Lossy Case Research Articles

Negative index modes in surface plasmon waveguides: a study of the relations between lossless and lossy cases

Surface plasmon modes in structures of metal-insulator-metal (MIM), insulator-insulator-metal (IIM) and insulator-metal-insulator (IMI) are studied theoretically for both lossless and lossy cases. Causality dictates which solutions of Maxwell's equations we accept for these structures. We find that for both lossless and lossy cases, the negative index modes and positive index modes are independent and should be treated separately. For the lossless case, our results differ from some published papers. By studying in detail the lossy case, we demonstrate how the curves should look like.

Material parameters characterization for three-dimensional pyramidal cloak

Arbitrarily three-dimensional (3D) pyramidal cloaks are proposed and designed theoretically based on the coordinate transformation. First, the general expressions of constitutive tensors of the cloaks are derived, and then there are some full-wave simulations which show that the cloak would bend incoming electromagnetic waves and guide them to propagate around inner region. Furthermore, the lossy cases are also considered and simulated. The results validate the constitutive tensors of the 3D pyramidal cloaks, and it is believed that the results are helpful for the practical design and analyze of the 3D cloaks.

Q‐anisotropy in finely‐layered media

Finely layered media behaves as an anisotropic medium at long wavelengths. If the constituent media are anelastic, Q‐anisotropy of qP, qSV and SH waves can be described by a generalization of Backus averaging to the lossy case. To test the theory, we introduce a novel method to obtain the complex and frequency‐dependent stiffnesses from numerical simulations of oscillatory (harmonic) tests based on a space‐frequency domain finite element method. We apply the methodology to a periodic sequence of shale and limestone and compute the quality factor and wave velocities as a function of frequency and propagation direction.

Electromagnetic circuits

The electromagnetic analog of an elastic spring-mass network is constructed. These electromagnetic circuits offer the promise of manipulating electromagnetic fields in new ways, and linear electrical circuits correspond to a subclass of them. The electromagnetic circuits consist of thin triangular magnetic components joined at the edges by cylindrical dielectric components. Some of the edges can be terminal edges to which electric fields are applied. The response is measured in terms of the real or virtual free currents that are associated with the terminal edges. The relation between the terminal electric fields and the terminal free currents is governed by a symmetric complex matrix $\W$. In the case where all the terminal edges are disjoint, and the frequency is fixed, a complete characterization is obtained of all possible response matrices $\W$ both in the lossless and lossy cases. This is done by introducing a subclass of electromagnetic circuits, called electromagnetic ladder networks, which can realize the response matrix $\W$ of any other type of electromagnetic circuit with disjoint terminal edges. It is sketched how an electromagnetic ladder network, structured as a cubic network, can have a macroscopic electromagnetic continuum response which is non-Maxwellian, and novel.

Spatial orientation and position distribution effect on the effective permeability of composites consisting of aligned flakes

In this work, the effective permeability of two-phase composite materials is studied based on a three-dimensional model. In this model, the magnetic inclusions embedded in a dielectric matrix are set with aligned orientation and calculated by finite-difference time-domain method in both lossless and lossy cases. First, the sensitivity of the effective permeability of composites to the spatial orientation and position distribution of inclusions is analyzed. Second, since it is difficult to give an accurate effective permeability with classic effective medium theories, we have modified the well-known Maxwell–Garnett mixing rule by introducing the equivalent demagnetization factors and two fitting parameters α and β, indicating the extent of position distribution chaos. An excellent agreement is obtained between the theoretical and simulation results in the quasistatic limit. Finally, in the case of inclusions oriented at several directions in the matrix, an “averaging method” is proposed to calculate the effective permeability.

