목차

CHAPTER 1 INTRODUCTION 1
1.1 Research Motivation 1
1.2 Research Objectives 3
1.3 Thesis Outline 7
CHAPTER 2 ULTRASONIC TRANSDUCERS FOR PLATES 11
2.1 Overview 11
2.2 Ultrasonic Guided Waves in Plate Structures 12
2.2.1 Guided wave based NDE and SHM of plates 13
2.2.2 Lamb and shear-horizontal (SH) waves 14
2.2.3 Advantages of using SH waves over Lamb waves 21
2.3 Magnetostrictive Patch Transducer (MPT) 23
2.3.1 Magnetostriction 23
2.3.2 MPTs for SH wave transduction 26
2.4 Electromagnetic Acoustic Transducer (EMAT) 27
2.4.1 Lorentz force mechanism for EMATs 28
2.4.2 EMATs for SH wave transduction 29
CHAPTER 3 OMNIDIRECTIONAL SHEAR-HORIZONTAL WAVE MAGNETOSTRICTIVE PATCH TRANSDUCER (OSH-MPT) 43
3.1 Overview 43
3.2 Development of OSH-MPT 45
3.2.1 Configuration and working mechanism 46
3.2.2 Coil winding strategy 50
3.3 OSH-MPT for a Nonferromagnetic Plate 51
3.3.1 SH wave transduction and transducer sensitivity 52
3.3.2 Omnidirectivity of the SH wave by OSH-MPT 56
3.3.3 Frequency characteristic 60
3.3.4 Optimal static magnetic field strength in patches 62
3.4 OSH-MPT for a Ferromagnetic Plate 64
3.4.1 Issue on OSH-MPT for a ferromagnetic plate 66
3.4.2 Investigation of magnetic flux leakage problem 68
3.4.3 Design of OSH-MPT for a ferromagnetic plate 74
3.4.4 Experimental verification and discussion 80
3.5 Concluding Remarks 83
CHAPTER 4 OMNIDIRECTIONAL SHEAR-HORIZONTAL WAVE ELECTROMAGNETIC ACOUSTIC TRANSDUCER (OSH-EMAT) 118
4.1 Overview 118
4.2 Fundamentals of OSH-EMAT 121
4.2.1 Configuration and coil winding 122
4.2.2 Working principle 123
4.3 Design of OSH-EMAT 125
4.3.1 Design issue on the magnet size and wavelength 126
4.3.2 Transducer design by simulations 128
4.3.3 The effect of magnet width ratio 131
4.4 Experiments 133
4.4.1 SH wave transduction using OSH-EMAT 133
4.4.2 Frequency characteristic 135
4.4.3 Radiation pattern of the SH wave by OSH-EMAT 136
4.5 Concluding Remarks 138
CHAPTER 5 CONCLUSIONS 162
APPENDIX A. EFFECT OF STATIC MANGETIC FIELD STRENGTH ON THE PERFORMANCE OF LAMB AND SH WAVE MANGETOSTRICTIVE PATCH TRANSDUCERS 166
A.1 Overview 166
A.2 Experimental investigation 168
A.3 Piezomagnetic theory 172
A.4 Analysis 177
A.5 Discussion 179
REFERENCES 189
ABSTRACT (KOREAN) 207