Theoretical and Numerical Analysis of Active Switching for Narrow-Band Thermal Emission with Graphene Ribbon Metasurface

Components smaller than the wavelength of electromagnetic waves are called meta-atoms. Thermal emission can be controlled by an artificial structure in which these meta-atoms are arranged on the surface. This artificial structure is called a metasurface, and its optical properties are determined by the materials and shapes of the meta-atoms. However, optical devices may require active control of thermal emission. In the present study, we theoretically and numerically analyze a wavelength-selective emitter using a graphene ribbon metasurface. The graphene ribbon metasurface consists of a graphene ribbon array, potassium bromide thin film, and silver substrate. The geometric parameters of the graphene metasurface are determined based on an equivalent circuit model that agrees well with the results of the electromagnetic field analysis (rigorous coupled-wave analysis). The proposed emitter causes impedance matching depending on the conductivity of the graphene ribbon in a very narrow wavelength range. The conductivity of graphene can be actively controlled by the gate voltage. Therefore, the proposed emitters may realize near-perfect emission with a high quality factor and active controllable switching for various wavelengths. In addition, the quality factor can be changed by adjusting the electron mobility of graphene. The proposed emitter can be used for optical devices such as thermophotovoltaic systems and biosensing.

Metalens Antennas in Microwave, Terahertz and Optical Domain Applications

Metamaterial is the artificial structure under sub-wavelength dimension and could be designed to manipulate the electromagnetic wave radiation across the broad frequency range through microwave to much higher frequency, such as terahertz and optical regime. Lens antenna can generate the focused beam with high gain and shrink the bulky refractive body and feeds into a shape of flat form. This chapter will discuss the general concepts of metalens and the technology of metalens-based antenna at microwave, terahertz and optical frequency. The recent progress in the research and development of metalens antennas is reviewed with designs principle and typical applications. At last part, some innovative techniques such as dynamic focus-tuning of metalen are discussed in details.

Static and dynamic analysis of the interface between the transport structure and the approached embankment

The article is devoted to the analysis of static and dynamic calculation of the interface of an approach embankment to artificial structures, such as a railway bridge and culverts? the main indicator of the stable operation of an approach embankment to an artificial structure is the stiffness of the base. Calculations are performed in the Midas software package, taking into account the interface of the transition sections from the unfixed roadbed to its fortified part with bored piles and the bridge abutment. A static loading scheme with a C14 time load and a dynamic loading scheme for an approach embankment with a time load from a high-speed train (South Korean KTX20 cars standard norms – 17,335 tons per wheel, 34,67 tons per axle) are considered, and the results are analyzed and compared. The analysis of calculation results is made. The boundary conditions are taken as "Springs on the base surface" – "Ground Surface spring". This function allows you to automatically create elastic or viscous boundary elements that are necessary for performing dynamic calculations. When selecting a grid, boundary conditions are automatically created on the left/right border of the selected grid, and an elastic constant is automatically calculated based on the material properties assigned to the elements. Based on the research, recommendations were made for the development of a detailed model, taking into account the dynamic impact of rolling stock on an artificial structure.