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.
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TL;DR: In this article, the electrical impedance of nanocrystalline diamond films was measured in the frequency range 50 Hz to 1 MHz using a Fluke PM6306 RCL meter.
Abstract: Nanocrystalline diamond films were synthesized by microwave plasma-enhanced chemical vapor deposition using Ar/H2/CH4 gas mixtures. A Fluke PM6306 RCL meter was used to study the electrical impedance of these diamond films in the frequency range 50 Hz to 1 MHz. The impedance dispersion measurement yields the real and imaginary parts in the form of a Cole-Cole plot in the complex plane. A single semicircular response of the impedance of nanocrystalline diamond films was observed at temperatures below 250 °C, with a second semicircular response appearing at low frequencies at temperatures above this. The semicircular responses were found to fit a double resistor-capacitor parallel circuit model. Physical mechanisms likely to be responsible for these observations are discussed in this paper.
68 citations
TL;DR: In this article, a discretization model was proposed to capture battery impedance characterization considering the temperature gradient, and several experiments, including experiments with artificial temperature gradients, were designed and implemented to study the influence of the internal temperature gradient on battery impedance.
Abstract: Battery impedance is essential to the management of lithium-ion batteries for electric vehicles (EVs), and impedance characterization can help to monitor and predict the battery states. Many studies have been undertaken to investigate impedance characterization and the factors that influence impedance. However, few studies regarding the influence of the internal temperature gradient, which is caused by heat generation during operation, have been presented. We have comprehensively studied the influence of the internal temperature gradient on impedance characterization and the modeling of battery impedance, and have proposed a discretization model to capture battery impedance characterization considering the temperature gradient. Several experiments, including experiments with artificial temperature gradients, are designed and implemented to study the influence of the internal temperature gradient on battery impedance. Based on the experimental results, the parameters of the non-linear impedance model are obtained, and the relationship between the parameters and temperature is further established. The experimental results show that the temperature gradient will influence battery impedance and the temperature distribution can be considered to be approximately linear. The verification results indicate that the proposed discretization model has a good performance and can be used to describe the actual characterization of the battery with an internal temperature gradient.
68 citations
TL;DR: In this article, a dc impedance model of an MMC is developed by harmonic transfer function method that considers the internal dynamics and typical controls of MMCs, while typical controls consist of dc voltage control, positive-negative sequence separation-based phase current control, circulating current control and some other linear controls.
Abstract: The dc impedance model of a modular multilevel converter (MMC) is the basis for analyzing harmonic resonances of MMC-based dc systems. As an MMC typifies a multiple harmonic response system, its internal dynamics and controls significantly influence its external characteristics. In this paper, a dc impedance model of an MMC is developed by harmonic transfer function method that considers the internal dynamics and typical controls of MMCs. The internal dynamics mainly include capacitor voltage fluctuation and multi-harmonic response characteristics, while typical controls consist of dc voltage control, positive–negative sequence separation-based phase current control, circulating current control, and some other linear controls. As a result, the proposed impedance model can be used not only to analyze the harmonic stability of an MMC-based dc system, but also to investigate the influence of additional controls in an MMC on system stability. Furthermore, the proposed model makes up for the deficiencies in harmonic stability analysis of MMC-based dc systems. The results of both the hardware-in-the-loop RT-LAB digital simulation and the physical experimentation validate the proposed impedance models and analyses.
68 citations
TL;DR: In this article, the authors presented new types of analog and digital micromachined impedance tuners, where the short-circuited shunt stubs are loaded with microelectromechanical system (MEMS) capacitive switches.
Abstract: Presents new types of analog and digital micromachined impedance tuners. Analog impedance tuners using resonant unit cells realized by tunable micromachined capacitors showed a wide tuning range equivalent to almost two quadrants of the Smith chart with a maximum voltage standing-wave ratio (VSWR) of 21.2 at the Ka-band. Frequency variability is also provided through the use of J-inverters with tunable capacitors. Also presented is a digital micromachined tuner, where the short-circuited shunt stubs are loaded with microelectromechanical system (MEMS) capacitive switches. The electrical length of the stub and the overall impedance of the tuner are thus controlled according to the switching states of the MEMS capacitors. The digital tuner presented impedance ranges suitable for load impedances of the RF power transistors and showed a high maximum VSWR of 32.3. Compared with the state-of-the art tuners using field-effect transistors, micromachined tuners of this paper show superior VSWR ranges as well as wide impedance ranges. Micromachined tuners are very promising for low-loss tuning of the monolithic circuits as well as for accurate noise and power characterization.
68 citations
TL;DR: The paper discusses the basic theory of switched resonators and the designing methodology of relevant RF signal processing applications, and a simple, compact and efficient RF pulse compression technique based on the switched resonator concept is introduced.
Abstract: Transient characteristics of switched resonators have been studied. The resonators exhibit controllable impedance and energy storage behaviors during an alternating charging and discharging process. It is discovered that these unique characteristics of switched resonators can lead to novel RF envelope signal processing functions. The paper discusses the basic theory of switched resonators and the designing methodology of relevant RF signal processing applications. Two applications are presented as examples. The first example is a variable, reflective attenuator which uses the controllable impedance of the switched resonators to achieve different attenuation/reflection levels. In the second example, a simple, compact and efficient RF pulse compression technique based on the switched resonator concept is introduced. It utilizes the charging/discharging characteristics of the circuit resonator by varying the resonator's Q-factor. The approach compresses the duration of the modulated pulse without changing the phase characteristics of the RF carrier. The pulse compression technique can also be implemented with other type of resonators including distributed resonators, as demonstrated through the experiments
68 citations