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.

Tests of 100 kW High-T/sub c/ superconducting fault current limiter

Abstract: An inductive superconducting fault current limiter has been built and tested. It mainly consists of a copper coil, a superconducting tube, and an iron core which are concentrically arranged. The device is essentially a transformer with the secondary winding being the tube. The tube has diameter of 20 cm, a height of 35 cm, and is made of Bi2212 ceramic, fabricated by partial melting. The ceramic has the voltage current characteristic V-I/sup /spl alpha// with /spl alpha//spl ap/5. The critical current density defined by the 1 /spl mu/V/em criterion is about 1400 A/cm/sup 2/. Depending on the number of turns of the coil, the nominal current of the device was between 130 A and 250 A. In short circuit tests in a 480 V circuit, the prospective fault current of 8 kA was limited to about 5 times the nominal current. The test results are in good agreement with detailed simulations of both the normal operation (e.g. impedance, AC-losses) and the behaviour under fault conditions (i.e. evolution of the current). >

Complex bioelectric impedance measurement system for the frequency range from 5 Hz to 1 MHz

Abstract: Analytic techniques that have been successfully employed in materials science, and to a lesser extent in the study of biologic systems, have potential for improving the application of bioelectric impedance provided that both real and imaginary impedance components can be measured with sufficient accuracy over a given frequency range. Since biologic tissue, particularly animal tissue, is typically highly conductive, phase angles are small, making accurate measurements difficult. A practical four-terminal system employing commercial lock-in amplifiers is described and error sources and corrective tech-niques are discussed.

High-power photonic millimetre wave generation at 100 GHz using matching-circuit-integrated uni-travelling-carrier photodiodes

Abstract: The design and characterisation of a millimetre wave uni-travelling-carrier photodiode with a monolithically integrated matching (impedance transform) circuit utilising a coplanar-waveguide short stub are presented. The device with the matching circuit shows about 50% higher efficiency at 100 GHz than the one without it. The frequency response was characterised through time-domain measurement by means of an electro-optic sampling technique. The 1 dB down bandwidth of the device is as wide as 40 GHz, and the frequency response characteristics are in good agreement with circuit model calculations. The maximum saturation output power is 20.8 mW at 100 GHz for a bias voltage of -3 V, which is the highest output power ever generated directly from a photodiode in the W-band.

Influence of loading on the electromechanical admittance of piezoceramic transducers

Abstract: Damage detection using electromechanical (EM) impedance in structural health monitoring (SHM) of engineering structures is rapidly emerging as a useful technique. In the EM impedance method, piezoceramic (PZT) transducers are either surface bonded to or embedded inside the host structure and are subjected to electric actuation. The EM admittance signatures of the PZT transducers, which consist of real and imaginary parts, serve as indicators to predict the health/integrity of the host structure. However, in real life, structural components such as slabs, beams and columns are constantly subjected to some form of external loading. The EM admittance signature obtained for such a constantly loaded structure is different from that obtained when damages are present in the structure. This paper presents an experimental and statistical investigation to show the influence of loading on EM admittance signatures. It is also observed that the susceptance signature is a better indicator than the conductance signature for detecting in situ stress in the host structure. This observation is further supported by a statistical analysis. This paper is expected to be useful for the non-destructive evaluation of engineering structures with external loading.

Stability Improvement for Three-Phase Grid-Connected Converters Through Impedance Reshaping in Quadrature-Axis

Abstract: Three-phase AC−DC and DC−AC power converters have been extensively employed as grid-interfaces in various applications, e.g., distributed generation and energy storage systems. In these applications, power converters should always synchronize with the mains grid so that active and/or reactive power can properly be regulated while maintaining desired waveforms of grid currents. Grid synchronization necessitates accurate information of grid voltages, which is normally obtained through phase-locked-loops (PLLs). However, the employment of PLLs may bring in stability concerns. Previous research revealed that the inclusion of PLLs shapes the impedance of power converters into a negative resistance in the quadrature-axis ( q -axis), and this should be responsible for instability. To resolve the instability issue caused by PLLs, this paper proposes an impedance controller for reshaping the q -axis impedance into a positive resistance in the low-frequency band. Without any extra burden on system hardware, the proposed controller can easily be implemented by directly relating the q -axis voltage to the q -axis current reference. As a result, the presented three-phase power conversion system can operate stably even under a severely weak grid condition, which are verified by simulation and experimental results.