Time domain analysis of thin‐wire antennas over lossy ground using the reflection‐coefficient approximation

This paper presents a procedure to extend the methods of moments in time domain for the transient analysis of thin‐wire antennas to include those cases where the antennas are located over a lossy half‐space. This extended technique is based on the reflection coefficient (RC) approach, which approximates the fields incident on the ground interface as plane waves and calculates the time domain RC using the inverse Fourier transform of Fresnel equations. The implementation presented in this paper uses general expressions for the RC which extend its range of applicability to lossy grounds, and is proven to be accurate and fast for antennas located not too near to the ground. The resulting general purpose procedure, able to treat arbitrarily oriented thin‐wire antennas, is appropriate for all kind of half‐spaces, including lossy cases, and it has turned out to be as computationally fast solving the problem of an arbitrary ground as dealing with a perfect electric conductor ground plane. Results show a numerical validation of the method for different half‐spaces, paying special attention to the influence of the antenna to ground distance in the accuracy of the results.

Analysis of photonic band structure in a one-

A theoretical analysis on the angle- and thickness-dependent photonic band structure in a one-dimensional photonic crystal containing single-negative (SNG) materials is presented. The photonic crystal consists of two alternating SNG materials, including that one has a negative permittivity (ENG) and the other has a negative permeability (MNG). It is found that there are two types of SNG gaps. The first is the low-frequency gap which is very insensitive to the incident angle in the transversal electric (TE) wave. The second gap, which strongly relies on the incident angle for both TE and transversal magnetic (TM) waves, will close at the zero bandgap frequency at which the impedance match as well as the phase match in the constituent ENG and MNG layers must be simultaneously satisfied. This zero bandgap frequency is also strongly dependent on the incident angle. The band edges and the gap maps are investigated rigorously as a function of the incident angle and the ratio of thickness of the two SNG layers. The analyses are made in the lossless and lossy cases for both TE and TM waves. The inclusion of the loss enables us to further clarify two fundamentally distinct second SNG gaps which are separated by a threshold angle of incidence.

Analysis of Hermite Lossy Nonuniform Transmission Lines Based on Hermite Function and Confluent Hypergeometric Function

The rigorous analytical solutions of the lossy Hermite nonuniform transmission lines (HNTL) are presented in this paper. These solutions are based on two special functions, namely, Hermite function and confluent hypergeometric function. The ABCD matrix of HNTL is given to obtain the corresponding frequency characteristic of the HNTL transformer. Through numerical simulations in different terminated cases, it is found that the lossless HNTL can be matched by resistance loads. This conclusion is different from the lossless one presented by D.torrungrueng. etc. In addition, the distributed power values of HNTL in the lossy case are calculated to show the attenuation character.

1-D chaincode pattern matching for compression of Bi-level printed farsi and arabic textual images

In some scripts, especially the Farsi/Arabic script, letters normally attach together and produce many different patterns, some of which are fully or partially similar. Detecting such patterns and exploiting them to reduce the library size, has a rather great effect on the compression ratio. In this paper, a lossy/lossless compression method is proposed for bi-level printed text images in archiving applications. For this, we propose a new 1-D pattern matching technique in the chain coding domain that uses the proposed technique of detecting the repetitive sub-signals in order to detect the fully or partially similar patterns. Experimental results show that the compression performance of the proposed method is considerably better than those of the existing bi-level printed text image compression methods as high as 1.8–4.2 times in the lossy case and 1.6–3.8 times in the lossless case at 300 dpi.

An improved pattern matching technique for lossy/lossless compression of binary printed Farsi and Arabic textual images

PurposeThe purpose of this paper is to propose a lossy/lossless binary textual image compression method based on an improved pattern matching (PM) technique.Design/methodology/approachIn the Farsi/Arabic script, contrary to the printed Latin script, letters usually attach together and produce various patterns. Hence, some patterns are fully or partially subsets of some others. Two new ideas are proposed here. First, the number of library prototypes is reduced by detecting and then removing the fully or partially similar prototypes. Second, a new effective pattern encoding scheme is proposed for all types of patterns including text and graphics. The new encoding scheme has two operation modes of chain coding and soft PM, depending on the ratio of the pattern area to its chain code effective length. In order to encode the number sequences, the authors have modified the multi‐symbol QM‐coder. The proposed method has three levels for the lossy compression. Each level, in its turn, further increases the compression ratio. The first level includes applying some processing in the chain code domain such as omission of small patterns and holes, omission of inner holes of characters, and smoothing the boundaries of the patterns. The second level includes the selective pixel reversal technique, and the third level includes using the proposed method of prioritizing the residual patterns for encoding, with respect to their degree of compactness.FindingsExperimental results show that the compression performance of the proposed method is considerably better than that of the best existing binary textual image compression methods as high as 1.6‐3 times in the lossy case and 1.3‐2.4 times in the lossless case at 300 dpi. The maximum compression ratios are achieved for Farsi and Arabic textual images.Research limitations/implicationsOnly the binary printed typeset textual images are considered.Practical implicationsThe proposed method has a high‐compression ratio for archiving and storage applications.Originality/valueTo the authors' best knowledge, the existing textual image compression methods or standards have not so far exploited the property of full or partial similarity of prototypes for increasing the compression ratio for any scripts. Also, the idea of combining the boundary description methods with the run‐length and arithmetic coding techniques has not so far been used.

