| With the fast expansion of the electronic information technology industry,the electromagnetic radiation produced not only interferes with the propagation of electromagnetic information but also has an influence on human health.At the same time,the development of multi-spectral combined detection technology seriously restricts the safety of various types of aircraft,and there is an urgent need to improve their multi-spectral stealth performance.Microwave-absorbing materials and structures are important ways to achieve human body protection,electromagnetic shielding,and radar stealth,which offer important application values in both civil and military defense fields.Traditional absorbing materials have technical bottlenecks such as narrow applicable frequency bands,high density,and easy to fall off,which seriously restricts the flight performance of aircraft.At present,there is an urgent need to develop novel radar stealth materials with broadband,multi-functional,high-performance to significantly improve the comprehensive stealth performance of weapons and equipment.Metamaterials are a kind of artificially designed periodic array structure that can flexibly regulate electromagnetic waves.Metamaterial-based absorbers provide greater design freedom to achieve perfect absorption.In this dissertation,for the problems of broadband radar absorption and multifunctional integration design and preparation,based on the broadband metamaterial absorber theory,the broadband radar stealth framework designed by stacked resistive film structure is established;the multifunctional radar infrared-compatible stealth integration design and method is extended;the structure with reconfigurable water-based absorption and polarization conversion function is optimally designed and prepared;and the design and preparation of active adjustable multifunctional broadband absorber and polarization conversion integrated devices are achieved.The main research contents are as follows:(1)A metamaterial absorber operating in the frequency range of 2.7-14.8 GHz is proposed,with its absorption bands covering the S,C,and X bands.The ITO microstructured resistive sheets are employed to achieve the effective energy loss of incident electromagnetic waves.The structure with a coplanar arrangement of multiple resonant units is optimally designed to achieve broadband absorption performance.The thickness of the structure is only 6.35 mm,which establishes the design and preparation method of a low-profile metamaterial absorber for broadband stealth.The introduction of the centrosymmetric structure effectively simplifies the structural design,reduces the processing difficulty,and achieves the polarization-insensitive property.In addition,the designed structure is optically transparent.The microwave absorption performance is verified by experimental platform,which provides significant applications in radar stealth as well as in devices such as aircraft windows.(2)Radar and infrared dual-function stealth metamaterial absorbers are developed.By introducing a suitable infrared shielding layer structure,combining frequency-selective surface theory as well as microwave absorption theory,a composite integrated structure of infrared stealth and radar stealth with low infrared radiation and broadband absorption properties is designed and prepared.The infrared radiation performance is reduced to0.283.The microwave absorption structure is based on ITO resistive film incorporating the dual mechanism of the planar multi-resonance unit and vertically stacked multi-layer,which achieves higher than 90% absorption in the frequency band from 2 to 18 GHz,and effectively improves the absorption bandwidth while maintaining the polarization insensitivity and wide-angle characteristics.The integration of the infrared shielding layer and the radar absorbing layer effectively optimises the design and method of the radar infrared compatibility problem and solves the problem of contradictory mechanisms between the two.The prepared samples were tested for microwave absorption and infrared radiation performance respectively.The measurement results are consistent with the simulation expectation,which provides a new idea for the development of military radar infrared stealth applications.(3)A multifunctional reconfigurable metamaterial design with integrated water-based absorption and polarization conversion is investigated.Combining a 3D-printed resin structure with a metal structure,it achieves more than 90% absorption in the 12.2-24.45 GHz band with a relative bandwidth of 66.84% by filling the resin interior with water,and at the same time possesses wide-angle,polarization-insensitive,and thermally stable properties.In addition,the water-based absorber not only reduces the radar scattering cross-section but also suppresses infrared radiation,demonstrating multi-spectral stealth potential.The metallic asymmetric structure acts as a polarization converter when there is no water inside the resin.The linear polarization conversion rate exceeds 90% in the12.5-16.5 GHz band.Finally,samples were prepared and measured to verify their multifunctional properties.The designed structure features high efficiency,wide angle,wide bandwidth,low cost,and easy fabrication.In addition,the design can achieve broadband absorption and polarization conversion in the same operating frequency band,which opens up a new way for the development of switchable devices for electromagnetic wave stealth and communication applications,and provides an effective strategy for the three-dimensional integration of novel devices.(4)A multifunctional metamaterial for active modulation of microwave broadband absorber and polarization converter has been investigated.A planar split-ring resonant structure is proposed,in which PIN diodes and lumped resistors are integrated at the gap of the resonant unit.Among them,the two states of the PIN diode on and off can achieve bifunctional switching,and the lumped resistor dissipates the incident electromagnetic wave.Firstly,when the PIN diode is on,the embedded lumped resistors deplete the electromagnetic wave,achieving broadband absorption from 3.2 to 8.5 GHz.The equivalent medium theory reveals the broadband stealth mechanism.Then,when the PIN diodes are disconnected,the designed metal split-ring structure achieves the polarization conversion function for the incident linearly polarized electromagnetic wave.At the same time,the bottom plate adopts a frequency-selective surface instead of the conventional metal plate to create a transmission window.The transmission window is maintained during any switching of the dual function for information transmission.Finally,the samples were prepared and the lumped elements were welded.The absorption,polarization conversion,and transmission properties of the designed structures were measured,verifying the effectiveness of the integrated design of multifunctional metamaterials and exploring the potential avenues for multifunctional devices,which show great potential for development in multifunctional applications such as tunable functional devices. |
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