Inhomogeneous Electric Conductivity Research Articles

Minimization of Winding AC Losses Using Inhomogeneous Electrical Conductivity Enabled by Additive Manufacturing

The electrical conductivity (EC) of additively manufactured conductors can be purposely controlled by changing as-built orientation and postprocessing conditions. This feature can be leveraged to minimize winding alternate current (ac) losses in electrical machines adopting solid conductors. This article deals with the additive-manufacturing-based winding design of a high-specific-power permanent-magnet (PM) machine for aerospace applications. Specifically, conductors near slot opening are designed with low EC to reduce winding AC losses, while conductors near slot bottom adopt higher EC to reduce direct current (DC) losses. Parametric finite element models are developed for a thorough design parametric analysis targeting high-specific power as well as high efficiency. The implementation of the proposed coil concept with inhomogeneous EC is discussed and demonstrated. The EC measurements on rod and coil samples are conducted for material characterization.

Enhanced dynamo growth in nonhomogeneous conducting fluids.

We address magnetic-field generation by dynamo action in systems with inhomogeneous electrical conductivity and magnetic permeability. More specifically, we first show that the Taylor-Couette kinematic dynamo undergoes a drastic reduction of its stability threshold when a (zero-mean) modulation of the fluid's electrical conductivity or magnetic permeability is introduced. These results are obtained outside the mean-field regime, for which this effect was initially proposed. Beyond this illustrative example, we extend a duality argument put forward by Favier and Proctor (2013) to show that swapping the distributions of conductivity and permeability and changing u→-u leaves the dynamo threshold unchanged. This allows one to make connections between a priori unrelated dynamo studies. Finally, we discuss the possibility of observing such an effect both in laboratory and astrophysical settings.

Features of modeling multiphase media in problems of electromagnetic generation of flows

The study of the electromagnetic force acting on a medium with inhomogeneous electrical conductivity has been carried out. The electrical conductivity changes abruptly which simulates the liquid–solid interface during the crystallization of a pure metal. The electromagnetic force is created by a traveling field inductor with one of the most demanded in metallurgy construction. The results showed a significant dependence of the electromagnetic force on the position of the interface with respect to the inductor. Consequently in the mathematical modeling of the directional crystallization process under the influence of an electromagnetic force created by an inductor of this type it is necessary during the movement of the interface, either to do the calculation of the electrodynamic part of the problem anew or to use the method of canonical domains.

Performance optimization of a two-stage parallel thermoelectric cooler with inhomogeneous electrical conductivity

A new concept of inhomogeneous thermoelectric materials is advanced recently. In the present study, a novel two-stage thermoelectric cooler (TEC) in electrically parallel configuration is investigated. It is made of the inhomogeneous materials with space-dependent electrical conductivity. The internal irreversibilities of the thermoelectric cooler are taken into account. The temperature profile and heat flux in the thermoelectric legs are derived. Thermal rectification can be realized through the modification of the constant properties model which can result in higher cooling capacity and coefficient of performance (COP). The optimal operating regions are explored. Furthermore, the ratio of thermocouples between two stages, the area-length ratio of legs and cold side temperature have significant effect on some important performance characteristics. In the case of optimal ratio of thermocouples between two stages and optimal area-length ratio of legs, coefficient of performance and cooling capacity rise 22.6% and 28.9% respectively by using inhomogeneous materials.

Locating Seismo-Conductivity Anomaly before the 2017 MW 6.5 Jiuzhaigou Earthquake in China Using Far Magnetic Stations

Changes in the underlying conductivity around hypocenters are generally considered one of the promising mechanisms of seismo-electromagnetic anomaly generation. Parkinson vectors are indicators of high-conductivity materials and were utilized to remotely monitor conductivity changes during the MW 6.5 Jiuzhaigou earthquake (103.82°E, 33.20°N) on 8 August 2017. Three-component geomagnetic data recorded in 2017 at nine magnetic stations with epicenter distances of 63–770 km were utilized to compute the azimuths of the Parkinson vectors based on the magnetic transfer function. The monitoring and background distributions at each station were constructed by using the azimuths within a 15-day moving window and over the entire study period, respectively. The background distribution was subtracted from the monitoring distribution to mitigate the effects of underlying inhomogeneous electric conductivity structures. The differences obtained at nine stations were superimposed and the intersection of a seismo-conductivity anomaly was located about 70 km away from the epicenter about 17 days before the earthquake. The anomaly disappeared about 7 days before and remained insignificant after the earthquake. Analytical results suggested that the underlying conductivity close to the hypocenter changed before the Jiuzhaigou earthquake. These changes can be detected simultaneously by using multiple magnetometers located far from the epicenter. The disappearance of the seismo-conductivity anomaly after the earthquake sheds light on a promising candidate of the pre-earthquake anomalous phenomena.

