Arbitrary Current Source Research Articles

Computation of Electric and Magnetic Fields Generated by Cloud-to-Cloud Lightning Channels

The paper presents analytical formulas for computation in the time domain of electromagnetic (EM) fields generated by tortuous cloud-to-cloud (CC) lightning channels over a perfectly conducting ground. For the first time, the study was not limited to a horizontal lightning path but was extended to take into account the natural, tortuous geometry of the lightning channel. After the calculation of the step response, a convolution integration was applied for the computation of the fields generated by an arbitrary current source. The produced electric and magnetic fields were then compared with the fields generated by a horizontal channel. The method can be of primary importance to evaluating the hazards for electric and electronic systems of flying aircraft, estimating the voltages induced on overhead transmission lines by CC lightning, and, in general, evaluating the induced effects on sensitive electric and electronic components. Moreover, it may represent a simple, robust, and time-saving tool for estimating important physical parameters that characterize lightning phenomena.

An Efficient Method for the Computation of Electromagnetic Fields Associated With Tortuous Lightning Channels

Lightning electromagnetic (EM) fields are typically computed by assuming the current propagation within a straight vertical channel of negligible cross section. However, it is well known that the lightning path is tortuous and this can significantly affect the radiated fields and the lightning-induced voltages on power lines. Lupò <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> (2000) proposed an analytical method evaluating the EM fields radiated by a tortuous channel assuming a step current source; to consider an arbitrary (realistic) current source, a slow-converging convolution integral was applied. The aim of this article is to reduce the computation time of such procedure by extending to the tortuous channel case the approach proposed by Brignone <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> (2021) for the evaluation of the lightning EM fields with arbitrary current source, originally developed for a straight vertical channel. The performances of the present method are evaluated by means of comparison with the solution proposed by Lupò <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> (2000), showing an excellent agreement with a significant reduction of the CPU effort. This in principle will allow the computation of lightning-induced overvoltages at both individual and statistical level without a prohibitive computational effort.

A Knowledge Based Method for Optimization of Decoupling Capacitors in Power Delivery Networks

For power delivery applications, a method for reducing impedance is through the addition of decoupling capacitors (decaps). In this article, we propose a knowledge-based optimization method to determine decap design in power delivery networks (PDNs). The proposed method provides the optimized PDN with the minimum number of decaps by iteratively assigning the decaps that maximize the frequency range where the target impedance is satisfied. In addition, by integrating the time-domain analysis into the proposed method, a voltage response arising from any arbitrary load current sources is guaranteed within the threshold level while preventing the over-design problem. Unlike the recent random search-based methods (genetic algorithm and machine learning (ML) etc.) requiring a large number of PDN simulations for learning and selection, the proposed method determines effective decaps through multiple steps based only on domain knowledge, significantly reducing the number of PDN simulations and computational cost to obtain the optimized decap solution. We apply the proposed method to three different PDN models. The results show that only 1.3% of the computing time is required to achieve the optimized decap design compared with the ML-based method while having the same number of decaps as the optimal number obtained by the full-search simulation.

Flexible, Highly Dynamic, and Precise 30-kA Arbitrary Current Source

High-power current sources with high dynamic performance, ultralow current ripple, and absolute reference tracking accuracy are the key elements for magnets (bumper and septum) that are used in accelerators. Similar requirements are also encountered in plasma research applications in fusion reactors, as well as plasma research for the future high voltage direct current circuit breakers. Therefore, the current source must be able to drive resistive/inductive and highly fluctuating loads without any compromise in its performance. In this paper, such a flexible, dynamic, and accurate current source is introduced, which able to provide amplitudes up to 30 kA and bipolar voltages up to 10 kV. The system’s operating concept is presented and its design procedure in order to fulfill a list of demanding specifications is demonstrated. In addition, a detailed description of its near-optimal, advanced control system is presented. Finally, the theoretical considerations are verified by extensive simulation results for various operating scenarios, including driving chaotic arc loads.

On the computation of plane-wave impressed fields and far-zone fields of arbitrary current sources in planar multilayer dielectric and plasmonic media

A unified and succinct transmission line formulation is presented for the computation of the plane-wave impressed fields and far-zone radiation fields due to arbitrary electric and magnetic current source distributions embedded in planar layered media. The equivalence principle and the spectral-domain transmission-line network analogue of the multilayer medium are used to express the fields in terms of the voltage and current transmission-line Green functions. The new formulation is applied to sample problems involving both dielectric and plasmonic multilayer media.

