The Properties And Applications Of Zero-index Media

In recent years, artificial electromagnetic(EM) materials with unusual EM properties that natural materials do not possess, have attracted much attention in the fields of electromagnetism, optics and material science. Zero-index media(ZIM) belong to an unusual kind of artificial EM materials with permititivity or/and permeability near zero. In ZIM, the EM waves possess inifintely large wavelength, uniform fields and other unique properties, which contribute to important applications, such as directive emission, perfect narrow waveguides, etc. Due to the novel and important properties and applications, ZIM have drawn extensive attention. This thesis focuses on the fundamental properties, important applications and design technique of the ZIM. The main results are as follows: 1. The properties and transmission coefficients of the ZIMWe discuss the classification of ZIM, the fundamental properties and transmission coefficients of different kinds of ZIM. For ease of presentation, we classify the ZIM into single-zero ZIM with either permittivity or permeability near zero and double-zero ZIM with both permittivity and permeablilty near zero, which can be further classified into isotropic zero-index media(IZIM) and anisotropic zero-index media(AZIM). In addition, based on the shapes of equal frequency contrours of the AZIM, they are classified into elliptical AZIM, hyperbolic AZIM and other types of AZIM.Moreover, we discuss the properties of different kinds of ZIM, and the transmission coefficients through the IZIM and hyperbolic AZIM slabs. It is found that, under normal incidence, the transmission coefficient through a single-zero IZIM slab decreases as the increase of the thickness of the slab, while the transmission coefficient through a doublezero IZIM slab is always close to unity, and is independent of the thickness and the impedance of the slab. Under oblique incidence, a total transmission peak exists very close to normal incidence, which corresponds to Brewster angle. For the hyperbolic AZIM, the Brewster angle does not necessarily exist. However, interestingly, there exist a series of transmission peaks induced by Fabry-Pérot resonance for large incident angles. 2. The influence of the defects on the transmission properties of the IZIM, and the percolation of EM wavesWe study the influence of the defects on the transmission properties of two-dimensional(2D) and three-dimensional(3D) IZIM. For the 2D IZIM, we mainly analyze the effect of the circular defects with multilayered shell. It is found that the multilayered shell can prevent the EM waves penetrating into the core of the defect under some circumstances, while maintain total transmission through the IZIM. As a result, one-dimensional(1D) cloak can be realized. On the other hand, if the core resonances happen, Fano resonance profiles will appear in the transmission spectrum. In this case, a tiny change of the parameters of the core will lead to a large change of the position of the Fano resonance profile. Furthermore, we propose to utilize 2D IZIM or AZIM with dielectric defects to realize equivalent perfect magnetic conductor(PMC). Interestingly, the shapes of the dielectric defects and the ZIM can be arbitrary.For the 3D IZIM, we discuss the effect of random defects. We show that the long-range connectivity rather than the EM properties of the defects is crucial to the transmission properties of the 3D IZIM. Bases on this unique feature, for the first time, we discover and propose the phenomena of EM wave percolation. As the consequence of the vector wave nature of EM waves, the EM wave percolation is unusual compared with the standard percolation model. 3. Arbitrarily control of EM flux and applications in waveguide devices by using AZIMWe propose a new method to arbitrarily control EM flux by using inhomogeneous AZIM, which is available in both wavelength and subwavelength scales. We find that when EM waves propagate in the direction that the EM parameters close to zero, evanescent waves propagating in the vertical direction will be induced by the inhomogeneity of the AZIM. Such evanescent waves can redistribute EM flux and contribute to averaging effect of the impedance of the inhomogeneous AZIM, resulting in robust high transmission. Based on the new mechanism of EM flux control, we propose some applications including EM flux focusing, cloak and subwavelength control. Furthermore, combined with transformation optics(TO), we design and explain a series of almost perfect waveguide devices, such as irregular straight waveguides, bending waveguides and irregular bending waveguides. Finally, we realize the similar EM flux control behavior in inhomogeneous anisotropic highindex media(AHIM), and point out that the EM flux control effect originates from strong anisotropy and inhomogeneity. 4. The design technique of the ZIMWe first introduce some design technique of the ZIM. Then, we design lossless singlezero IZIM based on dielectric photonic crystals(PCs). It is found that the dielectric PCs can operate as single-zero IZIM with permittivity near zero within some frequency ranges, and can also operate as single-zero IZIM with permeability near zero within some other frequency ranges. Finally, we discuss the properties of the ZIM based on metal-dielectric periodic multilayers. We find that the multilayer can operate as single-zero IZIM with permittivity near zero for transverse electric(TE) polarizations, while for transverse magnetic(TM) polarizations, the multilayer cannot be regarded as ZIM. Because surface plasmon polaritons may be excited at the interface of metal and dielectric layers. As a results, strong nonlocality will appear. Based on such strong nonlocality, all-angle negative refraction and subwavelength imaging are realized. 5. Imaginary part of permittivity/permeability-dominated media, and their properties and applicationsThe permittivity e or/and permeability m of ideal ZIM satisfy Im(7)e,m(8) ?Re(7)e,m(8) ?0, i.e., both the real part and imaginary part of e or/ and m are near zero. In particular, if the imaginary part of e or/and m is relatively large, i.e., the e or/and m satisfy Im(7)e,m(8)(29)(29)Re(7)e,m(8) ?0, the properties of such media will be dominated by the imaginary part of e or/and m. Specifically, we classify such unique media into two groups. One group satisfies Im(7)e,m(8)(29)(29)1, and the other group satisfies Im(7)e,m(8)(27)(27)1. It is found that the properties of the former have dramatic distinction from those of ideal ZIM. While the latter generally share same properties with the ideal ZIM, which actually can be regarded as ZIM with tiny loss or gain.Basd on such unique media, we propose a unified theory for the design of ultrathin perfect absorbers and antireflection coatings based on assumption that only electric or magnetic field is constant inside the ultrathin film. It is found that ultrathin films satisfying Im(7)e,m(8)(29)(29)Re(7)e,m(8) ?0 can operate as perfect absorbers under some circumstance, and can also operate as antireflection coatings under other circumstance. In addition, both lossy and gain ZIM can operate as antireflection coatings. And for TM polarizations, Brewster angle is a critical angle on which the requirement of antireflection coatings is switched from lossy media to gain media, or vice versa. Interestingly, if Im(7)e(8)(29)(29)1, the films can be realized by exploiting conductive films in low frequency range. With appropriate surface resistance, the conductive films can coherently absorb EM waves and can work as antireflection coatings in a broad band, which is demonstrated in microwave experiments. Furthermore, by using the conductive films, we eliminate Fabry-Pérot resonances in a dielectric slab in broad band and wide-angle range, and improve radiation properties of the dielectric-coated antenna. On the other hand, if Im(7)e,m(8)(27)(27)1, the films can be realized by using lossy ZIM. And under oblique incidence, such films can obtain perfect aborption or antireflection effects.Finally, we extend such unique EM media to the fields of acoustics and elastic waves. We propose to use ultrathin acoustic and elastic films to realize perfect absorbers. In addition, we propose a damping elastic model with its effective mass density being pure imaginary and inversely proportional to the frequency, which provides a feasible model to realize broadband ultrathin acoustic and elastic perfect absorbers.