Design And Research Of The Huygens Lens Based On Terahertz

The metamaterial is a three-dimensional artificial composite structure that can control electromagnetic waves,and it has some problems,such as difficult processing,large volume,and large loss.The metasurface is the two-dimensional equivalent of metamaterials,which can adjust and control different optical paths through a thin structure.Compared with traditional optical elements which realize wavefront control through phase accumulation of light propagating in a medium,the metasurface provides a new degree of freedom,which can control the phase,amplitude,and polarization response with sub-wavelength resolution,and complete wavefront shaping in a distance far less than the wavelength.Due to the limitation of technology,the actual size and design of traditional lenses have big errors,which lead to aberration and seriously affect the imaging quality.However,the lens based on metasurface structure can suppress aberration and breakthrough diffraction limit.But the metasurface lens still has some problems,such as low focusing efficiency,complex structure,and high processing cost.The Huygens metasurface is based on the equivalent wave source theory,which has the characteristics of"zero loss",high transmittance,and simple transmission mode,and solves the problems of low transmittance and lens focusing efficiency of the metasurface.In this paper,the Huygens unit structure with phase control function is designed,which is arranged into Huygens metasurface according to certain rules,and two kinds of electromagnetic wave deflection and convergence lenses are designed.Compared with the focusing efficiency of single-layer metasurface lens,the performance of the Huygens metasurface lens has been improved in a certain range of focal length and frequency.The main work of this thesis includes the following aspects:1.Combining C-shaped split-ring resonator(CSRR)structure with Huygens principle,a metal-dielectric-metal Huygens structure is designed.The electromagnetic response is analyzed by CST simulation software,and eight transmissions Huygens structures are designed,with 45°phase gradient and 360°phase coverage,and the transmission coefficients of the unit structures are all kept above 0.72.Secondly,the designed symmetrical and antisymmetrical unit structures have the same effect and are insensitive to the polarization direction of incident waves.Finally,combined with surface electric admittance,magnetic impedance,and surface current diagram of the unit structure,the reasons for the same effect of the two structures and the excitation conditions of Huygens resonance are further analyzed.2.The electromagnetic wave deflection lens is designed by using Huygens metasurface.Combining with generalized Snell’s theorem,the designed symmetrical and antisymmetrical Huygens metasurfaces have the same deflection effect on electromagnetic waves in the frequency range of 0.7THz～1.0THz and are insensitive to polarization.The output wave deflects to the left,showing broadband deflection characteristics.3.The electromagnetic wave converging lens is designed by using Huygens metasurface.According to Fermat’s principle,the designed Huygens metasurface lens has a good focusing effect on electromagnetic waves in the range of focal length 620μm to3920μm and working frequency from 0.5THz to 1.2THz.Comparing with the single-layer metasurface lens,the focusing efficiency of the designed Huygens metasurface lens is maximum improved by nearly 90%in the focal length range of 620μm～3920μm and is maximum improved by nearly 3 times in the working frequency range of 0.5THz～1.2THz,with broadband focusing characteristics.