Broadband Absorber Design Based On Metamaterials

Metamaterial is a class of composite material based on artificially designed structure,which presenting extraordinary physical properties that natural materials do not possess.The perfect absorber based on metamaterials has attracted much attention because of its broad application prospects in the fields of national defense and electromagnetic protection.Electromagnetic stealth and electromagnetic protection not only require strong absorption absorbers,but also need to meet practical requirements such as broadband,flexible,lightness,small size and portability.The design mechanism and implementation method of broadband,miniaturization,and flexible absorbers are still scientific and engineering problems to be solved urgently.Based on the above-mentioned problems and actual application requirements,this thesis studies a series of metamaterial basic unit structure design methods based on the principle of metamaterial absorption,and carries out modeling simulation,theoretical analysis and experimental verification.Meanwhile,a series of absorbers suitable for different bandwidths and frequency bands have been developed.The main work and innovation results are as follows:(1)The absorber design by single-resonance structure has a narrow frequency band,so the multi-resonance bandwidth expansion method based on composite structure such as fractal is studied.Firstly,through the establishment of equivalent circuit model,simulation and experiment,the absorbing mechanism and absorbing frequency adjustment method based on T-type single resonance structure are studied.Then,based on the mechanism of multi-resonance wave absorption,a design method of multi-resonance absorber based on the combination of different structures is proposed.The dual-resonance and three-resonance absorbers based on the fractal are developed,and the feasibility of the design method is verified through modeling simulation and experiments.The results show that the proposed three-beam broadband absorber has a fractional bandwidth of 18.5% with an absorption rate greater than 50%.It expands the absorber bandwidth without increasing the unit size and number of layers,and is better than the same type of absorber.At the same time,this kind of structure can be applied to many frequency bands such as terahertz,near infrared,infrared and visible light through scale conversion.(2)Aiming at the problem of large volume and narrow absorption band in the design of low frequency absorbers such as UHF(Ultra-high Frequency),a design method based on coupling enhancement of bending structure is proposed.First,by establishing the equivalent circuit model of the structure,the design method of enhancing the coupling between the units to reduce the resonance frequency to realize the miniaturization of the absorber is studied.Secondly,the design method of miniaturized absorbers based on the fractal curve structure to further reduce the resonance frequency under the specific unit size is studied.Finally,the method of reducing the frequency of absorber wave is studied by combining bending curve and coupling enhancement.Simulation and experimental results show that the proposed absorbing body has a significant miniaturization effect.The ratio of the unit size of the designed absorber structure to the absorber wavelength is 1/68,which is much smaller than the previous miniaturization design.Based on this design,the chip resistors are used to expand the bandwidth of a single resonance peak while realizing the miniaturization and broadbandization of the wave absorber.The miniaturized absorbers can be used to achieve electromagnetic protection in the communication band.(3)In view of the difficulty of rigid absorber structure to meet the actual demand of complex structure for surface absorber,a design method based on flexible materials and expanded bandwidth of lumped elements is studied.First of all,the wide-band metamaterial absorber loaded with lumped elements is studied.The loading of lumped elements in the unit structure can effectively improve the electromagnetic resonance characteristics and impedance matching characteristics,and enhance the Ohm loss to broaden the absorption band.Then,the equivalent electromagnetic parameters extracted by inverse method and structural surface current distribution are used to explain its absorption mechanism,and its absorption subject is analyzed by the characteristics of energy loss distribution.Finally,according to the loss structure,the unnecessary dielectric layer is reduced.And the design of the absorber body is a single-layer medium load resonant structure,developed with a thin,portable and low-cost high-volume production of single-layer multi-resonant structure ultra-broadband flexible absorber,and for the actual application of the cylinder scenario was measured.The results show that the ultra-broadband absorber has good flexibility,high degree of surface fit,and greatly enhances the practicability of the metamaterial absorber.The fractional bandwidth with an absorption rate of more than 90% reached 119%,which is higher than the existing design of the same type and can cover multiple radar bands.The use of fractal provides a new idea for the realization of broadband design of absorbers in any frequency band.The miniaturized absorber design based on the bending line provides more possibilities for the application of electromagnetic protection in the communication frequency band.Lightweight,flexible absorber design is of great significance to the further practical application of metamaterial absorbers.