| Love wave viscosity sensor has a broad prospect of application. Because it matches thedevelopment trend of miniaturization, integration and high sensitivity. Meanwhile, due to thecomplexity of its theoretical model, it has always been the research difficulty in the field of Lovewave liquid sensor. This paper will give comprehensive study on Love wave device loaded withviscous liquid from the following aspects: theoretical modeling, mechanism analysis, optimal design,the peripheral circuit design and the construct of whole testing system.First of all, the paper introduces the operating principle of Love wave sensor, and the characterof IDT and the the field quantities analysis in piezoelectric medium. Then the paper elaborates partialwave theory and the surface effective permittivity method which can separate and solve the vibrationcomponents in piezoelectric medium and give a general way to research the excitation andpropagation characteristics of Love wave.On the basis of above theories and the propagation characteristics of acoustic wave in laminatedmedium, the theory model of Love wave device loaded with viscous liquid is established. Theboundary conditions and weighting coefficients of every partial waves are derived.Then the propagation characteristics of Love wave is analyzed based on the surface effectivepermittivity method. And the two-dimensional search model joined with a attenuation factor on thedirection of x3is derived for the situation when the wave energy is leaky.Taking36°LiTaO3as substrate with a SiO2film overlaid, the influences of liquid viscosity anddensity on propagation velocity of Love wave as the thickness of the film increase are numericallyanalyzed, the change of the velocity and attenuation sensitivity with IDT periodicity are numericallyanalyzed, the thickness of the film is optimized and the Love wave device is designed according to thesimulation results.Love wave device is fabricated and tested. To improve the characteristics of the Love wavedevice, three kinds of optimal design for IDT are raised and those new Love wave devices are testedand compared.By numerical calculation and experimental analyses, the validity of liquid viscositysensing by love wave device is proved.In the part of measurement circuit, three kinds of measurement principles are introduced andcompared. Meanwhile, the way of combine phase difference measurement and amplitude-frequencymeasurement in application is analyzed and stated in detail. Finally, based on the Love wave device and measurement circuits designed above, the dualchannel system of Love wave device for the measurement of liquid viscosity is built. And theexperimental results prove the effectiveness of the system. |
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