A Frequency Reconfigurable Antenna based on Few Layer Graphene

In this paper, a frequency reconfigurable antenna was presented. This antenna is made up of a square loop and a microstrip line with a gap, in which the few layer graphene (FLG) sheet is located to achieve frequency reconfigurable. FLG is likes a lumped resistor with resistance. And the surface impedance can be adjusted by applying a direct current bias voltage, which obtains two work modes that imitate switch. Additionally, the experimental evidence show the proposed frequency reconfigurable antenna can provide a tunable bandwidth.

Investigation of the Influence of Direct Current Bias on Transformer Vibration

As a necessary electrical equipment for the construction of power grid, the safety and reliability of the transformer is the focus that people have always paid attention to. In recent years, the DC bias of the transformer has a serious impact on the safe operation of the power system, which has attracted wide attention of scholars at home and abroad. In view of this phenomenon, combined with the basic principle of transformer excitation, the simulation of the DC bias phenomenon is carried out by using Simulink software in this paper. According to the simulation results, the distortion characteristics of excitation current under DC bias are summarized. Then, based on the variation characteristics of excitation current under over excitation and DC bias, the law of transformer core vibration is deduced, and the cause of transformer abnormal vibration under DC bias is revealed. Finally, by analyzing the data of a transformer substation running under DC bias, it is found that the measured data are basically the same with our simulation results, which provides a basis and reference for further research on the phenomenon of transformer DC bias.