Fleld Distribution Research Articles

STUDY OF NONRECIPROCAL DEVICES USING THREE-STRIP FERRITE COUPLED LINE

This paper presents the investigations of nonreciprocal devices employing a novel ferrite coupled line junction. The structure is designed using coplanar line technology with the ground half-planes reduced to the strips. The investigated junction is composed of one ferrite section placed in between of two dielectric sections. In the ferrite section the longitudinally magnetized ferrite slab is located at the top or the bottom of the strips and is covered with the dielectric layers. In the dielectric sections the ports of the junctions are located. The wave parameters and fleld distributions of the modes propagated in the dielectric and ferrite sections are obtained from spectral domain approach. In order to determine the scattering matrix of the junction the mode matching method is utilized. The investigation of the circulator and isolator designed based on the S- matrix of the junction are presented. The obtained results are verifled by comparing them with HFSS simulations and own measurements of the fabricated devices. In both cases a very good agreement is observed.

Electromagnetic Tunneling in Nonconjugated Epsilon-negative and Mu-negative Metamaterial Pair

In this paper, the tunneling phenomenon occurring at the interface with great impedance contrast is investigated by numerical calculation. It is found even in this case, per- fect transmission can still be achieved theoretically when nonconjugated sub-wavelength epsilon- negative (ENG) and mu-negative (MNG) metamaterial pair is introduced. Moreover, the calcu- lated electromagnetic fleld distributions show that, only one component of the tunneling mode (either the electric or the magnetic fleld) is amplifled, suppressing another one at the same time. Therefore, the nonconjugated ENG-MNG pair is promising to be applied in modern optic and microwave communication systems for less re∞ection, compact device volume and ∞exible control of EM fleld distribution. 1. INTRODUCTION As is known, re∞ection is a common and inevitable optical phenomenon for interfaces with notable impedance contrast. To enhance the transmission, many methods are introduced. For instance, in optics, quarter-wavelength antire∞ective coatings are widely used to reduce the re∞ection of optical devices (1{3). In order to achieving perfect transmission e-ciency, multiple antire∞ective layers should be involved. Therefore, the length of these layers will be very long, which greatly restricts the possibility to design compact optical communication devices with high transmission e-ciency. Metamaterials (4{16), which have attracted wide interests recently, may be a solid candidate to solve this problem. Metamaterials include double negative (DNG) materials (both the permittivity and the permeability are negative) and single negative (SNG) materials (only one of the permittivity or the permeability is negative). In SNG materials, the EM waves are evanescent since their wave vectors are complex. In particular, a tunneling scenario will emerge when a pair of lossless ENG and MNG slabs is conjugated matched between two similar half spaces. In this paper, we investigate the tunneling phenomenon occurring at the interface between two difierent materials with great impedance contrast by numerical calculation. It is shown that, when a nonconjugated sub-wavelength epsilon-negative (ENG) and mu-negative (MNG) metamaterial pair is introduced between two difierent materials with great impedance contrast, perfect transmission can still be achieved theoretically. The tunneling condition of the nonconjugated ENG-MNG pair in above case is also flgured out. Moreover, the calculated electromagnetic fleld distributions show clearly that, by choosing proper parameters we can even amplify only one component of the tunneling mode (either the electric or the magnetic fleld), suppressing another one at the same time. Therefore, the nonconjugated ENG-MNG pair is promising to be applied in modern optic and microwave communication systems for less re∞ection, compact device volume and ∞exible control of EM fleld distribution.

OPTIMIZING NANO-OPTICAL ANTENNA FOR THE ENHANCEMENT OF SPONTANEOUS EMISSION

We study the characteristics of nano-optical antenna made of two gold nano-particles by three dimensional numerical calculations in visible and near infrared bands. To carry the computational burden and guarantee the precision and speed of a three dimensional FDTD calculation, adaptive mesh reflnement technology is used. In this paper, we flrst highlight the concrete way of controlling the emitter position and orientation to fulflll the requirements of larger spontaneous emission enhancement. Then, we analyze the far fleld distribution and flnd that the far fleld directivity is strongly in∞uenced by surface plasmon polaritons (SPPs). Choosing the incident wavelength of 600nm, we compute the decay rates and radiant e-ciency as a function of antenna geometry limitations. Next, the particle aspect ratio is optimized, and we obtain that L=R = 4 is the best for our optical-antenna. Furthermore, we present a spectrum analysis. Around 5000 fold spontaneous emission enhancement is successfully achieved. Finally, we flnd a piecewise linearity relationship between the particle length and resonant wavelength.