Small-Scale HVDC Circuit Breaker

Circuit breakers are anticipated for fault isolation in multiterminal HVdc networks. However, there are remaining challenges concerning the circuit breaker topology and operation. The passive oscillation principle circuit breaker is one of the topologies under consideration, the design of which requires examination of the arc characteristics. The design process is therefore presented, with the aim of constructing a small-scale prototype. First, a horizontal nozzle constricted arc setup with a blowing capability is built in order to study the stationary and transient arc characteristics P(g) and τ(g), which are essential for the design of this type of breaker. Second, after their extraction from measurements, these two arc parameters are inserted into a simulation model based on the Mayr-Schwarz arc equation, which predicts an effective breaker operation. Finally, a passive oscillation principle breaker is constructed and successfully tested with both an arbitrary current source and on a scaled voltage source converter network.

2-D quasi-static solution of a coil in relative motion to a conducting plate

PurposeThe aim of this paper is to present a method for calculating the electromagnetic fields, forces and current density distribution using Fourier series for a two-dimensional quasi steady state model consisting of a conducting uniform plate moving relative to an arbitrary current source with time harmonic excitation.Design/methodology/approachThe presented solution is valid for an arbitrary source. A specific source is chosen consisting of a single coil made up of two-time harmonic current filaments. The solutions are derived and presented in a form that allows its expansion to include an arbitrary number of spatially shifted coils conducting arbitrary harmonic currents.FindingsThe analytical solution is compared to simulations produced using commercial finite element analysis software, ANSYS Maxwell2D and COMSOL, and is found to be in good agreement. The analytical solution provides a direct method to analyze the spatial harmonics in the system and can be computationally significantly faster especially at high relative speeds between the primary source and conducting plate.Originality/valueThe presented Fourier series solution is applied to simple 2-D model of a single coil with AC current excitation moving relative to a conducting plate. An analytical solution and analysis of this system has not been presented before, to the authors’ knowledge, using Fourier series or any other method.

Optimal Test Current Shape for Accurate Arc Characteristic Determination

Arcs under high-current gradients ( >50 kA/ms) are created during fault interruption in passive resonant circuits of HVDC circuit breakers. Black-box models have been successfully applied to model the dynamic arc-network interaction for such breakers. This requires accurately known parameters, such as arc cooling power P(g) and thermal arc inertia τ(g) as a function of conductance. Their experimental determination is difficult and requires significant measurement effort. In a previous work, it was shown that these parameters can be determined more accurately with step-wise current measurements compared to sinusoidal test currents. In this contribution, the optimal nonsinusoidal current waveform is addressed, which maximizes the accuracy of τ at a minimum of required experiments. With a novel arbitrary current source complex, step-, slope- and spike-current waveforms are applied to a wall-stabilized arc. The best results have been obtained from a gradually increasing current slope of 0.3 kA/ms superimposed with repetitive current spikes of 5-15 kA/ms slopes. This enables a large number of evaluation points that showed high accuracy during a single experiment.

Improved Method for Direct Black-Box Arc Parameter Determination and Model Validation

Black-box models are a valuable tool to simulate dynamic arc-network interactions, such as those that occur during fault current interruption in ac or HVDC circuit breakers. However, accurate determination of characteristic arc parameters from voltage and current measurements is very challenging. This paper aims to improve the accuracy in arc characterization. A new arbitrary current source is used to simplify arc parameter determination through a more complex current waveform, for example, a series of staircase-like increasing steps. With this, the stationary and transient arc characteristics can be measured independently from each other. Therefore, current steps are well suited to: 1) validate the choice of a specific black-box model and 2) determine the arc parameters of the chosen model with higher accuracy. In principle, the source is also well suited to fill a table of the arc voltage response U, U at various current levels and slopes I, I. Thus, it would be possible to characterize arcs independent of any black-box model, but it would not be well suited to compare different arcs. Therefore, this paper focuses on an improved black-box parameter determination and the experimental validation of the Schwarz model, with P and τ being free functions of g.

