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Study On The Methods And Techniques Of FBG In The Harsh Aviation Environment

Posted on:2008-12-19Degree:DoctorType:Dissertation
Country:ChinaCandidate:M J GuoFull Text:PDF
GTID:1118360215492222Subject:Mechanical Manufacturing and Automation
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Aero aircraft is an embodiment of the nation integration and military strength.Its roles become more and more important in the modern war, and function isgreater and more in the systems of the Early Warning, military surveillance,anti-tank, Air Defense System, communication command and so on. Aerocraft hasbeen the most important weapon to win the war initiative and caused the importantand even crucial influence to the course and sequel of the war. Aerocraft usuallygoes wrong because its structure is very precise and complicated; the workingenvironment is extremely harsh; hypersonic flying speed and so on. It is a greatlydispensable and exigent task for safety monitoring of aero aircraft structure.The pressure in the active Aerocraft has been examined through the pressuremeter or pressure sensor/announciator to carry out distance measuring andcontrolling presently, the temperature has been examined and controlled by thetemperature wrap, the thermocouple, the thermoelectricity, the double sheet metaletc. The sensing theory of the sensors usually is based on the resistance orinductance. They pass the electricity signal to corresponding appearance and othersystem after they take the temperature and the pressure. The examining method ofthe machine-electron is influenced by the harsh flying environment to result in thetemperature and pressure to have low detection precision and reliability, measureerror, suffer from the electro-magnetic interference and so on.It is very fit for the safety monitoring of aero aircraft structure because FiberBragg grating(FBG) sensors posses a series of merits such as light weigh, smallsize, high precision, the number sensing signal, anti-exploding and being easy toimport integrated processor to process signal which the conventional electrical-basedsensors could not match.The basic theories and fundamental experiments of techniques of FBG and itsapplication in the harsh aviation environment financially supported by the NationalNatural Science Fund (60537050) and basic Pre-research Project of Committee ofDefense Science and Industry in this thesis,. The purpose is to develop the FBGtemperature and pressure sensors and their health monitoring system, and to usethem in aero aircraft construction.The low temperature properties of three structures of FBG temperature sensors, which are the bare FBG, FBGs with thin stainless steel tube encapsulationand nickel tube after the fiber with plating gold package, have been researched.There is good linearity of the former two FBGs. FBG temperature sensor withplating full metal package has solved the application problem of the Aerocraft inthe harsh environment. The reflecting spectrogram of FBG with thin stainless steeltube package at the breaking temperature point and other temperature point hasbeen studied. Simultaneously the cause of the center wavelength breaking has beenexpounded in details. The temperature of the Aeroengine is up to 1400℃, there arelots of disadvantages and deficiency of all kinds of the high temperature sensor,and so there is demand for the high temperature properties of the FBG. The hightemperature properties of three types of FBGs which are made of thecommunication, high Boron and Germanium co-doped fiber have been studied inthe thesis, and it provides the theoretical basis for the use of FBG in the hightemperature environment. When the temperature has been heated to the criticaltemperature, FBG will be destroyed, and there are different destroyingtemperatures when FBGs are fabricated with different types fibers. The thermaldegradation of FBGs is carefully experimental explained and analyzed.The force distributing and the displacement shift of all different structure FBGpressure sensors have been establishedin the thesis, and the geometry figure andspecification of the sensing probes have been confirmed by optimizing design andcontrasting. FBG pressure sensors with different structure based on the diaphragmhave been put forward and carried out an experiment in the high and low pressure,and the merits and demerits of theirs are analyzed. The design of the sensitivepressure probes of FBG pressure sensors and the solving methods and approachofthe key problem have been discussed in the harsh flying environment of the aeroaircraft such as strong electromagnetic fields and acutely vibration. The properstructures, materials and method related to the software have been brought forwardto compensate temperature in allusion to the harsh flying environment of the aeroaircraft and its structure characteristic. Consequently the temperature influence iseliminated really. The linearity, sensitivity, repletion, stability and fatigueperformance of FBG pressure sensors have been investigated.There must be high reliability and sensitivity, eximious performance for theaircraft airborne equipment. Because the aero aircraft usually suffers from the terribly harsh environment such as the intensively virbration, high impulsion, andhigh over loading and so on, the demodulating methods based on DSP have solvedthe problems of being liable to electro-magnetic interference and unable tomeasuring high frequency signals of the electric vibration sensor in the aeroaircraft.The reliability, stability and precision of the demodulating system havebeen improved. Especially it could respond in the urgent instance so all kinds ofaccidents is avoided to happen.
Keywords/Search Tags:fiber optic grating sensors, harsh environment, encapsulation, characteristic of high and low temperature, pressure characteristic, cross sensitivity, high speed demodulator
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