NUMERICAL EVALUATION OF THE MAGNETIC FIELD EXPOSURE NEAR THE TRANSITION TOWER OF AN OVERHEAD-UNDERGROUND HV LINE

The paper deals with the analysis of the magnetic fleld distribution near the transition tower of an overhead-underground transmission line of 110kV. The current density induced in the human body due to this fleld is also estimated. A hybrid numerical technique combining both the boundary element method and the charge simulation method is employed for this purpose. This technique is implemented in the author's own software package dedicated to the analysis of electromagnetic exposure in the vicinity of power objects. A simplifled numerical model of the human body of dimensions recommended by the IEC/EN standards is employed in computations. Obtained numerical results are related to the appropriate regulations regarding the human exposure to the electromagnetic flelds.

DESIGN OF A NOVEL DUAL-LOOP GATE ANTENNA FOR RADIO FREQUENCY IDENTIFICATION (RFID) SYSTEMS AT LOW FREQUENCY BAND

In this paper, a dual-loop gate antenna is designed to generate the magnetic fleld distribution in various directions. It is applied to Radio Frequency Identiflcation (RFID) systems for animal identiflcation operating at the low frequency (LF) band of 125kHz and 134.2kHz. The percentage of volume of magnetic fleld intensity is introduced and used as a flgure of merit in the design. The optimum antenna parameters are also designed by the genetic algorithm (GA) in conjunction with the Numerical Electromagnetic Code (NEC). The prototype antenna was fabricated and tested to conflrm the antenna performance in the LF-RFID system for animal identiflcation. It is found that the dual-loop gate antenna can be e-ciently used in the LF-RFID system.

PLASMONIC RESONANT LIGHT SCATTERING BY A CYLINDER WITH RADIAL ANISOTROPY

We apply the full-wave electromagnetic theory to study electromagnetic scattering by a small cylindrical particle with radial anisotropy for normally incident light with transverse magnetic (TM) polarization. The scattering coe-cients are derived, when the radial anisotropies in both the permittivity and permeability tensors are taken into account. It is shown that the surface and volume plasmon resonances can be identifled by the sign of dt=dq, in which t is the permittivity element in a direction tangential to the local r-axis, and q is the size parameter. The near fleld distributions for surface and volume modes are illustrated by flnite element method. It is found that small changes of anisotropy can afiect the scattering e-ciencies signiflcantly. Moreover, the quadrupole and octupole resonant peaks may be much higher and sharper than those of dipole resonance in the scattering e-ciency spectra.

POLARIZATION INSENSITIVE METAMATERIAL ABSORBER WITH WIDE INCIDENT ANGLE

This paper presents the design, fabrication and measure- ment of a polarization insensitive microwave absorber based on meta- material. The unit cell of the metamaterial consists of four-fold rota- tional symmetric electric resonator and cross structure printed on each side of a print circuit board to realize both electric and magnetic reso- nances to achieve e-cient absorption of the incident microwave energy. Both the full wave electromagnetic simulation and the measurement on the fabricated absorber demonstrate high microwave absorption up to 97% for difierent polarized incident electromagnetic waves. To under- stand the mechanism, analysis is carried out for the electromagnetic fleld distribution at the resonance frequency which reveals the work- ing mode of the metamaterial absorber. Moreover, it is verifled by experiment that the absorption of this kind of metamaterial absorber remains over 90% with wide incident angle ranging from 0 - to 60 - for both transverse electric wave and transverse magnetic wave.

ELECTRODYNAMICAL CHARACTERISTIC PARTICULARITY OF OPEN METAMATERIAL SQUARE AND CIRCULAR WAVEGUIDES

We present here the solution of the eigenvalue problems for the open metamaterial square and circular rod waveguides. The Maxwell's equations for the electrodynamical analysis of the open waveguides were solved by the Singular Integral Equations' (SIE) method and partial area method. Our SIE method is pretty universal and let us rigorously analyze open waveguides electrodynamically with any arbitrary cross-sections taking into account of the edge condition. The false roots did not occur applying the SIE method. The waveguide media can be of strongly lossy materials. The signs of the complex permittivity and permeability can be positive or negative in difierent combinations. We used our computer algorithms based on the two mentioned methods with 3D graphical visualization in the MATLAB language. We present here our numerical calculations of the metamaterial square waveguide with sides equal to 5 ¢ 10 i3 m and the metamaterial circular waveguide with the diameter equal to 5¢10 i3 m. We present dependences of phase constant and attenuation constant of metamaterial waveguides at the frequency range from 75GHz till 115GHz. We have compared the three dimension (3D) electric fleld distributions of the main mode and the flrst higher mode propagating in the square and circular metamaterial waveguides. The calculations of the electric flelds were fulfllled at approximately 10000 points in every cross-section. We discovered that the electric fleld is concentrated at the waveguide boundary. The distribution of the electric fleld along the perimeter of the waveguide is not uniform. There are two areas on the perimeter of the square and circular waveguides

