An analytical formulation is developed for an axial slot on an infinitely long conducting circular cylinder eccentrically coated with dielectric and partially embedded in a ground plane. A computer program has been developed based on the resulting formulation. The problem is highly significant since the ground plane could be the body of an aircraft, a ship, or any other mobile system. The effect of the ground plane can be used to enhance the radiation characteristics in some cases. It is also a support for the antenna instead of using other mechanical mounting supporting system. Numerical results for different antenna configurations are illustrated. The results show that how one may shape the pattern by offsetting the slotted cylinder from the center of the dielectric coating.
This paper introduces a modified enhanced transmission-line theory to account for higher-order modes while using a standard transmission line equation solver or equivalently a Baum, Liu and Tesche (BLT) equation solver. The complex per-unit-length parameters as defined by Nitsch et al. are first cast into an appropriate per-unit-length resistance, inductance, capacitance and conductance (RLCG) form. Besides, these per-unit-length parameters are modified to account for radiation losses with reasonable approximations. This modification is introduced by an additional per-unit-length resistance. The reason and explanations for this parameter are provided. Results obtained with this new formalism are comparable to those obtained using an electromagnetic full-wave solver, thus extending the capability of conventional transmission line solvers.
This article describes a method of guiding a moving ferromagnetic sphere. By using a magnetic field, it is possible to confine a moving object such as a steel sphere to motion along a curve. We have designed and built a device that uses the magnetic field in the gap of a steel tube to trap and guide a steel sphere along a circular path solely by a magnetic restoring force. A simple relationship between tangential velocity and magnetic field strength in the gap is developed. Excellent correlation between analytic, simulated, and measured results are shown.
The specific features of TM-polarized surface electromagnetic waves in a finite structure fabricated by a periodic alternating semiconductor and dielectric layers are investigated. Dispersion characteristics of eigenwaves are analyzed numerically and analytically. The complex Poynting energy flux and the surface wave's distribution are calculated. The influence of geometrical and physical parameters of the structure on the properties of surface waves is studied.
The Medium-Earth-Orbit SAR（MEOSAR）is one of the potential next-generation spacebarne SAR for its excellent performance, however, due to ionospheric effects, a MEOSAR may not be able to produce data useful for science applications. So study of ionospheric effects is one of the critical techniques for the development of MEOSAR. In this paper, we present ionospheric effects on azimuth imaging for MEOSAR. First, we establish an analysis model for ionospheric effects on azimuth imaging of MEOSAR based on the system characteristics of MEOSAR and the temporal-variability of ionosphere. Then, based on the analysis model, we analyze the effects caused by the quadratic and cubic phase errors induced by temporal-variability of ionosphere on azimuth imaging. According to the results of our analysis, we conclude that both the quadratic phase error and the cubic phase error neglected for Low-Earth-Orbit SAR(LEOSAR) will deteriorate the azimuth imaging for MEOSAR and ionospheric effects become more and more serious with the increase of SAR altitude and the improvement of azimuth resolution designed.
Dynamics of interference interaction of counter-propagating electromagnetic pulses on a magneto-dielectric slab is studied in time domain. Energy redistribution in the counter-propagating pulses with arbitrary waveforms is considered. The maximal energy redistribution in the diffracted field takes place under certain conditions. The conditions are found and their physical explanation is supplied. The problem of transient electromagnetic wave diffraction on homogeneous magneto-dielectric slab is solved analytically by means of Laplace transform. The analytical solution is in agreement with numerical simulation based on finite difference time domain approach.
This paper deals with the design of small-sized bio-implanted spiral circular coils (pancake) with an operating frequency of 13.56 MHz. The external and internal coils' geometric dimensions are dout = 56 mm, din = 10 mm and dout = 11.6 mm, din = 5 mm, respectively, in which the electrical performance is verified through the commercial field solver High Frequency Structural Simulator (HFSS 13.0), which employs the finite-element method (FEM) technique. Mathematical models for the proposed coils are developed. The simulation is performed-based on the developmental model in the air and at depths 6\,mm in a human biological tissue of dry and wet-skin. The results demonstrate that the external and internal coils have maximum near-field gains of 54.15 dB and 53.30 dB in air. The maximum gains of the external coil contacted the wet and dry skin are 49.80 dB and 48.95 dB, respectively. The maximum gains of the internal coil at depths of 6 mm in the wet and dry tissue are 41.80 dB and 41.40 dB, respectively. However, the external coil radiation efficiencies on wet- and dry-skin are 92% and 90%, respectively, compared with that on air. The internal coil radiation efficiencies on wet- and dry-skin are 78.4% and 77.6%, respectively, compared with that on air. In this study, the specific absorption rate (SAR) and radiated power results of the internal coil are investigated using SEMCAD 16.4 software. The SAR and power loss studies show that the designed implanted coil has a negligible effect on the wet and dry skin and can be ignored.
