| Today,the detection and real-time monitoring of pressure in aero-engines with high-performance has become the research hotspot.However,conventional pressure sensors are difficult to work in high temperature and high pressure environments inside the engine,due to structural and material limitations.Recently,a pressure sensor based on microwave resonator has been widely concerned because it is particularly suitable for pressure monitoring in high temperature and high pressure due to wireless passive structure and large signal transmission distance at high temperatures.Polymer-derived ceramics(PDCs)are potential excellent materials for devices in harsh environments,due to excellent properties such as high temperature resistance,corrosion resistance and radiation resistance.PDC-SiCN among PDC ceramics is particularly suitable as a material for wireless passive pressure sensors working in high temperature,due to mature preparation process,extensive research and low dielectric loss of PDC-SiCN.However,the PDC ceramic via powder consolidation route of polymer precursor has a large number of pores,which is not suitable as a component of the pressure sensor.Therefore,the polymer infiltration and pyrolysis(PIP)process is used for reducing the porosity of PDC ceramic.Based on the aforementioned background,the PIP enhanced ceramic film is prepared by using polyvinylsilazane(PVSZ)as precursor,and the effects of PIP process on the structure and properties of PDC-SiCN ceramics were studied through a series of experiments.Meanwhile,the PDC-SiCN is used as pressure sensing element and the wireless passive pressure sensor with resonant cavity is designed and fabricated.The content is as follows:1.The performances(resonance frequency and quality factor)of sensor were studied thought using electromagnetic simulation software to simulate the resonator and slot antenna.Then,the mechanical simulation software was used to study deformation and stress distribution of pressure sensing element by simulating pressure sensing element of the pressure sensor,and the value of parameter of the sensor is determined by combining with the data of electromagnetic simulation.2.The PDC-SiCN ceramic film and 304 stainless steel is used as the pressure sensor and the base of the pressure sensor,respectively.Then,the pressure sensor is assembled by silver paste.The accuracy of the simulation is verified by testing the variation of the resonant frequency and signal strength of the sensor.Comparing a series of simulated and measured data,the decided principle of the slot antenna with the maximum signal coupling is obtained.The wireless passive pressure sensor after optimizing has a maximum test distance of 25 mm and a sensitivity of 13.3 MHz/N.3.Through the research,the influence of PIP process on the structure and properties of ceramics was understand.The pores inside the ceramic are filled with pyrolysis products of PVSZ-2 in 1st and 2nd PIP process,and the properties of the ceramic reached or approached the optimum value in 3rd PIP process.The internal pores of the ceramic film cannot be filled resulting in invariability of performance in 4th PIP process,and that the filler continues to decompose at high temperatures and the nano-pores on the filler continue to grow,resulting in an increase in the average pore size of the ceramic film and cracking on the filler.4.The study showed that PIP reinforced ceramic film can reach the requirements of pressure due to good air tightness and strength.The test showed that the maximum pressure cycle of the pressure sensor with the PIP-reinforced ceramic film increased from 8N to 18N.This result indicates that the performance of the pressure sensor was greatly improved. |
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