Evolution of domain structure and formation of charged domain walls during polarization reversal in lithium niobate single crystals modified by vacuum annealing

The evolution of the domain structure during polarization reversal has been investigated in plates of lithium niobate with spatially inhomogeneous electrical conductivity produced by vacuum annealing. The formation of charged domain walls in the crystal bulk has been studied. Revealed features of the domain growth in the bulk have been attributed to the formation of nanodomains under the pyroelectric field and inhomogeneous spatial distribution of the electric field. Creation of the charged domain walls with controlled parameters is of great interest for domain walls engineering.

Эволюция доменной структуры и формирование заряженных доменных стенок при переключении поляризации в монокристаллах ниобата лития, модифицированных отжигом в вакууме

AbstractThe evolution of the domain structure during polarization reversal has been investigated in plates of lithium niobate with spatially inhomogeneous electrical conductivity produced by vacuum annealing. The formation of charged domain walls in the crystal bulk has been studied. Revealed features of the domain growth in the bulk have been attributed to the formation of nanodomains under the pyroelectric field and inhomogeneous spatial distribution of the electric field. Creation of the charged domain walls with controlled parameters is of great interest for domain walls engineering.

Global well-posedness of the two-dimensional incompressible magnetohydrodynamics system with variable density and electrical conductivity

Studied in this paper is the Cauchy problem of the two-dimensional magnetohydrodynamics system with inhomogeneous density and electrical conductivity. It is shown that the 2-D incompressible inhomogeneous magnetohydrodynamics system with a constant viscosity is globally well-posed for a generic family of the variations of the initial data and an inhomogeneous electrical conductivity. Moreover, it is established that the system is globally well-posed in the critical spaces if the electrical conductivity is homogeneous.

Theoretical investigation of HVDC disc spacer charging in SF6 gas insulated systems

It seems generally accepted that HVDC technology is to become increasingly relevant in power systems. With this expected future advance of HVDC, the use of gas insulated switchgear or lines for dc application are getting increasingly interesting. As in the case of dc the electric fields are determined resistively in contrast to the capacitive fields in the case of ac, gas insulated technology has to be revisited. In many previous works surface charging of model spacers was investigated. However, the ion flow problem to properly account for the electric conduction in the gas has not yet been solved. Further, no combination with inhomogeneous electric conductivity determined for example by temperature profiles from ohmic heating in nominal condition has been performed so far. In this paper, the gas conductivity arising from ions produced by natural radiation is computed by solving the ion flow field problem, and its role is compared to spacer bulk conductivities. Further, the impact of temperature profiles on spacer charging is investigated. The results indicate that for actual disc spacers, the spacer bulk conductivity is more important than that from the gas ionized by natural radiation. Especially in the case of polarity reversal, thermally enhanced spacer charging can result in considerable increase of tangential field strengths.

Usefulness of the Dipole Tracing Method with a Scalp-Skull-Brain Head Model: Relationship between the Epileptic Focus and Equivalent Current Dipole Locations

Purpose: We examined whether the dipole tracing (DT) method with a realistic three-shell head model and inhomogeneous electric conductivity is useful to estimate the epileptic focus from interictal spikes. Method: This study included 17 temporal lobe epilepsy (TLE) cases, classified into three types as type A (unilateral), type B (intermediate) and type C (bilateral) and 5 extratemporal epilepsy (XTLE) cases. The epileptic areas were determined by noninvasive and/or invasive examinations. Selected interictal spikes were analyzed and the calculated equivalent current dipoles (ECDs) of dipolarity greater than 0.98 were superimposed over the realistic head model in each patient. We evaluated the ECD concentration within and around the epileptic area. Results: In TLE cases, types A showed better ECD concentration (87%) within the epileptic area than other types (type B: 68%; type C: 74%). XTLE exhibited variable ECD distribution within and around the epileptic area. Conclusion: The DT method with a realistic head model and inhomogeneous electric conductivity can be useful to estimate the epileptic area from interictal spikes, especially in unilateral TLE cases.

Characterization of individual diamond crystals in micro diamond arrays using an AFM-based technique

Micro diamond arrays (MDA), in which thousands of diamond micro particles are aligned in μm scale accuracy, were fabricated by site-selective plasma chemical vapor deposition (PCVD). This method is based on the higher nucleation density of diamond on Pt than on SiO 2. When a Pt substrate covered with a SiO 2 film with photolithographically prepared holes of 2 μm in diameter was treated under appropriate PCVD conditions, a single diamond crystal particle nucleated selectively at the bottom of each hole where the Pt surface was exposed. In this manner, a MDA was formed on the substrate. Individual diamond crystals of the MDAs were characterized using an AFM-based technique in which topographic and electrical conductivity information could be simultaneously acquired. A DC bias with respect to the grounded gold-coated AFM-probe was applied to the Pt layer underneath the diamond crystals. Inhomogeneous electrical conductivity in each of the diamond microcrystals was clearly observed with resolution better than 50 nm. The peak current in conductive regions reached up to the μA order, while that in nonconductive regions was less than 10 pA. Such inhomogeneity was not observed in the corresponding topographic images obtained.