Research On Key Techniques Of Sapphire Optical Fabry Perot High Temperature Pressure Sensor

With the development of aerospace engines,there is an urgent need for high-temperature pressure sensors to monitor the pressure changes in their combustion chambers to optimize combustion chamber design,improve combustion efficiency,and ensure stable engine operation.Traditional electrical type pressure sensors are prone to piezoresistive coefficient degradation and ohmic contact failure under high temperature environment,limiting their maximum operating temperature to no more than 600°C.The sapphire optical Fabry Perot type pressure sensor itself has the property of high temperature resistance,which has attracted wide attention in recent years.However,there are still key technical problems that need to be solved,such as poor stability,fabrication of high-quality sapphire sensitive structures,low demodulation accuracy and slow speed,which limit the development and application of sapphire optical fiber type high-temperature pressure sensor technology.The purpose of this paper is to improve the sensor stability through the research of sapphire wet etching and direct bonding process technology,to study the high-precision demodulation technology of composite cavity interference spectrum based on discrete cross-correlation operation,to realize the simultaneous acquisition of pressure and temperature signals,to realize the temperature compensation of pressure measurement,and to improve the measurement accuracy of the sensor in the whole temperature region,and to study the high-speed demodulation technology of combined interference and intensity self-compensation to improve the demodulation speed of the sensor.The main work of this thesis can be summarized as follows:（1）For the problem of large surface roughness of sapphire pressure sensitive diaphragm micromachining,a wet etching processing scheme is proposed,and the effect of the ratio of phosphoric acid to sulfuric acid in the etching solution,the temperature of the etching solution and the etching time on the surface roughness after etching is experimentally studied,and the results show that with the increase of the ratio of sulfuric acid in the etching solution,the surface roughness after etching decreases,while the corrosion rate becomes smaller,and with the increase of the temperature of the etching solution,the Surface roughness becomes larger,the corrosion rate becomes larger,corrosion time on the corrosion of the surface roughness after the impact is not significant.When the corrosion solution phosphoric acid and sulfuric acid volume ratio of 1:3,corrosion fluid temperature of 290℃,the corrosion rate of 0.9μm/min,corrosion surface roughness of 0.39nm.（2）In order to get the sapphire pressure sensitive chip to meet the strength requirements of engineering applications,the sapphire direct bonding technology was studied experimentally,and the research results show that the bonding strength increases with the increase of bonding temperature,bonding pressure and bonding time,and the sapphire sensitive chip with the bonding strength of 7.89MPa is obtained when the bonding temperature is 1200°C,bonding time is 40h and bonding pressure is 4Kg,and the leakage rate is only 1×10^-11Pa-m³/s after testing.In addition,in order to ensure that the sensor maintains good sealing performance under high temperature environment,a high temperature resistant encapsulation scheme is proposed,which firstly bonds the sapphire pressure sensitive chip with the sapphire column,and then encapsulates the sapphire column with the high temperature alloy shell through the elastic sealing structure,which absorbs the stress due to the mismatch of material linear expansion coefficient through the elastic sealing structure.The problem of high-temperature resistant encapsulation of the sensor is solved by absorbing the stress caused by the mismatch of the material linear expansion coefficient through the elastic sealing structure.（3）To improve the testing accuracy of the sensor,a decoupling spectral matching of thepressure-temperature in wavelength-domain method is proposed for the demodulation,by constructing interferometric spectra near pressure and temperature sensitive cavities simultaneously and decoupling the collected interferometric spectra in the wavelength domain,simultaneous measurement of pressure and temperature signals is achieved.Finally,the temperature compensation for pressure measurement is realized and the full temperature range test accuracy of the sensor is improved to 3%FS.To improve sensor demodulation speed,combining the interference with intensity,a self-compensating high-speed demodulation technique is proposed,which screens the pressure-sensitive cavity interference signal by a reasonable matching design of sapphire sensitive structure size and optical path coherence length,this demodulation technology increases the demodulation speed of the sensor to tens of k Hz.（4）In order to evaluate the high temperature pressure testing capability of the sensor,a high temperature pressure test platform was built,firstly,the sensor was designed using gold-plated optical fiber transmission optical signal,and the pressure test of 0～5MPa was conducted on the sensor under the environment of room temperature～800℃,and the accuracy of the sensor reached 3%FS in the full temperature range after temperature compensation.in order to increase the working temperature of the sensor to 1200℃,another proposal was made to use Sapphire optical fiber transmission optical signal design sensor,and the sensor was tested at room temperature～1200℃environment for 0～5MPa pressure test,the test results show that the sensor can still maintain good pressure measurement repeatability and linearity at 1200℃high temperature environment.In order to evaluate the dynamic pressure testing capability of the sensor,based on the coherence length theory,the sensor was designed and a dynamic pressure test platform was built.The test results showed that the 3d B bandwidth of the amplitude and frequency characteristic curve of the sensor was 10k Hz,and the phase shift of the sensor was less than 10°in this frequency range.The test results of the inherent frequency of the sensor show that the inherent frequency of the sensor reaches 430k Hz.