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Full-wave simulation of arbitrary structures in 2D and 3D space, whose parts are made of homogenous, linear and isotropic materials, most often can be performed efficiently and accurately by solving Surface Integral Equations (SIE) using Method of Moments (MoM) [1], [2]. In addition, for parts of structures that are highly inhomogeneous, or continuously inhomogeneous, or anisotropic, the advantage is on the side of Finite Element Method (FEM). Although MoM/SIE and FEM are well established methods, continuous demands to solve larger and more complex structures/scenarios with increased accuracy/efficiency gives motivation to scientist to search for new algorithms/strategies.

The class Φ 2 resonant converter is one of the most promising very-high-frequency (VHF) power converter topologies. It comprises a class Φ 2 resonant inverter, which provides low switch voltage stress compared to other resonant inverter topologies, and a class E resonant rectifier. In this paper, a design optimization and performance evaluation of the class Φ 2 VHF dc/dc converter are presented. Two different topologies are considered. Due to the complexity of the converter operation, the design is performed in several iterations aided by Simplis simulations. The design procedure is illustrated on a 90-W, 160-170-V input and 33-V output voltage class Φ 2 dc/dc converter operating at 30 MHz. The experimental circuit is described in details and measurement results are presented. Practical issues with the currently available GaN devices are also discussed.

Arbitrary 2D periodic composite material structures, which are excited by plane wave of arbitrary polarization and incoming direction, are analyzed by applying the method of moments (MoM) to surface integral equations (SIEs). Flexibility, efficiency and accuracy is achieved owing to a) Ewald transformation for evaluation of doubly periodic Green's functions, b) general technique to connect material regions through interface of successive cells, and c) higher order basis functions.

Towards the short-range multigigabit data transfer, we investigate the possibility of employing the orbital angular momentum (OAM) of electromagnetic (EM) waves in the unlicensed millimeter wave frequency band around 60 GHz (from 57 GHz to 66 GHz). We investigate the effects of OAM source spatial discretization, with respect to the radial and azimuthal coordinates, on a wireless transmission system performance and the quality of OAM radiation patterns. First, second, and third OAM mode are taken into account. Short-range wireless transmission system capabilities are modeled and estimated for realistic values of input parameters. The estimated data transmission rates are very promising.

Graphene-metal combined waveguide resonators were proposed earlier, as a solution for obtaining frequency tunable resonator responses at the sub-millimeter-wave frequencies. A methodology for combining these waveguide resonators into the frequency tunable filters has been studied subsequently. Here, we discuss the possibilities and limitations of this type of waveguide resonators, illustrated by several examples of tunable filter designs.

IT enabled enterprise organizations are embracing multi-cloud to handle their peak loads in addition to their private cloud (own data centers) and the market prediction indicates that by year 2020, about 80% of enterprise will have or working towards multi-cloud enablement for their IT needs. There are multiple products from third-party supporting multi-cloud and also some of the cloud service providers have already enabled the service using proprietary cloud management tools with custom built plug-ins. One of the major challenges in multi-cloud is efficient resource utilization and cost savings without vendor/broker lock-in. At present, multi-cloud interface standardization is still in draft. In this paper we propose handling of cloud burst at peak load with our OpenStack [9] Middleware Framework, which uses default OpenStack services. It also has built-in support for prediction, resource allocation and proactive workload migration techniques which can be integrated easily with cloud provider solutions.

Acceleration of in-core LU decomposition of a dense MoM matrix by using multiple GPUs in parallel, is presented in this paper. Results for nonsymmetrical and symmetrical matrices are shown. Limitations for further increasing the parallelization efficiency and the ways for overcoming these limitations are discussed. The achieved acceleration efficiency is high (about 65%), but remains limited by the speed of data transfers between CPU RAM and GPUs VRAM.

Proper implementation of max-ortho bases enables effective usage of ultra high order basis functions. Significance of ultra high order bases is demonstrated in the case of p-refinement of 2λ cube scatterer, in which case mean absolute RCS error of 0.001 dB is attained using expansion order of n = 20. In particular, it was shown that taking edge effects into account this level can be further reduced to 0.0001 dB.