Excited spherical waves in unbounded cold magnetoplasma and applications in radio sounding

The electromagnetic field excited by an arbitrary current source embedded in an unbounded uniform cold magnetoplasma is investigated in this paper. The Green's function method for solving the radiation equation is used, and the derived solution is valid for any cold plasma parameters. There are always two wave modes excited, and in the far field each mode has the form of a spherical wave. A refractive index for spherical waves is introduced to describe the propagation. The properties of these excited spherical waves are discussed in this paper in comparison with the plane wave representation. It is shown that the energy flow of the spherical wave is always in the radial direction, i.e., parallel to the wave normal.

Full frequency-domain approach to reciprocal microlasers and nanolasers–perspective from Lorentz reciprocity

We develop a frequency-domain formulation in the form of generalized eigenvalue problems for reciprocal microlasers and nanolasers. While the goal is to explore the resonance properties of dispersive cavities, the starting point of our approach is the mode expansion of arbitrary current sources inside the active regions of lasers. Due to the Lorentz reciprocity, a mode orthogonality relation is present and serves as the basis to distinguish various cavity modes. This scheme can also incorporate the asymmetric Fano lineshape into the emission spectra of cavities. We show how to obtain the important parameters of laser cavities based on this formulation. The proposed approach could be an alternative to other computation schemes such as the finite-difference-time-domain method for reciprocal cavities.

A validated SPICE network simulation study on improving tunnel diodes by introducing lateral conduction layers

ABSTRACTIn this work, network simulations using LTSpice (Linear Technology, Milpitas, CA, USA) for monolithic triple‐junction solar cells have been performed. In order to simulate the internal structure correctly, the integration of the tunnel diode into the network simulation was mandatory. The tunnel‐diode characteristics are modeled by LTSpice's arbitrary behavioral current sources. The integration of tunnel‐diode characteristics into the network model was validated by comparison of simulated and experimental data. Lattice‐matched triple‐junction solar cells were examined under homogenous illumination between 1 and 1900 suns as well as under non‐uniform digital irradiance. The verified model was then used to study the influence of lateral current spreading in layers surrounding the tunnel diodes. It is shown that a lateral current spreading from high to low illumination intensity regions cannot prevent the tunnel diode from switching to thermal diffusion under the used Gaussian illumination profile as it appears in concentrator photovoltaic applications. Furthermore, resistance regimes of the lateral conducting layers were identified, which would enable a current spreading that is high enough to transport all current exclusively by tunneling. It is shown that the presence of at least one additional layer above and one below the tunnel diode is mandatory. Finally, the necessary layer thicknesses using Alx−1GaxAs as lateral conducting layers are calculated for different doping concentrations and mole fractions x. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Improving Gain Efficiency in Planar Impact Ionization Devices

The Solid-state Impact-ionization Multiplier (SIM) was designed to amplify signals from arbitrary current sources through impact ionization. A primary application is amplification of signals produced by photodiodes. Photodiodes made from any semiconductor can be wired directly to the SIM's injection node. Previous versions of the SIM suffer from non-ideal impact ionization efficiency as a result of injected carriers drifting through the device's depletion region without passing through the highest electric field regions and undergoing ionization events. Low impact ionization efficiency can lead to an increased excess noise factor, temperature sensitivity, and voltage sensitivity. This manuscript describes increasing SIM ionization efficiencies by introducing an insulator between the SIM's injection and output electrodes, effectively directing the carriers into the highest electric field. This method has shown to greatly increase the impact ionization efficiency in simulation and experimental results. Ionization efficiency improvements are demonstrated primarily through decreases in voltage sensitivity.

SiO$_2$ Barriers for Increasing Gain Events in Solid-State Impact-Ionization Multipliers

A solid-state impact-ionization multiplier (SIM) was designed to amplify signals from arbitrary current sources through impact ionization. A primary application is amplification of signals produced by photodiodes. Photodiodes made from any semiconductor can be wired directly to the SIM's injection node. Planar versions of the SIM suffer from nonideal impact ionization efficiency as a result of injected carriers drifting through the device's depletion region to the output electrode without passing through the highest electric field regions and undergoing ionization events. Low impact ionization efficiency can lead to an increased excess noise factor, higher temperature sensitivity, and higher voltage sensitivity (rate of gain change with respect to applied voltage). This paper describes increasing SIM ionization efficiencies by introducing an insulator between the SIM's injection and output electrodes, effectively directing the carriers into the highest electric field. This method has shown to greatly increase the impact ionization efficiency in simulation and experimental results. Ionization efficiency improvements are demonstrated primarily through decreases in voltage sensitivity.

