Simulation Of The Effects Of Stress On Crystal Resonator

Quartz crystal resonator is a resonant frequency control device used to provide frequency standard.As the "heart" of modern electronic communication system,with the increasing requirements of electronization and informatization in the fields of aerospace,military industry,national defense,machinery and chemical industry for frequency reference source,the requirements for various parameters of quartz crystal resonator are also higher and higher,which also puts forward higher requirements for its basic research.In this thesis,the vibration modes and frequency changes of crystal resonators under different conditions are studied by ANSYS.The main contributions of this thesis are as follows.1.The finite element simulation model of AT cut circular crystal resonator is established,and its low-order vibration modes under different boundary conditions are simulated and analyzed..The modeling software used in this thesis is ANSYS Mechanical,which is modeled through APDL command flow.In the resonator,because the electrode is connected to the crystal surface,it is equivalent to adding mass to the crystal surface,which will also affect the vibration of the resonator.In order to more accurately and conveniently study the influence of various size parameters of the electrode on the vibration of the resonator,the shell element modeling method which can best describe the electrode structure is adopted in the modeling.In this model,the shell element is used to describe the electrode,and the solid element is used to describe the quartz wafer.The energy trapping effect of the thickness shear vibration of the crystal resonator is simulated.Then,the low-frequency vibration modes of AT cut crystal resonator under free boundary conditions are analyzed by finite element method.On this basis,the low-frequency vibration modes of the resonator under constraints and stress are analyzed,which makes preparations for the subsequent study of the thickness shear vibration of quartz crystal resonator under stress conditions.2.The working modes of quartz wafer and electrode of crystal resonator under different parameters are simulated by finite element method.The change of quartz wafer diameter has little effect on the crystal frequency,but the inappropriate diameter size will increase the coupling degree of crystal parasitic vibration,and then affect the vitality of crystal vibration.The increase of quartz wafer thickness will lead to the decrease of frequency,and too large or too small thickness will affect the thickness shear vibration of the resonator.Therefore,in the design of quartz wafer,its diameter should be considered first,and then the wafer thickness should be determined.The error caused by the cutting angle of quartz wafer will also affect the resonator,and the mass adsorption effect will also lead to the frequency drift of the resonator.This thesis also analyzes these factors.For the electrode part,the effects of the electrode diameter and electrode thickness to the crystal resonator are analyzed respectively.The electrode diameter mainly affects the coupling degree of the thickness shear vibration of the resonator,and the frequency offset of the resonator will be caused by the mass effect.The thickness of electrode only affects the frequency of the resonator and has no effect on the working mode.Therefore,in the design of resonator,the appropriate electrode diameter can be designed according to the selected quartz wafer frequency,and then the thickness of the electrode can be processed to obtain the required resonant frequency.3.The temperature frequency characteristics and force frequency characteristics of the resonator are verified by simulation,and the method of force frequency characteristics compensating temperature frequency characteristics is verified.Firstly,the frequency offset of the crystal resonator under different angles of stress and constraints is simulated,and the results basically accord with the force sensitive characteristic curve.The simulations are also carried out for different sizes of stress and the results are fitted with data,and it is concluded that the frequency shift caused by different stresses basically shows a linear proportional relationship.Then the temperature frequency characteristics are analyzed and verified,and the scheme design and simulation experiment are carried out to compensate the frequency offset caused by temperature change through the force frequency characteristics.It is concluded that the strip compensation film in the x-axis direction of the crystal sheet is the best coating shape,and the best thickness of the coating is 0.5 times the electrode thickness.This method reduces the cost and consumption,and has a certain inspiration for the improvement of the frequency stability of the resonator.