Experimental Study Of Intelligent Electromagnetic Invisibility Cloaking And Superscattering

Metamaterials refer to one class of artificial composite materials composed of periodic or aperiodic structures with a subwavelength lattice constant.By engineering the geometrical structure and spatial arrangement of these elements,it is possible to obtain user-desired electromagnetic responses that are not necessarily available in natural materials,such as negative refraction.In the past two decades,with the advent of transformation optics and generalized Snell's law,metamaterials have experienced a fast-paced development,not only shining a new light into conventional microwave and optical devices,but also leading to a plenty of exciting electromagnetic functional devices.In this dissertation,we focus on the electromagnetic scattering,and carry out a series of theoretical,simulated,and experimental work about suppressing scattering--invisibility cloak,enhancing scattering--superscattering,and intelligent scattering--optical computing.To address the critical bottlenecks involved,such as unclear transient responses,narrow working bands,structural complexity,fabrication difficulty,and fixed working background,we investigate in-depth the flexible manipulation of electromagnetic scattering based on metamaterials and deep learning,and achieve some exciting functions,such as intelligent cloak,multi-frequency superscatterer,and multi-functional optical logic unit.These achievements promote both the state-of-art scientific research and the industrial process of novel metamaterials.Below is the brief summary of the main contents in this dissertation.1.Research on the method of intelligent cloak and superscatterer.For widely-used frequencydomain methods,it is difficult to simulate the transient illumination,broadband,and dispersion of a cloak and superscatterer.To overcome this,we build up a general finite-difference timedomain model capable of dealing with dispersion,anisotropy,and inhomogeneity simultaneously,and based on this,we simulate their transient response mechanism in the time domain.Furthermore,we summarize the analytical,numerical,and experimental methods used in this dissertation.To be specific,the analytical methods include transformation optics,scattering reconstruction,and classical scattering theory;the numerical method is based on an anisotropic dispersive finite-difference time-domain algorithm;and the experimental methods include equivalent circuit and intelligent design methods.All these methods lay a theoretical and experimental foundation for the following research.2.Research on the deep learning enabled intelligent cloak.To tackle the problems of stringent electromagnetic parameters,narrow working bands,and a fixed working background in conventional cloak,we for the first time propose an intelligent cloak driven by deep learning,which shows an excellent chameleon-like adaptability to an ever-changing background environment and external stimuli without any human intervention.In the finite-difference timedomain simulation and proof-of-concept microwave experiment,we build up a full set of perception-response-cloaking system,demonstrate in detail its working principle and dynamic cloaking capability on a millisecond timescale,and fully validate the characteristics of real-time,robustness,and intelligence.3.Research on the multi-frequency superscatterer by metamaterials.To tackle the problems of a single working frequency,structural complexity,high material loss,and fabrication difficulty in conventional superscatterer,we carry out two pieces of work.First,we propose a new approach of multi-frequency superscatterer from hyperbolic metamaterials,build up the dispersive model of planar hyperbolic waveguide and a scattering model of hyperbolic cylinder,and illustrate its high-efficiency and underlying physical principle.Second,we propose a new approach of spoof surface plasmon based superscatterer by multi-layered conformal metasurfaces.With the classical scattering theory and simulated annealing algorithm,we design a low-loss subwavelength superscatterer working at multiple frequencies,and for the first time,we observe the superscattering phenomenon in a microwave experiment.4.Research on the intelligent scattering enabled optical logic operation.To address the challenge that a conventional optical logic operation involves bulky and complex optical controllers,which hinder its miniaturization,integration,and robustness,we for the first time propose a general method for optical logic operation by intelligent scattering.To be specific,we firstly verify the feasibility and completeness of this method in theory;secondly,we employ a high-efficiency dielectric metasurface to facilitate a multi-functional optical logic gate for the numerical simulation and microwave experiment;finally,we discuss its universality,scalability,cascading and on-chip integration schemes.