Abstract—Voltage-current characteristics of free burning arcs in SF6 and air have been known for decades. As the demand for an SF6-free solution is increasing, there is an accompanying need to determine arc parameters in the alternative gases. An unblown arc experiment has been established to determine the voltagecurrent characteristics of SF6 alternative gases, which have not yet been thoroughly studied. In this experiment free burning arc measurements were performed in a number of gases under consideration of SF6 alternatives, including CO2 and mixtures of CO2 / O2 with and without C4F7N or C5F10O additives at concentrations of up to 10 %. Measurements were also performed in air and SF6 for comparison. Arc voltage was measured in each gas at pressures ranging from 1 bar to 5 bar absolute, and electrode separations ranging from 20 mm to 95 mm. Voltagecurrent characteristic measurements for air and SF6 show good agreement with previously published results. A linear relationship of the arc voltage to the arc length is shown, as well as fourth root dependence of the arc voltage on the gas pressure. It was shown that neither the O2 nor the fluorinated additives to CO2 have any significant influence on the voltage-current characteristic. The minimum arc voltage in all measured gases was slightly higher than in SF6, but the arc in SF6 was the least stable and had the highest elongations resulting in high voltage peaks. The arc voltage in air had a similar minimum value to the CO2 based gases, but the arc was much more stable, resulting in lower effective voltage, especially at low currents.

A simple concept to perfectly decouple the reflection magnitude and phase of a reflective metasurface is proposed. For a linearly-polarized illumination, a full 2? phase is achieved in reflection by physically displacing the unit cell normal to the surface, with respect to a fixed reference and source, while the reflection magnitude is independently controlled via an integrated resistive element inside the unit cell. This proposed concept is demonstrated using full-wave simulations, which is the first step towards an electromechanical metasurface with truly independent real-time amplitude and phase control.

This short communication considers the results of developing novel glass-metal coaxial waveguide reactors. They are designed on the base of the Liebig condenser, where the central glass channel is occupied by wire. The outer shield is made of copper foil. A liquid flows between the central glass tube and the shielded outer pipe, being pumped in and out through the shielded tubes. The reactors are excited through coaxial connectors. The developed devices show moderate loss and increased penetration depth needed for smooth heating of flowing liquids. The components are studied by measurements and simulations.

We investigate the problem of electromagnetic radiation in massive electromagnetism with focus on the directive radiation characteristics of Proca antennas (sources embedded into Proca metamaterial domains.) It is theoretically demonstrated that the recently proposed nonlocal Proca metamaterial implies the existence of point nonlocal sources possessing a perfectly isotropic radiation pattern. Based on this rigorous analysis, we derive exact expressions for the directive radiation patterns of arbitrary discrete distributions of Proca sources, i.e., radiating arrays emitting massive photons. Examples of linear discrete Proca arrays are given and comparison with massless photon radiation sources is provided.

In this paper, MATLAB based computational approaches for the design and analysis of time-varying capacitors using the finite-difference time-domain (FDTD) technique and the Simulink design environment are presented. The FDTD formulation for multiple lumped capacitors loaded in series on a transmission line is discussed and extended to include time variation of capacitance. The design methodology for the same is also discussed using MATLAB’s Simulink using the RF Blockset Library. The developed FDTD formulation and the Simulink method are then used to design a mixer with time-varying capacitors loaded transmission line.

This paper presents a novel technique for improving the performance of a modal filter by using an electromagnetic absorber. The study considers a two-conductor modal filter based on a microstrip transmission line. The authors analyzed the effect of the absorber on the MF performance in suppressing conducted and radiated interferences (in the near and far fields). The frequency characteristics of the device were then redefined into the time characteristics in the Advanced Design System. As an excitation, the authors used an ultra-wideband interference pulse of 155 ps (at 0.5 level) and then employed N-norms to estimate and characterize the decomposed pulses. The results show that the use of the absorber can significantly improve the attenuation of the ultra-wideband interference. It was experimentally demonstrated that the value of N1 decreased by a factor of 4.31, N2 – by a factor of 6.52, N5 – by a factor of 1.87. In terms of radiated interference in the near field, the improvement in attenuation of each norm achieved at least 2.81 times. The analysis of the characteristics in the far field showed that the use of the electromagnetic absorber allows reducing the transmission coefficient on average by 2.25 times at a distance of 1 m. To validate the measurement results, the electrodynamic simulation of the modal filter characteristics in the frequency range up to 6 GHz was carried out and showed full agreement with the experimental results.

