Nonlinear Electro-Mechanical Behavior of Carbon Nanotube Based NEMS Actuators under Electric Fringing-Fields Actuation

The principal aim of the proposed research is to develop an electro-mechanical model and utilize it to investigate the nonlinear structural behavior of carbon nanotubes electrically actuated using fringing electric fields. A critical issue for the commercialization of nano-devices made with carbon nanotubes as principal components is their survivability when actuated electrically by the classical parallel-plates type of actuation. This type of actuation configuration can lead to various damage mechanisms, such as stiction and related short circuit problems (due mainly to the so-called pull-in instability) of the carbon nanotube based nano-structures. The proposed work aims to suggest a novel and efficient actuation approach that is capable of stimulating the motion of the carbon nanotubes structures without any short circuits problems. One of the configurations we will consider in this particular research is the electric fringing-fields arrangement. In this arrangement, the resultant actuating load is produced by the unevenness of the fringing electric fields, mainly due to an out-of-plane asymmetry of the actuated beam (the carbon nanotube in our case) and its two actuating stationary rectangular electrodes. Such an investigation can shed light on the potential of utilizing carbon nanotubes as reliable nano-scale devices and actuators of pull-in free behavior. In this research project, we will focus on two commonly used carbon nanotubes based structures: clamped-clamped and cantilever. Several examples of nanotubes, of various natural frequencies, of real devices in the literature will be studied to span variety of geometrical and loading situations. The fringing-fields electric force will be estimated through fitting the outcomes of a 2Dl numerical solution of the electric problem using Finite-Element Method (FEM) algorithm. Then, we propose to examine the influence of the design parameters on the actuating resultant electrostatic force in this particular arrangement. Four key design parameters will be considered: the geometrical properties of the actuating electrode (width and thickness) and the actuated carbon nanotube (radius) as well as the lateral and vertical separation distances between the both electrodes. Through several simulations, we will manage to show the effect of the lateral and vertical offsets as well as the electrodes thickness in the optimization of the performance of the actuator in such configuration. We will also try to simulate the effect on the resultant actuating force level with the electrode thickness as well as the electrodes lateral separation distance. For the electro-mechanical model of the nanotube based actuator, a reduced-order model (ROM) will be derived using the Galerkin expansion with mode-shapes of each considered beam as basis functions. The ROM equations will then be solved numerically to compute the structural behavior of the considered nano-actuator under the applied electric field. We will generate several curves for the electric forces versus shock amplitude for various values of the nondimensional design parameters of the ROM. These curves will present valuable information about the new actuator configuration and the fringing-fields electrostatic forces and how to utilize this interaction to build new devices and propose new technologies in the nano-scale.