Characterization Of Physical Phenomena And Expansion Of Information System Based On Digital Coding Metasurfaces

The controllable physical degrees of freedom increase with the diversification of material forms.The advent of metamaterials makes reserchers have a deeper understanding of electromagnetic(EM)parameters.It is very convenient to manipulate EM phenomena and develop novel wave-control devices by regulating the electric and magnetic resonances of the meta-structures,which effectively promotes the development of EM fields.Metasurfaces are planar arrays,consisting of artificially subwavelength meta-elements periodically distributed on a two-dimensional plane.Through introducing abrupt EM changes on an ultrathin interface,metasurfaces can control both space wave and surface wave with great flexibility,leading to various equipment such as anomalous reflection/refraction,ultrathin cloaking,polarization conversion and absorption,etc.Because the idea of providing abrupt changes on the interface is applicable to many fields involving boundary conditions,the promising technology has quickly attracted much attention all over the world.Digital coding metasurfaces is a new research field,which brings fancy perspective on the connection between physics and information science.Digital coding metasurfaces aim to explore the following two aspects: a,How to use simple digital coding sequences to manipulate EM phenomena or create new wave-control apparatus? b,How to combine this powerful technology with the current information processing system,in order to enrich or simplify the existing system?This thesis focuses on the above two topics,discusses in detail the effect of digital coding metasurfaces on the representation of physical phenomena and the expansion of information system from the perspective of theory and practical application.The main contents and contributions of this research are summarized as follows:1)Multitasking shared digital coding metasurface.Higher information capacity of the digital coding metasurface means more powerful ability to control EM waves.Here,through prudent adjusting and optimizing geometric parameters,2-bit digital states at three separate frequency bands(C,X,and Ku)are realized.It is shown that the coding states on each working frequency only depends on specific geometric parameter,and no influence on other working bands.Based on this advantages,multiple functions can be designed on a single aperture just by designing corresponding coding sequences in every operating band.To demonstrate the capability and the compatibility,an optical illusion is performed at C band,which can make the radar confused that considering a plate as a stepped object;at X band,a cloaking device that can achieve-10 d B reduction of radar cross section(RCS)is engineered;and a vortex beam is generated at Ku band.Besides,the one-layer configuration makes it easier and more flexible to integrate on the microwave applications.2)A type of digital coding metasurface that can control both acoustic and EM waves simultaneously.The proposed metasurface can control wave behaviors of dual-physical fields.Various functions for both EM and acoustic fields,such as multiple-beam generation,beam steering and forming,and anomalous reflection can be realized in a common metasurface.Besides,this new kind of metasurface can be used to reduce the scattering cross section of both radar and sonar.The basic structure of this work is the Helmholtz resonator made of aluminum.The reflective responses of dual-physical waves can be manipulated through adjusting the geometric configuration of the resonator,and high bit coding states can be achieved.Only one metallic material is used in the design,which greatly reduces the fabrication complexity.The proposed device can be regarded as the alliance of an EM reflectary array antenna and a sonar array,which may have potential use in safety detection or target exploration in some complex application scenarios.3)Mimicking of Aharonov-Bohm(AB)effect with metasurfaces.The famous quantum phenomenon AB effect describes that the charged particles impinging on an impenetrable solenoid may acquire a quantum phase,called an AB phase,which is proportional to the magnetic flux inside the solenoid.The discovery of AB effect makes people realize the importance of geometric phase.In this work,we illustrate how to use meta-atoms to simulate AB effect,and acquire a new kind of geometric phase that is similar to AB phase.By combining this geometric phase and Pancharatnam-Berry(PB)phases,the symmetric restriction of the geometric phase is finally broken.In this way,desired phase profiles can be easily imposed on arbitrary polarization states,such as arbitrary linear and elliptical polarizations.The merged geometric phases allow flexible manipulations of the photonic spin-Hall effect and break the conjugate constraints of the spin-to-orbital angular momentum conversion.This study provides a feasible metamaterial platform to mimic quantum effect.4)Representing quantum information with digital coding metasurfaces.Digital coding metasurfaces has built an alternative bridge between wave-behaviors and information science.Different from the logic information in traditional circuits,the digital bit in coding metasurfaces is based on wave-structure interaction,which is capable of exploiting multiple degrees of freedom.However,to what extent the digital coding metasurface can expand the information representation has not been discussed.In this work,we show the classical metasurfaces have the abilities to mimic qubit and quantum information.An approach for simulating a two-level spin system with meta-atoms is proposed,from which the superposition for two optical spin states is constructed.We further propose that using geometric-phase elements with non-separable coding states can induce the classical entanglement,and give the condition to achieve the maximal entanglement.This work expands the information representing range of coding metasurfaces and brings new inspiration to mimic quantum information.5)Construct a new digital wireless communication architecture based on programmable metamaterial.This work proposes a method to transmit digital information directly via programmable coding metasurface.By distinguish the complex far-field scattering patterns,the system can recognize all the available coding states used for communication,and build a mapping relationship between the coding sequences and far-field patterns.The information,represented by the available states,is loaded to a programmable metamaterial,and is directly radiated into free space in a form of an ever-changing far-field pattern under the illumination of a feeding antenna;the receiving system collects electric field values received by receiving antennas located at different positions of a far-field region to obtain a far-field pattern,and recovers the transmitted original information according to a mapping relationship between the far-field pattern and a coding sequence.The communication system does not require modules for digital-to-analog conversion and frequency mixing,which greatly simplifies the complexity of current system,and reduces the cost of the communication system.It also features an inherent secrete communication in the physical level.Besides,the system has some intelligent characteristics as self-adaption and self-perception.