Studying On Sensitivity And Temperature Drift Of High Temperature Piezoelectric Accelerometer Based On CTGS And YCOB

High temperature accelerometer had become imperative requirement in the field(above 600℃,even up to 1000℃)of aero-engine,high speed aircraft,nuclear reactor,internal combustion engine and other high temperature device for the structural monitoring.High temperature accelerometer based on piezoelectric materials had been received widely attentions due to its advantages of high sensitivity,high stability,high bandwidth at the high temperature environment.At present,the foreign commercial high temperature piezoelectric accelerometer can work stably at 650℃ for a long time while short time at 777℃;domestic commercial product only can work stably below 482℃,obviously these cannot be able to apply at high temperature field as mentioned above.The high temperature instability of the piezoelectric material in the accelerometer is an important reason for limiting its development to higher working temperature.For example,traditional piezoelectric ceramics lose its piezoelectric property due to exceed its Curie temperature(typical temperatures such as PZT is 100～200℃);quartz show α to β phase transition at 573℃;lithium niobate was found to have chemical decomposition above 300℃.YCOB and CTGS have been reported to be promising high-temperature piezoelectric materials for sensing above 600 ℃ even higher temperature due to their high resistivity,good chemical stability and stable piezoelectric performance at elevated temperatures.So far the development of accelerometer based on these two materials is still preliminary,and one main factor for limiting its application is that the sensitivity is too small and the temperature drift is too large.To solve the above two problems,the method of optimizing the crystal cuts to improve sensitivity and using multilayer of different temperature coefficient piezoelectric materials to reduce the temperature drift had been proposed for exploring the application of the compression accelerometer based on high temperature crystal(CTGS and YCOB)at elevated environment.The main works in this articles as follows:1.According to mass-spring vibration of one-dimensional mathematical model,the sensitivity of the compression piezoelectric accelerometer is proportional to piezoelectric strain coefficient(dii).Thus,theoretically high temperature piezoelectric accelerometer can increase the sensitivity by improving of dii with the cutting optimization.Considering that the dii of YCOB and GdCOB(with YCOB belong to ReCOB series)has opposite temperature characteristics,it is proposed to use piezo multilayer with YCOB and GdCOB to reduce the temperature drift of sensitivity.2.In order to optimize the sensitivity and temperature drift of high temperature piezoelectric accelerometer based on CTGS or YCOB crystals,we have measured the parameters changing with temperature of two crystals.We have measured the resistivity of CTGS and YCOB changing with temperature at the range from 450℃ to 800℃,and the result show the resistivity of YCOB is bigger than that of CTGS at high temperature,also the variation of resistivity with temperature is less than that of CTGS.Just from the point of resistivity,YCOB is more suitable for application at high temperature.All the piezoelectric strain constants has been measured by impedance method from 20 to 800℃,the piezoelectric strain coefficient at different cuts which is rotating a single axis has been study by transpose equation for finding the crystal cut with maximum piezoelectric constants,which means the compression accelerometer based on this cut has maximum sensitivity.X cut of CTGS and YZl/45°cut of YCOB was found having maximum piezoelectric constants.3.In order to verify that optimizing the cuts of crystal can improve the sensitivity and piezo multilayer of different temperature coefficient of piezoelectric materials can reduce the temperature drift,firstly we fabricated the high temperature piezoelectric accelerometer,than tested the sensitivity of the accelerometer at temperature range of 20～800℃.For accelerometer based on CTGS,it is invalid above 500℃ due to its resistivity sharply decreased with temperature.For accelerometer based on YCOB,we had fabricated and measured sensitivity for two different cuts YZl/45° and YZl/15°,results shows that the sensitivity of accelerometer based on YZl/45° cut higher than that of YZl/15°,this proved that we can improving sensitivity by cuts optimazition.Using negative temperature coefficient crystal GdCOB to combine with positive temperature coefficient YCOB for reducing the temperature drift.Results show that the accelerometer only using YCOB with temperature drift 34.17%and GdCOB with temperature drift-65%,the accelerometer after using GdCOB combined with YCOB at quantity ratio 2:1 and its temperature drift minimum 12%,this show that the method mentioned above can reduce temperature drift.