In this paper, we propose a brief and general process to compute the eigenvalue of arbitrary waveguides using meshless method based on radial basis functions (MLM-RBF) interpolation. The main idea is that RBF basis functions are used in a point matching method to solve the Helmholtz equation only in Cartesian system. Two kinds of boundary conditions of waveguide problems are also anlyzed. To verify the e±ciency and accuracy of the present method, three typical waveguide problems are analyzed. It is found that the results of various waveguides can be accurately determined by MLM-RBF.
The absorption and dispersion properties of a Kobrak-Rice 5-level quantum system are investigated. It is shown that the dressed states of such a system are phase-dependent. It is also demonstrated that the absorption, dispersion and group index can be controlled by either the intensity or relative phase of driving fields. Moreover, we have shown that by applying an incoherent pumping field the absorption doublet switches to gain doublet, and the absorption free superluminal light propagation appears which can be used in the transfer of information process.
This paper describes the design and analysis of a Microstrip Reflectarray Antenna (MRA) with Minkowski shape radiating element at frequency of 11 GHz. This structure has been analyzed and compared with the traditional reflectarray element (square element patch). It is found that this antenna array has lower sidelobe level (SLL) characteristic which is down to -25 dB. This MRA has maximum realized gain of 29.6 dB with half-power beamwidth (HPBW) of 3.7°. The validation for the proposed MRA is done by comparing the simulated and measured E-plane radiation pattern. The difference margin between sweeping realized gain (simulation) and sweeping power received (measurement) had been compared within the frequency range of 10--12 GHz. A very good agreement is found from the comparison between simulation and measurement.
An efficient hybrid method is presented to obtain the current distribution of both non-uniformly linear and planar arrays By sampling the array factor of a desired radiation pattern, the proposed method provide Fourier coefficients and uses the Least Mean Square method (LMS) to solve the system of equations in order to obtain current distribution in associate with the desired radiation pattern. Obtained side lobe level is 3 dB lower than conventional methods such as LMS method or Legendre function method.
Accurate approximations of the conductance and the conductance bandwidth of an electrically small antenna valid in resonant and antiresonant ranges were found. It is shown that the conductance bandwidth of an efficient antenna tuned on maximal power of radiation is inversely proportional to the magnitude of the frequency derivative of the input impedance |Z'(ωcd)| of the antenna at frequency of maximal conductance. That is a generalization of the well known relationship according to which, the conductance bandwidth of an antenna tuned on resonance in resonant ranges is inversely proportional to the magnitude of the frequency derivative of the input reactance of the antenna |X'0(ω0)| at resonant frequency. Obtained approximate formulas display inverse proportionality of the conductance bandwidth to the approximate quality factor of the antenna throughout resonant and antiresonant ranges. A differential definition of the fractional conductance bandwidth was formulated, which is convenient for the case of closely spaced resonances of an antenna. As an example, numerical calculations for oblate spheroidal and spherical antennas in shells with negative permittivity in resonant and antiresonant ranges was used to confirm accuracy of the obtained approximations of the conductance and the conductance bandwidth of an electrically small antenna.
We report an analytical exciton emission model based on Green function for simulating the radiation characteristics of near-infrared Quantum Dot-light emitting devices (QD-LEDs). In this model the internally emitted light can be classified into the following modes: substrate, indium tin oxide (ITO)/organic waveguided, surface plasmonic modes, and external emitted mode. We investigate the influence of the thickness of different layers and the distance between the emitting center and the cathode metal on the emitted power distribution among these modes. In addition, we study the angular radiation profile for the externally emitted radiation and substrate waveguided mode in comparison with lambartian radiation profile. We show the change of the thickness of the different layers, and the positions of the emitting centers are critical to the optical performance of the device. The optimization of optical performance through device geometry increases the outcoupling efficiency more than five times.
The concept of partially coherent four-petal Gaussian (PCFPG) beam is introduced and described in analytical forms. Based on the Huygens-Fresnel integral formula, average intensity and beam spreading in turbulent atmosphere are derived in analytical expressions. Effects of beam parameters and atmospheric structure constant on intensity distributions and effective beam sizes are investigated in detail, respectively. Results show that PCFPG beams carrying larger coherence lengths or higher beam orders would be less affected by turbulence. It is also indicated that, when the propagation distance increases, the PCFPG beam would convert into the Gauss-like profile sooner or later, but this degradation can be reduced by modulating beam parameters. Results in this paper may provide potential applications in free-space optical communications.
