Ion Of Artificial Electromagnetic Material Properties And Its Application

In order to describe the interaction between electromagnetic(EM) waves and matters, people introduce two important parameters-permittivity(ε) and permeability(μ).In principle,as long as we can change permittivity and permeability arbitrarily,we can tune the propagating properties of EM waves as we need.However,the varieties and freedoms for tuningεandμof natural materials are limited.For the sake of changingεandμat will,people propose the concept of metamaterials.Metamaterial is an artificial "super" material at a certain wavelength,which comprises many subwavelength man-made unit elements arranged periodically or non periodically.The functionality of these unit elements is like "atoms".The EM properties of metamaterials are determined by these "artificial atoms".The proposal of metamaterials is dated back to the idea of negative index materials.There are many fantastic properties based on negative index materials,such as:reversed Doppler shift,negative Cerenkov radiation,etc.. Subsequently,scientists continued to explore other extraordinary EM phenomena related to metamaterials,which are not realized by conventional materials.By use of adjusting the reflection phase of metamaterials,we can achieve subwavelength cavity and modulate the polarization state of EM waves.Through designing suitable resonant unit elements,people can cloak EM waves,etc..Many attentions are paid on the study of the unit elements and special properties of metamaterials.As one of the most important case of metamaterials,negative index materials can not only collect propagating waves,but also evanescent waves radiated from the sources.It can use for subwavelength imaging,but the image can not be stable ifε=μ=-1.In order to stabilize the image,people need to add absorption,while it greatly degrades the achieved image resolution at the same time.In practice,we are facing an awkward dilemma.In chapterⅡ,we show that a stable image with the highest possible resolution can be obtained in the shortest duration,if the source's "switchingon" time matches the intrinsic focusing speed of the lens.Then,we demonstrate that the image oscillations,with different types of sources including various polarizations and dimensions,are all dictated by the interactions between the source spectra and the lens surface modes.At last,we illustrate the image oscillations depend on the thick- ness and material parameter of the lens,which can be efficiently modulated the image oscillations for practice.Surface plasmon polaritons(SPPs) are elementary electromagnetic(EM) excitations bounded at metal/dielectric interfaces.Due to two important features-local field enhancement and subwavelength effect-of the SPP,it has attracted considerable attention recently.However,for a natural material,its plasmon frequency is fixed by electron density.This restriction limits the applications to a wider frequency regime.It is highly desirable to tune the SPP properties of a material in order to meet application requirements at arbitrary frequencies.In chapterⅢ,we demonstrate that a metallic plate drilled with fractal-shaped slit patterns exhibits well-defined SPPs with an effective dictated by the fractat geometry.We note that the plasmon frequencies can be changed via adjusting the fractat geometry and scaling the unit cell size,so that one can in principle design a plasmoinc metamaterial at an arbitrary frequency.Owing to the all-dimensional subwavelength nature of the fractal pattern,our system supports both transverse-electric and transverse-magnetic surface plasmons.This structure can be employed to focus light sources with all-dimensional subwavelength resolution and enhanced field strengths.The image resolution is determined by the periodicity.Microwave experiments and FDTD simulations prove our ideas.The split-ring resonator(SRR) was proposed as the first candidate to realize a negative permeability.As its special status,many studies have been performed on it.At the recent years,the research related to magnetic plasmons is becoming a hot topic,which needs various magnetic resonance elements.Therefore,the research on SRR becomes more important.In chapterⅣ,we extend the previously established mode-expansion theory,with some basic assumptions,to study the eigenmodes of metallic ring systems made by thin wires possessing filmlike rectangular cross sections,the finite-differencetime -domain simulations on realistic structures justify our theory.We then apply the theory to study the resonance properties of a broadside coupled split-ring resonator and show that such a planar resonator exhibits magnetic responses along all three dimensions under different conditions.At the same time,we reveal that mutual-SRR interactions in a periodic SRR array may lead to the reversal of the frequency sequence for two resonance modes.We finally employ FDTD simulations to design a realistic layered metamaterial that exhibits magnetic responses along all three dimensions. age oscillations,Surface plasmon polaritons,Fractal plate,Subwavelength imaging, Extended mode-expansion theory,Magnetic response,Broadside coupled split-ring resonator.