The Probability Distribution of the EM Fields in Single-cavity System and the Application of PWB Method

Based on full-wave analysis method, the probability distribution curves of elec- tromagnetic (EM) flelds inside a single cavity with and without a mode stirrer are obtained, which obey a kind of unimodal functions. Although this unimodal function does not satisfy the assumption of power balance (PWB) method, the power losses of cavity wall at difierent frequencies evaluated by PWB method and those calculated by full-wave analysis method are comparable. The change trends of the power losses with frequency almost coincide with each other, and the difierence is no more than an order of magnitude. It is remarkable that PWB method costs less than one minute while full-wave analysis method costs more than two hours, and PWB method saves almost 70% memory space. It means that PWB method can indeed give efiective data that meet certain accuracy requirement with much smaller computational cost than full-wave analysis method. Finally, for further study of PWB method the inhomogeneous degree is deflned to measure the inhomogeneity of EM fleld distribution inside the cavity.

MAGNETIC FIELD CREATED BY A UNIFORMLY MAGNETIZED TILE PERMANENT MAGNET

This paper presents a general analytical formulation for calculating the three-dimensional magnetic fleld distribution produced by Halbach structures with radial or axial polarization directions. Our model allows us to study tile permanent magnets of various magnetization directions and dimensions. The three magnetic fleld components are expressed in terms of analytical and semi-analytical parts using only one numerical integration. Consequently, the computational cost of our model is lower than 1s for calculating the magnetic fleld in any point of space. All our expressions have been checked with previous analytical models published in the literature. Then, we present two optimized permanent magnet structures generating sinusoidal radial flelds.

CAN MAXWELL'S FISH EYE LENS REALLY GIVE PERFECT IMAGING? PART II. THE CASE WITH PASSIVE DRAINS

We use both FEM (flnite element method) and FDTD (flnite difierence time domain method) to simulate the fleld distribution in Maxwell's flsh eye lens with one or more passive drains around the image point. We use the same Maxwell's flsh eye lens structure as the one used in recent microwave experiment (10): Maxwell's flsh eye lens bounded by PEC (perfect electric conductor) is inserted between two parallel PEC plates (as a waveguide structure). Our simulation results indicate that if one uses an active coaxial cable as the object and set an array of passive drains around the image region, what one obtains is not an image of the object but only multiple spots resembling the array of passive drains. The resolution of Maxwell's flsh eye is flnite even with such passive drains at the image locations. We also found that the subwavelength spot around the passive drain is due to the local fleld enhancement of the metal tip of the drain rather than the flsh eye medium or the ability of the drain in extracting waves.

CAN MAXWELL'S FISH EYE LENS REALLY GIVE PERFECT IMAGING?

Both explicit analysis and FEM numerical simulation are used to analyze the fleld distribution of a line current in the so-called Maxwell's flsh eye lens (bounded with a perfectly electrical conductor (PEC) boundary). We show that such a 2D Maxwell's flsh eye lens cannot give perfect imaging due to the fact that high order modes of the object fleld can hardly reach the image point in Maxwell's flsh eye lens. If only zeroth order mode is excited, a good image of a sharp object may be achieved in some cases, however, its spot-size is larger than the spot size of the initial object fleld. The image resolution is determined by the fleld spot size of the image corresponding to the zeroth order component of the object fleld. Our explicit analysis consists very well with the FEM results for a flsh eye lens. Time-domain simulation is also given to verify our conclusion. Multi-point images for a single object point are also demonstrated.

THEORETICAL ANALYSIS OF A PASSIVE ACOUSTIC BRAIN MONITORING SYSTEM

An approach based on acoustics and its theoretical analogies to electromagnetism is used in the present research to study the detection of the acoustic wave energy radiated by the thermal random motion of material particles of the brain during activation or caused by pathology. Pressure and particle velocity are calculated in analytical mathematical forms for the case of human brain monitoring, which can be implemented by a prototype passive acoustic brain monitoring system (PABMOS). A sphere to model the human head and an internal point source in order to simulate potential pressure alterations due to intracranial abnormalities or local functional activations, are used in the theoretical representation of the present approach. Finally, numerical results for arbitrary positions of the internal source, concerning the particle velocity (pressure fleld distribution) at the surface of the head model which can implicitly be measured by the suitable piezoelectric sensors, are presented.

Numerical Simulation of EM Environment and Human Exposure When Using RFID Devices

In this work, RFID readers and active tags, operating at 2.4GHz and 5.8GHz, are simulated to calculate the electromagnetic fleld distribution generated in their surroundings, considering the presence of the user's body and possible scattering obstacles, and including the analysis of the speciflc absorption rate (SAR) in the human models (which can be very close to the tag). The flnite-difierence time-domain (FDTD) method and the flnite elements (FE) method are used. Results show that signiflcant fleld level can be found in regions far from the tag-reader direction. This fact could constitute a risk because of the possible presence of general public and eventual eavesdroppers. Nevertheless, the calculated values of SAR are always below the basic restrictions.

