Theoretical And Experimental Research On Optical Fiber Vibration Sensing

Vibration detection has been widely used in condition monitoring of electrical equipment,large engineering structure,infrastructure and etc,which can realize health condition assessment,fault warning and diagnosis.Therefore it has important practical significance.Compared with conventional sensors,optical fiber vibration sensor offers important advantages such as EMI immunity,electrical insulation,corrosion resistance,multiplexing capabilities,easy networking and etc.It is more suitable for application in power system and many other harsh environments.The existing fiber optical vibration sensor has the problems of narrow bandwidth and complex structure,so it is necessary to study new optical fiber vibration with different types and structures.Aimed at the shortcomings of optical fiber vibration sensor,the thesis proposes and develops new wavelength modulation and intensity modulation optical fiber vibration sensors respectively.To reduce the influence of temperature on the intensity modulation sensor,the thesis designs FBG wavelength demodulation system and improves the structure of the sensor.Based on the analysis of sensing characteristic and vibration sensing principle of FBG,the thesis proposes and develops a new type FBG vibration sensor packaged by aluminum cylinder.The principle the sensor adopts is the coupling of optical wave and mechanical wave.To demodulate the FBG wavelength,a matched FBG sensing demodulation system is set up,under which the sensor characteristics are tested.By means of packaging the matched FBG appropriately,the effects of temperature on vibration sensing are reduced.The thesis analyzes the modes in fiber and the principles of existing intensity modulation optical fiber vibration sensor,and then proposes and develops a new type vibration sensor based on cantilever structure.It also studies the influences of the fiber location and the dimension parameters of the cantilever on the frequency response.In addition,the stability,linear and temperature characteristics are tested.The two types of sensors mentioned above adopt new package structure,and have the characteristics of large bandwidth and simple structure.But the performance of the sensors can be influenced by temperature.Aimed at the temperature stability of the intensity modulation sensor,the thesis proposes a method of temperature compensation by FBG.To obtain the wavelength of FBG,the thesis designs and develops FBG wavelength demodulation system.By using F-P etalon the wavelength demodulation accuracy is improved.Furthermore,the thesis improves the structure of the intensity modulation sensor.Combined with the FBG demodulation system,the thesis designs and develops sensing system which can measure vibration and temperature simultaneously.The mutual influences of vibration and temperature measurement,the results of temperature compensation and the sensitivity of vibration measurement are tested.The temperature stability and sensitivity of vibration measurement are enhanced obviously after improvement of the sensor.