Researches And Applications Of Metasurface In Stealth Technology

Metasurface is a 2D equivalence of metamaterial,which is constituted by thin planar array of elements with sub-wavelength scale.It has attracted a great deal of attention during the past decade for its ability to provide full control of the wave-fronts,enabling many applications in microwave and optical engineering,such as anomalous reflection,polarization splitting,ultrathin lens,and optical holography.In this thesis,a detailed research is made on the stealth technology based on metasurfaces.The main contents and contributions of this thesis are summarized below:· A polariztion-insentive tunable metasurface absorber is designed with the varactor diodes embedded between the metamsurface units.The basic unit shows excellent absorptivity in the designed frequency band over a wide range of incident angles.By regulating the reverse bias voltage on the varactor diode,the absorption frequency of the designed unit can be controlled continuously.The mechanism of the absorption is interpreted using the electromagnetic-wave interference theory.When the basic units are placed along two orthogonal directions,the absorber is insensitive to the polarization of incident waves.The tunability of the absorber has been verified by experimental results with the measured bandwidth of 1.5 GHz(or relative bandwidth of 30%).· A new strategy is proposed to realize the random metasurface with desired diffusion bandwidth.Different from the earlier work,the current design is carried out within a broad spectrum instead of at a single frequency,giving rise to the arbitrarily desired bandwidth.Three basic elements are proposed to construct the new random metasurface,and the diffuse reflection feature can be attributed to their destructive interferences with the change of operating frequency.The intrinsic loss of the meta-atoms is also taken into account to make the theoretical model more accurate in the practical design.Excellent scattering-suppression features are observed in the predefined frequency bands in both simulated and experimental results,which have very good agreements with the theoretical predictions.· A method for fast design of broadband random metasurface is porposed and experimentally characterized.The proposed random metasurface is composed by three kinds of simply patterned elements with different resonant properties.To obtain the best broadband performance with the lowest backward reflections,a genetic algorithm is developed to manipulate the resonances for the fast determination of element geometries.An inverse discrete Fourier transform method is used to predict the scattering pattern of the metasurface with high accuracy and low time consumption,significantly enhancing the efficiency of the array pattern design.The proposed fast design flow will benefit a broad range of microwave and terahertz applications,such as biological detection and imaging.· To realize reflection suppression with the simultaneous control of wave absorption and interference,we propose a new metasurface constituted by two kinds of unit cells in a pseudorandom arrangement.By use of the indium tin oxide(ITO)with moderate sheet resistance in the meta-atoms,enhanced absorption of energy can be achieved in a broad spectrum when interacted with illuminated waves.In the meanwhile,electromagnetic diffusion will be invoked from the destructive interference among the meta-atoms,leading to significant reduction of specular reflection as a result.Excellent agreement are observed between simulation and experiment with pronounced reflection suppression from 6.8 GHz to 19.4 GHz.In addition,the optical transparency of the patterns and substrates makes the proposed metasurface a promising candidate of future applications like photovoltaic solar cells and electromagnetic shielding glasses.