Magnetic dipole excitation of a long conductor in a lossy medium

A formulation is presented for the excitation of currents on an infinitely long conductor by electric or magnetic dipoles of arbitrary orientation. The conductor can be either insulated or bare to model ungrounded or grounded conductors. Specific calculations are presented for a vertical magnetic dipole source because this source produces the appropriate horizontal polarization and could be used in a borehole-to-borehole configuration. Numerical results for the induced current and secondary magnetic field indicate that long conductors produce a strong anomaly over a broad frequency range. The secondary magnetic field decays slowly in the direction of the conductor and eventually becomes larger than the dipole source. Results have been presented for frequencies from 20 kHz to 2 MHz, and the entire frequency range appears to be useful     

Investigation of a Dipole Model for Transient Analysis of Electromagnetic Field Coupling into Long Cables

The authors describe a mathematical model for a long conductor exposed to a high-intensity transient electric field to aid in determining interface requirements at connected equipment. Dipole characteristics of the conductors are used to simulate the impedance and in turn to calculate the induced currents. Example calculations for four models, two conductor lengths, and two conductor sizes, are presented and compared.     

Introduction to "some laws concerning the distribution of electric currents in volume conductors with applications to experiments on animal electricity"

Muscle and nerve cells are electrically active and give rise to currents and potentials in the surrounding tissues, which are conductors of electricity. The study of the relation of these bioelectric sources to currents they produce in the surrounding tissue is called the volume conductor problem. The basic physics of the volume conductor were worked out by Helmholtz. The Helmholtz paper is still extensively cited. Just who was Helmholtz and exactly what did he contribute so many years ago? What events and circumstances molded the life of such an individual? An attempt is made to answer these questions.     

Recent issues in fabrication of Ag-clad BSCCO superconductors

Long lengths of mono-and multifilament Ag-clad BSCCO superconductors were fabricated by the powder-in-tube technique. Critical current density (J_c) up to 12,000 A/cm² has been achieved in an 850 m long multicore conductor. Long length conductors were formed into pancake-shaped coils by the wind-and-react approach. Test magnets were then fabricated by stacking the pancake coils and connecting them in series. The magnets were characterized as a function of applied magnetic field at various temperatures. A test magnet, fabricated with ≈770 m of BSCCO tape, generated fields of ≈1 T at 4.2K and ≈ 0.6 T at 27K, both in an applied background field of 20 T. Additionally, the strain tolerance of both mono-and multifilament conductors at 77K in 0.5 T applied field has been studied. We observed that multifilament conductors have better strain tolerance than monofilament tapes, retaining more than 90% of the initial critical current (at 0.5 T) with strain ≥1%.     

Some laws concerning the distribution of electric currents in volume conductors with applications to experiments on animal electricity

The basic laws for the solution of problems involving the distribution of electric currents in bodily conductors are explained by Smaasen and Kirchhoff. Our mathematical aids, however, are only sufficient for some of the simplest cases. In addition, we have only recently been able to measure electric fields in linear conductors. Thus, the results of the theory for the internal flow through a bodily conductor cannot even be compared to experiments. All the more, such tasks-in which current intensity in connection with bodily and linear conductors might be determined-now have a great practical importance. First, I will prove the relevant theorems which I have demonstrated. Then, I will report about experiments in which I have attempted as much as possible to confirm them. Finally, I will briefly explain the nature of their application in animal-electric experiments.     