Polarization-independent 2D omni-directional photonic band gaps in a 1D periodic metal-dielectric (anisotropic) structure

It is shown that there is no polarization-independent two-dimensionally (2D) omni-directional photonic band gap (PBG) for any conventional one-dimensional (1D) metal-dielectric (isotropic) structure. Through the study of band diagrams and some asymptotic analysis, a 1D periodic metal-dielectric (anisotropic) structure is proposed to achieve a polarization-independent 2D omni-directional PBG. Theoretical predictions for both the lossless and lossy cases are verified with finite element method (FEM) simulation of a point source in such a structure.

A NAM Representation Method for Data Compression of Binary Images

A representation method using the non-symmetry and anti-packing model (NAM) for data compression of binary images is presented. The NAM representation algorithm is compared with the popular linear quadtree and run length encoding algorithms. Theoretical and experimental results show that the algorithm has a higher compression ratio for both lossy and lossless cases of binary images and better reconstructed quality for the lossy case.

A lossy/lossless compression method for printed typeset bi-level text images based on improved pattern matching

Pattern matching is the most widely used technique for the compression of printed bi-level text images. In some printed scripts, letters normally attach to each other, or some letters have a simple relation to each other, or there may be undesired touching characters. Detecting such situations and exploiting them to reduce the library size, has a rather great effect on the compression ratio. In this paper, a lossy/lossless compression method for printed typeset bi-level text images is proposed for archiving purposes. For this, three techniques are proposed. First, the number of library prototypes is reduced by detecting and exploiting the mentioned situations. Second, a new effective encoding scheme is proposed for patterns and numbers. Third, three levels are proposed for lossy compression. Experimental results show that the proposed method works better, as high as 1.4–3.3 times in lossy case and 1.2–2.7 times in lossless case at 300 dpi, than the best existing compression methods or standards.

PRACTICAL LIMITATIONS OF AN INVISIBILITY CLOAK

We studied the practical limitations of a linearly transformed invisibility cloak due to the loss and discretization. We found that in order for the cloaking applications to be practically useful, for example, to reduce the scattering by two orders, the maximum loss tangent allowed in the cloak needs to be of or within the order of 0.01, which also limits the radius of a concealed object to be roughly within one wavelength. For a large cloak, if its size is increased by one order, the maximum allowed loss tangent needs to be reduced by one order accordingly. For discretization, we studied both lossless and lossy cases and found that a little loss will expedite the convergence of scattering with increase of the number of layers. Insufficient layers may increase the scattering and thus make the object more visible instead of invisible. Corresponding author: B. L. Zhang (bzhang@mit.edu). 408 Zhang, Chen, and Wu

Closed-form Analysis of Lossy Cosine-Squared Tapered Nonuniform Transmission Lines

The rigorous analytical solutions and the ABCD matrix of the lossy Cosine-Squared tapered nonuniform transmission lines (CSTNTL) are presented in this paper. According to different boundary conditions, the unique solution is obtained mathematically. Through the numerical calculations based on analytical solutions, the distributed voltages and currents in different terminated cases are shown to explain the transmission characteristics of CSTNTL. Especially in the lossy case the distributed power values are simulated to show the attenuation phenomenon.

