**Thermoelastic Energy Dissipation under Multiphysics Coupling of Typical Micro Structure(Material)**

Author:Li Chang Long

Supervisor:gao shi qiao

Database:Doctor

Degree Year:2017

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Pages:168Size:5060K

Keyword:Energy Dissipation，frequency shifting，MEMS，multiphysics coupling，size effect，thermoelastic damping

As the MEMS system technology has been growing remarkably and applying extensively in the area of aerospace and smart weapons,the higher requirements are proposed for its performances,such as sensitivity and low power consumption.At present,the majority MEMS system is working at the multiphysics coupling environment,such as micro gyroscope and piezoelectric harvester,which involve in multiphysics coupling of force field,electric field and thermal field.Among them,the thermal coupling field will cause thermal dissipation problems in the micro structures,which include the decreased quality factor,the shifted natural frequency and the reduced harvesting efficiency.However,the analysis of thermal coupling problem is too superficial to further improve the micro system performances,such as sensitivity,resolution,quality factor and harvesting efficiency.Therefore,the research of thermoelastic energy dissipation mechanism is a key problem that urgently needs to be studied,which has important academic value and application potentiality.In this paper,the force-electric-thermal coupling model for analyzing thermoelastic coupling problem is established,which based on the micro structure and material’s every single physics field.The mechanical electric coupling and thermal elastic coupling control equations of micro structures are established,also,the piezoelectric coupling and piezoelectric thermal elastic coupling control equations of piezoelectric harvester are derived.With that,the theory base is formed for analyzing the effect of thermal elastic coupling on micro structure and piezoelectric material.Considering that the transformation of energy exists in multiphysics coupling,the thermal energy dissipation problem will generates while the irreversible heat energy loses.Meanwhile,the shifted frequency and decreased quality factor problems of microstructure will come out due to thermal elastic dissipation.Thus,in this paper,the thermal elastic coupling characteristics of the cantilever and the comb finger structure under different vibration manners are discussed.The thermal elastic coupling motion differential equations are derived,which are based on the Euler-Bernoulli theory and thermal conduction model.By means of numerical calculation and simulation,the variation of structure frequency shifting and thermoelastic damping are studied.Moreover,the effect of structural geometry size,boundary conditions,electrostatic parameters,environment temperature and material properties on the thermoelastic dissipation of micro structure is analyzed.With that,the influences of thermoelastic dissipation on the micro gyroscope performances are researched.In order to realize energy harvesting from outside environment,the piezoelectric material can be applied on structure to form the piezoelectric harvester.Also,the thermoelastic dissipation will influence the performances of piezoelectric harvester,which is reflected on the energy harvesting efficiency variation.Therefore,in this paper,the effect of thermoelastic dissipation on the piezoelectric harvester is discussed with the numerical calculation,simulation and experiment verification methods.The influences of thermal field on piezoelectric structure under different vibration manners are derived,and the thermoelastic dissipation characteristics within different coupling forms are researched.Meanwhile,the piezoelectric structure thermoelastic dissipation characteristics variations are discussed under structure geometry size and piezoelectric layer material.Base on that analysis,the effect of piezoelectric thermoelastic dissipation on the piezoelectric harvester is studied.In addition,when structure geometry size is decreased to the level of micro or much smaller scale,at this time,the geometry size will close to the material particle size.Thus,the material particle size will influence the structure performance which cannot be ignored.Therefore,the material particle size and its nature characteristic need to be adequately considered when we analyze the structure thermoelastic vibration.In this paper,based on the microscale theory,the size-dependent thermoelastic coupling control equations of micro beam and piezoelectric structures are established.And,the influence of size-dependent thermoelastic coupling effect on the micro structure is considered.Meanwhile,the comparison is made between size-dependent thermoelastic dissipation and the thermoelastic dissipation within classical elastic theory.At last,under different material characteristic size,the relationship between size-dependent thermoelastic damping,structure frequency shifting and different environment temperature,material properties,geometry size is researched.