| As a necessary and effective way of information collection in today's information age,sensing technology plays an important role in social production.Among them,pressure is one of the most basic,common,and important parameters.Fiber-optic pressure sensors have emerged among various pressure sensors due to their unique advantages,such as inherent passive nature,strong resistance to harsh environments,anti-electromagnetic interference,remote telemetry,and easy networking and multiplexing.They can be used in some key areas,such as clinical medical testing,structural health monitoring,oil and gas exploration,etc.Although the fiber-optic pressure sensing technology is relatively mature,it needs to be further improved in terms of sensing performance and the anti-interference ability of the external environment.At present,there are three key problems that need to be solved urgently.(1)It is hard to achieve fast frequency response and high-sensitivity dynamic pressure measurement in harsh environments with high temperature,high pressure,and strong vibration.(2)Pressure sensing performance based on a traditional interferometer and grating principles is difficult to improve.(3)It is difficult to simultaneously achieve multi-point pressure measurement with high spatial resolution,temperature insensitivity,and high precision.Aiming at the above-mentioned key problems,the principle and method of optical fiber microstructure pressure sensors are studied in this thesis.The main research contents are as follows.1.Fiber micromachining technology based on 193 nm deep-ultraviolet excimer laser micromachining technology and the ultraviolet(UV)nanoimprinting technology are studied.Experimental results show that the laser micromachining system can realize high-quality processing on fiber end-face,and the UV nanoimprint system can realize 100-nanometer-scale microstructure fabrication.This study has laid a foundation for the high-quality fabrication of optical fiber microstructure sensors.2.An enhanced-sensitivity temperature-insensitivity fast-response all-fiber micro-FP pressure sensor was proposed and demonstrated by innovatively using a hard-core diaphragm structure.This diaphragm makes the sensor owe the characteristics of a short cavity length,long gauge length,and simultaneous deformation of its sidewall and diaphragm induced by pressure.Results show the pressure sensitivity of the sensor was about doubled when the hard-core diaphragm thickness reduces from 5 mm to 11?m.The sensor has stable pressure sensitivity(0.23 V/MPa),low mechanical hysteresis(<1.5%),and fast response frequency(>10 k Hz)in the range of 40??200?.In addition,the sensor was successfully applied to the dynamic pressure measurement of internal combustion engines at high temperature(>350°C),high pressure(>20 MPa),and high-frequency response(>10 k Hz).The experimental results are basically consistent with that of traditional electronic sensors.This study has laid a solid foundation for the engineering application of this pressure sensor to internal combustion engine pressure measurement.3.An all-quartz micro-grating pressure sensor based on the guided-mode resonant(GMR)effect is proposed and demonstrated.The sensor innovatively utilizes the unique advantages of narrow linewidth,high diffraction efficiency,and sensitivity to structural parameters of the GMR effect to achieve high-pressure sensitivity,easy to network multiplexing sensing characteristics.A GMR diaphragm with a resonant wavelength of760.3 nm was successfully fabricated by using UV nanoimprinting process,and the sensitivity of the all-quartz micro-grating pressure sensor based on the diaphragm was found to be 1.2 nm/MPa.This part of the research provides a new idea for improving the sensing performance of the current fiber-optic pressure sensor.4.A high-spatial-resolution and temperature-insensitive quasi-distributed fiber-optic pressure sensing technique based on an optical carrier based on microwave interference system(OCMI)and fiber-optic microstructure sensors is proposed and demonstrated,for the first time to our knowledge.In addition,the OCMI system based on a tunable single-wavelength light source can realize the full-spectrum reconstruction of different fiber-optic microstructure sensors.Results show that the array quasi-distributed optical fiber pressure sensor based on the Fresnel end-face has a low temperature-pressure cross-sensitivity coefficient(about 3×10-4 MPa/?).To further improve the sensing performance,a cascaded quasi-distributed optical fiber pressure sensor based on the hollow-core photonic bandgap fiber Fabry-Perot(FP)structure is proposed and demonstrated.Its single sensing unit can achieve pressure sensitivity,temperature sensitivity,and measuring precision of–30.4 pm/MPa,0.5 pm/?,and 0.4 MPa,respectively.Furthermore,the optical interferograms of three cascaded EFP units acquired by the OCMI system are well in agreement with those used by an optical spectrum analyzer.This part of the research opens up a new way to achieve high-precision quasi-distributed pressure sensingThe above innovative work not only enriches the system of optical fiber microstructure pressure sensors but also provides new ideas for the development of high-performance and new optical fiber microstructure sensing structures,which have important scientific significance.Furthermore,it lays a foundation for the wide application of optical fiber microstructure pressure sensors,which has important application value. |
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