Theory of variable-capacitance parametric amplifiers

Recently, an increasing concern has been raised about turn-to-turn faults (TTFs) in power transformers, because these faults can lead to severe transformer insulation failure and consequently, its outage. Generally, it is impossible to experimentally analyze the transformer behavior under such faults, since the implementation of those experiments may be substantially destructive. Therefore, computer-aided models should be developed to investigate the performance of transformer protective relays under turn-to-turn faults. So far, existing transformer models are mainly formulated to implement in the EMTP-based softwares. However, most of power system protection engineers and researchers develop their protective algorithms in other softwares, such as MATLAB. In this paper, two simplified and accurate equivalent circuits of single phase, two winding transformer (under TTF condition) are proposed. These equivalent circuits can be simply simulated in any desired software. This accurate model closely translates the state-of-art existing TTF models into a comprehensive equivalent circuit. However, precise estimation of its parameters requires a supplementary finite element analysis. This paper employs some justifiable simplifications to the accurate model and results in a simple TTF equivalent circuit. The parameters of this model can be obtained by employing just the transformer routine test datasheet. The simple equivalent circuit is simulated under several turn-to-turn fault conditions and its accuracy has been validated.

This work presents the theory and experimental demonstrations of frequency-controlled energy absorption in parametric mixing circuits which may find applications in the design of tunable notch filters and frequency-selective surfaces. A time-varying capacitance model is used to describe the energy exchange among the pump, signal, and idler frequencies in parametric mixing circuits. Analytical derivations reveal that under specific frequency ordering, the system exhibits a positive conductance at the signal frequency that is correlated with the pump frequency, leading to measurable energy absorption. A fabricated on-chip circuit operating between 1.3 and 2.3 GHz serves as a physical representation of the theoretical model, experimentally validating the predicted energy transfer behavior. The results establish a unified framework linking circuit-level phenomena to the fundamental physics of energy redistribution in parametric systems.

A Superconducting QUantum Interference Device (SQUID) modulated by a fast oscillating magnetic flux can be used as a parametric amplifier, providing gain with very little added noise. Here, we develop linearized models to describe the parametrically flux-pumped SQUID in terms of an impedance. An unpumped SQUID acts as an inductance, the Josephson inductance, whereas a flux-pumped SQUID develops an additional, parallel element which we have coined the ``pumpistor.'' Parametric gain can be understood as a result of a negative resistance of the pumpistor. In the degenerate case, the gain is sensitive to the relative phase between the pump and signal. In the nondegenerate case, gain is independent of this phase. We develop our models first for degenerate parametric pumping in the three-wave and four-wave cases, where the pump frequency is either twice or equal to the signal frequency, respectively. We then derive expressions for the nondegenerate case where the pump frequency is not a multiple of the signal frequency, where it becomes necessary to consider idler tones which develop. For the nondegenerate three-wave case, we present an intuitive picture for a parametric amplifier containing a flux-pumped SQUID where current at the signal frequency depends upon the load impedance at an idler frequency. This understanding provides insight and readily testable predictions of circuits containing flux-pumped SQUIDs.

Mechanism of enhanced secretion in the warmed Malpighian tubule of the tsetse fly, Glossina morsitans morsitans

The impedance dependence of resonant tunneling diode (RTD) based on InGaAs/InAlAs heterostructure was measured in 0.1...50 GHz frequency range. It is shown, that the simplest equivalent circuit, consisting of parallel resistor and capacitance and connected to them in series resistor, describes the experimental behavior rather well. The RTD equivalent circuit parameters dependences on applied bias were obtained and standard deviations of these parameters were evaluated with methods of mathematical statistics.

In lightning impulse withstand voltage tests for substation equipment, waveforms regulated in the standard are sometimes difficult to generate on large equipment of the UHV class due to the level of capacitance of the test equipment "Ct" and the level of the residual inductance of the test circuit including the power supply "Ls". In the present study, the relationships between the capacitance of the test equipment, residual inductance of the circuit, the front time "Tf" of generated waveforms, and the overshoot rate "ß" were obtained using a simple equivalent circuit by assigning parameters systematically. Consequently, it has been found that, while Ct and Ls are small, there is a series resistance "Rs" range in which both the Tf and ß conditions are met and that, as Ct and Ls grow larger, there is an Rs range in which only one of the conditions is met but not both the conditions, and in the end even the Tf condition alone is not achieved. An increase either in ß or Tf increases the testable Ct upper limit or permissible Ls limit value, and an increase in Tf is found to be more effective.

Different d-q-axis inductances hinder the representation of synchronous reluctance motors by a simple equivalent circuit, and two d-q equivalent circuits are usually adopted. This obscures simple analysis and physical insight into the machine behaviors. This problem is solved by introduction of the complex inductance concept by which the saliency is parametrized in terms of the current angle. From the circle diagram of the complex inductance, the vector diagram of the motor can then be drawn, and machine behaviors can be graphically visualized and investigated. The proposed equivalent circuit is further modified to include the magnetic cross coupling and core loss. The complex inductance concept can be extended to other types of machines with saliency such as IPMSMs.