This paper presents a comprehensive switching performance evaluation and the loss breakdown analysis of a 3-level Neutral Point Clamped (NPC) bidirectional AC/DC converter with SiC MOSFETs. The switching transient of SiC devices in different 3-level commutation loops is characterized and compared for design optimization. The loss analysis for the NPC converter at various operating modes is carried out, based on a detailed loss model for both power switch and filter inductor. Based on the evaluation, a 15-kW 3-level NPC bidirectional AC/DC converter is implemented with SiC devices to operate at various conditions for design verification.

In this paper, the primary side phase leg topology for a multilevel DC/DC converter is explored for a power cell in solid state transformer (SST) that converts medium-voltage (MV) AC input to low-voltage (LV) or medium voltage DC output. To take the high voltage DC bus provided by the multilevel AC/DC front end, two different topologies for the isolated DC/DC stage are thoroughly investigated based on the LLC resonant circuit operation. The key performance such as soft switching conditions and requirements for the two topologies with different modulation schemes are analytically compared. The design procedure for the selected topology is presented and experimental performance evaluation was done on a 15-kW isolated DC/DC converter at various operating conditions.

An isolated bi-directional dc-dc converter that exchanges energy between the high-voltage battery (330 V±30%) and low-voltage battery (12 V±30%) of fuel cell electric vehicle is introduced. To achieve optimal performance in both directions, a full-bridge (FB) series resonant converter (SRC) is employed because of its symmetrical input-to-output characteristic and soft-switching operation. In addition, a novel secondary-switch delay and/or lead time control method is incorporated with conventional frequency control to make the converter operate in a wide voltage range in both directions and achieve zero-voltage switching (ZVS) over the entire load range. Moreover, a frequency fold-back is automatically achieved by the lead time control, which makes it possible to regulate the output at light load without employing a conventional burst-mode control. The performance of the proposed control method was evaluated on a 1-kW prototype operating between the 240-450-V high-voltage battery and the 9.5-15.5-V low-voltage battery. To increase the power density of the converter, the prototype is implemented by using planar magnetics, as well as GaN switches operating above 300 kHz switching frequency. The prototype circuit exhibits the maximum efficiency of 96.1%.

Acceleration of in-core LU decomposition of symmetrical dense MoM matrices by using multiple GPUs in parallel is presented in this paper. Memory limitations of GPUs are overcome by using block LU decomposition, where the entire system matrix is stored in CPU RAM, while only processed blocks are stored in GPU VRAM. The presented algorithm for LU decomposition enables highly efficient utilization of an arbitrary number of GPUs. Comparison of performance of up to 4 GTX 680 GPUs and up to 4 GTX 1080 Ti GPUs is shown. Presented results show that a symmetrical dense MoM matrix with 100 000 complex unknowns in single precision can be LU decomposed in about 3.5 minutes, on a personal computer equipped with 4 GTX 1080 Ti GPUs.

We investigate the influence of internal impedance-matching network for an axial-mode helical antenna on its radiation pattern. This network, proposed in our previous work, comprises a single wire attached to the helix. We show that the matching wire, mounted on a tubular dielectric support and attached to the helix close to the reflector, does not degrade the antenna radiation pattern.

We critically assess the possibilities for utilization of orbital angular momentum (OAM) of electromagnetic (EM) waves, alongside and in combination with other existing data transfer methods, for further capacity improvement of 5G systems. Special attention is devoted to inherent limitations imposed by the OAM beams. Trade-offs between the desired function and unavoidable limitations are discussed.

Polynomial higher order basis functions defined over quadrilaterals are regularly used with patches of maximum edge up to 2λ and expansion order up to $n$ = 8. In this paper it is demonstrated that these limits can be significantly extended if max-ortho bases are implemented in a proper way. Numerical results demonstrate effective usage of patches up to 8 λ and expansion orders up to n = 24.

This paper addresses shooting-bouncing rays (SBR) ray-tracing techniques and their applications in computational electromagnetics. It specifically discusses uniform random, low-discrepancy deterministic, and uniform sampling techniques for the standard SBR formulation and compares their effects for a simple waveguide model.

Acceleration of in-core LU decomposition by using multiple GPUs in parallel and comparison of performance of two different GPU types, is presented in this paper. The presented algorithm for LU decomposition enables highly efficient utilization of an arbitrary number of GPUs. Comparison of performance of up to 8 GTX 680 GPUs and up to 4 GTX 1080 Ti GPUs is shown. The results presented show that a dense MoM matrix with 100 000 complex unknowns in single precision can be LU decomposed in 3.7 minutes, on a personal computer equipped with 4 GTX 1080 Ti GPUs.