ANALYTICAL SOLUTIONS FOR THE VARIATIONAL EQUATIONS DERIVED FOR THE NONLINEAR SCHRÖDINGER EQUATION: DISPERSION-MANAGED FIBER SYSTEM

We consider the nonlinear Schrödinger equation which governs the pulse propagation in dispersion-managed (DM) optical fiber transmission systems. Using a generalized form of ansatz function for the shape of the pulse, we derive the variational equations. For a particular case of DM fiber systems when the Hamiltonian is zero, we solve the variational equations analytically and obtain the expressions for the pulse energy, amplitude, width and chirp. Finally for Gaussian and hyperbolic secant shaped pulses, we show through numerical simulations that the analytically calculated energy (for the given pulse width and chirp) is good enough to support the periodic evolution of the DM soliton. The simulations are carried out for conventional and dense DM fiber systems for both lossless and lossy cases.

Modelling superradiant amplification of Casimir photons in very low dissipation cavities

Recent advances in nanotechnology and atomic physics may allow for a demonstration of the dynamical Casimir effect. An array of film bulk acoustic resonators (FBARs) coherently driven at twice the resonant frequency of a high-quality electromagnetic cavity can generate a stationary state of Casimir photons. These are detected using an alkali atom beam prepared in an inverted population of hyperfine states, with an induced superradiant burst producing a detectable radio-frequency signal. We describe here the results of the simulations of the dynamics of superradiance and superfluorescence, with the aim to optimize the parameters for the detectability of Casimir photons. When the superradiant lifetime is shorter than the dissipation time, we find superradiant evolution to be similar in character but dramatically slower than in the usual lossy case.

Electromagnetic Fields of Hertzian Dipoles in Layered Negative Refractive Index Materials

The electromagnetic fields of a Hertzian dipole in layered negative refractive index material (NIM) are efficiently calculated using the fast all modes method (FAM) combined with the numerical modified steepest-descent path method (NMSP). The exact locations of all surface wave modes and all leaky wave modes are found for various NIM slab thicknesses. Both lossless and lossy cases are studied. It is observed that there are different types of surface wave modes or even no surface wave mode at certain slab thicknesses. The electromagnetic fields vary significantly when modes are excited or disappear at certain thicknesses.

Realization of a super waveguide for high-power-density generation and transmission using right- and left-handed transmission-line circuits

In an earlier work [Cheng and Cui, Phys. Rev. B 72, 113112 (2005)], we have shown theoretically that extremely high power densities can be generated and transmitted in a super waveguide which is filled with homogeneous bilayers of right- and left-handed materials. In this paper, we realize such a super waveguide using right-handed transmission-line (RHTL) and left-handed transmission-line (LHTL) circuits. After a rigorous design of the RHTL-LHTL structure, we observe the generation and transmission of high-power densities in the super circuit waveguide from accurate simulation results. Both lossless and lossy cases have been studied for the LHTL circuit. From the simulation results and the rigorous analysis of energy speeds, we show that high-power flows with opposite directions are excited in the RHTL and LHTL parts of the super waveguide, which form the energy vortices in the waveguide cross section.

Channelled waves in anisotropic mesh metamaterials

Channelled waves in 2D periodic anisotropic L-C mesh metamaterials have been investigated. Circuit simulation and the newly developed analytical model of a unit cell have demonstrated full qualitative agreement for both lossless and lossy cases. Isofrequencies for a lattice unit cell and the circuit simulations of finite meshes have shown that propagating waves are channelled from a point source as pencil beams which can travel only along specific trajectories. The beam direction varies with frequency, and at resonance frequency ω=1/(LC)1/2, the phase and group velocities of the transmitted wave are orthogonal. The effect of losses was explored, and it is shown that losses can cause qualitative changes of the channelled wave type. It is shown that the channelled waves do not follow the laws of geometrical optics (Snell's law, specular reflection and so on) at the interfaces of L-C meshes but are governed by the conditions of phase synchronism and impedance matching. Only in the special case of dual L-C and C-L meshes with the interface parallel to the axis of rectangular grid excited at the resonance frequency (X=1) do the channels follow the trajectories of optical rays. A planar mesh test cell has been designed and applied to retrieving the unit cell L-C parameters from the S-parameter measurements.