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Dynamic Characteristics Of Micro-Diaphragm Of Resonant Biochemical Sensors Considering The Effect Of Residual Stress

Posted on:2016-09-24Degree:DoctorType:Dissertation
Country:ChinaCandidate:H Y WuFull Text:PDF
GTID:1108330461985397Subject:Process and equipment engineering
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As an important sector in the research field of MEMS, resonant micro-diaphragm biochemical sensor has found wide applications in microbiology detection, chemical analysis, clinical medicine and environmental monitoring. The sensitivity and resolution of the sensor depend mainly on the dynamic characteristics of the micro-diaphragm. The dynamic characteristic of micro-diaphragm differs from that of macroscopic diaphragm due to the features of microstructure and the effects of microenvironment. The presence of residual stress is inevitable since the diaphragms are generally fabricated via surface micromachining processes; the flexural rigidity of the micro-diaphragm depends heavily on the attached mass; and at microscale, liquid media imposes a marked impact on the coupling of micro-diaphragms. Focusing on the burning issues of micro-diaphragms, the paper examined the impact of residual stress, liquid media, and attached mass on the dynamic characteristics of the micro-diaphragms. The work is meaningful for the development of detection techniques with resonant micro-diaphragm biochemical sensors.In this paper, the fabrication process and the structure of the micro-diaphragm were considered. The distribution of the residual stress in the composite membrane was analyzed. The method used to prevent buckling and to enhance the reliability and yield of the micro-diaphragm biochemical sensors was proposed. According to the analysis the residual stress of composite membrane was expressed with the equivalent in-plane stress and equivalent bending moment. The Ritz solution was performed to obtain the deflection of the composite membrane subject to initial in-plane stress load and bending moment load. Vibration characteristics of the composite membrane were analyzed using equivalent classical theory and the curved membrane with initial residual stress was modeled mathematically. The effects of the residual stress and the deflection on the natural frequencies of the sensors were studied. Results indicate that the distribution of residual stress imposes an obvious impact on the natural frequency and the deflection.The mechanical behavior of the micro-diaphragm with residual stress has the dual natures of micro-plate and micro-membrane. According to the mechanics model the analytical solution of micro-diaphragm with residual stress under clamped boundaries was derived. The value of residual stress parameter k was used to determine the diaphragm property. The transition from plate behavior to membrane behavior was described in terms of the residual stress parameter k. Then the variations of natural frequencies, mode shapes and amplitude with respect to the residual stress were analyzed.The mass and stiffness of the micro-diaphragm are changed due to the absorption of the sensitive layer. The distribution of the adsorbed mass is determined by the area of biomaterial immobilization. The paper considered the localized uniform adsorption and distributed uniform adsorption. The adsorption area was described by the step function and the extended equation of micro-diaphragm considering the adsorption was developed. To calculate the resonant frequency, Rayleigh-Ritz method was applied. The relations between the resonant frequency shift and the residual stress, distribution of the adsorbed mass, added mass, and the adsorbed stiffness were investigated.Considering the coupling effect of the micro-diaphragms and the liquid media, free vibrations of micro-diaphragms in liquids were analyzed for the extensive scope of applications in liquid environment. The micro-diaphragm movement was described by the dynamic equation of the diaphragm with residual stress. The liquid movement was described by the Laplace equation. The assumption of equal normal velocity of the liquid and the diaphragm was used to examine the coupled action. The assumed mode method and the Rayleigh-Ritz method were applied to solve the free vibration of fluid-diaphragm coupled system. The effects of residual stress and liquid media on the natural frequencies and on the mode shapes of the diaphragm in contact with liquid were presented. The results show that the natural frequencies using the Rayleigh-Ritz method have better accuracy. The difference between the dry and wet axisymmetric mode shapes turns to be more pronounced as the residual stress decreases.According to the structure of resonant micro-diaphragm biochemical sensors, the dynamic response model of the diaphragm with residual stress in contact with liquid on one side was built. The energy dissipation mechanism and damping characteristics during the vibrating process of micro-diaphragm in liquid were explored. The dynamic response of a sensor diaphragm with residual stress in contact with liquid was studied. It is shown that the residual stress imposes an obvious impact on the quality factor; the effect of the liquid is more significant for the membrane than the plate. The change of the displacement amplitude at the diaphragm center and the mass sensitivity displays an opposite tendency as the residual stress increases.In this paper, based on comprehensive consideration of the impact of residual stress, liquid media, and attached mass, the dynamic characteristics of micro-diaphragms were analyzed. The research results provided the basic theories for the optimization design, detection and control of resonant micro-diaphragm biochemical sensors.
Keywords/Search Tags:Dynamic characteristics, Micro-diaphragm, Resonant biochemical sensor, Residual stress
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