Research On Multifunctional Microwave Devices Based On Metamaterials

Electromagnetic metamaterials are also called metamaterials.As a new type of artificial electromagnetic materials,metamaterials have unique electromagnetic properties.Metamaterials can be used to effectively control the loss,transmission and polarization characteristics of electromagnetic waves,and achieve a series of extraordinary functions that traditional materials cannot or are difficult to achieve,such as negative refraction,perfect wave absorption,perfect lens and wireless Energy transfer.However,a metamaterial often has only one function.With the rapid development of modern integrated systems,single-function metamaterial devices are increasingly unable to meet the needs of system integration,and it is still a challenge to use metamaterials to achieve multi-functions.This thesis first reviews the definition,basic properties,development and application of metamaterials,and discusses the current research status of multifunctional metamaterials in detail.The analysis theory of multifunctional metamaterials is emphatically described,including the principle of wave absorption,the theory of equivalent medium,and the theory of polarization control.The thesis focuses on the design of multifunctional microwave devices based on metamaterials,and designs and fabricates a zigzag absorber and wideband polarization converter,as well as a half reflection and half transmission cross-polarization converter.The zigzag absorber and wideband polarization converter is formed by folding planar metamaterials with the same unit cell along the midline.Compared with the planar structure,it has better performance in absorption and polarization conversion.It can achieve multiple absorption in different frequencies of microwaves,wideband cross-polarization conversion,circular polarization conversion,and it also exhibits wideband linear-to-circular and circular-to-linear polarization conversion.The results show that the absorption of the proposed design at 4.48GHz,10.54GHz and 21.02GHz are 94.76%,97.90%and 99.60%,respectively.It can achieve cross-polarization conversion and circular-polarization conversion well at 14.43GHz-20.32GHz.Similarly,excellent wideband linear-to-circular and circular-to-linear polarization conversion effects are achieved at 10.98GHz-13.96GHz.The half reflection and half transmission cross-polarization converter is composed of a spindle-shaped metal upper surface and a metal bottom similar to a gradient grating,and can realize half reflection and half transmission cross-polarization conversion and ultra-wideband transmission cross-polarization conversion.Simulation and experimental results show that metamaterials can achieve half reflection and half transmission cross-polarization conversion at 12.51 GHz-13.67GHz,and achieve transmission cross-polarization conversion in the ultra-wideband range of 2.58GHz-14.85GHz.The polarization converter has the combined features of a general reflection polarization converter,a transmission polarization converter and a half mirror.The metamaterial microwave device designed and studied in this thesis has the advantages of simple design and manufacture,multi-functional integration,etc.,compared with the previous multi-functional metamaterials,it has a wider bandwidth.This thesis has made an inspiring exploration of the multi-functional integration of metamaterials,which is conducive to the miniaturization and integration of optical systems,and has potential application value in antennas,imaging systems,remote sensors,and radiometers.