Magnetic dipole excitation of an insulated conductor of finitelength

Excitation of currents on an insulated conductor of finite length and with arbitrary terminations is studied for a magnetic dipole source. For matched terminations, the results agree closely with previous results for an infinitely long conductor, but other terminations produce end reflections that cause standing waves. Specific calculations for a vertical magnetic dipole source are presented, because this source produces the appropriate horizontal electric field and could be used in a borehole-to-borehole configuration. Numerical results for the induced current and secondary magnetic field indicate that long conductors produce a strong anomaly over a broad frequency range for any type of termination     

On the Phenomenon of Oscillations in the Method of Auxiliary Sources

When one applies the method of auxiliary sources to scattering problems involving perfect conductors, one first seeks fictitious auxiliary currents located inside the conductor, and then determines the field from these currents. For a simple two-dimensional problem involving an infinite circular cylinder illuminated by an electric current filament, it has recently been shown analytically that it is possible to have divergent auxiliary currents (to make this statement precise, one must properly normalize the currents), together with a convergent field. It was also shown-through numerical investigations-that the aforementioned divergence appears as abnormal, rapid oscillations. In the present paper, we investigate such phenomena in more detail, with particular emphasis on oscillations. For a perfectly conducting ground plane illuminated by an electric current filament, we once again demonstrate the possibility of having divergent, oscillating currents producing a convergent field. We develop an asymptotic formula for the oscillating current values, which sheds light on the nature of the oscillations. We revisit the circular-cylinder problem to develop a similar asymptotic formula. We also discuss roundoff errors, and possible generalizations to scatterers of other shapes. The present study is to a great extent analytical, with the analytical predictions confirmed and supplemented by numerical results     

Modal network theory of skin effect in flat conductors

A new theory of skin effect in linear conductors of arbitrary cross-sectional shape is proposed and illustrated by calculating the ac resistance of a flat conductor. The current flowing in any conductor may be decomposed into an infinite set of normal mode currents, all of which exist independently of each other. Each modal current may be calculated from the conductor terminal conditions by simple circuit theory. Use of this method presupposes knowledge of the normal modes, which are different for every cross-sectional shape. A general method of finding the normal modes is given. Excellent agreement with experimental data is reported.     

Comments, with reply, on `Generation of electromigration groundrules utilizing Monte Carlo simulation methods' by B. A. Beitman and A.Ito

For original paper see ibid., vol.4. no.1, pp.63-66 (Feb. 1991). The method employed by B.A. Beitman and A. Ito for determining appropriate maximum allowed currents in narrow conductors on VLSI circuits is examined. The literature reveals that the relationship between MTF and conductor geometry and between σ and conductor geometry is much more complex than that employed in their simulation. The authors clarify the various points raised by the commenter     

Cross‐Stacked Superaligned Carbon Nanotube Films for Transparent and Stretchable Conductors

Transparent and stretchable conductors are essential components in many stretchable electronics. However, it is still a challenge to make this kind of conductor easily and cost‐effectively. Here, a way to utilize cross‐stacked superaligned carbon nanotube films to make transparent and stretchable conductors is reported. The as‐produced cross‐stacked films are isotropic in electrical conductivity, but anisotropic in mechanical properties, because of their microscale cross structures. Along some directions, the films can sustain a high strain, of more than 35%, which is helpful for applications as stretchable conductors. These cross‐stacked films can be further made into composite films with polyvinyl alcohol by a dip‐coating method, and with polydimethylsiloxane by an embedding method. The former composite films have similar isotropic electrical and anisotropic mechanical properties to SACNT films, but much larger capability in terms of tensile load. The latter composite films possess quite highly stretchable and reversible electrical behaviors, which can be used in stretchable touch panels, solar cells, strain sensors, and implanted conductors.     

High Field Superconducting Solenoids Via High Temperature Superconductors

High-field superconducting solenoids have proven themselves to be of great value to scientific research in a number of fields, including chemistry, physics and biology. Present-day magnets take advantage of the high-field properties of Nb₃Sn, but the high-field limits of this conductor are nearly reached and so a new conductor and magnet technology is necessary for superconducting magnets beyond 25 T. Twenty years after the initial discovery of superconductivity at high temperatures in complex oxides, a number of high temperature superconductor (HTS) based conductors are available in sufficient lengths to develop high-field superconducting magnets. In this paper, present day HTS conductor and magnet technologies are discussed. HTS conductors have demonstrated the ability to carry very large critical current densities at magnetic fields of 45 T, and two insert coil demonstrations have surpassed the 25 T barrier. There are, however, many challenges to the implementation of HTS conductors in high-field magnets, including coil manufacturing, electromechanical behavior and quench protection. These issues are discussed and a view to the future is provided.     

