Research On Frequency Band Control Technology Of Radiation Devices Based On Subwavelength Structure

Amplitude,phase and polarization are three basic parameters of electromagnetic wave.Traditional materials can control these three parameters,but they are usually cumbersome.Recent advances in the study of metasurface(a two-dimensional metamaterial)have enabled us to manipulate electromagnetic waves in unprecedented ways.Metasurfaces can adjust the amplitude,phase and polarization of electromagnetic wave by arranging sub-wavelength unit structure in two-dimensional plane properly.Besides,these devices have very high compactness and are much smaller than the traditional counterparts.In addition to the advantages of compact structure,metasurface devices can even achieve abnormal performance that traditional optical natural materials can not achieve,so this artificial surface material has attracted wide attention.In this paper,two key problems of metasurface devices are studied:First,the chromatic aberration of metasurfaces.Because of the special mode of electromagnetic wave manipulation,there is a certain correlation between the characteristics of multi-wavelength or certain bandwidth electromagnetic waves.However,the period of the super-surface unit structure is fixed.Therefore,in order to solve some problems such as focusing and imaging,there will inevitably be chromatic aberration.At present,it is feasible to use a variety of sub-wavelength unit structures to form a metasurface device to achieve achromatic function to a certain extent.In Chapter 3 of this paper,a super-surface material with double open rings as its unit structure is proposed.The variation of the angle difference between the inner and outer rings of the cell structure can break the correlation between the wavelengths within a certain bandwidth.A large amount of structural data can be obtained by adjusting the spatial orientation angle of the unit structure and the angle difference between the inner and outer rings.The achromatic effect can be achieved by using particle swarm optimization(PSO)algorithm to design the layout of cell structure.Second,the powerful ability of metasurfaces to manipulate electromagnetic waves should be endowed with more complex and diverse functions.In Chapter 4,a multifunctional metasurface material is proposed,which can operate these three parameters effectively at two different frequencies.The planar sub-wavelength device can not only realize the asymmetric transmission of linearly polarized electromagnetic wave similar to diode,but also realize dual-band low crosstalk holographic imaging.The experimental results show that when the linear polarized wave incident in one polarization direction,the information contained in the metasurface(hologram)can be read out in the transmission field,while the incident wave in another vertical polarization mode will be completely blocked.The experimental results strongly support the theoretical design.The average transmittance coefficient and extinction ratio of the designed metasurface are higher than 84% and 58:1,respectively.These two indicators have made great progress compared with similar materials.We believe that this anisotropic dual-frequency metasurface is a powerful tool for the complete control of electromagnetic waves and has many potential applications in the field of communication and encryption.