Study On The Active Manipulation Technology Of Microwave Scattering Wave Based On Subwavelength Structure

It has been a longstanding dream for mankind to achieve electromagnetic(EM)invisibility by manipulating the scattering wave of the target objects at will.In recent years,metamaterial,as an exotic artificial electromagnetic structural material,has caused much interest due to its powerful capability of controlling EM wave,and many novel EM invisibility techniques using metamaterials have been proposed,such as the invisibility cloaks and the absorbing materials.Nevertheless,metamaterial has insuperable difficulties in manufacture,preventing its widespread application.Therefore,metasurface,a two-dimensional?equivalent of metamaterials,has been presented,which can significantly relax the fabrication requirement due to its planar design of the subwavelength structure.It can control the scattering wave through the local phase modulation of the field,and so far several ultra-thin EM invisibility devices and low-scattering materials have been invented.However,there are still some bottlenecks to block their development in the real-application,such as narrow bandwidth,passive EM response and single EM functionality.This dissertation focuses on the EM scattering manipulation with metasurface,and some constructive approaches have been proposed to address the above issues.The main achievements include 1)The reconfigurable and broadband carpet cloaks have been proposed by using metasurface.2)The ultra-wideband RCS(Radar Cross Section)-reduction material has been proposed by using the mixed meta-atoms combined with PSO(Particle Swarm Optimization)algorithm.3)the bi-functional metamaterial for both EM invisibility and communications has been invented by using graphene tuning techniques.The detailed works and conclusions have been listed as follows:1.In order to expand the operation bandwidth of the current metasurface-based carpet cloaks,a cascaded metasurface is adopted to realize a dual-wavelength cloak,which can produce cloaking effect at both 6.1 GHz and 10.2 GHz.In addition,the dual-wavelength cloak can make different EM physical shapes at the two operating frequencies.Furthermore,a novel reconfigurable carpet cloak is designed by using the varactor-loaded phase modulation meta-atoms,which can generate different EM virtual shapes by tuning the surface phase distribution without changing its physical shape.The reconfigurable carpet cloak is experimentally verified at 2.4GHz,and it can make various physical EM shapes under the voltage control.2.In order to increase the RCS-reduction bandwidth of the phase cancellation material,the mixed meta-atoms with different dimensions are adopted to construct the whole RCS-reduction material and the PSO algorithm are utilized for guiding its optimization design.The proposed phase-cancellation material can realize a 10 dB RCS reduction over an ultra-wide frequency band with a fractional bandwidth of about 110%,and its total thickness is less than one-tenth of the wavelength at the lowest frequency.In addition,by combining absorbing and phase-cancellation mechanisms,a novel active RCS-reduction material is proposed.By tuning the PIN diode and varactor loaded in each unit cell,it can dynamically tune the RCS-reduction frequency from 3.5 GHz to 12 GHz.3.A full-space electromagnetic device based on the multilayer metasurface is presented,which can manipulate the reflected wave and transmitted wave simultaneously.By integrating the resonant phase and geometry phase to design this metasurface,the multifunctional device simultaneously deflects the transmitted and reflected beams to the predesigned angles in the X band the C band,respectively.Moreover,a reconfigurable metasurface based on the graphene tuning technique is proposed,which can dynamically control the reflection magnitude and meanwhile generate a transmission window at two different frequency bands.By simply controlling the bias voltages applied to the graphene,the proposed metasurface has been experimentally verified to have the capability of tuning the reflection magnitude in a large dynamic range between 5 and 15 GHz.In addition,a broadband transparent window is obtained at the central frequency of 24.5 GHz,ensuring the high efficient transmission of EM wave.