Research On Designing And Test Data Fitting Of SAW Micro Pressure Sensor

The continuous improvement of sensor technology and application requirements has promoted the development of sensors toward miniaturization and high precision.Pressure is an important measurement parameter in the fields of automotive,medical,industry,etc.Various types of pressure sensors have been developed and applied in different environments depending on their own advantages and disadvantages.At present,most pressure sensors tend to measure pressure in gas pressure,high-range pressure and other aspects,which is difficult to meet the application requirements of contact micro-pressure measurement.The appearance of surface acoustic wave(SAW)technology and drilling have promoted the wide application of sensor,and accelerated the research process of contact micro-pressure detection.On the one hand,the reduction of pressure range further requires the sensor itself to have high measurement accuracy.On the other hand,the reliability of results is easily reduced due to the external environment and human operation in the actual application of sensor.Therefore,in this paper,a delay line SAW micro pressure sensor is designed to measure the contact micro pressure in the range of 0-0.2N.Meanwhile,the function advantage of the sensor is enhanced on the system by improving the internal structure and optimizing the curve of test data fitting.(1)In order to improve the measurement accuracy of the delay line SAW micro pressure sensor,the internal electrode reflection problem of the interdigital transducer(IDT)as the internal core component is mainly analyzed.According to the reflection principle of single finger IDT and split finger IDT,it is determined that split finger IDT plays a certain role in inhibiting the internal reflection of the electrode.This paper proposed that split finger structure is used at the input and output of IDT,and cosine square function weighting is used at the input.By comparing the properties of different piezoelectric materials and IDT materials on the market,the appropriate materials are selected.Meanwhile,according to the basic characteristics and theoretical basis of IDT,the parameters of IDT are designed to ensure the accuracy and effectiveness of the micro-pressure measurement of the sensor.(2)Based on the finite element theory and analysis process,the physical models were constructed with COMSOL software by combining the parameters of single finger IDT,split finger IDT,and piezoelectric substrate structure.Then the propagation of SAW in the substrate was simulated by dividing the grid,and the output frequency and total displacement curves were drawn in the frequency domain,so as to further compare that the split finger IDT has certain advantages in inhibiting the reflection.At the same time,the pressure state of the substrate was simulated by COMSOL software,and the cloud map of stress,strain and displacement provided a basis for the deposition position of IDT on substrate surface.(3)Perform test work on the prepared sensor to verify the feasibility of measuring SAW micro pressure sensor in the range of 0-0.2N,and record multiple test data at the same time.Aiming at the problem that the accuracy of output data is affected by external factors,the least square method and general regression neural network(GRNN)are used to fit the micro-pressure-frequency difference curve.The polynomial is established according to regression idea,and the least square method is used to solve and draw the fitting curve.Moreover,multiple sets of source data were trained according to GRNN to predict micro pressure and fit the prediction curve.The final results show that the error of GRNN is significantly reduced and the fitting accuracy is higher.