In this work, we exploit photonic crystal heterostructures formed by the combination of periodic and Fibonacci structures to design promising optical devices acting in the visible and the near infrared domains. An hybrid structure of the type Bragg mirror-(Fibonacci)S is proposed to enhance the high reflection band through the one dimensional photonic crystal in the near infrared. The use of the configuration exhibits a large photonic band gap at any angle of incidence and for both polarizations. The proposed structure is a quarter wavelength omnidirectional mirror of 37 layers with a bandwidth larger than that of the periodic structure with an increasing ratio 3.7, and it covers all the optical telecommunication wavelengths 0.85, 1.3 and 1.55 μm. Then a second structure of the type Bragg mirror-(Fibonacci)S-Bragg mirror with varied optical thicknesses permits to confine strongly the light giving a rise to a microcavity through the visible range with strong mode localisation. Since different physical phenomena have their own relevant physical scales, we exploit the physical properties of the proposed structures in different wavelength domains to obtain different optical devices. The transmission spectra are determined by using a theoretical model based on the Transfer Matrix Method (TMM).
We present an efficient scheme for the analysis of electromagnetic scattering from target and environment composite model. In this scheme, the whole computed domain is divided into a target part and an environment part, and each part is formulated by different integral equations. The two parts are solved one by one until the relative residual error is less than a given value. Compared with conventional solution with pure electric field integral equation (EFIE), the proposed scheme has a better convergence and lower memory requirement. Additionally, the multilevel fast multipole algorithm (MLFMA) is utilized to accelerate the computations of matrix vector product. Simulated radar-cross-section (RCS) results of several examples demonstrate its validity and efficiency.
In this work, theoretical analysis and numerical results are given for time-reversal (TR) focus gains of polarization-varying electromagnetic fields in a rectangular resonant cavity. To demonstrate the gains in different polarization states of the static transceivers and the ones of the rotatable transceivers, the 3 dB attenuation areas of TR angle gain (AG) and AG flatness are first calculated. The flat area is about equivalent to the range of two centrosymmetric octants in a three-dimensional Cartesian coordinate. Phase-frequency waterfalls verify the polarization-rotational rheology of the TR focus gain, in which uniform and smooth areas will contribute higher gain than uneven and rough areas.
In this paper, we propose a very simple technique that offers an extra degree of freedom to optimize the design of a tire dust-based absorber with reduced height. Cladding is a technique that is used to enhance the surface properties of a part, and it has been used in many applications for many years. In this technique, a clad layer is created on the core material, and the composition of the clad layer is adjusted to enhance the performance of the core material. We use a rice husk-clad layer to enhance the impedance matching characteristics of the low-loss, tire-dust core, microwave absorber. The overall design is a two-layer, geometrically-tapered, pyramidal structure composed of two lossy waste materials. Our main goal was to make the front surface less reflective (impedance matched), hence the material of the outer layer (clad) of the absorber was selected on the basis of the analysis of the dielectric properties of the candidate materials. Optimum thickness of the clad was obtained by using CST simulation software and found to be 12 mm, for which a reflectivity performance of less than -20 dB was achieved in the frequency range of 4 to 20 GHz. The results were found to be better than those provided by an earlier design of the absorber, which was composed of a mixture of tire dust and rice husks.
The design of an efficient quasi-optics Frequency Selective Surface (FSS) filter which is required to provide a -3 dB pass band from 405 GHz to 441 GHz is presented. For atmospheric remote sensing application, this space-borne spatial device consists of a silicon layer and a thin copper layer which is perforated with periodic arrays of resonant dipole slots and circular apertures. FSS unit cell has a dimension much smaller than its operating wavelength. Unique features of this complex dense FSS structure include wide pass band properties with superb performance of frequency response and incident angles independence for TE polarization. Floquet mode analysis and finite element method (FEM) models are used to establish the geometry of the periodic structure and predict its spectral response.
This paper proposes a new logging while drilling (LWD) method to evaluate rock moisture content and reservoir hydrocarbon saturation. Transient signal with broadband spectrum covering the sensitive range of fluids contained formation was used as excitation signal in the near-bit MWD system. Continuous measurement in the whole spectrum with both fluid type and saturation changes caused differences in frequency distribution of response signals and achieved integrated evaluation of formation hydrocarbon and water saturation. Linear system analysis was optimized by adding oil/water saturation parameters, and analytic calculating results were presented to verify the performance of the proposed transient MWD system. Compared with conventional wireline and LWD tools, the method presented in this paper provided higher resolution and signal intensity.
This paper presents the analysis of novelistic fractal optical antenna arrays in a conceptual manner. Fractal antennas are array antennas with converging and diverging growth of basic element or elements for multi-wideband capturing of the electromagnetic waves. Most of these antennas relay on two components for their characteristics. First one is the basic stage shape and second one is the number of stages of growth. For computing the direction of radiation the well-defined fractal array manifold and a good estimate of the covariance matrix of the fractal array response is needed.
