A three-dimensional finite element model of an electrothermal microactuator (so-called ‘hot–cold-beam actuator’) is developed using the ANSYSTM finite element analysis (FEA) simulation program (ANSYS 1992 User's Manual for Revision 5.5.1 (Houston, PA: Swanson Analysis Systems, Inc.)). The actuator is geometrically scaled (except the thickness) to explore the effect of dimension variation on the performance of the actuator. The model is then used to optimize the actuator for robust design. Two types of actuator are also studied here: one with a suspended polysilicon structure and the other with additional gold-layer deposition. The results reveal that a greater deflection can be obtained for gold-plated actuators. An L18 Taguchi matrix is developed to investigate the effects of dimensional variation on the performance of the actuator. It is found that total actuator length contributes the major influence to the performance of the actuator. A maximum deflection is realized as the cold-beam length reaches about 86% of the hot-beam length of the actuator. Experiments are also conducted to verify numerical data. The results are in good agreement with analytical simulations to a certain electrical current regime. Finally, our robust design concludes that a gold-plated actuator with a 250 μm long, 3.5 μm thick, 2 μm wide hot beam and a 215 μm long, 3.5 μm thick, 15 μm wide cold beam can deflect up to 20.2 μm at a driving current of 6.2 mA.

One of the key factors in designing a motor built-in high speed spindle is to assemble the motor rotor and shaft by means of hot-fit. Presented in this paper is a study of the influence of a hot-fit rotor on the local stiffness of the hollow shaft. Dynamic analyses of the rotor-hollow shaft assembly using contact elements are conducted. The normal contact stress state between the rotor and the hollow shaft is obtained through the use of contact elements with friction effects included. The normal contact stress, considered as the pr-stress between the rotor and the hollow shaft, is then adopted for subsequent modal analyses. In this study, the modal analysis results are verified by a modal testing experiment. The percent errors of the first natural frequency and the second natural frequency are down to about 0.58% and 0.79%, respectively.

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Understanding the interaction between hydrogen and carbon nanotubes is crucial to enhancing the performance of hydrogen storage and nanofluidic carbon-adsorbent systems. Accordingly, this study performs a series of molecular dynamics simulations to investigate the transport properties of hydrogen molecules confined within a flexible narrow carbon nanotube. The tube's diameter is 10.8Å at temperatures in the range of 100∼800 K. The particle loadings inside carbon nanotubes are ranging from 0.01∼1 No/Å. The results show that the hydrogen molecules exhibit three distinct diffusion regimes, namely, single-file, Fickian, and ballistic, depending on the value of the Knudsen number. In addition, it is shown that with the Knudsen number of less than 1, the tube-wall long wavelength acoustic phonons induced Rayleigh traveling wave prompts a longitudinal wave slip and compression-expansion of the hydrogen molecule crowds within the CNT, which leads to a significant increase in the mean square displacement of the molecules.

Developing a motor-built-in high speed spindle is an important key technology for domestic precision manufacturing industry. The dynamic analysis of the rotating shaft is the major issue in the analysis for a motor-built-in high speed spindle. One of the major concerns is how the motor rotor is mounted on the shaft, by interference (shrink) fit or else. In this study, dynamical analyses are carried out on a motor-built-in high speed spindle. The motor rotor is mounted on the spindle shaft by means of interference fit. Modal testing and numerical finite element analyses are conducted to evaluate the dynamical characteristics of the spindle. The stiffness of the shaft accounting for the interference fit is investigated for the finite element model of the spindle. This study also proposes an analysis procedure to dynamically characterize the high speed spindle with a built-in motor. Based on the results of modal testing and the numerical analyses, it may conclude that the proposed procedure is feasible for the spindle and is effective for other similar applications.