City Research Online

Abstract

This thesis reports the development of a suite of FBG-based optical fibre sensors for non-destructive testing (NDT) and illustrating their potential for several specific industrial applications in the marine and railway sectors. These arose from work driven by the needs of project collaborators from these industries and are intended to be illustrative of the wider potential applications that optical fibre sensors have for measurements in different industrial sectors. The research has involved the development of new sensor system designs to meet these needs, building as they do upon a comprehensive review of NDT technologies and solutions, discussed in some detail.

In this research for the marine sector, a single FBG-based acoustic sensor was specifically developed and evaluated and compared with the performance of conventional sensors. To do so, a metal plate to which the sensors were fixed was excited with a sonotrode, at a resonant frequency of 19.5 kHz. The signal reflecting that acoustic excitation was captured by the FBG sensors designed and implemented and their performance has been shown to be comparable with that from conventional, industry-standard piezoelectric transducers (PZTs). Preliminary work undertaken for the sponsors then lead to the further development of an acoustic sensor array comprising of 3 FBGs, which was subsequently validated against co-located PZTs which all were installed on a glass plate and excited in an industry-standard way, through the acoustic signal from a 0.2 g steel ball dropped onto the plate. When signals were analysed and compared, the positive comparative performance outcomes from the sensors used enabled further the design and implementation of instrumentation for a marine lifting surface using a different array, designed comprising 4 FBG-based acoustic sensors. Extensive tests on the smart marine lifting surface created were undertaken under water with a sonotrode set at 26 kHz as an excitation source. Based on the arrival time of acoustic signals captured by each grating and the use of triangulation method, the location of the excitation source could thus be determined, to meet the needs of the industrial sponsor and show good agreement with the outputs of conventional sensor systems.

In parallel with the above, a further new industrial application of FBG-based sensor arrays was developed for a major player in the field, for the first time successfully instrumenting a railway current-collecting pantograph to allow reliable, remote in situ monitoring of key parameters: the contact force and contact location of the pantograph against the catenary. The optical fibre sensor approach has been shown to be an excellent means of measurement whose performance can be extrapolated to situations where the train is driven at high speeds up to 125 mph and powered from a high voltage line at 25 kV, in this design taking full advantages of the immunity of the optical fibre sensors to electromagnetic interference. In this research, key technical performance challenges were addressed and successfully overcome, including the temperature compensation needed for ‘all-weather’ performance, due to the intrinsic cross-sensitivity problems of using a FBG-based design being been fully addressed. This ensures the accurate measurement of the contact force/location between the pantograph and the catenary under all weathers.

The research concludes by considering future directions for the work in these and other industry sectors.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TJ Mechanical engineering and machinery
Departments:	Doctoral Theses School of Science & Technology > Engineering School of Science & Technology > School of Science & Technology Doctoral Theses

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