| The structural design and performance optimization of new electromagnetic metamaterials,the interaction between electromagnetic field and matter,and the fabrication of metamaterials and metamaterial-based devices are of great significance for promoting their practical applications,such as electromagnetic stealth and optical devices.This thesis is focusing on the electromagnetic properties of curved materials;the characteristics of absorption,polarization conversion and transmission are studied via the numerical simulation,theoretical analysis and experimental verification.Main work and innovation achievements are as follows:(1)An absorber based on zigzag metamaterial is presented.When the electric field direction of incident electromagnetic wave is perpendicular to the serrated ridge,the absorber can almost perfectly absorb the incident electromagnetic wave at four frequency points.The current distribution in the metal layer on the surface of curved metamaterial indicates that the curved metamaterial can generate fundamental,second,third and fourth order magnetic resonance under the excitation of incident electric field,which is the fundamental reason that the metamaterials have multi-frequency absorbing properties.The real part of the equivalent impedance of the curved metamaterials is approximately equal to 1,while the imaginary part is approximately zero at the four absorption peak,which indicating that the equivalent impedance theory is still applicable to our curved metamaterial absorber.Our designed curved metamaterial absorber has been greatly improved the performances compared to the traditional planar metamaterial absorber-with the same metal pattern.Meanwhile,the simulation results show that the polarization of incident electromagnetic wave has significant influence on the absorption property,while the bending of curved metamaterial has negligible influence on the absorption property in a certain range.Therefore,our design can pave a new way for the research on designing the multi-frequency and even wideband metamaterial absorbers using single structures.(2)A zigzag birefringent reflective multifunctional metamaterial was designed and fabricated.It can absorb the electromagnetic waves at multiple frequency points in the low frequency band of 2-8 GHz,and to convert the polarization of the polarization linearly incident wave to arbitrary direction in the high frequency band of 8.43-11.55 GHz.The reason of this exotic phenomenon is that,on the one hand,the curved metamaterial maintains the characteristics of multi-frequency absorption;on the other hand,zigzag configuration the curved metamaterial makes the electromagnetic characteristics of metamaterials become sensitive to the polarization states of electromagnetic waves.The incident waves with the polarizations are perpendicular and parallel to the serrated ridge would be completely reflected across the zigzag metamaterial in the wide band of 8.43-11.55 GHz,but the phase difference was 180 degree.In practical application,we can flexibly select and utilize the electromagnetic control characteristics of the metamaterial by adjusting its position or the polarization direction of the incident wave.(3)A zigzag reflective and transmissive multifunctional metamaterial is designed and fabricated.It can adjust the energy ratio of reflected and transmitted waves in the broadband from 5.24 GHz to 14.52GHz for linearly polarized incident waves.For circularly polarized incident waves,the designed metamaterial can also convert circularly polarized waves into linearly polarized wave both in reflection and transmission mode.The reason of this phenomenon is that the configuration heterogeneity of the zigzag curved metamaterials,which makes them significantly different in response to electromagnetic waves with different polarization states.Specifically,the polarization waves along the x direction can be transmitted completely,while the polarization waves along the y direction can be reflected completely.The zigzag curved surface metamaterial can be used as ultra-wideband beam splitters,circular-wire polarizer or half wave plate for antenna,sensor and stealth applications.(4)We propose and fabricate a 3D printed chiral metamaterial,the two surfaces of which are one-dimensional sinusoidal faces with double L-shaped metal patterns.The designed metamaterial can realize the dual-broadband asymmetric transmission of electromagnetic wave in two bands of 8.26-9.13 GHz and 9.21-11.16 GHz,respectively,keeping the asymmetric transmission coefficient greater than 0.6.At the same time,the ultra-wide broad polarization conversion can be realized in the transmission with a 43.64%relative bandwidth.The simulation results show that our design can also be used in the research of metamaterials working in THz band.Our metamaterial has the advantages of simple structure and wide working band,which have potential application value in the fields of electromagnetic switch,filter and frequency selection.(5)A two-dimensional origami structrual metamaterial with chiral characteristics was designed and fabricated by 3D printing technology.Compared with the planar metamaterials with the same metal patterns,our two-dimensional curved metamaterials can realize the giant circular dichroism at two frequency point,and also can adjust the chirality of electromagnetic wave.The results shows that the direction of the equivalent magnetic dipole generated by the surface current on the metal at the resonant frequency is parallel to the electric dipole direction,which is the reason for chiral selection of metamaterials.Meanwhile,the calculated results show that the curved metamaterial can effectively reduce the relative density of materials,which is conducive to the development of functional materials towards light-weight.In this thesis,the electromagnetic characteristics of zigzag,sinusoidal and origami configuration curved metamaterials are studied through the combination of simulation design,theoretical analysis and experimental verification.The research contents involve the adjustment of the amplitude,phase and propagation direction of electromagnetic wave.Our curved metamaterials can be used in many fields such as stealth,sensor,antenna,etc.Our design idea is conducive to promoting the development of metamaterials functional devices towards miniaturization,integration and lightness. |
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