Transmission-type reconfigurable metasurface for linear-to-circular and linear-to-linear polarization conversions

We present a transmission-type polarization conversion metamaterial (PCM) whose functions can be dynamically switched among the linear-to-circular (LTC) and linear-to-linear (LTL) polarization conversions. The proposed PCM consists of a grating, a polarization conversion surface and a reconfigurable polarization selective surface incorporated with PIN diodes. By changing the states of diodes, the PCM can achieve the reconfigurable manipulations for incident waves. The Fabry-Pérot (F-P) resonances excited by the PCM contribute to the polarization conversions, as is illustrated. Moreover, through establishing the F-P-like cavity model and analyzing the electric field components of the transmitted waves, the conditions for realizing LTC polarization conversion are revealed, which can guide the construction of PCM. The prototype of PCM is fabricated and measured, which can achieve LTC and LTL polarization conversions within 3.31-3.56 GHz and 2.76-4.24 GHz, respectively, the polarization conversion ratios of two functions are higher than 0.95. The measurement results are in agreement with the simulation data.     

时间反演电磁波在金属丝阵列媒质中的超分辨率聚焦

本文利用一种已有的金属丝阵列结构, 验证了时间反演技术的时空聚焦特性, 并证明了在该阵列结构中, 时间反演电磁波具有超分辨率聚焦特性. 利用金属丝阵列能为凋落波提供传播渠道这一特性, 通过改变信号对时间反演镜的激励方式, 得到了多种亚波长异地成像的仿真结果. 本文的分析和仿真结果证实了利用时间反演技术, 可以采用传统的材料和设备, 在远场实现超分辨率聚焦成像, 并能在多个位置实现对源信号的提取和分析. 关键词： 时间反演 金属丝阵列 超分辨率聚焦 异地成像     

Design of a low-frequency miniaturized piezoelectric antenna based on acoustically actuated principle

An acoustically actuated piezoelectric antenna is proposed for low frequency (LF) band in this paper. The proposed antenna is theoretically calculated, numerically optimized by the finite element method (FEM), and experimentally analyzed. The measurement results show that the near-field radiation pattern of the piezoelectric antenna is similar to that of the electric dipole antenna. The radiation efficiency of the piezoelectric antenna is 3－4 orders of magnitude higher than that of electrically small antenna (ESA), with their sizes being the same size, and the maximum transmission distance obtained experimentally is 100 cm, which can be improved by increasing the input power. In addition, the gain, directivity, and quality factor of piezoelectric antenna are also analyzed. In this paper, traditional antenna parameters are creatively used to analyze the performance of piezoelectric antenna. The research conclusions can provide reliable theoretical basis for realizing LF antenna miniaturization.