Our aim is to develop next generation of MEMS (microelectromechanical systems) devices that are composed Ni-Mn-Ga and silicon layers. Due to the large magnetic-field-induced strains of Ni-Mn-Ga, actuating components can be fabricated in the Ni-Mn-Ga layers. Other functional components can be manufactured in the silicon layer. Single crystalline Ni-Mn-Ga alloys that are grown by using the Bridgman vertical growth technique have thus far obtained the largest magnetic field-induced strain (MFIS), a magnetic shape memory (MSM) effect. Similar to silicon wafers, Ni-Mn-Ga wafers are also sliced from crystal-oriented single crystalline ingots. To fabricate hybrid MEMS devices such as micromanipulators and robots, lab-on-chip containing micropump manifolds and valves, or vibration energy harvesters, the fabrication processes used for MEMS devices will be used are also be used to fabricate components in the Ni-Mn-Ga layer of the hybrid MEMS devices. One of the most important processes for MEMS fabrication is the structuring of materials by chemical etching. The main goal of this study is to obtain evidence that the etchant etches silicon but not Ni-Mn-Ga and to identify an etchant that etches Ni-Mn-Ga but not silicon. The present paper reports on a novel experiment in dissolving Ni-Mn-Ga alloys. An etchant composition of 69% HNO3, 98% H2SO4, and CuSO4•5H2O is proposed for dissolving Ni-Mn?Ga alloys and the variation in the dissolution rate by adjusting the concentrations of HNO3 and ultrapure water (UPW) is demonstrated. This etchant was demonstrated to etch Ni-Mn-Ga but not silicon. The HF+HNO3 acidic solution commonly used for etching silicon does not dissolve Ni-Mn-Ga

We present a rigorous semi-analytical formulation for the analysis of electromagnetic (EM) scattering from a cylinder constructed from a metasurface represented using surface susceptibilities. The formulation uses the Generalized Sheet Transition Conditions (GSTCs) to represent the surface and eigenfunction expansion (EFE) of the incident and scattered fields, by exploiting their angular periodicity. Incorporating a completely general non-uniform surface formulation of 36 susceptibility components, a matrix equation is formulated that can be solved for the field harmonic coefficients. The paper illustrates the methodology with a number of examples; including two formed from a finite sized practical unit-cell exhibiting a normally oriented magnetic resonance which is compared with commercial EM full-wave solver; other examples present surfaces that have a modulated gain/loss profile (i.e. amplitude modulation) and polarization conversion. It is found that for all cases the EFE solution very accurately captures the scattered fields in both the interior and exterior regions of the surface. Detailed convergence studies are further presented including the effect of susceptibility modulation on the number of terms needed in the EFEs, to reach a correct field solution. The proposed EFE framework is further compared with a second GSTC based simulator using an Integral Equations (IE) approach and it is found that the IE-GSTC simulated fields approach that of the EFE as the surface discretization is increased. The proposed EFE approach is thus a quick, rigorous methodology which, although limited in the geometry which it can model, has many advantages for investigation into the use of GSTCs, application development and providing a baseline for simulation studies.

