Rodamientos magneticos

SUPERCONDUCTING LEVITATI0N
Applications to Bearings and Magnetic Transportation

FRANCIS C. MOON
Cornell University

With selected sections by

Pei-Zen Chang
National Taiwan University

WILEY-

VCH

WILEY-VCH Verlag GmbH & Co. KGaA

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SUPERCONDUCTING LEVITATION

This Page Intentionally Left Blank

SUPERCONDUCTING LEVITATI0NApplications to Bearings and Magnetic Transportation

FRANCIS C. MOON
Cornell University

With selected sections by

Pei-Zen Chang
National Taiwan University

WILEY-

VCH

WILEY-VCH Verlag GmbH & Co. KGaA

All books published by Wiley-VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to befree of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate. Library of Congress Card No.: Applied for British Library Cataloging-in-Publication Data: A catalogue record for this book is available from the British Library Bibliographic information published by Die Deutsche Bibliothek Die DeutscheBibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data is available in the Internet at .

0 1994 by John Wiley & Sons, Inc. 02004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form nor transmitted or translated into machine language withoutwritten permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.
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Printed in the Federal Republic of Germany Printed on acid-free paper Printing Strauss GmbH, Morlenbach Bookbinding Litges & Dopf Buchbinderei GmbH, Heppenheim ISBN-13: 978-0-47 1-55925-2 ISBN-10: 0-471-55925-3To My Teacher, Colleague, and Friend, Professor Yih-Hsing Pao

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CONTENTS
xiii
1

PREFACE
1

INTRODUCTION TO MAGNETIC LEVITATION

1-1 Introduction / 1 1-2 Magnetic Levitation Systems / 4 Active Magnetic Bearings Versus Passive Superconducting Bearings / 5 1-3 Stability and Levitation / 6 Earnshaw’s Theorem / 8 1-4 Magnetic Fields and Forces / 11Induced Magnetic Forces / 13 Magnetic Stiffness / 15 Magnetic Stresses / 16 1-5 Bearings and Levitation / 19 Active Magnetic Bearings Using Normal Conductors / 21 Passive Superconducting Bearings / 23 1-6 Magnetically Levitated Vehicles / 26
2

PRINCIPLES OF MAGNETICS

32

2-1 Basic Laws of Electromagnetism / 32 Magnetic Stresses / 34 Nondimensional Groups / 37
vii

Viii

CONTENTSMaxwell’s Equations / 38 Low-Frequency Electromagnetics / 39 Electromagnetic Constitutive Relations / 40 Stationary Media / 41 Moving Media / 42 2-2 Magnetic Forces / 43 Dipole-Dipole Forces / 44 Special Cases / 45 Current-Current Forces / 47 Current-Filament-Magnetized-Body Forces / 49 Body-Field Forces / 49 Magnetic Dipole-Field Forces / 50 Current-Field Forces / 51 The Magnetic Stress Method /53 2-3 Magnetic Stiffness / 54 Magnetic Stiffness and Magnetic Energy / 56 Nonlinear Effects / 58 2-4 Magnetic Materials and Magnetic Circuits / 58 Magnetization Properties / 60 Domains / 64 Magnetic Circuits / 66 Demagnetization / 67 Forces on Magnetized Materials (J = 0) / 69
3 SUPERCONDUCTING MATERIALS

73

3-1 The Phenomena of Superconductivity / 73 Zero Resistance / 74 Flux Exclusion /78 Flux Vortex Structures-Type I and Type I1 Superconductors / 79 Critical Current / 79 Flux Quantization / 83 Penetration Depth / 84 3-2 Review of Theory / 84 3-3 Low-Temperature Superconducting Materials / 86 3-4 High-Temperature Superconducting Materials / 90 Cuprates-Crystal Structure / 92 Cuprates-Superconducting Properties / 93

CONTENTS

iX

Critical Currents / 93 Thin Films / 95...