Design And Research Of Broadband Metamaterial Absorber

With the rapid development of modern microwave electronics,electronic products for the convenience of public life,while triggering electromagnetic pollution and interference.Noise pollution,air pollution,water pollution,and electromagnetic wave pollution have been listed by the World Health Organization as the four major hazards threatening human existence.Electromagnetic absorbers can absorb the energy of incident waves in the specified working frequency band,effectively alleviating the electromagnetic pollution and interference caused by various electronic products.The size of conventional electromagnetic absorbers is large.Due to the advantages of small size,high absorption rate,and low cost of metamaterial absorbers,they have attracted wide attention from scholars at home and abroad.At present,the metamaterial absorber is mainly developed in the direction of ultra-thin,multi-frequency,broadband,polarization-insensitive and tunable.This thesis focuses on the study of broadband metamaterial absorbers.This thesis firstly introduces the background and current research status of metamaterials and metamaterial absorbers and then introduces some basic theoretical knowledge applied in this thesis:surface plasmon resonance and magnetic excitation element resonance theory,etc.Then the numerical simulation methods used in this paper are also explained,and three broadband metamaterial absorbers are designed based on the theoretical knowledge introduced in this paper.The absorption performance of the three designed absorbers is explained in relation to the field distribution,and the effect of the structural parameters of the absorber on the absorption characteristics of the absorber is investigated in order to obtain the optimal structural parameters.The specific work of this thesis is as follows:(1)A broadband absorber based on bismuth(Bi)is designed,which is a four-layer structure with a periodic array composed of a titanium nitride(TiN)substrate,a silicon dioxide(SiO2)dielectric layer,a thin film of Bi,and a titanium dioxide(TiO2)rectangular pair of different heights in the uppermost layer from the bottom to the top,respectively.The field distribution analysis shows that TiO2 rectangular pairs of different heights absorb better relative to the absorber of TiO2 rectangular pairs of the same height,and it is known that the cause of broadband absorption is due to the combined effect of local surface plasmon resonance and propagating surface plasmon resonance.Then the absorption performance with and without Bi material and replacing Bi with different metals are compared,and the comparison results show that the choice of Bi has a great effect on absorption.Finally,the effects of structural parameter variations,polarization angle,and temperature on the absorption characteristics of the absorber are investigated.The designed absorber achieves an average absorption of more than 90%in the wavelength range of 500～3500 nm and 99%in the wavelength range of 811～3162 nm.(2)A non-metallic refractory broadband metamaterial absorber was designed.Although Bi played an important role in broadband absorption in the previous work,the low melting point of Bi limited the application of the absorber at high temperatures,so a high melting point material was chosen for the current absorber design.Meanwhile,in most of the absorber designs,metallic materials are used,but now it is found that some compounds can replace the position of metals to achieve the same or even better functions,such as TiN used in the first work,which has a positive dielectric constant at short wavelengths and exhibits metallic properties,while at long wavelengths,because of the larger imaginary part of the dielectric constant,it exhibits plasma properties,which are useful for visible-near infrared absorption.Due to its stable physical and chemical properties and high melting point,TiN is still chosen as a component of the structure in the design of the nonmetallic refractory broadband absorber in this thesis.Several compounds with different melting points were also used for comparison of light absorption with TiN film combinations.Finally,a four-layer structure of zinc oxide(ZnO)and TiN was selected,namely ZnO/TiN/ZnO/TiN film combinations and ZnO/TiN/ZnO/TiN disc arrays.The thin film structure can achieve an average absorption of 97%in the wavelength range of 380～780 nm,and the disc array can also achieve an average absorption of 97%in the wavelength range of 600～2500 nm.In this thesis,their absorption mechanisms are investigated.The thin film structure forms two quality factor cavities above and below,and the two cavities are coupled to each other resulting in absorption.The absorption mechanism of disk array structure is due to the effect of surface plasmon resonance and Fabry-Perot resonance.The comparison of the absorption results for the thin film structure and the disc array also shows that combining multiple resonators is an effective way to broaden the absorption bandwidth.(3)A moth-eye structure broadband metamaterial absorber has been designed.Scientists found that the moth’s eye has a nano-periodic columnar array,which has good anti-reflection properties,so the moth-eye structure can be used to design a metamaterial absorber.In this thesis,several commonly used moth-eye structure models-parabolic,conical,and square cone are investigated for comparison,among which the parabolic structure is closer to the motheye.TiN is still chosen as the substrate of the absorber,and alumina(Al2O3)is used as the intermediate dielectric layer,with titanium(Ti)thin film and moth-eye pattern of Ti material as the upper layer.The absorption principle of the moth-eye structure is investigated by field distribution,in which local surface plasmon resonance still plays an important role,and the anti-reflection function of the moth-eye itself is equally important for broadband absorption.The effect of the three structures and their structural parameters on the absorption properties are also investigated.Since the moth-eye structure has a high aspect ratio,this thesis focuses on comparing the effect of different heights on the absorber.This thesis also compares cylindrical and square columns without refractive index gradient with parabolic,conical,and square cone shapes with refractive index gradient,and finds that the structures with gradient refractive index have significantly better absorption,and the gentle gradient refractive index can achieve good impedance matching which is also an important reason for the high absorption of the moth-eye structure.Our designed moth-eye absorber is able to achieve an average absorption of more than 99%in the wavelength range of 300～2500 nm.