Investigation Of Electromagnetic Low Scattering Manipulation Technology Based On Subwavelength Structure

Stealth technology is used to make military target undectable thourgh the low-scattering design,which can be also called as low observable technology.As a significant research direction in the stealth field,electromagnetic absorber is one of the most effective methods to achieve stealth by converting the incident wave into Ohmic loss.However,with the rapid development of composite detection technology,the target recognition and tracking capabilities of the detection system have been greatly improved,so that traditional electromagnetic absorbers cannot meet the continuous improvement of the stealth demand.The emergence of subwavelength structure provides a new route to solve this problem.Sub-wavelength structured materials consisted of array structures are artificial materials with special electromagnetic properties.Under the condition of wave vector matching,the high-order diffraction waves generated in the material can be trapped inside the structure and cannot propagate to free space.Thus,perfect absorption could be generated by the lossy medium through electric or?and?magnetic resonances,bringing in a novel way to design high-performance low scattering materials.In this paper,we focused on the manipulation technology of electromagnetic low scattering materials.Four kinds of electromagnetic stealth materials have been designed as follows:Dual-band infrared electromagnetic absorber based on sub-wavelength structure;transparent and flexible microwave-infrared bi-stealth material;Bidirectional and broadband dynamically tunable electromagnetic absorber based on vanadium dioxide material;A multifunctional dynamic low scattering material based on an active sub-wavelength structure.The above methods can be developed for potential applications in the stealth field and promote the development of stealth technology.The main research contents of this paper include the following four points:Firstly,a design method of a dual-band wide-angle infrared electromagnetic absorber is proposed.Dual-band near perfect absorptions at 1.064?m and 10.6?m based on Helmholtz resonance and localized surface plasmon resonance are achieved,and the absorptivity is over 99.7%.The wide-angle absorption and polarization insensitivity of the electromagnetic absorber have been also verified by full-wave electromagnetic simulation.Through the electric field and current distributions,the dissipative mechanism of electromagnetic energy is theoretically analyzed,and the physical mechanism of the dual-frequency electromagnetic absorber is further explained.Secondly,a flexible and transparent microwave-infrared bi-stealth structure is proposed to avoid composite detection in microwave and infrared band.By combining the intrinsic material properties with proper design,the proposed flexible metamaterial can simultaneously achieve high absorption in microwave band,low emission in infrared band,as well as optical transparency.As a proof of concept,the measured results demonstrate that our structure exhibits wide-angle?40°?,broadband?7.7-18 GHz?and high-efficiency?>90%?absorption.Besides,by further using our structure to cover a metallic column,a 10 dB radar cross section?RCS?reduction in7.5-18 GHz is achieved.The thermal emissivity of our structure is about 0.23 in the infrared atmosphere window,which is closed to that of metal.Furthermore,the elaborately designed metamaterial keeps optical transparency and flexibility due to the use of indium tin oxide?ITO?films and polyvinyl chloride?PVC?substrates.Thirdly,a novel electrically-controlled resistive layer?ECRL?based on VO₂ phase transition characteristics is proposed.The effective resistance of ECRL is numerically verified to be tuned from 18 ohm/sq.to 300 ohm/sq by the electrothermal effect.Based on this characteristic,a bidirectional dynamic electromagnetic absorber and a non-planar wide band dynamic electromagnetic absorber are constructed.The bidirectional dynamic electromagnetic absorber can realize large-scale dynamic modulation of absorptivity from 18%to 98%in two directions,while the non-planar dynamic electromagnetic absorber can realize broadband electromagnetic absorption from 1.08 THz to 2.5 THz,and its absorption amplitude can be dynamically controlled.Both dynamic electromagnetic absorbers described above have good angular adaptability in the case of normal incidence.Fourthly,the design method of multi-functional electromagnetic device based on sub-wavelength structure is proposed,which realizes the dynamic reconfigurable feature of electromagnetic functions such as RCS reduction control,beam scanning and polarization conversion.A PIN diode and a varactor diode are integrated in the unit cell of the sub-wavelength structure.By changing the bias voltage,180°phase difference can be generated to achieve RCS reduction.Besides,the 180°phase difference generation band can be further modulated to dynamically control the reduced frequency band of RCS.At the same time,a continuous reflection phase difference covering 360°can be realized by controlling the above two diodes,which achieves wide-angle beam scanning effect.By further changing the bias voltage configuration of the diodes,the material can produce 0°,90°and-90°phase differences on two orthogonal polarizations,enabling dynamic switching of linear polarization and different rotational circular polarization states.The above three electromagnetic functions can be realized only by regulating a single-layer active sub-wavelength structural material.