| Carbon nanotubes (CNTs) with both hollow layer structure and unique electromagnetic properties are ideal quasi-one-dimensional nano-materials. At present, the electromagnetic wave (especially microwave) absorbing and shielding properties of CNTs is one of the focus research areas in materials science. Considerable advances have been made experimentally in exploring the microwave absorbing properties of CNTs materials. In recent years, some excellent microwave absorbing materials containing CNTs have been synthesized, having broad application prospects in both military stealth and microwave radiation protection. In this dissertation, the microwave absorbing mechanisms of intrinsic CNTs are studied systematically. We mainly investigate the hydrogen adsorption properties of CNTs, the microwave absorbing mechanisms of hydrogen plasma in CNTs, both the dielectric characteristics and the absorbing mechanisms of CNTs/polymer at microwave frequencies, and the microwave absorbing mechanisms of ferromagnetic metals-filled CNTs etc.The advances in researches for CNTs, such as structural characteristics, synthesis and purification, growth mechanics, physical and chemical properties, applications prospect, research fields, methods and achievements are reviewed entirely. Physical mechanism of electromagnetic wave absorbing materials is described. The research situation about the microwave absorbing materials containing carbon nanotubes are discussed systematically. The source of study and main study content are introduced in brief.Based on the experimental data for both the electromagnetic parameters and the microwave absorbing properties of CNTs, the microwave absorbing mechanisms of CNTs are investigated and revealed systematically. The following conclusions are obtained. (1) Under microwave irradiation, charge dipoles form on the surface of carbon nanotubes. The charge dipoles generate an inductive current in electromagnetic field. The inductive current then causes a loss current and energy dissipation. And the interaction of microwave electric field with charge dipoles causes crystal lattice libration, resulting in the losses of microwave energy through heating. (2)For helical CNTs, the cross-polarization of electromagnetic fields will give rise to the chiral microwave absorption. (3)Microwave is reflected and scattered repeatedly in the pore structures of CNTs, which could also lead to the loss of electromagnetic energy. (4)The structural defects of CNTs can enhance charge polarization, which will cause more dielectric loss. (5)CNTs have a series of novel physical effects, such as small size effect, effect of large specific surface area, quanta-size effect and tunneling effect, contributing to microwave absorption. (6)The complex permittivity of CNTs is large, but their microwave permeability is comparatively small. Therefore, intrinsic CNTs display weak absorption to microwave.The hydrogen adsorption properties of CNTs are first discussed, and then the microwave absorbing mechanisms of HiPco CNTs are investigated. Using double-fluid theory and phenomenological model, the complex permittivity, the attenuation coefficient as well as absorption coefficient of hydrogen plasma in HiPco CNTs at microwave frequencies are deduced. Then a microwave absorption model of hydrogen plasma in HiPco CNTs is developed. It is theoretically proved that microwave energy loss is predominantly caused by the collisional absorption of the charge particle in hydrogen plasma of HiPco CNTs. The numerical results indicate that both the maximum attenuation coefficient and the maximum absorption coefficient increase, and absorption peak shifts towards high frequency with liberal electron density increasing. Both the maximum attenuation coefficient and the maximum absorption coefficient decrease, and absorption peak shifts slowly towards low frequency with electronic effective collision frequency increasing. It is proposed that as long as liberal electron density in plasma in CNTs is modestly controlled, strong microwave absorption, for specified frequency range, can be obtained.Based on both the material microstructure-properties correlation theory and an equivalent resistance-capacitance(RC) network, the complex conductivity, the complex permittivity and electromagnetic wave absorption coefficient of CNTs/polymer composite are theoretically deduced in microwave frequency range using the logarithmic rule. Then a microwave absorption model, which can predict microwave absorbing properties of CNTs/polymer composite, is developed. In this model, the size and shape of CNTs, the real and imaginary parts of the permittivities of CNTs and polymer are considered in detail. It is theoretically proved that the addition of CNTs to the polymer result in explicit increases of the complex conductivity, complex permittivity and microwave absorption coefficient of the sample due to the RC network formation and introduction of conducting paths to the composites. In addition, a good linear relationship between microwave conductivity (or microwave absorption coefficient) of the composite and frequency is found.The preparation methods of metal-filled CNTs are described systematically. Then the microwave absorbing mechanisms of ferromagnetic metals-filled CNTs are investigated. It is theoretically revealed that strong microwave absorption by ferromagnetic metals-filled CNTs is predominantly caused by the magnetic resonance of ferromagnetic metal nanoparticles in the sample. It is found that resonance frequency vy shifts towards low frequency with the increase of ferromagnetic metals-filled CNTs film thickness, and vγshifts towards high frequency with ferromagnetic nanoparticle content percentage increasing in the sample. Thus, strong microwave absorption by ferromagnetic metals-filled CNTs can be realized via the control of the sample thickness or ferromagnetic nanoparticle content percentage among CNTs.The aim of this investigation is to supply valuable theoretical basis for the preparation of excellent microwave absorbing materials containing CNTs.
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