Energy conversion of nano-cantilever beam with forced vibration in low vacuum housing

Abstract

The study of damping as the micro-resonator is vibrating has been a most important aspect which effects and pushes the development of resonator. The most effective measure to achieve high working capability is to encapsulate the resonator structure in housing where air is rarefied. However, in most cases, it is very difficulty to realize the absolute vacuum in the housing. Therefore, it is important to study the effect of damping for resonator. In this paper, nano-cantilever beam which is widely used in resonator is analyzed, and molecular dynamics simulation method is used to study energy conversion problem when the beam is encapsulated in different vacuum degree housing. The width and high of the nano-cantilever beam is equal and is 2.172nm, and the length is 10.860nm. By adopting Tersoff function, potential energy between beam atoms is calculated. After relaxation, it is found that the length of beam is shorten about three percent, and the area of cross section is increased slightly, furthermore the area of cross section on two end sides is lightly more than the area of the middle cross section of the beam. On the other hand, the distortion of the beam with forced vibration is simulated on the condition that the pressure in the housing is from 1000pa to 1pa. From experimental data we can found that the losing energy for collision between air molecules and beam atoms is gradually decreased with the pressure reduced. In the same condition, the losing energy is almost linear increasing with the time increased. The line slope was decreased from 0.03934362 at 1000pa pressure to 0.00003964 at 1pa pressure. When the pressure in the housing js reduced to zero, namely absolute vacuum, the energy got by the beam from outside force is changed periodically with the time change. For the energy from beam gravity is at 10-12 ev degree, the gravity effect for whole beam system is so small that it can be neglected as well as the macro-structure. The above-mentioned results are useful to design and optimize the parameters of nano-structure, and provide the academic foundation for MEMS/NEMS developing