No abstract

In this paper, a nondiffracting beamforming scheme employing 3-bit coding metasurfaces to adjust the beam lengths is proposed. The 3-bit coding is implemented with a four-layer phase control unit whose phase can be adjusted by tuning the side length of the metal square. Simulation and measured results show that the electric field distributions generated by the metasurface is independent of the polarization of the incident wave due to the central symmetry of the structure. Experimental results are provided which verifies the feasibility of the proposed scheme in adjusting the nondiffracting beam lengths. A relative error as small as 6.0% in the beam lengths is observed, and all results prove the proposed 3-bit coding metasurfaces can be applied to generate different nondiffracting beam lengths.

A district energy system based on “thermal bus” was proposed, in which the heating and cooling water transmission processes shared one set of the distribution pipe network. Combined with the gas energy stations, ground source heat pumps, small-scale photovoltaic power stations and rooftop solar collectors and other facilities, it provided the users in the region with heating in winter, cooling in summer and power supply all year round. From the perspective of the bidirectional (supply/return) flow of heat energy along the thermal bus, the mathematical model of the main equipment applied for the source, pipe network, load and storage was established. The optimization model with the lowest system operation cost was proposed considering the fuel cost, the external electricity purchase fee and the satisfaction degree of all users' energy demand. The operation cost and energy consumption of the regional energy system scheme and the traditional distributed energy system scheme are studied by a practical case study. The results showed that the new scheme reduces the operating cost by 21.5% and 16.8% respectively under the typical weekly scenarios of cooling in summer and heating in winter. When no storage equipment was used, the new scheme reduced the amount of purchased electricity in summer and winter by 4.1% and 5.2% respectively.