Keming Ma

Preparation and low-frequency microwave-absorbing properties of MWCNTs/Co–Ni/Fe3O4 hybrid material

MWCNTs/Co–Ni/Fe3O4 hybrid material has been successfully prepared by electroless plating and coprecipitation method, which is applied to the low-frequency microwave absorption. Their surface morphology, structure, magnetism and electromagnetic properties in the low-frequency range of 1–4GHz were characterized by field-emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and vector network analyzer. Results indicated that magnetic Co–Ni/Fe3O4 particles were attached on the surface of multi-walled carbon nanotubes successfully. The saturation magnetization of MWCNTs/Co–Ni/Fe3O4 hybrid materials was 68.6emu/g and the coercivity is 17.9 Oe. The electromagnetic and microwave absorbing properties analysis in the low-frequency range of 1–4GHz indicated that the hybrid material exhibited excellent magnetic loss and the maximum reflection loss could reach −13.57dB at 1.51GHz with 1.05GHz bandwidth below −5dB.

Real-time monitoring of low-velocity impact damage for composite structures with the omnidirection carbon nanotubes’ buckypaper sensors

A novel, omnidirectional, nanomaterial-based sensor technology which can provide wide area damage detection of composite structures was proposed in this work. The behaviors of the buckypaper sensors subjected to both tensile and low-velocity impact were investigated. The experimental results showed that the rectangle buckypaper sensor has a large range of sensing coefficients from 21.40 to 35.83 at different directions under tensile. However, the circular buckypaper sensor has a steady sensing coefficient of about 155.63. Thus, the circular buckypaper sensor as a kind of omnidirectional sensor was chosen to monitor the impact damage. The low-velocity impact damage of composite structures is characterized by the gauge factor of omnidirectional buckypaper sensors and the results of C-scanning. Omnidirectional buckypaper sensors’ electrical resistance increases with repeated impact loading; composite structure elastic deformation and damage evolution can be identified from resistance change. Experiment results show that structure monitoring based on the omnidirectional buckypaper sensor not only can detect small barely visible impact damage flaws and the damage evaluation of composite structures subjected to impact but also can determine the location of low-velocity impact damage through the analysis of results. Through comparison with C-scan, the results have preliminarily demonstrated that the omnidirectional carbon nanotubes’ buckypaper sensor can serve as an efficient tool for sensing the evolution of impact damage as well as serve structural health monitoring of composite structures.

Very high S-band microwave absorption of carbon nanotube buckypapers with Mn nanoparticle interlayers

Flexible and high-performance electromagnetic absorbing materials of multi-walled carbon nanotube (MWCNT) buckypapers with Mn nanoparticles (NPSs) interlayer were fabricated via monodisperse solutions through layer by layer vacuum filtration method. The morphology and element composition of buckypapers were characterized by scanning electron microscopy, energy dispersive spectrometer, and X-ray diffraction. The formation of flexible MWCNT buckypapers with Mn NPS (0–30 wt. %) interlayer was attributed to nanostructure and morphology of the samples. When the blended Mn NPS content in buckypapers is 20 wt. %, there are evidently two larger absorption peaks (−13.2 dB at 3.41 GHz, −15.6 dB at 3.52 GHz) of the buckypaper with an absorbing thickness of 0.1 mm. The fundamental microwave absorption mechanism of the buckypapers is discussed. This work opens a new pathway towards tuning microwave absorbers performance and this method can be extended to exploit other excellent microwave absorbers with interlayer.