Absorption Mechanism Study And Device Preparation Of Cross-spectrum Metamaterials With Micro And Nano Functional Structures

Electromagnetic metamaterials（EM Metamaterials）functional devices such as absorbers,cross-polarization converters,filters and modulators with sub-wavelength size,ultra-thin thickness,light weight,etc.,have urgent needs in the fields of energy harvesting,stealth,communication and sensing,and are currently the international academic frontier and hotspot in this field.However,electromagnetic metamaterial functional devices have expected structural design difficulties,vulnerable to ohmic losses,and difficult to take into account the multi-frequency domain broadband operation and other problems.This paper uses a combination of theoretical analysis,numerical simulations and experiments to study the theoretical modeling and experimental verification of the forward design of GHz metamaterial absorbers,the design analysis of GHz/THz/IR cross-band absorbers,and the mapping theory of surface quality and electromagnetic wave absorption performance of metamaterial absorbers.To create a theoretical model for the forward design of metamaterial absorbers,to explore the mechanism of metamaterial absorption,and to study new processing methods for complex microstructured functional surfaces.The details are as follows:（1）The idea of forward design of metamaterial absorber is proposed,and the theoretical model of forward design of GHz metamaterial absorber is established based on the improved BP neural network training model.In order to verify the validity and feasibility of the developed theoretical model,the multi-band narrowband metamaterial absorber is studied using the developed forward design model,a more accurate prediction of the structural parameters of the metamaterial absorber was achieved,and the influence law of the structural parameters on the absorber performance was revealed.After the forward design based on the improved BP neural network training model,electromagnetic simulation and measurement tests show that the model has strong robustness and generalization ability.Using the electromagnetic simulation results,the effects of different polarizations and incidence angles on the absorption performance of the on-demand designed multi-band metamaterial absorber are analyzed,and the loss mechanism is revealed through the analysis of the electromagnetic response characteristics.The absorber is insensitive to different polarization angles and incidence angles of low-frequency electromagnetic waves.Meanwhile,the absorption performance of the absorber was tested by the arch method measurement test,and the causes of parasitic peaks and errors were elucidated.It was found that the processing error of the sample,structural anisotropy and environmental deviation are the main factors affecting the performance of the absorber.（2）A mathematical model of the metal resonator configuration,geometric parameters and dielectric layer thickness with respect to the equivalent circuit system is established,and the intrinsic connection between electromagnetic response and energy loss is revealed based on electromagnetic field and surface current distribution data.The simulation and experimental results show that the absorption performance of the microwave rigid absorber is mainly influenced by the transverse dimension（m）,and the energy loss comes from the combined action of the excited magnetic resonance and electrical resonance.The absorption performance of the terahertz flexible absorber is mainly affected by the dielectric constant of the medium and the current flow path（l₁,l₂,l₃）,and the internal losses are mainly accomplished by the Mie resonance and the local surface plasmon.In addition,the dipole-dipole interactions achieve cross-polarization conversion.（3）A guideline for the regulation of dimensional parameters to improve the absorption performance was established,and the intrinsic connection between the absorber plane area and the absorption performance was revealed by using numerical simulations and sample tests to design a cross-band full dielectric broadband metamaterial absorber.A design method of cross-band metamaterial absorber with integrated electromagnetic loss function is proposed,which realizes simultaneous absorption in multiple frequency domains without changing the parameters of the absorbing unit.It is found that the energy loss mainly originates from multiple reflection interference and is accomplished by the joint collaboration of cavity resonance and Mie resonance.The square slot structure is a key element in the generation of multiple reflection interference,thus proposing a geometrical dimensional control method to improve the overall structural absorption performance.Meanwhile,this paper reveals that the absorption performance of the cross-band absorber is positively correlated with the incident angle of electromagnetic waves,i.e.,the absorption performance increases when the incident angle increases,thus providing a key configuration idea for the design of non-resonant absorbers.（4）The mapping law between surface roughness and absorption performance of metamaterial absorber is studied,and a corresponding mapping model was established.Theoretical calculations,data analysis and experimental results show that the reflection number within the rough contour increases as the incident angle increases,and the absorption performance is then improved.This study predicts the propagation path of electromagnetic waves under different surface roughness conditions,and proposes a design method of full-dielectric hard and brittle metamaterial absorber to improve the absorption performance.To address the problem of difficult preparation of complex structured metamaterial absorbers for hard and brittle materials,a combination of single-point diamond multiple trajectory synthesis and virtual solid cutting is proposed to turn and machine periodic arrays of micro-nano-structured doped silicon metamaterial absorbers,which ensures the feasibility of manufacturing micro-nano-structured doped silicon metamaterial absorbers.