IMPROVED ANALYTICAL MODEL FOR SURFACE-MOUNTED PM MOTORS CONSIDERING SLOTTING EFFECTS AND ARMATURE REACTION

This paper presents an exact analytical method for the computation of the magnetic fleld distribution in surface-mounted permanent-magnet (PM) motors for any pole and slot combinations including fractional slot machines. The proposed model takes into account the slotting efiect and the armature reaction magnetic fleld. The analytical method is based on the resolution of the two- dimensional Laplace's and Poisson's equations in polar coordinates (by the separation of variables technique) for each subdomain, i.e., magnet, airgap and slots. Magnetic fleld distributions, back electromotive force and electromagnetic torque (cogging torque and load torque) computed with the proposed analytical method are verifled with those obtained from flnite element analyses.

TUNABLE METAMATERIAL DESIGN COMPOSED OF TRIANGULAR SPLIT RING RESONATOR AND WIRE STRIP FOR S- AND C- MICROWAVE BANDS

In this paper, we study tunable metamaterial structures whose unit cell has triangular split ring resonator and wire strip for S- and C-microwave bands. Three types of new metamaterials, concentric and non-concentric conflgurations, are designed, and their electromagnetic response is investigated. Constitutive and S parameters are computed using retrieval algorithm to demonstrate the properties of the proposed new metamaterial designs. In addition, the electric fleld distribution on the metallic parts of the structure is illustrated for one design of the each sample. It is shown that the studied new metamaterials exhibit double negative properties in the frequency region of interest. The main advantage of this study based on the proposed structures is having the tunability in terms of the substrate thickness and the possibility of pronounced loss reduction.

ENHANCEMENT OF BLUE LIGHT EMISSION USING SURFACE PLASMONS COUPLING WITH QUANTUM WELLS

dimension flnite-difierence time-domain (FDTD) method is used to simulate the enhanced blue light emission of gallium nitride light emitting diode (GaN-LED) using the surface-plasmons (SPs) cou- pling with the quantum wells. The numerical simulation results demon- strate that when the silver fllm is coated on GaN-LED, the excited SPs play a key role in the enhanced blue light emission, and the en- hancement depends on the geometries of GaN-LED and silver fllm. An enhancement factor is given to describe the enhancement efiect of light emission. By changing the structure parameters of GaN-LED and sil- ver fllm, the enhanced peak of the light emission in the visible region can be controlled. Under the optimal parameters, about 17 times en- hancement at 460nm can be obtained, and the enhancement efiect is evidently demonstrated by the SPs fleld distribution.

NOVEL PLANAR MULTIMODE BANDPASS FILTERS WITH RADIAL-LINE STUBS

This paper presents a novel approach for designing planar multimode wideband bandpass fllters with good selectivity. The multimode resonator is composed of an open-ended microstrip line with length of half-wavelength (‚=2) and several radial-line stubs. By using difierent kinds of radial-line loaded stubs, difierent kinds of responses including three-pole and four-pole bandpass fllters can be realized. Depending on electric fleld distribution and equivalent circuit model, the characteristics of the fllter are analyzed. To verify the proposed method, two fllters are implemented. The measured results exhibit good agreement with the simulation.

TRANSPARENT SHELLs --- INVISIBLE TO ELECTROMAGNETIC WAVES

In this paper, we study metamaterial-based transparent shells, which are invisible to electromagnetic waves and flelds. More general topics, including material loss, material discretization and far fleld distribution etc. are covered in order to facilitate possible realization. We design and analyze the transparent shells using optical transformation. Unlike the widely-studied cloaking devices which make the objects inside invisible, the transparent shells physically cover and shield the devices inside without sacriflce of their electrical performance since they are transparent to incoming electromagnetic waves. Due to the simple constitutive parameters, these transparent structures could be realized using artiflcial metamaterials in a wide frequency band, which may have wide applications in civil and military areas.

DETERMINATION THE MATERIAL PARAMETERS FOR ARBITRARY CLOAK BASED ON POISSON'S EQUATION

We propose a general method to determine the material parameters for arbitrary shapes of cloak based on the Poisson's equation to map the coordinate transformation. As a result, we can obtain the diverse deformation material properties and then the fleld distribution. This method, compared with the previous technique presented in literature, can determine the countless transformation forms, so it may provide the opportunity to choose the optimization transformation and the material parameter map which is easily to be fabricated using the metamaterial technology.