A novel triple-walled carbon nanotube screwing oscillator: a molecular dynamics simulation

Abstract

A novel triple-walled carbon nanotube (TWCNT) screwing oscillator is proposed, in which screwing motion signals of both inner tube and middle tube are outputted simultaneously by applying an axial excitation to the inner tube and a rotating excitation to the middle tube. The molecular dynamic method is used to investigate the oscillatory behavior of the TWCNT oscillator under screwing motion. In the simulation process, the fixed outer tube acts as the oscillator stator, while the inner tube and the middle tube keep free oscillation after applying a certain initial excitation respectively. The simulation results show that the rotation frequency of the inner tube increases with the increase of the initial rotation excitation frequency of the middle tube when the inner tube is pulled out at a certain distance, and eventually tends to a stable value slightly lower than the rotation excitation. When the applied initial rotation frequency is within 400 GHz, the self-excited stable ration frequency (<inline-formula><tex-math id="M4">\begin{document}$ {\omega _{\rm{I}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="22-20200821_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="22-20200821_M4.png"/></alternatives></inline-formula>) of the inner tube can be expressed as a function of the initial rotation excitation frequency (<inline-formula><tex-math id="M5">\begin{document}$ {\omega _{{\rm{M}}0}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="22-20200821_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="22-20200821_M5.png"/></alternatives></inline-formula>), <inline-formula><tex-math id="M6">\begin{document}$ {\omega _{\rm{I}}} = 46{{\rm{e}}^{0.0045{\omega _{{\rm{M0}}}}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="22-20200821_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="22-20200821_M6.png"/></alternatives></inline-formula>. Although increasing the initial rotation excitation frequency can enhance the rotation frequency of the inner tube, as the initial rotation frequency of the middle tube increases, the axial performance of the inner tube is degraded and the unstable oscillations is aggravated. At the same time, the stability of the axial oscillation of the middle tube is related to the frequency of the initial rotational excitation applied to it. Too high an initial rotational frequency will not only increase the off-axis rocking motion distance, resulting in a degradation in axial oscillation performance, but also the rotation loss will increase as the initial rotation frequency increases. Therefore, a reasonable control of the amplitude of the initial rotation frequency is the key to designing a low-loss TWCNTs screwing oscillator.