Preparation And Performance Study Of PDC-SiCN Ceramic Based Wireless Passive Pressure Sensor For High Temperature

With the development of modern industry,it is inevitable to measure pressure in combustion chamber in the aviation field.The pressure in combustion chamber often directly affects the safety of aeroengine.However,the environment in combustion chamber of aeroengine is extremely harsh.Sensors working in this environment need to obey high temperature,high vibration,high radiation and high chemical corrosion.In order to prepare pressure sensors that can work in the extreme environment,the following two problems need to be solved.The first is to design and prepare sensor’s structure suitable for this extreme environment.The second is to study and prepare the sensor materials which can exist stably in the harsh environment.The unique features of wireless passive sensors are that they can sense only with the smallest environmental disturbance and use external energy,such as incident electromagnetic radiation or vibration,to provide energy to the sensor without separate power supply and wired connection,and without position limit,so they are very suitable for application in harsh environment.Compared with other wireless passive sensors,microwave scattering(resonant cavity)sensor has advantages of accurate signal output,strong anti-interference ability and high-quality factor(Q),which is very suitable for application in aeroengine.However,sensing distance of this kind of sensor is low and should be further improved.Another factor is the performance of sensor’s material.Polymer derived ceramics(PDCs)are promising materials for pressure sensor use.Compared with traditional ceramics,PDCs have many advantages,such as low sintering temperature,various molding methods,good thermal stability,strong corrosion resistance,high piezoresistance gauge,adjustable conductivity and low dielectric loss.These make it suitable to be used as matrix material of high-temperature wireless passive pressure sensor.When considering PDCs for the material of wireless pressure sensor,the most critical issue is to fabricate dense PDCs to improve the gas tightness because fabrication process of PDCs occurs with severe shrinkage,gas release and formation of pore due to the decomposition of organic precursor polymers.There are many ways to improve the air tightness of PDCs.In order to reduce the cost,polymer infiltration and pyrolysis(PIP)process is used to densify PDCs.In order to improve gas-tightness and sensing distance of the pressure sensor,HFSS software was used to optimize the parameters of the pressure sensor cavity according to required range of working frequency,quality factor,sensitivity and signal coupling of slot antenna.SiCN ceramics were synthesized by crosslinking and pyrolysis of PVSZ,and then pressure sensors were prepared with SiCN ceramics as sensor material according to the determined size.Two pressure sensors were tested and found to have a measuring pressure range of 0-8 N,a measuring temperature of 500℃,and a sensitivity of 9.6 MHz/N and 8.44 MHz/N,respectively.In order to measure the pressure accurately,the intercept and slope of the pressure frequency fitting line under different temperatures were polynomial fitted,and the intercept temperature and slope temperature fitting curves were obtained,so that the intercept and slope of the pressure frequency fitting line were determined first according to the ambient temperature,and then the pressure value was determined according to the measured frequency,which shows that the designed sensor can realize the pressure measurement under a certain temperature.In order to improve measurement accuracy and sensing distance of sensors,high-gas-tightness polymer derived SiCN ceramics were fabricated by PIP process.The effect of viscosity,contact angle and surface tension of the infiltration liquid on PIP process was discussed.As a result,PVSZ/Ethanol(2:1)and PVSZ/Ethanol(1:1)were chosen as the first PIP cycle and the last two cycles of PIP,respectively.Air tightness of infiltration ceramics and transmission distance of the corresponding pressure sensors were tested.It was found that the air tightness of infiltration ceramic can be maintained for 8 days,and the transmission distance of the pressure sensor is 39 mm,which indicates that air tightness and transmission distance of the pressure sensor can be improved with densification of sensing element,laying a foundation for its application in the air pressure test.