Use of transmission lines in telecommunications is considered. It is stressed that signals' behavior in the lines exerts considerable influence on the characteristics of telecommunication networks. Analytical methods of studying signals' behavior in the telecommunication lines is shown to encounter substantial difficulties. It is proposed to use computer simulation of the lines in Matlab environment. For a long line with distributed parameters, its simplified equivalent circuit with lumped components is introduced. It is shown that the circuit can be described using Kirchhoff's laws and relationship between voltage and current for the individual elements of the equivalent circuit. Systems of differential equations that determine the behavior of the line are obtained. To facilitate digital computer simulation, transition from the system of differential equations to the system of difference equations is performed. As an example, behavior of the beforehand charged telecommunication line with twenty typical elements is studied for the case of its discharge on a resistive load. Simulation results prove that the corresponding model in Matlab environment correctly reflects all the underlying electromagnetic processes in the line as well as helps to elucidate some aspects that are not possible to observe in real-life experiments. The proposed method can be effectively used to study any telecommunication lines that can be reduced to the equivalent circuits with lumped parameters.

This paper presents a methodology to estimate the parameters of a single-phase induction motor (SPIM) equivalent circuit using a dc test, a locked-rotor test, and a no-load test. By neglecting the core-loss resistance, the SPIM parameters can be first directly calculated using a simplified equivalent circuit. However, an equivalent circuit using the resultant parameter values fail to match the power input measured at the motor terminals, especially for the active power under the no-load test. We include the core-loss resistance into the parameter estimation framework and use the Newton-Raphson (N-R) algorithm to improve the estimates obtained by the direct calculation method. Experimental results on a laboratory SPIM demonstrate the effectiveness of our proposed N-R based parameter estimation scheme, in terms of excellent match with the active and reactive power measurement data from the aforementioned tests, and mismatch reduction at other operating conditions.

A simple equivalent circuit is proposed which can form the basis for undergraduate courses in circuit design. The circuit sacrifices a small amount of accuracy in gaining a great deal of simplicity. Since this equivalent circuit applies to all areas of design, a unified, practical approach to transistor design can be developed. Several justifications are presented for using this equivalent circuit rather than other design methods.

The multilayer piezoceramic actuator was replaced with an equivalent circuit composed of R, L, and D, represented in a state variable diagram. The charge-discharge characteristics were tested with simple experimental circuits, replacing the circuits with a simple equivalent circuit. The experiments conducted estimated constants in the circuit and investigated the speed of the response. In the case of the ceramic actuator, the impedance of the power supply greatly influenced the time constant. According to the measurements, the capacity of the dielectric as a characteristic of the ceramic material is about 1 mu F. Therefore, the time constant would grow smaller if the impedance of the power supply and the load resistor were small.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electromagnetic acoustic transducers (EMATs) generate ultrasonic waves in metals through an electromagnetic coupling mechanism. A concept for EMAT generation, using a coil alone without a permanent magnet, but with a pulse generator and a sample, is introduced. A simplified equivalent coil circuit is given and has been validated by experimental measurements. Such an equivalent circuit can be used for variations in excitation current calculations, which have often been neglected in previous publications in this area but have proved to be of great importance in considering the efficiency and frequency characteristics of ultrasonic generation. The equivalent coil inductance is dependent on the distance between the coil and the sample, due to coil interactions with eddy currents and the Ampere current of the magnetization mechanism. Analytical solution for an annular coil above metal samples is given, and the influences of the lift-off, coil radius, material magnetic permeability and electrical conductivity on the equivalent coil inductance are discussed. Experimental measurements agree well with predictions.

Unusually low noise, combined with high stable gain over fairly wide bands, has been obtained with electron beam amplifiers of a new kind. This paper explains how this performance is achieved by the action of a transverse quadrupole field upon a fast cyclotron wave. The first two sections give a qualitative description of the device and of the amplifying mechanism. A physical picture of the fast cyclotron wave is used to explain the interchange of signal and noise in the input coupler and the mechanism of parametric amplification in the quadrupole region. The third section presents a detailed analysis of the amplification process. It shows that the fast cyclotron wave is amplified in accordance with a cosh function of distance traveled through the quadrupole, and that a new cyclotron wave at idler frequency (difference between pump and signal frequencies) is generated which grows as a sinh function of distance. The fourth section describes experimental tubes built to date. These operate on frequency bands between 400 and 800 mc. Typical bandwidth is 40 to 50 mc independent of gain, which may be adjusted to 20 or 30 db. Residual noise temperature of the electron beam in good specimens within this experimental lot is 70°K; input coupler loss raises this figure to about 100°K. This is equivalent to a noise figure of 1.4 db if the device is used, for instance, in radio astronomy.

This paper describes the analysis of time-variant networks in the frequency domain applied to resistive, inductive, and capacitive sinusoidally varying networks. It leads to a common equivalent circuit. This equivalent circuit is based on some previous work done by Desoer and by the author. The equivalent circuit is applied to the analysis of resistive modulators, parametric amplifiers, and frequency multipliers. It is shown how simple time-invariant two-port equivalent circuits can be derived for these transmission networks, such that the practical engineer can obtain quick insight into their behavior. The derived linear two-port equivalent circuit can be used as a basis for a small-signal nonlinear analysis of the above mentioned transmission networks.

This paper explores the fundamental properties of a family of zero-current-transition (ZCT) inverters in a systematic and comparative approach. The inverters studied include several schemes for a circuit configuration with six auxiliary switches and one topology that requires only three auxiliary switches. First, a simplified equivalent circuit is presented to unify common traits of ZCT commutations and their design criteria. Mechanisms for achieving zero-voltage turn-on in ZCT inverters are investigated. Then, with the visual aid of state planes, behaviors of individual inverters, including switching turn-on and turn-off conditions, circulating energy, and device/component stresses, are analyzed against the simplified equivalent circuit. Finally, a comparison of major features is conducted. Both simulation and experimental results are provided for verification.