Search

A reflective beam splitter is proposed and verified. The unit cell of the beam splitter is composed of a metal pattern, a dielectric substrate, and a metallic ground. Each subarray structure of the device is composed of four unit cells, which are gradually rotated at 45°. The horizontal and vertical subarrays form a 4×4 gradient metasurface supercell. In the operating frequency band, the incident linearly polarized terahertz wave is reflected and divided into four beams of approximately equal power but different propagation directions. The proposed terahertz beam splitter based on metasurface has the advantages of small size, low cost and easy processing, and can be applied to terahertz stealth and imaging.

In this paper, a transmissive terahertz (THz) quarter wave plate (QWP) has been proposed to realize the linear-to-circular polarization conversion in terahertz range. This quarter wave plate is composed of two dielectric layers and one metallic layer with asymmetric cross slots. In the range of 0.894–1.378 THz, the axis ratio of proposed device is less than 3 dB, and its polarization conversion efficiency is more than 45%. The distributions of surface currents and electromagnetic field density had been proposed to understand the physical mechanism of proposed device. The linear-to-circular polarization conversion can be attributed to the asymmetric transmission along slots. Finally, the simulation results are validated by experiments in terahertz region. The proposed device has simple geometry and good performance, which can be used as a key component in applications of terahertz communications, terahertz imaging and terahertz sensing.

The boiler air distribution system has an important influence on the stable operation of the thermal power unit. It directly affects the combustion efficiency, which in turn affects NOx emission of the boiler. However, boiler efficiency and NOX emission are a pair of contradictory goals, which will be one-sided if one is adjusted separately. In addition, thermal power units often face the impact of variable boundary conditions in operation. In this study, DNN-PSO modeling optimization was performed on air distribution system of a 1000MW double-tangential boiler. The deep neural network (DNN)is used to establish the boiler’s air distribution system model, and the particle swarm optimization algorithm (PSO) is used to optimize the opening of the secondary air baffle and the over fire air baffle. According to the on-site adjustment test based on the optimized guidance value, the NOX emission was reduced by 36.31mg/Nm3, and the boiler efficiency was increased by 0.09%, which proved the feasibility of using this model to guide the operation of the boiler air distribution system.

A tri-layered terahertz metamaterial based on the gratings-polarization converter-gratings (GPCG) structure is proposed, which is composed of a double L structure array sandwiched by two orthogonal metallic sub-wavelength gratings (SWGs). Simulation results show that two cascaded Fabry–Perot-like resonance cavities result in broadband polarization conversion with significant asymmetric transmission (AT) phenomenon. The improved polarization conversion rate (PCR) is over 0.99 from 0.20 THz to 1.97 THz with a relative bandwidth of 163.13%, almost 1.74 times that of other work, and the enhanced AT parameter is beyond 0.8 from 0.37 THz to 1.73 THz with a relative bandwidth of 129.52%. Moreover, in a wide range of incident angles, the proposed metamaterial maintains great AT performance, thus showing great potential applications in circulators, direction-dependent polarization converters and polarization-sensitive sensing and imaging.

The micro-mechanism of the silicon-based waveguide surface smoothing is investigated systematically to explore the effects of silicon-hydrogen bonds on high-temperature hydrogen annealing waveguides. The effect of silicon-hydrogen bonds on the surface migration movement of silicon atoms and the waveguide surface topography are revealed. The micro-migration from an upper state to a lower state of silicon atoms is driven by silicon-hydrogen bonding, which is the key to ameliorate the rough surface morphology of the silicon-based waveguide. The process of hydrogen annealing is experimentally validated based on the simulated parameters. The surface roughness declines from 1.523 nm to 0.461 nm.