Elegant design of carbon nanotube foams with double continuous structure for metamaterials in a broad frequency range

Carbon nanotube (CNT) foams with negative permittivity and permeability are successfully prepared by chemical vapor deposition (CVD) and post-treatment. A double negative metamaterial in the 1-1000 MHz frequency range with double continuous structure results by effectively compounding the CNT foam with a polymer material, i.e. epoxy or nanosilver silicone resin. The negative permeability is specifically attributed to the three-dimensional CNT interactions as clear from the study of the relation of the material microstructure and the macroscopic measurements. Compared to CNT foam/epoxy composites, CNT foam/nanosilver/silicone composites have a lower permeability but a more excellent electrical conductivity or permittivity. It is also shown that the carbon source time during CVD and post-pressurization can be adjusted to allow for both negative permittivity and permeability. This contribution highlights a convenient method to obtain a metamaterial in a much larger frequency range (ca. 1 to 1000 MHz) than the state-of-the-art. It thus supports the expansion of the application range of metamaterials and simplifies their preparation, which is of great significance for the wider use of these materials

Preparation and electrochemical performance of hollow activated carbon fiber self-supported electrode for supercapacitor

Hollow activated carbon fiber (HACF) with high specific surface area and high charge storage capability was prepared by pre-oxidation, carbonization and KOH-activation from polyacrylonitrile (PAN). HACF was used as self-supported working electrode directly without any binder and conductive agent. The effect of the activation time on specific surface area of HACF was studied intensively. The results show that the specific surface area of HACF increased with the increase of activation time from 0.5 h to 1.5 h, and then decreased with further increase of activation time. Highest specific surface area of 1873 m(2)g(-1) and micropore volume of 0.61 cm(3)g(-1) were obtained in HACF activated for 1.5 h. Electrochemical properties of HACF can be improved with increase of activation time, but excessive activation results in the decrease of specific surface area and increase of internal resistance of HACF. The self-supported electrode of HACF possesses a large specific capacitance of 323 F g(-1) at 0.05 A g(-1) and 216 F g(-1) at 1 A g(-1). Therefore, HACF can be a promising self-supported electrode for high performance supercapacitors

A Visibility-based Algorithm for Multi-robot Boundary Coverage

Cell decomposition is often used in autonomous area coverage. We propose a visibility-based decomposition algorithm for single robot boundary coverage and a corresponding multi-robot algorithm in unknown environment. A graph data structure is exploited for completeness of coverage and incremental description of partially observed world. Visibility-based decomposition facilitates the construction of graph and algorithms operated on it. In the context of multi-robot, a dynamically selected highest priority robot is in charge of information share and synchrony through communication, polygon set operations provide tools for environmental information mergence, a distributed algorithm for multi-robot boundary coverage is proposed based on those technologies. Finally the experimental results show the relationships between robot number and traversable gate number, some future subjects of researches are introduced

A Visibility-Based Algorithm for Multi-Robot Boundary Coverage

Cell decomposition is often used in autonomous area coverage. We propose a visibility-based decomposition algorithm for single robot boundary coverage and a corresponding multi-robot algorithm in unknown environment. A graph data structure is exploited for completeness of coverage and incremental description of partially observed world. Visibility-based decomposition facilitates the construction of graph and algorithms operated on it. In the context of multi-robot, a dynamically selected highest priority robot is in charge of information share and synchrony through communication, polygon set operations provide tools for environmental information mergence, a distributed algorithm for multi-robot boundary coverage is proposed based on those technologies. Finally the experimental results show the relationships between robot number and traversable gate number, some future subjects of researches are introduced

Combining carbon nanotube foam with nanosilver/silicone resin or graphene foam for advanced metamaterial design

Advanced metamaterials are designed upon the combination of (1) carbon nanotube (CNT) foam, which is obtained from chemical vapor deposition by fully consuming the initial nickel foam, and (2) nanosilver/silicone resin or graphene (Gr) foam. The CNT foam/nanosilver/silicone composite simultaneously exhibits a negative permittivity and permeability in the frequency range from 1 MHz to 1 GHz provided that the appropriate CNT foam amount is considered (20 m%). Double-negative performance in a similar frequency range is obtained with both 3/1 and 1/1 (mass basis) Gr/CNT-based composites. On the other hand, 3/2 (mass basis) Gr/CNT exhibits a negative permeability in the shared frequency range from 6 x 10(2) MHz to 1 GHz with still negative permittivity in the full range. The Gr amount allows to control the frequency behavior, with a variation in absolute permittivity and permeability values and a switch between a concave and convex behavior. Hence, the work contributes to the further expanding of the application range of metamaterials