Research On The Traveling Wave Mode SAW Angular Rate Sensor

Surface acoustic wave?SAW?angular rate sensors have gained increasing attraction because of their unique properties such as simple fabrication,low cost and excellent inherent shock robustness due to no suspended mechanical structure.In addition,compared to standing wave mode SAW angular rate sensor,traveling wave mode SAW rate sensor can eliminate common error sources by a differential scheme,such as temperature drift.And the test signal is a shift in oscillation frequency,which is easy to detect.Therefore,the traveling wave mode SAW rate sensor has far-reaching application potential in motion brakes and military guidance system.Based on the research of the current traveling wave mode SAW angular rate sensor,this paper has carried out in-depth research on the problem of low sensitivity.The main research work and results are as follows:1.The SAW gyroscopic effects of a SAW angular rate sensor in the propagation region were theoretically analyzed.The propagation region is divided into three parts:firstly,SAW propagation on free surface.In this part,the SAW gyroscopic effect in 128°YX-LiNbO₃ and ST-X quartz was conducted by using the piezoelectric coupling wave equation in rotating frame.According to the calculation,128°YX-LiNbO₃ was selected as the substrate for the SAW angular rate sensor;Secondly,SAW propagation in interdigital transducers?IDTs?.In this part,a COM model including the reflection and rotation was developed and it is used to analyze the relationship between the SAW gyroscopic effect and the reflection.The relationship shows that for the same substrate,the lower reflection,the larger gyroscopic effect;Finally,SAW propagation in metallic dot arrays.From the two points of improving the energy distribution in metallic dots and the frequency difference between the two modes along x axis,their properties with different dot thicknesses and different dot areas are analyzed by the method of Finite Element Method?FEM?.The results of analysis show that the sensitivity can be improved by increasing the metallic dot thicknesses.This situation has already been proved by experiments.The sensitivity also can be improved by designing appropriate dots areas.According to our analysis,it has the best sensitivity when a dot area duty ratio is 0.19.2.The method of extracting COM parameters by using the COMSOL MUITIPHYSICS software is comprehensively analyzed and summarized.Combined with P matrix cascading technology,the method of designing SAW device by COM theory is completed.Based on the theoretical analysis and the existing experiment results in the literature,the sensitivity of a SAW angular rate sensor combining with metallic dot arrays can be improved by designing a delay line structure with low insert loss and high degree of undirectionality.we focused the cell structure with low insertion loss on electrode width controlled single phase unidirectional transducer?EWC/SPUDT?.The analysis of the EWC/SPUDT cell structure shows that the insertion loss will decrease when the reflection coefficient increased with a 90°undirectionality angle.Finally,we designed an optimized EWC/SPUDT structure with a 90°unidirectional angle and a reflection coefficient more than 5%on a 128°YX-LiNbO₃ substrate.3.A SAW delay line with an input withdrawal transducer and an output withdrawal transducer was designed in view of improving the frequency stability of the SAW oscillator.The frequency response of the SAW delay line using the optimized EWC/SPUDT cell structure is simulated by Coupling-of-models?COM?theory.A set of optimized design parameters is obtained.The insertion loss of the SAW delay line device under this design parameter can reach-5.2dB.At the same time,a differential oscillating circuit and a frequency acquisition module were designed and developed to complete the test of the SAW angular rate sensor.4.From the perspective of experimental verification and experimental exploration,the following three sets of devices were prepared and tested:First group are SAW angular rate sensors with three different interdigital transducers?IDT??split finger,EWC/SPUDT and bidirectional?structure;Second group are two placement SAW delay line structures,each of which uses the traditional EWC/SPUDT?EWC/SPUDT-1?and optimized EWC/SPUDT?EWC/SPUDT-2?for the purpose of verifying that the optimized cell structure has lower insertion loss and higher high degree of undirectionality;Third group are several SAW delay lines with an input withdrawal transducer and an output withdrawal transducer adopting the EWC/SPUDT-1 and EWC/SPUDT-2 were fabricated,which including with metallic dot arrays and without metallic dot array.The test results indicate that:?1?The sensitivity of the split IDT is best,then EWC/SPUDT,and the bidirectional IDT is worst,these confirms the predictions of our theoretical hypothesis.?2?The lower insertion loss of a SAW delay line with EWC/SPUDT-2 and a higher degree of undirectionality can be proofed by the insertion loss experiment.The performance of the SAW angular rate sensor combining with metallic dot arrays was evaluated by experiments.The final results showed our designed traveling wave mode SAW angular rate sensor have a high frequency stability and high sensitivity?5.92 Hz/?deg/s??with EWC/SPUDT-1,9 Hz/?deg/s?with EWC/SPUDT-2.