Derivation is presented for analysing the shielding effectiveness of an enclosure with apertures and inner windows with Transmission Line Method (TLM). Theoretical values of shielding effectiveness are in good agreement with the simulation results. Results indicate that the capacitive window lowers the resonance frequency while the inductive window enhances the resonance frequency, and both of them improve the shielding effectiveness of the enclosure. The effects of location of the inner windows is discussed. Moreover, the present method can also be used in the condition that the enclosure has both inductive and capative windows.
Time-of-flight (TOF) has been used to estimate sound velocity (SV) distribution of heterogeneous tissue to relieve the effect of acoustic heterogeneity in microwave-induced thermo-acoustic tomography (MITAT). Accurately picking the TOFs is significantly important to ensure high accuracy SV images, which greatly help to reconstruct the microwave absorption distribution accurately. However, current methods for picking the TOFs are designed for single source case. For breast tumor detection in MITAT, these methods become ineffective or even fail at the situation where multiple tumors are embedded in a normal breast tissue. In order to accurately reconstruct the microwave absorption properties of tumors in heterogeneous tissue in MITAT, an efficient method for picking tumors' TOFs is proposed. Combining the advantages of the wavelet transform and Akaike information criterion (AIC), the proposed method introduces a concept of separate extraction of TOFs. It can efficiently and accurately pick the TOFs of different tumors from the measured data in MITAT. Using the TOFs picked by the proposed method can efficiently help to reduce the effect of acoustic heterogeneity and greatly improve the accuracy and the image contrast of reconstructed microwave absorption properties. Some numerical simulations are given to demonstrate the effectiveness and feasibility of the proposed method in this paper.
A novel suspended twin-core fiber (STCF) based on a single-nanoweb structure for optical switching is proposed. The singlenanoweb structure of the STCF is an ultrathin glass membrane (nanoweb) suspended in air and adhered to the inner ring of a glass fiber capillary, which substantially provides a built-in transducing mechanism to boost the pressure-induced index change in the fiber core region of the STCF. Two fiber cores locate symmetrically in the center of the nanoweb, resulting to the mode coupling for the guiding light in the STCF. Optical and mechanical properties of the proposed STCFs under different pressure force are numerically investigated. Optical switching based on the STCF is achieved by controlling the pressure force applied to the STCF. Our simulations show that optical switching from one core to the other in the STCF is realized based on a low switching force of only 8 N. The performances of the optical switching based on STCFs with different structure parameters are presented.
The problem of the motion of a magnetic field due to the motion of a permanent magnet has been subject of scientific controversy for many decades. However, the similar question, pertaining to the motion of an electric field due to the motion of a permanent charge, has been neglected by the scientific community, tacitly admitting this specific purely kinematical phenomenon. Such an evidently skew position is under theoretical consideration on an experimental ground. It is shown a profound symmetry between electro-kinematics on the one hand and magneto-kinematics on the other, and also the radical dissimilarity of both from electrodynamics.
Consider a plane wave incident on a multilayered planar anisotropic structure composed of conventional materials and metamaterials and surround by two half-spaces. In this paper, we aim to prove three theorems which indicate a kind of duality in these structures. Assume an arbitrarily polarized plane wave obliquely incident on the structures. Theorem 1: Assume that an arbitrarily polarized plane wave is obliquely incident on the structure. Now each layer is filled with by dual media according to the interchanges DPS ↔ DNG and ENG ↔ MNG. Then, the reflection (R) and transmission (T) coefficients of the structure become the complex conjugates of their counterparts. Consequently, the reflected power and transmitted power from the structure are the same for the two dual cases of anisotropic media. Theorem 2: If the interchanges DPS ↔ DNG and ENG ↔ MNG are made in all the layers except in the half spaces on the two sides of the multilayer structure (which is more realizable), then the reflection coefficients become complex conjugates and the reflected power remains the same. Theorem 3: If the structure is backed by a perfect electric conductor and the media interchanges DPS ↔ DNG and ENG ↔ MNG are made in the layers, then the reflection coefficients of the two dual structures become complex conjugates of each other, and the reflected powers are equal. Independent of wave frequency, the number of layers, their thickness, and the type of polarization, these theorems hold true in case of any change in any of these conditions. In the last section, some examples are provided to verify the validity of the proposed theorems.
We incorporate high-order symplectic time integrators into multiresolution time domain (MRTD) schemes. The stability and numerical dispersion analysis are presented. The proposed scheme preserves the symplectic structure of Maxwell's equations and can be easily implemented in program codes. Compared to Runge-Kutta (RK)-MRTD, the suggested scheme is more accurate in long-term simulations and requires less computational resource.