This paper uses the accurate and computationally efficient complex image technique (CIT) to find the electric field and SAR distributions inside a human head illuminated by a finite-length dipole. The human head model used consists of 3 planar layers of lossy dielectrics. The accuracy of the results is verified by comparison with HFSS software. It was found that the CIT requires about 1 minute and 16 MB of RAM, while HFSS requires about 2 hours and 1.5 GB of RAM to find the SAR distribution using a 2.19 GHz Core 2 Due PC. The CIT method can also efficiently solve other types of antennas on other planar head models.
It is a current need of research to extensively use the freely available satellite images. The most commonly available satellite images are Moderate Resolution Imaging Spectroradiometer (MODIS) and The Advanced Very High Resolution Radiometer (AVHRR). The problems with these images are their poor spatial resolution that restricts their use in various applications. This restriction may be minimized by application of the fusion techniques where high resolution image will be used to fuse with low resolution images. Another important aspect of fusion of different sensors data as optical and radar images (where both can provide the complimentary information), and the resultant fused image after fusion may give enhanced and useful information that may be beneficial for various application. Therefore, in this paper an attempt has been made to fuse the full polarimetric Phased Arraytype L-band SAR(PALSAR) image with MODIS image and assess the quality of fused image. PALSAR image has a advantage of availability of data in four different channels. These four channels are HH (Transmitted horizontal polarization and received also in horizontal polarization), HV (Transmitted horizontal polarization and received vertical polarization), VH (Transmitted vertical polarization and received horizontal polarization) and VV (Transmitted vertical polarization and received vertical polarization), which provides various landcover information. The curvelet based fusion technique has been applied to MODIS band 1 and 2 and PALSAR HH (HV and VV bands for assessing the effect of fusion in land cover distinction). The three major land covers agriculture, urban and water are considered for evaluation of fusion of these images for the Roorkee area of India. The results are quite encouraging, and in near future it may provide a better platform for maximize the use of MODIS images.
The development of compact antennas plays an important role in the rapidly growing mobile communication market. This paper presents a novel design technique of the quad-band small internal antenna covering GSM-900/DCS-1800/PCS-1900/IMT-2000 bands. The innovative quad-band built-in handset antenna is developed within the limit of a 44×25×4 mm3 volume. The following document describes a new idea of increasing operational bandwidth for the compact planar inverted F antenna (PIFA). The proposed compact antenna introduces the open-end slots in the ground plane almost all under the radiating patch. The size reduction method is attractive for practical antenna implementations. In addition, the end user's hand handling effects on the performances of the proposed antenna are studied.
Planar waveguides with an isotropic chiral core, called chirowaveguides, support the propagation of elliptically polarized modes, making them natural candidates for chiral sensing. We investigate the potential of chirowaveguides as optical sensors responding to changes in the circular birefringence of a medium covering the waveguide. Using first order approximations, we derive expressions for the sensitivities to refractive index and to changes in circular birefringence. The chiral sensitivity is proportional to the achiral sensitivity and to the eccentricity of the mode under consideration. Possible combinations of materials and design conditions for chirowaveguide sensors are discussed with reference to these results. The motivation for this study, besides its theoretical and academic importance, comes from potential applications for enantiomeric integrated optical devices.
The aim of this paper is to discuss the effects of the exposure to Extremely Low Frequency ElectroMagnetic Fields (ELF-EMFs) on non- and excitable cells using in vitro cell models, namely neuron-like cell line (PC12), glioblastoma GL15 as glial model and C2C12 myocytes as muscle model, focusing our attention on standardized protocols for ELF-EMFs generation and exposure. A major issue in laboratory -and likely in natura- studies about possible biological effects of ELF waves is the difficulty in providing standard, reproducible environmental conditions. Hence, as part of the work we have developed an exposure system including a probing scanner, able to sample a given volume and to measure the time-varying magnetic field vector. The system allows detection, monitoring and removal of electromagnetic noise sources, as well as means to assess field homogeneity in terms of intensity and polarization.
This paper presents the design, fabrication and measurement of a dual band switchable metamaterial electromagnetic absorber. The unit cell of the metamaterial consists of dipole mode electric resonators coupled by microwave diodes on one side of a dielectric substrate and metallic ground plane on the other side. Simulation and measurement results show that by forward or reverse biasing the diodes so as to change the coupling between the resonators, the absorber can be dynamically switched to operate in two adjacent frequency bands with nearly perfect peak absorption. Field distribution reveals the physical origin of the switchable performance based on the dipole mode of the electric resonator in the unit cell. It is also demonstrated that the frequency difference between the two bands can be tuned by adjusting the loading positions of the diodes with unchanged high absorption, which helps to design absorbers with specific switchable working frequencies in practical applications.
