Detecting Acoustic Emission Signals from High Temperature Superconducting Tapes during Quenching in a Solid Nitrogen Cooling System
- 주제(키워드) piezoelectric ceramic , acoustic emission sensor , superconductor
- 발행기관 고려대학교 대학원
- 지도교수 이해근
- 발행년도 2010
- 학위수여년월 2010. 8
- 학위구분 석사
- 학과 일반대학원 신소재공학과
- 원문페이지 52 p
- 실제URI http://www.dcollection.net/handler/korea/000000023999
- 본문언어 영어
- 제출원본 000045609427
초록/요약
Acoustic emission (AE) technique is a suitable method for detecting the presence of thermal and mechanical stresses in superconductor, which have adverse effects on the stability of their application systems. However, the detection of AE signals from a high temperature superconductor (HTS) tape in a bath of liquid cryogen (such as liquid nitrogen, LN2) has not been reported because of its low signal to noise ratio, due to the large amount of noise caused by the boiling of the liquid cryogen or mechanical vibration from the cryo-cooler. The AE sensor is generally manufactured using piezoelectric ceramics, which produce an electrical change when a mechanical stress is applied. In an attempt to improve the sensitivity of the AE sensor, Pb(Zr0.54Ti0.46)O3 + 0.2 wt.% Cr2O3 + 1.0 wt.% Nb2O5 PZT ceramic discs of various thicknesses were fabricated. The capacitance value, minimum resonance and its harmonic frequencies of AE sensor increased as the thickness of PZT ceramic specimen decreased. In order to obtain the AE signals from the HTS tapes during quenching, repetitive quench tests for YBCO coated conductor (CC) tapes in a cooling system using solid nitrogen (SN2) were carried out. During the 3rd quench test, two AE events were detected by AE sensor with PZT ceramic of 1.0 mm thickness. After the 3rd quench test, the Ic value was 10 % lower than that of the virgin sample and further quench test destroyed the sample completely. By analyzing AE signals induced during repetitive quench tests, it was possible to evaluate the quench detectability of AE sensor varying with the thicknesses of a PZT ceramic specimens.
more목차
1. INTRODUCTION 1
2. BACKGROUND 4
2.1 YBCO Superconductors 4
2.2 Acoustic emission techniques on superconductors 6
2.3 Piezoelectric ceramics 7
2.3.1 Perovskite type crystal structure 9
2.3.2 Thickness mode of piezoelectric specimens 10
2.3.3 Resonance and anti-resonance frequencies 12
2.3.4 Electro-mechanical coupling factor k 17
2.3.5 Piezoelectric constant d 19
2.3.6 Mechanical quality factor Qm 20
3. EXPERIMENTS 21
3.1 Fabrication of AE sensors 21
3.1.1 Fabrication of piezoelectric specimens 21
3.1.2 Manufacturing AE sensor 23
3.1.3 Installation of AE sensors on YBCO CC tapes 23
3.2 SN2 cooling system 26
3.3 Repetitive quench tests 28
4. RESULTS AND DISCUSSION 29
4.1 The effect of the specimen shapes 29
4.2 Repetitive quench tests 29
5. CONCLUSION 38
6. REFERENCE 39
