiresonant frequency of the imaginary part of the complex impedance. Also provided are manufacturing or monitoring systems comprised of an RFID sensor wherein the RFID sensor comprises, a memory chip, an antenna, and a sensing film wherein analytical fit coefficients are stored on the memory chip to allow calibration of the RFID sensor. Also provided are manufacturing or monitoring systems comprised of an RFID sensor wherein the RFID sensor comprises, a memory chip, an antenna, and a complementary sensor attached to the antenna where the complementary sensor in a pre-calibrated fashion predictably affects the impedance of the antenna.

134 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,514
20223,479
20211,009
20201,579
20191,924
20181,809