Solid-State Impact-Ionization Multiplier With P-N Junction Injection Node

The Solid-state Impact-ionization Multiplier (SIM) was designed to amplify signals from arbitrary current sources through impact ionization. A primary application is amplification of signals produced by photodiodes. Photodiodes made from any semiconductor can be wired directly to the SIM's injection node. In previous versions of the SIM, this injection node was a Schottky contact to silicon. This paper describes a SIM design that injects electrons into the SIM's depletion region through a p-n junction. The injection node is analyzed including how the node's floating voltage changes versus input current. Devices were made using epitaxial silicon and modeled using commercial software. The measured gain characteristics match closely to simulated results and are influenced by high electric fields near the SIM's depletion region edges. Measured frequency response was dominated by charging effects related to the floating node, leading to a response that scales with the inverse of the input current.

High Gain Effects for Solid-State Impact-Ionization Multipliers

We report the demonstration of a current amplification device, built from silicon and based on impact ionization, which can be cascaded to achieve very high gains. Arbitrary current sources including photodiodes can be interfaced with this device. Testing was done by amplifying the output signal from an independent silicon photodiode. Current gains over 600 were measured for initial photocurrents of 10 nA when two amplifying devices were cascaded together. Additionally, the gain saturation phenomenon of the amplifier due to space-charge effects is investigated. The measured gain saturation is observed to match very well with theoretical predictions. We also present guidelines for obtaining high current gain from the cascaded structure while avoiding gain saturation. Because of the low-noise gain mechanism employed, this device is of potential interest to a variety of fields requiring high-sensitivity optical or electronic detection.

Solid-state current amplifier based on impact ionization

The operation principle, fabrication, and measurement results for a stand-alone amplifier based on impact ionization are reported. The device was built in silicon using standard microelectronic processes. Testing was performed by connecting the device to both silicon and indium-gallium-arsenide photodiodes to demonstrate its compatibility with arbitrary current sources. Preamplified leakage currents of less than 1nA were measured along with current gains greater than 100.

Surface structure silicon based impact-ionization multiplier for optical detection

This paper presents an innovative solid-state current amplifier based on impact ionization. The operation principle, fabrication, and test results for this device are reported. This amplifier was built on a silicon surface using standard microelectronics processes including ion implantation. Testing was performed by connecting the device to both silicon and indium-gallium-arsenide photodiodes to demonstrate its compatibility with arbitrary current sources. Current gains above 100 along with pre-amplified leakage currents of less than 10 nA were measured.

Simulation study on reconstruction of electric conductivity distribution from magnetic vector field measurements

We describe an effective, versatile technique for reconstructing the electric conductivity distribution from magnetic vector field measurements. Using magnetic vector field data measured over a region of interest (ROI), the assumed steady current vector field is reconstructed to perform conductivity reconstruction. As the current sources/current flow outside the ROI significantly contribute to magnetic fields over the neighbourhood of the ROI border, the extra contributions are reduced in the measured magnetic field data using a derived spatial weight function. The remaining magnetic field measurement errors are coped with utilizing a mollification method in conjunction with a regularization method. In a straightforward manner, our current field reconstruction technique is combined with our previously reported conductivity reconstruction technique. The combined non-contact conductivity reconstruction technique in principle allows handling of an arbitrary geometry of the target conductive ROI and arbitrary current sources existing outside the ROI. The technique is particularly effective when an inherent current flow exists and only field measurements are needed. Technique feasibility is simply verified by reconstructing a 2D conductivity distribution using simulated, noise-filled, magnetic field data. Resultant reconstructions indicate the technique to be a practical means for robustly reconstructing target conductivity distributions.

Radiation Green's function of a DBR cavity containing a quantum well: vacuum photons and cavity polaritons on equal footing

Radiation Green's function has been derived for cavity polaritons, which describes the propagation of electromagnetic field in- and outside the system consisting of DBRs and a quantum well with an exciton resonance. This Green's function equally describes both the cavity polaritons with leakage to vacuum and the vacuum photons disturbed by the cavity. The convolution of this Green's function with an arbitrary current source, such as those due to various nonlinear polarizations, pump phonons fields, and so on, directly gives the signal field due to the source.