DC Internal Inductance for a Conductor of Rectangular Cross Section

In this paper, the dc internal inductance for conductors with rectangular cross section is investigated. Using a quasistatic Green's function, the magnetic fields inside a rectangular conductor are derived. These magnetic field expressions are used to formulate the internal inductance of the conductor. We present numerical results and closed-form expressions for the dc internal inductance for this geometry. Comparisons to various expressions found in the literature are made, and the inaccuracies of these other results are presented and discussed. Finally, we discuss some of the subtleties associated with the inductance of a single current path, in which we examine why the total and external inductances of a single infinitely long conductor have no physical meaning, whereas the internal inductance does.      

Theoretical study of magnetic field of current monopoles in specialvolume conductor using symmetry analysis

The authors derive a formula for the magnetic field outside volume conductors having axial symmetry with radial and axial symmetrically distributed source currents. The magnetic field is shown to have components only along the cylindrical polar angle direction and its magnitude to depend only on the topological structure of the volume conductor and the location of the source current. With this formula, the magnetic field generated by the volume current of a current monopole within and on the symmetrical axis of several volume conductors (such as semi-infinite volume, infinite slab, sphere, infinite cylinder, semi-infinite cylinder, finite cylinder, prolate spheroid, and oblate spheroid) is shown to be equivalent to the magnetic field generated by a line current calculated using the Biot-Savart's law. In the first three volume conductors, the monopole solution of the magnetic field allows the calculation of magnetic fields generated by arbitrarily distributed (and balanced for finite volume conductors) current monopoles     

Application problem of flat multifilamentary Nb3Sn Superconductors

Results are presented concerning the superconducting properties of flat multifilamentary Nb₃Sn conductors fabricated by the bronze route. We investigated degradation caused by winding the prereacted conductor on relatively small diameters, the influence of Zr and Ti doping of the Nb filaments and the anisotropic behaviour of critical current for the two principal orientations of the flat conductor with respect to the magnetic field. The performance of flat conductors in high field insert coils wound after the conductor has been heat treated (the R&W technique) is discussed.     

Stimulatory Current at the Edge of an Inactive Conductor in an Electric Field: Role of Nonlinear Interfacial Current–Voltage Relationship

Cardiac electric field stimulation is critical for the mechanism of defibrillation. The presence of certain inactive epicardial conductors in the field during defibrillation can decrease the defibrillation threshold. We hypothesized this decrease is due to stimulatory effects of current across the interface between the inactive conductor and the heart during field stimulation. To examine this current and its possible stimulatory effects, we imaged transmittance of indium–tin-oxide (ITO) conductors, tested for indium with X-ray diffraction, created a computer model containing realistic ITO interfacial properties, and optically mapped excitation of rabbit heart during electric field stimulation in the presence of an ITO conductor. Reduction of indium decreased transmittance at the edge facing the anodal shock electrode when trans-interfacial voltage exceeded standard reduction potential. The interfacial current–voltage relationship was nonlinear, producing larger conductances at higher currents. This nonlinearity concentrated the interfacial current near edges in images and in a computer model. The edge current was stimulatory, producing early postshock excitation of rabbit ventricles. Thus, darkening of ITO indicates interfacial current by indium reduction. Interfacial nonlinearity concentrates current near the edge where it can excite the heart. Stimulatory current at edges may account for the reported decrease in defibrillation threshold by inactive conductors.      

