Steady-state and transient analysis of electro-thermal microactuators using finite element methods

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Title: Steady-state and transient analysis of electro-thermal microactuators using finite element methods
Author: Atre, Amarendra
Abstract: Recent techniques in radar and communication systems favor the development of phased arrays. The major problems to such systems are size and cost due to the large number of individual transmit/receive modules required. Photonic systems implemented in MEMS technology have reduced bulk optical systems to microscale proportions. This reduction in scale is particularly important to phased arrays since it allows flexibility in deployment. This thesis aims to understand the steady state and transient characteristics of an electrically heated, thermally driven, surface micromachined MEMS polysilicon beam flexure actuator to be employed for the rotation of an r-f phase shifter utilized in phased array systems. The characteristics of the thermal actuator are examined through finite element analysis by investigating the relative importance of the temperature dependencies of the material properties of MUMPs polysilicon. The comprehensive finite element model of the thermal actuator developed using ANSYS 5.6, a commercial finite element package, has the ability to include full temperature dependencies of all parameters and also has the capacity to impose all heat transfer modes, which are beyond the capabilities of current analytical models. Steady-state thermal profiles of the thermal actuator are presented for the thermal actuator in an environment of air and vacuum. The model is validated indirectly by comparing the steady-state deflections with measured data of six thermal actuators of different geometries. The finite element simulations are also validated with a previous analytical model to compare model accuracy. The dynamic behavior of the thermal actuator is examined in both air and vacuum, which gives an insight into power and energy consumption of the thermal actuator. Initial results show a limited power and energy savings for the thermal actuator operated in vacuum over that operated in air. Design optimization of the thermal actuator is investigated using the ANSYS Parametric Design Language (APDL) with the Subproblem Approximation Method for maintaining low power consumption. An indirect method is employed by maximizing the steady-state deflection for unloaded actuators and minimizing the steady-state deflection for loaded actuators for the same applied voltage. A significant reduction in power consumption with an increase in the maximum steady-state deflection has been observed for unloaded actuators. For loaded actuators the available force output is increased slightly, the steady-state deflection decreased slightly and the power consumption increased slightly.
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Date: 2003-06

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