Research On Fiber-optic Strain Measurement System Based On Low-coherence And Its Signal Processing

Structural health monitoring has become one of the hottest research points in recent years,especially for the stress and strain measurement of structures. It plays an extremely significant role inthe operation, maintenance and damage warning of large-scale equipment, including large-size windturbine blades and other composite materials, as well as bridges, dams, tunnels and other large civilianfacilities. Fiber-optic low-coherence strain measurement distinguishes itself from much many testingmethods and has been widely used in above fields for its unique advantages: high sensitivity, highanti-electromagnetic ability, flexible changing of the length of sensors, simple system structure, andabsolute measurement of optical path.First, a general overview of common and fiber-optic methods for strain and stress measurementwas given to describe their development and research status. The principle of fiber-optic strainmeasurement was presented and changes of optical path difference caused by strain were discussed.Second, fiber-optic strain measurement system was designed. Hardware components of thesystem such as the light source, optical fiber couplers, collimators and optical detections wereintroduced detailedly, including parameters, performance and selection criteria.Third, wavelet denoising of the interference signal was studied. The system error and noisesources were also analyzed. Selection standards of wavelet thresholds and basis functions wereresearched to reduce or even remove some of the noise. Experiments showed that this wavelet noisereduction program has better denoising results. In addition, wavelet was chosen to extract signalenvelope after studying traditional envelope extraction method; processing program was designedcorrespondingly. Strain measurement and calculation programs were also designed, which combinedgross error elimination and mean filter. Results showed that this method could improve the accuracyeffectively and simplify the measurement process.Finally, the fiber-optic strain measurement system was experimentally studied and strain of steelplate was tested three times. Results was analyzed and compared with those from Ansys finite elementsimulation. Strain transmission coefficient between optical fiber and steel plate is also calculated,which showed that this thesis can realize the strain measurement of the steel plate.