The hull of an Autonomous Underwater Vehicle (AUV) is one of the main factors that determine its overall compressibility and drag. The hull as well, acting as a pressure vessel, is the most essential part that will allow the vehicle to accomplish deep diving. In order to minimize the total weight and volume of the vehicle, many modern vehicles benefit from composite materials rather than conventional materials. Moisture absorption, known as the hygral effect, has a significant impact on the mechanical properties of the material. Not to mention it also has an effect on the buoyancy of the vehicle, since the overall weight changes. This paper characterizes the seawater absorption and diffusivity of Carbon Fiber Reinforced Epoxy (CFRE) pressure hull samples in ambient conditions at sea level and at 1000m depth. The tests were performed using seawater taken from Oslo fjord in Norway and using a pressure vessel. Twelve specimens, all manufactured from CFRE using filament winding technique, were tested in both conditions, and the moisture absorption curve is compared. Periodic gravimetric measurements were taken, where the equilibrium state was reached after approximately 65 days at sea level and after 35 days at 1000m depth. The results showed that moisture diffusivity for composites used in underwater applications should be defined by both pressure and temperature since it changes with respect to submersion depth.

This paper outlines the design and testing process of the hull of a deep small Autonomous Underwater Vehicle (AUV), rated at 2000m depth. Many existing AUV pressure housings use aluminum or other isotropic traditional metals, instead of composites due to the complexities of the design of composites at such big load. The research at hand explains the process of design starting from setting the geometrical constraints for the design to mass production. To the best of the authors’ knowledge, none of the previous studies has presented such detailed description of the work. Carbon fiber reinforced epoxy material was chosen thanks to its high strength-to-weight ratio and similarity of its compressibility to sea water. Material characterization was performed to obtain the material properties under loading conditions using a modified method of the Combined Loading Compression testing technique. A specific fixture was designed and manufactured to test filament-wound tubes. An analytical model was developed using MATLAB, a finite element model was created using ABAQUS, and the results of the two models were compared. A set of recommendations was introduced for the stacking sequence to provide the lowest possible stresses, regardless on the diving depth of the vehicle. Afterwards, a quality control set of tests was conducted, including seawater absorption under high pressure and void analysis using destructive and non-destructive tests. Pilot samples were manufactured and tested in a pressure vessel, where it was cycle-tested and inspected using visual and ultrasonic testing. Other samples were fail-tested and showed a failure at ∼93% of the expected failure load. Such range can be considered good to provide safe operation for the vehicle at the designated depth, given that the factor of safety included covers more than 7% of the failure load. The proposed design methodology has shown that CFRE can be safely used even at such high depths.

The 2-D structure of graphene, an allotrope of carbon with remarkable characteristics, is revolutionizing the technology world. This article provides a synopsis of three popular methods for graphene synthesis. The mechanical exfoliation method attempts to separate graphene layers from bulk graphite and is used for small-scale production. The next method is the chemical vapor deposition (CVD) synthesis, which uses a reaction between a gaseous hydrocarbon and a solid substrate to promote graphene growth. Finally, the modified Hummer’s method involves the use of oxidizing and reducing agents to obtain graphene oxide (GO) from graphene flakes under low-temperature conditions from which graphene is synthesized as the final product.

Carbon nanotubes (CNTs), nanoscale hollow tubes of carbon atoms with their unique characteristics, have been revolutionizing the technology world because their unique structural and electrical properties make them ideal for a wide variety of nanotechnology-based applications. This article gives a synopsis of three prevalent methods of CNT synthesis. The field of nanotechnology and nanoscience promote their investigation forward to produce CNTs with acceptable parameters for future applications. Therefore, new approaches to their synthesis need to be developed and optimized. Throughout this paper, the history, the types, the structure, and the distinct well-developed synthesis methods for preparing CNTs will be reviewed, including arc discharge, laser ablation, and chemical vapor deposition (CVD).

Design of a semiconducting Bio-Wire developed from Silane Self-Assembled Monolayers, Neutravidin bio-films, and Carbon nanomaterials. The development of Self-Assembled Monolayers and highly specific Neutravidin bio-films have been characterized.

