A fiber-optic sensor of curvature is made with the sensitivity sufficient to make it ideal for measurement of deflection of structures under mechanical loading. Typically, deflection-curvatures are extremely small, with the curvature-radii in the kilometre range. Although this sensor is intensity modulated, as summarised further in this dissertation, its sensitivity exceeds by far that of several long-period grating sensors of curvature reported recently, and sets it apart as the only sensor of deflection curvature. The application domain is specified in this dissertation where the deflection-curvature measurement concept provides benefits over the alternative of measuring strain in terms of the sensitivity, flexibility to choose the location for the sensor placement, and immunity to the effects of microstructural interfacing between dissimilar materials that the sensor presence introduces. Naturally, specifics of the sensor itself are also provided. Two types of breakthroughs of the deflection-curvature sensor are reported in this dissertation: • main highlights of the earlier sensor configuration have been optimised experimentally, and • a better configuration has been suggested with the two-way light transmission across the sensor for increased modulation effects and a better integration in/on structures for more design flexibility…
Contents
1. INTRODUCTION
1.1 STRUCTURAL DEFORMATION MEASUREMENT
1.2 CURVATURE GAUGE
1.3 AIMS OF THIS RESEARCH
1.4 OBJECTIVES
1.5 METHODOLOGY
1.6 STRUCTURE OF THE THESIS
1.7 SUMMARY
2. LITERATURE REVIEW
2.1 BRIEF INTRODUCTION TO FIBER OPTIC SENSING TECHNOLOGY
2.1.1 MEANS OF SENSING
2.1.2 CATEGORY
2.2 BRIEF INTRODUCTION TO CURVATURE
2.3 RELEVANT RESEARCH FINDINGS IN CURVATURE MEASUREMENT
2.3.1 REVIEW OF LITERATURE ON LIGHT BEHAVIOR
2.3.2 REVIEW OF LITERATURE ON MEASURING CURVATURE
2.4 RELEVANT RESEARCH FINDINGS ABOUT MAKING MIRRORED ENDS
2.5 SUMMARY
3. PROBLEM STATEMENT
3.1 THE NEED FOR CURVATURE MEASUREMENT
3.1.1 CONDITION MONITORING OF STRUCTURES IN INDUSTRY
3.1.2 MONITORING OF MANUFACTURING PROCESSES
3.1.3 POTENTIAL MEDICAL APPLICATIONS
3.2 RESEARCH FOCUS
3.3 SUMMARY
4. CURVATURE MEASUREMENT
4.1 ADVANTAGES OF MEASURING CURVATURE
4.2 WORKING PRINCIPLE OF THE CURVATURE SENSOR
4.3 SENSOR FABRICATION
4.4 CURVATURE SENSOR OPTIMIZATION
4.4.1 DIMENSIONAL OPTIMIZATION OF SENSITIVE ZONE
4.4.2 SENSOR CONFIGURATION WITH A MIRRORED END
4.5 CROSS-COUPLED SENSOR CONFIGURATION
4.6 EXPERIMENTAL SET-UP DESCRIPTION AND RESULTS
4.7 BRIEF INTRODUCTION TO A FAILED CONCEPT ATTEMPTED
4.8 SUMMARY
5. BENEFITS AND FABRICATION OF MIRRORED END
5.1 INTRODUCTION
5.2 BENEFITS OF PRODUCING THE MIRRORED END
5.2.1 THE CONCEPT
5.2.2 EXPERIMENTAL INVESTIGATIONS OF TWO-PASS CONFIGURATION
5.3 FABRICATION OF THE MIRRORED END
5.3.1 SOME AVAILABLE TECHNIQUES FOR MAKING THE REFLECTIVE SURFACE
5.3.2 BRIEF INTRODUCTION OF MAGNETRON SPUTTERING AND EVAPORATION…
Source: City University of Hong Kong