The 2×2 MMI polymer thermo-optic switch in a high refractive index contrast (0.102) with a new structure design is realized. This device was fabricated using standard fabrication techniques such as coating, photolithography, and dry etching. A crosstalk level of -36.2 dB has been achieved. Meanwhile the extinction ratio of 36.1 dB has been achieved in this device. The polarization dependent loss (PDL) of 0.3 dB and Insertion loss of 1.4 dB were measured at 1550 nm wavelength. In terms of wavelength dependency, the device shows a good performance within C-band wavelength with vacillation of the insertion loss value around 0.88 dB. The power consumption of 1.85 mW was measured to change the state of the switch from the cross to bar state. The measured switching time was 0.7 ms.
A finite length cylindrical FSS is proposed as a spatial filter for both transmitting and receiving antennas. This filter has the advantage of not perturbing the omnidirectional property of the enclosed antenna. The proposed surface is constructed up as cylindrical array of rectangular conducting patches. The strips are arranged periodically in the φ- and z-directions. The electric field integral equation (EFIE) approach is used for analyzing the characteristics of the proposed spatial filter. The Rao-Wilton-Glisson (RWG) basis functions are used for current expansion on the conducting strips. The mutual effects between the filter and the antenna can be accurately investigated. The effects of some dimensional parameters on the filter characteristics, such as, the axial and angular spacing between the array elements, the length and the radius of the cylindrical surface are studied over a wide frequency range. The oblique incidence of plane waves on such a cylindrical filter is studied with varying the direction of incidence. The performance of the proposed spatial filter is examined when operating with nearby antennas. The effects of such a filter on the input impedance, VSWR, and radiation pattern of an enclosed bowtie antenna are investigated over a wide frequency range.
A toroidal field coil (TFC) is composed of several individual toroidal coils (ITCs), which are connected in a series and distributed in a toroidal and symmetrical form. Cross section of ITCs is rectangular or negligible. This paper presents analytical equations for mutual inductance of two ITCs applicable to Tokamak reactors using the filament method. These equations are based on those formulated by Neumann. The numerical analysis of the integrations resulting from these equations is solved using the extended three-point Gaussian algorithm. The finite element method (FEM) is employed to verify the mutual inductance equations of ITCs. The results obtained using the FEM, when dimensional parameters of ITCs are changed, confirm the analytical and empirical results showing an error of less than 0.2043% in the worst case. This indicates the reliability of the presented equations.
Using magnetic composite material as the substrate for RFID metal tag has several advantages over conventional metal tags, such as flexibility and miniaturized size. In this paper, the radiation intensity contributed by a half-wave dipole is derived based on the result of an ideal Hertzian dipole, which leads to a simple relation for thin substrate. Later on, the material constants of two materials are measured and the one capable of generating greater radiation intensity is used in the course of antenna design. A primitive pattern design demonstrates the metal tag has a satisfactory 2.7 m reading range, and a dimension of 80×22×2 mm3.
In this paper, extending the design technique presented by the authors in a previous work, we propose the study of a new family of polygonal patch antennas for portable devices of communication systems. Such antennas are suitable to be mounted in modern terminals, enabling wideband/multi-frequency operation and new multimedia features. The desired electromagnetic behaviour of the proposed radiators is obtained by adding either shorting posts, properly located between the polygonal patch and the ground plane, or circular slots, drilled at the appropriate position on the patch surface. Circular slots are also useful to easily accommodate a photo-camera in the terminal, in order to enable multimedia services and video calls. Some practical layouts of polygonal patch antennas to be used in: a) modern PDAs and Smart Phones integrating cellular phone operation and wireless functionalities; b) UMTS terminals integrating also GSM functionalities, are, finally, presented. The effectiveness of the proposed designs is confirmed through proper full-wave numerical simulations.
This paper presents a general analytical formulation for calculating the three-dimensional magnetic field 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 field 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 1 s for calculating the magnetic field 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 fields.
This paper studies the potential of ultra-wideband (UWB) microwave imaging for detection and localization of breast cancer in its early stages. A method is proposed for locating tumors which is based on the time-of-flight of the signal backscattered at the tumor. Time-of-flight is detected using a wavelet transform algorithm. The main contribution of this paper is that it proposes to determine the position of the tumor by using an adapted version of the centroid localization method used in wireless sensor nodes. Its main advantage is that it does not require knowing a priori neither the propagation velocity of the breast nor its dielectric permittivity. The feasibility of the method has been investigated by means of simulated and experimental results with an ultra-wideband radar and a phantom.