Cross-silo federated learning (FL) allows organizations to collaboratively train machine learning (ML) models by sending their local gradients to a server for aggregation, without having to disclose their data. This paper proposes SVFL, an efficient protocol for cross-silo FL, that supports both secure gradient aggregation and verification. We evaluate the performance of SVFL and show, by complexity analysis and experimental evaluations, that its computation and communication overhead remain low even on large datasets, with a negligible accuracy loss (less than $1\%$). Furthermore, we conduct an experimental comparison between SVFL and other existing FL protocols, and show that SVFL achieves significant efficiency improvements in both computation and communication.

Temporal metamaterials have been recently exploited as a novel platform for conceiving several electromagnetic and optical devices based on the anomalous scattering response arising at a single or multiple sudden changes of the material properties. However, they are difficult to implement in realistic scenarios by switching the permittivity of a material in time, and new strategies to achieve time interfaces in a feasible manner must be identified. In this paper, we investigate the possibility to realize a temporal metamaterial without acting on the material properties, but rather on the effective refractive index and wave impedance perceived by the wave during the propagation in an empty guiding structure by varying the boundaries in time. We demonstrate analytically and through numerical experiments that suddenly changing the physical distance between the metallic plates of a parallel-plate waveguide will induce an effective temporal interface. In addition to the standard backward and forward scattered fields at different frequencies due to the temporal interface, we also identify the presence of a static field necessary to satisfy the continuity of the electromagnetic field across the interface. The proposed concept can be extended to temporally controlled metasurfaces, opening an easier path to the design and realization of novel devices based on time-varying metamaterials at microwave and optical frequencies.

We have established mathematically that there exists the potential to realize a positive required energy density in order to warp spacetime. By using a complex shaping function where the imaginary part is greater than the real part, the solution to the expression for the required energy density is positive. This ultimately makes it feasible to selectively bend spacetime for the purposes of propelling a craft. We have devised an experiment that utilizes a material having the properties of possessing a greater imaginary component to the dielectric constant than real component. This material, introduced into a resonant cavity, sets up the conditions to realize a shaping function in the form as is utilized in the Alcubierre's metric. We have established a potential structure from which to build better experiments.

In this paper, we continue the analysis of electrooptical studies of the prebreakdown stage in water in the submicrosecond range. We consider a cathode streamer developing in a system of the spherical electrodes. Computer simulation of electric showed that at a constant e = 80, the field strength at the head of the cathode streamer should not exceed E = 1.9 MV/cm. Taking into account the nonlinearity of the permittivity e = e(E) made it possible to estimate this field strength as E ~ 2.4-3.1 MV/cm. It is shown that even with some excess of the strength over the threshold value (ES ~ 3 MV/cm), at which the state of dipole saturation is possible; its consideration does not lead to a noticeable change in the result. Thus, a significant decrease in the field strength near the cathode streamer compared to the anode streamer was confirmed.

Memristor-based crossbar architecture emerges as a promising candidate for 3-D memory and neuromorphic computing; however, the sneak current through the unselected cells becomes a fundamental roadblock for their development as it results in misreading and high power consumption. In this regard, we investigate Pt/Ti/NbO2/Nb2O5−x/Pt-based self-selective memristor, which combines inherent nonlinearity of NbO2 switching layer and non-volatile operation of Nb2O5−x memory layer in a single device. The results show that Pt/Ti/NbO2/Nb2O5−x/Pt memristor offers the sneak current of 310 nA, selectivity of around 174, and on/off current ratio of 4.79 compared to the sneak current of around 70 µA, selectivity of about 4.02, and on/off current ratio of around 1.55 for Pt/Ti/Nb2O5−x/Pt-based memristor. Our self-selective memristor minimizes the sneak current, but a small on/off current ratio limits their readout margin and power efficiency for crossbar array size greater than 212. Further, we demonstrate that breaking down a large-scale crossbar array into smaller subarrays and separating them by transistor switches is a more efficient way of eliminating the sneak current. The memristor-transistor split crossbar architecture essentially provides the readout margin and power efficiency of subarray for large size crossbar array and allows high-density array integration over 1Transistor-1Memristor architecture.