Carbon Nanotube Reinforced Conductors for Flexible Electronics

This study demonstrates carbon nanotube (CNT) reinforced conductors for flexible electronics. The supreme mechanical strength of the CNT is toughened by the structure of the metal conductor. Conventional metal lines, fabricated using a screen printing technique on flexible substrates, usually suffer a great deal of stress when bending plastic substrates. These stress-strain educed micro-fractures in the metal line reduce the reliability of the electronic system. We fabricated a durable conductor, integrating CNTs into the conventional metallization process. It was found that the CNT–silver composite can be screen-printed on flexible substrates and the durability of the resulting conduction was enhanced. Compared to CNT-polymer-based materials, the CNT–silver composite exhibited higher conductivities of $10 ^{4} ~{hbox{S}}/{hbox{cm}}$. These results show that such an approach offers a promising of enhancing the reliability of flexible electronic systems by utilizing reinforced CNTs in the metallization process.      

Scale model experiments on optimum transmitter-receiverconfigurations for resolution of electromagnetic response of multipleconductors

Electromagnetic scale modeling response curves over two parallel dykes embedded in resistive or conductive media have been obtained by using horizontal loop inline and broadside systems. It previously was established that inline configuration can electromagnetically resolve the individual conductor only when the separation between them is greater than or equal to transmitter-receiver separation. Fortunately for field geophysicists, broadside configuration can relax such a limit and resolve the two conductors even when the separation between them is half of the transmitter-receiver separation. The experimental results show that the inline configuration gives a better quantitative idea of the identity of the two resolved conductors. A combined use of these two configurations is recommended to the induction prospectors in their ground-based or airborne search for sulphide dykes     

碳纤维复合芯导线初始伸长的探讨

碳纤维复合芯导线是一种全新结构的节能型增容导线,与常规导线相比具有众多优点,代表了未来架空导线的技术发展趋势,有助于构造安全、环保、高效节约型输电网络。在施工架线过程中其与普通的架空导线（钢芯铝绞线）一样,需要考虑导线的初始伸长。通过两个碳纤维复合芯导线的架线施工的实例,对其初始伸长的特点进行了探讨。根据碳纤维复合芯棒...     

Lattice electromigration in narrow Al alloy thin-film conductors at low temperatures

At low temperatures, electromigration in polycrystalline Al thin-film conductors has been considered to occur predominantly along grain boundaries. As conductor widths decrease below the average grain size, however, other transport mechanisms will become important. Here we examine electromigration transport mechanisms in narrow AlSiCu conductors in the temperature range 190 to 290°C using the stripe drift technique. For conductors with widths between 0.9 and 2.75 μm both the absolute values of the drift velocity and the activation energy for drift are consistent with a lattice diffusion mechanism. Over this linewidth range the Al microstructure ranges from near-bamboo to approximately 20 μm long polycrystalline segments. The independence of the drift data from the linewidth shows that steady state transport is controlled by the bamboo regions of the conductors, which results from the slower rate of diffusion of Al through the lattice compared to along grain boundaries.     

Transparent,Highly Stretchable,Rehealable, Sensing,and Fully Recyclable Ionic Conductors Fabricated by One‐Step Polymerization Based on a Small Biological Molecule

To date, various stretchable conductors have been fabricated, but simultaneous realization of the transparency, high stretchability, electrical conductivity, self‐healing capability, and sensing property through a simple, fast, cost‐efficient approach is still challenging. Here, α‐lipoic acid (LA), a naturally small biological molecule found in humans and animals, is used to fabricate transparent (>85%), electrical conductivity, highly stretchable (strain up to 1100%), and rehealable (mechanical healing efficiency of 86%, electrical healing efficiency of 96%) ionic conductor by solvent‐free one‐step polymerization. Furthermore, the ionic conductors with appealing sensitivity can be served as strain sensors to detect and distinguish various human activities. Notably, this ionic conductor can be fully recycled and reprocessed into new ionic conductors or adhesives by a direct heating process, which offers a promising prospect in great reduction of electronic wastes that have brought acute environmental pollution. In consideration of the extremely facile preparation process, biological available materials, satisfactory functionalities, and full recyclability, the emergence of LA‐based ionic conductors is believed to open up a new avenue for developing sustainable and wearable electronic devices in the future.