City Research Online

Abstract

An investigation of methods of optical pressure sensors using a novel polarimetric interferometric approach are presented. The use of several techniques and their experimental arrangements are demonstrated and discussed, for which results have indicated possible applications in pressure measurement. A comparison of their sensitivities to applied force has been made, using coated and uncoated standard single mode fibre as the sensing medium, and the stability of the output to temperature variations over the range 20 °C to 95 °C also demonstrated. This scheme has been discussed as a possible element for a differential pressure flow sensor.

An optical pressure sensor, using a low-coherence technique and a photoelastic material as the sensing element, is also presented. A change in the optical path of light propagating in the stressed sensing element has been observed by monitoring a corresponding change in that optical path in a "recovery" optical interferometer. Results have shown a linear relationship between this change in path difference and applied pressure.

Further, the measurement of force/pressure-induced birefringence has been investigated using a photoelastic technique, and in this case, the light source employed was a "quasi-white light", short coherence light source, a light emitting diode (LED). Its output was coupled into a multimode fibre before entering the processing interferometer. With the use of the processing interferometer, the sensing element birefringence was observed when a force was applied. The sensing material properties such as elastic limit, stress-relaxation and thermal effects were also investigated and are discussed, in light of the applications of the technique.

The characteristics of three individual types of polarisation maintaining fibres (Hi-Bi), for pressure sensing applications using a quasi-distributed sensing technique are presented. The output light from a low-coherence source was coupled into the fibre via one of the two polarisation modes, where the location of the coupling point was located by using a basic Michelson interferometer. The theoretical aspects of the sensor system and its experimental arrangement are discussed and demonstrated. A number of sensor applications such as a pressure/force sensor, or a position sensor, in addition to an investigation of fibre characteristics such as beat length and birefringence measurements are demonstrated. The device sensitivity to variations in temperature for these measurement is investigated.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TK Electrical engineering. Electronics Nuclear engineering
Departments:	School of Science & Technology > Engineering > Electrical & Electronic Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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