| In recent years,with the rapid development of radar detection and information communication technologies,the demand for multifunctional and intelligent electromagnetic manipulation is increasingly improved in practical applications,which brings tremendous challenges to the design of electronic devices.Limited to the fixed electromagnetic functions,the traditional material can not meet the diverse needs of varying applications.Hence,it is necessary to broadened the research field for metasurfaces from a new perspective,and the concept of intelligent metasurface is proposed.By employing a tunable meta-atom and elaborate design of the subwavelength structure,the reconfigurable metasurface can change propagation frequency,amplitude,or phase in real time,performing outstanding capability of dynamic wave manipulation.The emerging reconfigurable metasurface provides a good research platform for material design,because it can integrate various EM functionalities into itself,and these functionalities can be rapidly and dynamically switched with the external stimuli.Therefore,the reconfigurable metasurface could be considered as a desirable candidate to construct intelligent EM material.In order to achieve intelligent manipulation of EM waves without human intervention,reconfigurable metasurface should be further equipped with a sensor,actuator,and memory unit,which could rapidly and selfadaptively adjust its EM functionalities within the varying environment,just like a chameleon.Similar schemes have been proposed to design intelligent metasurfaces.However,the existing intelligent surface still suffers from some bottlenecks in terms of single-function modulation,narrow operation bandwidth,distinguishing forms between sensing and manipulation objects,and polarization sensitivity due to the mandatory need for bias networks,and they are all obstacles for metasurface into practicality.This dissertation mainly focuses on the common problems that intelligent material faces in the application.Moreover,the methods to achieve broadband dynamic electromagnetic regulation,multi-electromagnetic parameter collaborative manipulation,and the integration of sensing and executing are investigated.The relevant research achievements are expected to promote the future progress of intelligent electromagnetic manipulation.The detailed works and conclusions have been listed as follows:1.Two multifunctional reconfigurable metasurfaces are proposed based on the research of dynamic electromagnetic manipulation technology.Firstly,a multifunctional reconfigurable absorber,which can be flexibly switched among wideband absorption mode,frequency-reconfigurable narrowband absorption mode,and amplitudecontrollable absorption mode,is proposed and demonstrated.All the functionality switching is dependent on the predesigned bias voltage configurations applied to the graphene capacitor layer and the loaded actuation material of shape memory alloy(SMA).We have verified its tunable absorption performance by both simulations and measurements.The corresponding results show that such an absorber can realize strong absorption over a wide band ranging from 3.6 to 18 GHz.By tuning the height of the loaded SMA,the absorber is switched to a narrowband absorption state and its absorption peak frequency can be dynamically tuned from 8.7 to 13.5 GHz.When further changing the graphene resistance,the reflection amplitude can be also controlled in the above broadband and narrowband absorption modes.Hence,it is believed that the proposed design provides multifunctional absorption manipulation,which may have promising prospects in EM protection and camouflage fields.In addition,a multifunctional metasurface based on absorption and phase canceling mechanism is proposed.Combining with the wideband absorbing structure and phase canceling mechanism,the proposed metasurface can realize 10 d B RCS reduction in an ultra-wideband band of 4～40 GHz.By integrating an electronic controllable SMA spring,the metasurface can also achieve frequency tunable RCS reduction ranging from 12 GHz to 40 GHz.Meanwhile,the RCS reduction can also be improved to 20 d B.These two multifunctional reconfigurable metasurfaces with the integration of active materials are proposed to achieve dynamic RCS reduction in wideband,which have tremendous potential applications for smart and reconfigurable stealth devices and systems.2.An intelligent metasurface with the self-adaptive EM manipulation capability is proposed.It integrates the sensing-and-feedback components to construct a closed-loop system,which can automatically adjust EM functionalities for the different incident power information.The sensing module in this metasurface can first perceive the incident EM power intensity,and then provide the feedback signal to the field programmable gate array(FPGA)controlling platform that can send the corresponding instruction to the executing material for switching the EM functionality among transmission,reflection,and tunable absorption.Good self-adaptive reaction capability and practicability of the proposed metasurface have been demonstrated by the experiment.It has the capability of making a real-time response with adaptive EM behavior to the varying incoming wave power without the aid of human beings.Our design provides an avenue towards intelligent and cognitive metasurfaces,which have extensive application prospects in smart skin,intelligent absorbers,and the related EM fields.3.We propose an intelligent metasurface that can automatically manipulate its transmission/absorption frequency and amplitude to adapt to the complicated and ambiguous EM environment.By integrating an RF sensing module and a closed-loop feedback system,the incident wave frequency and amplitude information can be recognized and then the corresponding instruction would be generated to make such a metasurface achieve the predefined EM functions.Experimental results have demonstrated that it can realize the dynamic switching between transmission and absorption with the variation of incident power intensity,and meanwhile the transmission/absorption amplitude can be also further adjusted.In addition,this metasurface possesses the frequency-agile capability,which can self-adaptively control its transmission/absorption frequency to match the incident frequency.The proposed approach opens a new avenue to promote the development of multifunctional intelligent metasurface towards a wide range of real-time application fields,such as smart EM window and active camouflage. |
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