Research On Selective Radiators Based On Metamaterials

Electromagnetic metamaterials are artificial materials formed by arranging unit cell structures in space according to certain rules.Through the rational design of the micro-unit structure,the coupling effect with the incident electromagnetic can be produced,and the special electromagnetic capability can be obtained.The metamaterial absorber can completely absorb the incident electromagnetic wave and consume the incident energy through dielectric loss and ohmic loss;polarization converters can change the polarization properties before and after the incidence of electromagnetic waves.Compared with traditional devices,metamaterial-based wave absorbing devices and polarization conversion devices have the advantages of high efficiency,thin thickness,easy integration and artificial design,and have high application value in the fields of military and people’s livelihood.In this paper,the electromagnetic properties of metamaterial functional devices in the terahertz band are studied.The main contents are summarized as follows:1.A quad-band terahertz metamaterial absorber is designed.The metamaterial absorber is based on a traditional"sandwich"structure with periodic arrangement of honeycombs in space.The electromagnetic properties of the metamaterial were numerically calculated by the finite element method.After parameter optimization,four narrow-band perfect absorption peaks were obtained.Benefiting from the high symmetry of the structural unit,it is insensitive to the polarization angle,and the performance is better under the condition of large angle incidence.According to the equivalent medium theory and the surface current mode analysis method,the physical mechanism of narrow-band absorption is analyzed.The sensing performance of the metamaterial is significantly improved,the quality factor Fo M reaches 4.55,and the Q value reaches 25.It has the advantages of simple structure,perfect absorption,high sensitivity,polarization insensitivity,and wide-angle incidence stability.2.A metamaterial device that operates in the terahertz frequency band with broadband absorption and polarization conversion effects is designed.The functional switching of the metamaterial is based on the phase transition properties of vanadium dioxide.When vanadium dioxide is in the metallic state,the metamaterial exhibits broadband absorption performance,and the absorption rate exceeds 90%in the range of2.51～6.51 THz.The absorption properties have polarization stability and wide-angle stability.The physical mechanism of broadband absorbing and the influence of structural parameters on absorbing performance are also discussed.When vanadium dioxide is in an insulating state,it is"transparent"to terahertz electromagnetic waves,exploiting the anisotropy of the metamaterial to achieve polarization conversion properties.The metamaterial structure has a polarization conversion rate of over 90%in the broadband range of 1.42～2.59THz.The performance of polarization conversion can still be achieved for electromagnetic waves obliquely incident at a certain angle.In addition,the influence of geometric parameters on performance is discussed.3.A tunable THz ultra-broadband absorption metamaterial is designed.The phase-change material vanadium dioxide is added to the design of the ultra-broadband absorber,and the dynamic adjustment of the absorption rate is realized by changing the electrical conductivity of vanadium dioxide.In the process of increasing the conductivity of vanadium dioxide from 200 S/m to 2×10~5S/m,the absorption rate can vary from 3.1%to 100%.When the conductivity increases to 2×10~5S/m,the absorption bandwidth of the metamaterial reaches 5.12THz,which has the effect of ultra-broadband absorption,and the ultra-broadband absorption performance is significantly improved.Due to the quadruple rotational symmetry of the structural unit,the absorption performance of the metamaterial is insensitive to the polarization angle,and the incident angle stability is good.