Proximity effects conductors

Having identified methods to deposit conductive polymer and molecular metal systems onto cuprate superconductor structures without damage to either material, it becomes important now to consider the electronic interactions that occur when the two conductors are in contact with one another. Of particular importance is the interaction that occurs between the polymer-derived charge carriers and the superconducting Cooper pairs. Important background information related to this area can be obtained from the well-documented behavior of the more classical metal/superconductor and semicon-ductor/superconductor systems. Thus, prior to considering experimental data and theoretical treatments for organic conductor proximity effects, we review previous studies of proximity effects in the more classical systems. 

Skin and proximity effects on a current-carrying conductor 28/873... 

In a d.c. system the current distribution through the cross-section of a current-canying conductor is uniform as it consists of only the resistance. In an a.c. system the inductive effect caused by the induced-electric field causes skin and proximity effects. These effects play a complex role in determining the current distribution through the cross-section of a conductor. In an a.c. system, the inductance of a conductor varies with the depth of the conductor due to the skin effect. This inductance is further affected by the presence of another current-carrying conductor in the vicinity (the proximity effect). Thus, the impedance and the current distribution (density) through the cross-section of the conductor vaiy. Both these factors on an a.c. system tend to increase the effective... 

A three-phase system has three current-carrying conductors in close proximity. While the conductors of phases R and B will have an almost identical impedance, with the same skin and the proximity effects, the conductor of phase Kis under the cumulative effect of electric fields... 

Influence of electric fields of conductors R and B is offset in a 3-ip system. The proximity effect in phase Y therefore gets nullified... 

However, there may not be an appreciable improvement in the proximity effect between each section, unless the transpositions are increased infinitely, as in the case of a stranded three-phase cable which has continuously twisted conductors and represents an ideal transposition. In addition, there is no change in the skin effect. This arrangement therefore has the purpose primarily of achieving an inductively balanced system and hence a balanced sharing of load and equal phase voltages at the far end. 

It reduces the proximity effects between the main current-carrying conductors of the adjacent phases to almost zero due to magnetic shielding, on the one hand, and large centre spacing, on the other. 

Carsten, B. Calculating Skin and Proximity Effect, Conductor Losses in Switchmode Magnetics , 1995, PCIM Conference... 

Proximity effect A nonuniform current distribution in a conductor, caused by current flow in a nearby... 

This chapter is divided into a number of sections that describe important details related to the conductive polymer/superconductor structures. First, information is provided concerning the preparation and characterization of various polymer/superconductor structures. Chemical and electrochemical deposition methods for localizing the polymers onto a number of cuprate phases are discussed. Section III is devoted to relevant background information related to the induction of superconductivity into metals and semiconductor systems via the proximity effect. More specifically, the four basic methods that have been used to study the occurrence of proximity effects in classical solid-state conductors are described (i.e., contact resistance, modulation of superconductivity in normal/superconductor bilayer structures, passage of supercurrent through superconductor/ normal/superconductor systems, and theoretical analyses). Sections IV and V are devoted to experimental studies of conductive polymer/superconductor interface resistances and modulation of superconductivity in the hybrid systems. Finally, there is a discussion of the initial experimental results that explores the possible induction of superconductivity into organic materials. 

One of the most dramatic manifestations of the proximity effect is a supercurrent, or flow of current without resistance, which can be observed to occur over a mac-roscopically large distance through a normal conductor. The first set of experiments in which a supercurrent in a normal metal was directly observed were conducted in 1969 by Clarke [71]. A three-layered superconductor/ metal/superconductor sandwich was created in which copper was employed as the normal metal and lead was... 

In the following section, contact resistance experiments are described, based on three- and four-point probe measurements that evaluate the chemical compatibility of organic conductors with a number of / -type cuprate phases. These experiments also explore polymer/superconductor charge transfer phenomena at temperatures above and below 7c and are relevant to organic conductor/superconductor proximity effects. 

The decrease of the poly(3-hexylthiophene)/high-7c superconductor contact resistance can be attributed possibly to the induction of superconductivity at the interface caused by a proximity effect. This enticing result represents the initial evidence for the induction of superconductivity into doped organic polymeric conductors. 

Although the reduction of contact resistance at 7c provides evidence for the induction of high temperature superconductivity into these organic conductors, the possibility of spreading resistance contributing to the measurement was noted previously [4]. This phenomenon occurs commonly in structures such as these when the resistance of one element, in this case the cuprate superconductor, drops suddenly to zero. Therefore, it is desirable to search for additional evidence for the organic proximity effect in crystalline organic conductors. 

The significance of the proximity effect on conductor impedance is well-known. There are a number of papers that derive a theoretical formula of impedance and admittance [23, 24, 25, 26, 27, 28-29] and discuss impedance variation due to proximity based on numerical simulations [30, 31, 32-33]. The proximity effect may be very important in a steady-state power system s performance from a power loss viewpoint some quantitative results at a frequency of 50 or 60 Hz have been published [34, 35, 36-37]. 

It has been pointed out that the proximity effect is also significant in a transient state because a surge waveform is noticeably distorted by the increase in conductor resistance due to the proximity effect. Unfortunately, almost no data exist investigating the proximity effect on a transient [33]. 

Schelkunoff s impedance was derived under the condition that a conductor was in a free space corresponding to Equation 7.1. Therefore, the impedance is not applicable to finite-length conductors with proximity. This fact suggests that an internal impedance of the finite length with the proximity effect is to be developed. 

Figure 28.18 Current distribution in round conductors, illustrating the effect of proximity...

From the proximity curves it may be noted that X, rises with. S. While a higher centre spticing would reduce the effect of proximity on the current-carrying conductors and which is so much desired, it will increase X, which would mean a lower p.f for the power being transferred... 

The losses, and hence the effective resistance, are also increased by passing the line in close proximity to a nonmsulatmg surface—for example, passing the line over seawater. The metal from which the conductor is made is also vei y important—for example, copper has a lower resistance, for the same geometry, than aluminum does. Also related to the losses of the transmission Hue is the shunt resistance. Under most circumstances, these losses are negligible because the conductors are so well insulated however, the losses become much more significant as the insulators supporting the transmission line become contaminated, or as atmospheric and other conditions result in corona on the line. 

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