This paper presents a flyback converter with a hybrid clamp, i.e., a combined passive RCD and active clamp, and a corresponding power management circuit that substantially optimizes the performance of the flyback converter in the entire line and load ranges. By sensing the operating conditions, the power management circuit configures the clamp circuit either as a passive clamp or as an active clamp. In the passive-clamp configuration, the clamp switch is kept turned off and the main switch turns on with valley switching, whereas, in the active-clamp configuration, the clamp switch operates with pulse-width modulation (PWM) which enables zero-voltage-switching (ZVS) turn-on of the main switch. Performance of the flyback converter with the hybrid clamp is evaluated on a laboratory prototype of a 65-W (19.5-V, 3.33-A) universal-line-voltage-range (90–264 Vrms) adapter.

In this paper, a new, three-phase, single-stage, isolated ac-dc converter (rectifier) that employs only two switches and achieves less than 5 % total harmonic distortion (THD) of the three-phase input currents and provides a tightly regulated, isolated, output voltage is introduced. The rectifier features zero-voltage-switching (ZVS) of both switches over the entire input and load range without any additional soft-switching circuitry. The rectifier is derived by combining the three-phase, frequency-controlled, power-factor-correction (PFC), discontinuous-current-mode (DCM) boost rectifier with the conventional LLC resonant half-bridge converter. The evaluation was performed on a 1-kW prototype operating with a three-phase line-voltage range from 180 V L-L to 264 V L-L and delivering a tightly-regulated, isolated, output voltage of 54 V.

Computational tools for full-wave three-dimensional (3-D) simulations of linear passive electromagnetic (EM) components have reached a point where they became both practical and necessary in computer aided design (CAD) of RF devices. Although circuit-based solvers still offer unprecedented speed and true real-time tuning, full-wave software tools, which take into account almost all physical EM phenomena, rapidly approach similar efficiency and applicability. This, however, is not possible by just using modern hardware environment, but it also requires the numerical method of choice, encapsulated within a software tool, to be extremely precise and conservative in consumption of computer resources, i.e., CPU and memory. We here report a case study which demonstrates highly efficient utilization of higher order large-domain method of moments (MoM) modeling and optimization using WIPL-D. The example includes an RF exciter, based on axial-mode helical antennas mounted on a dielectric support, designed for utilization in the state-of-the-art pre-clinical magnetic resonance imaging (MRI) scanners.

This paper presents a comprehensive experimental evaluation and comparison of several state-of-the-art 1.2-kV silicon carbide (SiC) power switches. Specifically, the latest generation of planar and trench SiC MOSFETs as well as the cascode SiC JFET are characterized and compared with respect to their static and dynamic performance. The switching performance of these devices are evaluated with both their intrinsic body-diode and external SiC Schottky Barrier Diode (SBD) as the freewheeling device. Based on the evaluated performance, the advantages and disadvantages of tested SiC devices are summarized.

Power converters interfacing single-phase ac and dc power sources and loads typically require an energy storage device to handle the double-line frequency power ripple. Among the active power storage solutions, called power-pulsation buffers (PPBs), the bidirectional buck topology is popular for its low component count and voltage stress, as well as good performance. However, existing control methods of the buck PPB are rather complex and typically employ at least two feedback loops. This paper presents a simplified, single-loop control of the buck PPB. To achieve the dc-bus-voltage-ripple magnitude below 3 % of the average bus voltage, the voltage feedback loop action was supplemented with current feedforward control. The performance of the proposed control was evaluated on a 1-kW PPB experimental prototype.

In this paper, the performance of a bidirectional ac/dc converter which utilizes silicon MOSFETs and operates in continuous-conduction mode (CCM) with 100-kHz switching frequency is evaluated. The converter is implemented with an active snubber that virtually eliminates losses related to the reverse-recovery charge of the body diodes of Si MOSFET switches and also provides for their zero-voltage switching (ZVS). The circuit operation was verified with a 3.3 kW PFC/inverter experimental prototype designed for 230-Vrms nominal ac voltage and 400-V dc voltage. The measured circuit efficiency in both directions is greater than 97.9% at loads greater than 45%.

We present a shooting-bouncing approach to ray-tracing as applied to signal propagation modeling in electrically large waveguides, such as underground mine tunnels at wireless communication frequencies. The method is verified for a dominant-mode rectangular metallic waveguide excited by a dipole antenna.