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The Basic Research On Cross Sensitivity Of Fiber Bragg Grating Sensor

Posted on:2006-02-27Degree:MasterType:Thesis
Country:ChinaCandidate:Y ZhangFull Text:PDF
GTID:2168360155452609Subject:Physical Electronics
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The modern information technology is composed of information gathering, the transmission and the processing technology, therefore the sensor, the correspondence and computer technology become the main three supports in the realm. With the rapid development of photo-communication, the optic fiber sensor, which immune to electromagnetic interference, light and handy, and high in sensitivity, combines transmission and sensing into an organic whole, showed its talent with the unique advantage. As a member of fiber sensor, the fiber Bragg grating (FBG) become one of the all-fiber passive devices with the fastest developing speed in recent years because of the excellent properties such as its compatibility with optic fiber system and its low insertion loss, easy fabrication, small size and low cost. Optic fiber grating sensor gradually become the research focus among the sensors and its application is a field in the ascendant, there are very wide development prospects. In this paper we first introduced the progress of fiber grating and its basic structure, then we explained the mechanism of photo-induced change of refractive index and the manufacture method. The sensing principles of all kinds of sensors were given according to coupling mould theory. Bragg fiber grating is one type of fiber gratings whose optical period (product of grating's effective refractive index varies periodically) is about 10-1 μm .When a light source is input a fiber with Bragg grating, one very narrow little section of spectrum will be reflected in the incidence light wave while other light waves will be hardly influenced. The central wavelength to the specific reflected spectrum is called Bragg wavelength. The Bragg wavelength will "shift"as the strain or temperature changes, in reverse we can get the change by measuring the offset of Bragg wavelength, that's why fiber Bragg grating can be used as the sensor. The work of this thesis is deeply studying the principle, fabrication properties and applications of fiber Bragg grating. The main achievements of this thesis are shown as following: 1. High quality fiber Bragg gratings were fabricated by the method of UV writing using phase mask, before which we process the fiber on special-purpose to increase the photosensitive. The UV light was sent out by KrF(248nm) excimer laser. One of the fiber gratings we made is about 15mm long, the index of peak value reflection is close to 100% , the width of reflection spectrum at the half height of the peak is 0. 165nm, the reflected wavelength center is 1546. 908 nm. 2. And then, we have proposed and demonstrated experimentally a simple method for strain and temperature measurement after a theoretical research to FBG's sensing mechanism in detail. In the experiment, we have studiedthe FBG's response characteristic of strain and temperature, thus proved the reflected wavelength centre of FBG present a good linear fit with strain and temperature, we have obtained the strain sensitivity and temperature sensitivity respectively as: 1. 32727nm/N and 0. 01019nm/0C. In view of the above, we have designed a set of strain sensor using a single FBG which has a sensitivity coefficient of 13.5377nm/N, namely ?λs=1.35377 ? ε. Assisted by the computer, we fulfilled the screen catching and computational analysis, realized on-the-spot reading that accorded with actual value very well, which proved the rationality and feasibility of our design. 3. Further more, to overcome the cross sensitivity problem, we have designed a set of FBG strain sensor based on cantilever, proposed a new type measurement with double gratings. In the free end of cantilever we added weights, which resulted in different microstrain in two hollow areas; then we stuck two gratings respectively on the up surface of the hollow areas and arrayed them in series. When the strain changes, the reflected wavelength center of two FBGs shift to opposite directions, as a result we enhanced the strain sensitivity; on the other hand, the two FBGs were in the same environment, so we could consider their ? Twere accordant and the effects on the reflected wavelength center were mainly the same. By this means we have not only solved the cross sensitivity but also increased the strain sensitivity. This project need only one light source, one demodulation system, so its light path is simple and it's quite different from the method of double FBGs array because it is not necessary that the two FBGs, even they are completely identical, which reduce the...
Keywords/Search Tags:Sensitivity
PDF Full Text Request
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