A high-Q reflection notch method for measuring large dielectric losses in absorbing materials when using a stack resonator, which is a one-dimensional analogue of a capillary-in-a-waveguide technique, has been proposed. A detailed explanation of the effects that lay the basis of the method has been presented. The method is particularly accurate and sensitive for highly absorbing materials when other techniques are inadequate. The method can be used for dielectric spectroscopy of a broad range of liquid and solid materials, with applications in chemical, pharmaceutical and food industry, biomedical sciences, agriculture etc, in those frequency bands of infrared, millimeter wave and, especially, THz waves where dielectric losses are significant.
One of the main techniques for the Finite-Difference Time-Domain (FDTD) analysis of dispersive media is the Recursive Convolution (RC) method. The idea here proposed for calculating the updating FDTD equation is based on the Laplace transform and is applied to the Drude dispersion case. A modified RC-FDTD algorithm is then deduced. We test our algorithm by simulating gold and silver nanospheres exposed to an optical plane wave and comparing the results with the analytical solution. The modified algorithm guarantees a better overall accuracy of the solution, in particular at the plasmonic resonance frequencies.
This paper is devoted to the experimental validation of two direct near-field-far-field transformations with cylindrical scanning for elongated antennas requiring a minimum number of near-field measurements. They rely on the nonredundant sampling representations of electromagnetic fields and employ two different source modellings suitable to deal with electrically long antennas. These transformations allow the accurate reconstruction of the antenna far-field pattern in any cut plane directly from the collected near-field data without interpolating them. Their effectiveness is assessed by the good agreement between the so recovered far-field patterns and those obtained by means of the classical near-field-far-field transformation with cylindrical scanning.
A TM mode analysis in a metamaterial based dielectric waveguide is proposed and introduced. Rigorously derived from Maxwell's equations, the dispersion properties are focussed on the fundamental properties of bound, surface and leaky modes of metamaterial based dielectric waveguide. Comparing with the conventional right handed material based waveguide, typical backward wave characteristic of volume and surface wave modes are found from the distribution of Poynting power to the transverse direction of waveguide.
Overhead-line power conductors do not run parallel to the ground; they actually sag between adjacent towers, defining catenary curves. However, in the analysis of inductive coupling phenomena between power lines and neighboring circuits, the standard approach to deal with the sag effect is to assign a constant average height to power line conductors. The purpose of this research is to assess the accuracy of such an ordinary procedure. To do that, two different approaches are developed in order to more accurately account for the sag effect: a pure segmentation method, and a corrected segmentation method which takes into consideration the real curvature of the sagged conductors. The latter, and novel, approach is compared with the other options. Calculations presented in this work utilize magnetic vector potential as an analysis tool.
A low frequency (50 Hz) dielectric barrier discharge (DBD) system with a single dielectric cover on copper coil anode is designed to generate and sustain the microdischarge plasma which is very practical for material processing applications. The DBD system is powered by a high tension ac source consisting of a conventional step up transformer and variac. The dielectric barriers (quartz and glass) between the conducting electrodes appreciably influences the discharge plasma characterized by optical emission spectroscopy technique. Using intensity ratio method, the electron temperature and electron number density are determined from recorded spectra as function of ac input voltage, type and thickness of dielectric barrier and inter-electrode gap. It is observed that both the electron temperature and electron number density increase with the increase in ac input voltage and εr/d ratio, while a decreasing trend is observed with increase in inter-electrode gap.
The 35GHz and 96GHz electromagnetic wave propagation characteristics in plasma are studied theoretically and experimentally in this paper. The variations of the incident electromagnetic wave attenuation along with the plasma density, collision frequency and electromagnetic wave frequency are acquired based on the physical model. The electromagnetic wave propagation properties in plasma are studied experimentally with the shock tube, and the experimental results match well with the theoretical ones. The theoretical and experimental results show that increasing the electromagnetic wave frequency is an alternative and effective method to solve the reentry blackout problems.
