Steady and Unsteady Thermo-Strucural Simulation of Thermally Actuated Micro- and Nano-Structures
This dissertation provides a thermo-structural simulation for nano-scale and micro-scale structures with pinned and fixed boundary conditions which are either thermally positioned, buckled, or actuated. The study begins with simulating a pinned-pinned beam in micro-scale and nano-scale. The steady state thermo-structural equation is solved numerically using an implicit Finite Difference method implemented in Matlab to obtain the thermal positioning response, which is the thermally steady state center displacement, by adding a constant, time-independent heat flux to the structure. The results show the steady state thermal displacement of the system is a function of the geometry, pressure, material properties, and constant heat flux in the free molecular model, while this value is independent of pressure in the continuum model. The thermal positioning simulation is used to improve the thermal efficiency of a thermal micro-switch by introducing various heating configurations. The second thermal mode is thermal buckling which is used to introduce a new thermal buckling storage nano-memory. Using an unsteady simulation, the power requirements for thermal actuations, optimal geometry, and write time of the device for various materials are investigated. The results show that this memory consume a low power in the order of 1 nJ per bit and has a data storage density of 10e11 bits/cm3,which is acceptable in comparison with the current memory devices. Thermal buckling nano-memory is also radiation-protected, making it a good alternative for space exploration computer systems operating in high radiation and electromagnetic environments. In contrast with thermal positioning and buckling, thermal actuation applies time-dependent heat load leading to vibration in the structure. An implicit Finite Difference method implemented in C++ was used to solve the coupled transient thermo-structural equations with constant thermal properties, while an explicit approach was used to solve the variable properties thermo-structural equations. The response, the center displacement in a doubly-clamped bridge, is tracked by time and decomposed to the steady state and vibration amplitudes. The results show that constant thermal properties assumption is limited for small heat additions lower than 1 mW. Thermal actuation results are applicable in simulating the dynamic behavior of nano-scale devices used for switching, nano-manufacturing, and measurement.
MEMS and NEMS, Thermal actuation, Heat transfer
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