DYNAMIC ANALYSIS OF CARBON NANOTUBE BASED NANO RESONATORS

Abstract

Carbon Nanotubes are a lately discovered allotrope of carbon with a cylindrical carbon molecule structure. Carbon nanotubes were discovered by Sumio Iijima in 1991. Since then, these have gained much attention, both from the research point of view and from practical applications point of view. Carbon nanotubes can be applied to a broad area of applications such as nanotechnology, electronic devices, biological sensing, and many more areas including material sciences. They demonstrate a very high strength and specific electrical properties. CNTs also have very good thermal conducting properties. In the present work, dynamic analysis of carbon nanotube based resonators has been done where the excellent mechanical properties of the CNTs are used to study its dynamic characteristics which can be used in many sensing applications. CNTs have a remarkable mechanical properties with its young’s modulus taken as 1 TPa if considered isotropic (ideal case) which is approximately 5 times higher than that of the steel. But in real cases it is anisotropic in nature with elastic modulus 4.2 TPa which is even more higher. CNTs have huge applications based on the mechanical strength, forming nano-composites, in building automobiles body and chassis. The very next thing which CNT is capable of it’s the mass sensing. It has been observed that the CNTs are sensitive to mass as small as 10-28 kg, this implies that it can sense a smallest change in the attached mass of the particle and this change in the mass is incorporated by the change in its dynamic characteristics i.e. frequency and mode shapes. Also, it not only shows a change in its dynamic character when a mass is altered but also to the position where it is attached. The primary objective of this work is to study the dynamic analysis of carbon nanotube based resonators. The computational methods employed in this work includes: Continuum Mechanics approach and molecular structural mechanics approach using finite element method. Modal analysis of CNT based nano-resonator has been done for various combinations of masses and its locations. This is important from the sensing point of view that how the natural behavior of nanotube is changing with attachment of different masses and their magnitude. iv Firstly, Continuum mechanics approach has been applied to study the effect of mass variations on single-walled CNTs. The effect of different positions of mass over the length of single walled carbon nanotube on the computed frequencies and mode shapes have been investigated for possible applications of vibrating mass sensors or electromechanical resonators. Theoretical results has been obtained for the CNT in the fixed-free configuration and validated the use of continuum mechanics approach in mass sensing applications and the comparison have shown an optimum level of resemblance between the results of the theoretical model derived and the computational technique employed. Also, the simulation of responses of SWCNT modeled as a space frame structure with each bond treated as a beam element has been done using finite element method. The resonant frequencies of these fixed-free structures are studied. According to the analysis, there is a shift in the natural frequencies of single-walled CNTs in different modes which is due to the changes in the position of mass over the length of the individual carbon nanotube and also due to change in the magnitude of mass at the free end of the nanotube. These results indicate that the sensitivity of SWCNTs decreases initially as we move towards the fixed end and then increases. Based on this sensitivity feature of the CNTs an application has been proposed which is used to check the pollution level from the vehicles and if implemented practically can solve the problem of air pollution taking place due to automobiles to some extent.