Application of advanced materials to rotating machines

In discussing the application of advanced materials to rotating machinery, the following topics are covered: the torque speed characteristics of ac and dc machines, motor and transformer losses, the factors affecting core loss in motors, advanced magnetic materials and conductors, and design tradeoffs for samarium cobalt motors

The critical current density of advanced internal-Mg-diffusion-processed MgB2 wires

Recent advances in MgB2 conductors are leading to a new level of performance. Based on the use of proper powders, proper chemistry, and an architecture which incorporates internal Mg diffusion (IMD), a dense MgB2 structure with not only a high critical current density Jc, but also a high engineering critical current density, Je, can be obtained. In this paper, a series of these advanced (or second - generation, "2G") conductors has been prepared. Scanning electron microscopy and associated energy dispersive X-ray spectroscopy were applied to characterize the microstructures and compositions of the wires, and a dense MgB2 layer structure was observed. The best layer Jc for our sample is 1.07x105 A/cm2 at 10 T, 4.2 K, and our best Je is seen to be 1.67x104 A/cm2 at 10 T, 4.2 K. Optimization of the transport properties of these advanced wires is discussed in terms of B-powder choice, area fraction, and the MgB2 layer growth mechanism.Comment: 13 pages, 3 tables, 7 figures (or 8 pp in published version

Two-dimensional electronic transport in rubrene: the impact of inter-chain coupling

Organic semi-conductors have unique electronic properties and are important systems both at the fundamental level and also for their applications in electronic devices. In this article we focus on the particular case of rubrene which has one of the best electronic transport properties for application purposes. We show that this system can be well simulated by simple tight-binding systems representing one-dimensional (1D) chains that are weakly coupled to their neighboring chains in the same plane. This makes in principle this rubrene system somehow intermediate between 1D and isotropic 2D models. We analyse in detail the dc-transport and terahertz conductivity in the 1D and in the anisotropic 2D models. The transient localisation scenario allows us to reproduce satisfactorily some basics results such as mobility anisotropy and orders of magnitude as well as ac-conductivity in the terahertz range. This model shows in particular that even a weak inter-chain coupling is able to improve notably the propagation along the chains. This suggest also that a strong inter-chain coupling is important to get organic semi-conductors with the best possible transport properties for applicative purposes.Comment: 21 pages, 17 figure

Niobium based intermetallics as a source of high-current/high-magnetic field superconductors

The article is focused on low temperature intermetallic A15 superconducting wires development for Nuclear Magnetic Resonance, NMR, and Nuclear Magnetic Imaging, MRI, magnets and also on cryogen-free magnets. There are many other applications which would benefit from new development such as future Large Hadron Collider to be built from A15 intermetallic conductors. This paper highlights the current status of development of the niobium based intermetallics with special attention to Nb 3 (Al 1-x, Ge x). Discussion is focused on the materials science aspects of conductor manufacture, such as b-phase (A15) formation, with particular emphasis on the maximisation of the superconducting parameters, such as critical current density, Jc, critical temperature, Tc, and upper critical field, Hc2 . Many successful manufacturing techniques of the potential niobium-aluminide intermetallic superconducting conductors, such as solid-state processing, liquid-solid processing, rapid heating/cooling processes, are described, compared and assessed. Special emphasis has been laid on conditions under which the Jc (B) peak effect occurs in some of the Nb3(Al,Ge) wires. A novel electrodeoxidizing method developed in Cambridge whereby the alloys and intermetallics are produced cheaply making all superconducting electromagnetic devices, using low cost LTCs, more cost effective is presented.This new technique has potential to revolutionise the existing superconducting industry enabling reduction of cost orders of magnitude.Comment: Paper presented at EUCAS'01 conference, Copenhagen, 26-30 August 200

Electro-optic architecture for servicing sensors and actuators in advanced aircraft propulsion systems

A detailed design of a fiber optic propulsion control system, integrating favored sensors and electro-optics architecture is presented. Layouts, schematics, and sensor lists describe an advanced fighter engine system model. Components and attributes of candidate fiber optic sensors are identified, and evaluation criteria are used in a trade study resulting in favored sensors for each measurand. System architectural ground rules were applied to accomplish an electro-optics architecture for the favored sensors. A key result was a considerable reduction in signal conductors. Drawings, schematics, specifications, and printed circuit board layouts describe the detailed system design, including application of a planar optical waveguide interface

Accurate study of the electromagnetic and circuit behavior of finite conducting wedges and interconnects with arbitrary cross-sections

The manufacturing of interconnects often leads to conductors with a non-rectangular cross-section. Especially for sharp edges, it is therefore important to study the influence of corner effects on the interconnect circuit characteristics. Firstly, the electromagnetic behavior of a finite conducting 2-D wedge is investigated. Secondly, as an application example, a broadband transmission line model is used to study the influence of the conductors' shapes on the circuit behavior of a grounded coplanar waveguide. Both frequency and time domain results are presented

On the Inequivalence of Weak-Localization and Coherent Backscattering

We define a current-conserving approximation for the local conductivity tensor of a disordered system which includes the effects of weak localization. Using this approximation we show that the weak localization effect in conductance is not obtained simply from the diagram corresponding to the coherent back-scattering peak observed in optical experiments. Other diagrams contribute to the effect at the same order and decrease its value. These diagrams appear to have no semiclassical analogues, a fact which may have implications for the semiclassical theory of chaotic systems. The effects of discrete symmetries on weak localization in disordered conductors is evaluated and and compared to results from chaotic scatterers.Comment: 24 pages revtex + 12 figures on request; hub.94.