Research And Design Of Active Wave-transmitting Stealth Integrated Materials

Frequency Selective Surface（FSS）plays an important role in many civil defense communication systems due to its spatial filtering properties.In many applications,it is highly desirable that the electromagnetic metasurface only transmits the signal within the desired frequency band,with out-of-band signals being absorbed.However,the application range of traditional passive wave-transmitting stealth integrated materials is limited due to problems such as excessively thick profile and non-adjustment.This thesis intends to break through the performance limit of traditional passive electromagnetic structures by introducing active components such as active circuits and active components（switching diodes,varactors）into electromagnetic metamaterials.This dissertation takes active electromagnetic materials as the research topic,and focuses on the wave-transmitting broadband tunable absorbers based on switching diodes and varactors,narrow-band wave-transmitting absorbers based on electrical and mechanical tuning,and non-foster circuits（Non-Foster Circuits,NFC）low-frequency wave-transmitting stealth integrated materials,the main research content is divided into three parts.First,a new method to realize adjustable frequency selection is proposed.The structural inductance and structural capacitance are realized by using the metal strip line.In order to realize the functions of electrical adjustment and electrical switchability,the switching diode and the varactor diode are introduced into the structural capacitor.Two adjustable gears can expand the relative adjustable bandwidth of the bandpass frequency selection（this thesis reaches 87.3%）.In addition,adjustable frequency selection can also be achieved by using the electrical tunable characteristics of the dielectric constant of the liquid crystal.The liquid crystal is sandwiched between two frequency selection surfaces,surrounded by metal pillars to form a coplanar waveguide structure,and the positive and negative electrodes are respectively added to the upper and lower on the metal layer,the dielectric constant of the liquid crystal can be changed by adjusting the magnitude of the voltage,so that the continuous adjustment of the wave transmission point can be realized in the frequency range of 12.18GHz～13.86 GHz.Then,the loss layer is designed,and the co-simulation is carried out with the first adjustable frequency selection to realize the function of low transmission and high absorption,and the wave transmission point can be adjusted.Second,a mechanically adjustable band-pass frequency selector is proposed and designed,and the shift of the wave-transmitting point is realized by adjusting the inclination angle of the metal sheet;then the switching diode and the varactor diode are used to design the adjustable frequency band in the corresponding working frequency band.The lossy layer is tuned to achieve in-band electromagnetic wave passing and out-of-band electromagnetic wave absorption functions.The material finally realized can change continuously in the range of 3.94GHz～4.52 GHz,the maximum insertion loss is 0.49 d B,and the minimum is only 0.1d B.The relative transmission bandwidth of-1.5d B reaches 22.5%,and the material has good stability within the incident angle of30°.Third,based on the negative impedance characteristics of non-foster circuits,the theory and method of thinning of low-frequency active wave-transmitting and stealth integrated materials are firstly studied;then an active wave-transmitting and stealth integrated material including 3D electromagnetic calculation and circuit simulation is established,study the material’s wave absorption and transmission performance and optimization theory and methods;also study the stability of non-Foster circuit,which is the basis for the stable operation of this low-frequency absorption and transmission material.The simulation results show that the absorption rate of the material is greater than 80% in the range of 270MHz～1.17 GHz,and the insertion loss at the wave transmission point of 1.32 GHz is 0.26 dB.