| Shock waves can be generated by explosions,supersonic flying aircraft,collisions of high-speed objects,laser plasma technology and so on.Shock waves generated by explosions can cause large-scale indiscriminate damages.In comparison,laser plasma shock wave technology has the advantages of energy efficiency and controllability,which is widely used in industrial,medical,petroleum and environmental fields.Shock wave generation is accompanied by a huge peak pressure,the rise time of the peak pressure is very short.Therefore,the fiber-optic Fabry-Perot sensor used for shock wave pressure measurement must have a short response time and withstand high pressure,and its demodulation system needs to achieve high speed demodulation.In this thesis,we have designed a thin transparent film fiber-optic Fabry-Perot pressure sensor and a pressure demodulation system based on the dual-wavelength orthogonal principle.Performances of the sensor has been verified,the shock wave signal is successfully acquired,and the pressure of the shock wave is measured.Main research contents of the thesis are as follows.Firstly,the structure of the fiber-optic Fabry-Perot sensor is introduced,and from the response time,the sensor structure is determined to be a thin film fiber-optic Fabry-Perot pressure sensor.The sensing principle of the the fiber-optic Fabry-Perot sensor is discussed,and the theoretical equation between the light intensity and the cavity length of the sensor is derived,which provides the theoretical basis for the demodulation scheme.The characteristics of the main demodulation methods are compared and analyzed,and the pressure demodulation system based on the principle of dual-wavelength orthogonal method is determined by considering the demodulation speed.Then,the pressure demodulation system is designed and built,including sensor design,optical path design,device selection,circuit design and algorithm research.The thin film fiber-optic Fabry-Perot pressure sensor is made by coating the fiber end face of the fiber with the coating layer removed,and the pressure-sensitive element is a Parylene layer,and the Fabry-Perot cavity structure of the sensor is a gold-Parylene-gold film structure.In the optical path design,two tunable lasers are used as the light source for the demodulation system,which facilitates the realization the orthogonal condition of the two beams in phase.In the electric circuit design,a photoelectric detection circuit and a signal processing circuit are designed.The photoelectric detection circuit converts the interfering light signal into voltage signal output,which is changed into the digital form through an A/D conversion circuit and processed by the the signal processing circuit based on the STM32 chip.The design,board making,welding and debugging of each corresponding module circuits are carried out.In the algorithm part,the traditional dual-wavelength orthogonal method is improved,and the demodulation accuracy is increased.Finally,the experimental test systems for static pressure measurement and shock wave pressure measurement are built,and the thin film fiber-optic Fabry-Perot pressure sensor for static pressure measurement and shock wave signal acquisition are packaged to complete the static pressure measurement experiment with an upper pressure limit of 60 MPa,and shock wave pressure measurement experiment.The static pressure measurement experiment verifies the performance of the sensor,and the pressure sensitivity is 0.95nm/MPa,when the cavity length of the sensor is demodulated during pressurization by the dual-wavelength orthogonal method.The shock wave measurement experiment collects shock wave signal and shows that the rise time of the shock wave is about 142 ns,and the maximum pressure is 6.39 MPa. |