The authors discuss and demonstrate the feasibility of using ultra wide band microwave radar to detect and identify small arms fire. Detection and tracking is by standard radar techniques, but identification is carried out by exciting the projectiles Complex Natural Resonances and using this aspect independent information to assign a caliber to the incoming projectiles. The typical sizes of small arms projectiles (calibers 5.56 mm through to 13 mm) imply that ultra wide band illumination in the microwave region of the spectrum between 1.5-5.5 GHz is required to excite these object's fundamental resonances. The authors give a discussion of the effects of motion on the quality of the complex natural resonance data obtainable and present both simulated and laboratory data for the radar cross section of three different caliber projectiles (5.56 mm, 7.62 mm and 13 mm).
In this paper, the electromagnetic field distribution inside a jet engine is studied through full wave analysis. Results are statistically analyzed by comparisons to the models used for the reverberation chamber with a mechanical mode stirrer. The jet engine is simulated as an open cylinder containing one set of rotating blades by using 'Ansys R HFSS'. A simple Hertzian dipole illuminates the interior structure as an incident wave excitation representing a transmitting antenna radiating continuous wave fields. The field distribution inside the engine, which results from a distinct set of rotating positions of the blades, is primarily studied through the simulation program. In our case, the mechanical stirrer is represented by the rotating set of blades. The field values are extracted at different planes along the cylindrical engine, and the average field is statistically analyzed. We show that the squared magnitude of the field component along the engine's main axis has an exponential distribution compared to the theoretical exponential distribution proved in a reverberation chamber. This approach promises to act as a novel effective method to analyze the engine system without dealing with the complex details inside the engine cavity.
Thinning of large arrays in order to produce low side lobes is a difficult task. Conventional gradient methods often stuck in local minima and hence are not capable of obtaining optimum solutions. As a result, global optimization methods are required to thin large antenna arrays. In this paper, a global evolutionary method, Biogeography based optimization (BBO) is introduced as a new tool for thinning large linear and planar antenna arrays of uniformly excited isotropic antennas. The aim is to synthesize linear arrays so as to yield the maximum relative sidelobe level (SLL) equal to or below a desired level while also keeping the percentage of thinning equal to or above the desired level. The results obtained by BBO are compared with the previous published results of Genetic Algorithm (GA), Ant Colony Optimization (ACO), Immunity Genetic Algorithm (IGA) and Binary Particle Swarm Optimization (BPSO).
Linear embedding via Green's operators (LEGO) is a diakoptics method that employs electromagnetic ``bricks'' to formulate problems of wave scattering from complex structures (e.g., penetrable bodies with inclusions). In its latest version the LEGO integral equations are solved through the Method of Moments combined with adaptive generation of Arnoldi basis functions (ABF) to compress the resulting algebraic system. In this paper we review and discuss the convergence properties of the numerical solution in relation to the number of ABFs. Besides, we address the issue of setting the threshold for stopping the generation of ABFs in conjunction with the adaptive Arnoldi algorithm.
This paper deals with resonant transmission through a pair of ridge-loaded circular sub-wavelength apertures in an infinite perfect electric conductor (PEC) plane. The effect of the distance between the two resonant circular sub-wavelength apertures allocated along the ridge direction (``parallel'' case) and perpendicular to the ridge direction (``collinear'' case) on the transmission cross section (TCS) is analyzed numerically by using a method of moments (MoM). It is found that the TCS for the parallel case varies more sensitively to the distance than that for the collinearly located case, and the maximum TCS for the parallel case is tripled compared to the TCS value of a single resonant aperture. For the case of maximum TCS in the parallel configuration, the directivity in the broadside direction is about 8.76 times (=9.43 dB) compared to that for the single resonant aperture. For the purpose of validation, the single resonant aperture and a pair of resonant apertures in the parallel configuration with a distance for maximum TCS are fabricated on a stainless steel plate with 0.3 mm thickness, and their transmission characteristics are measured. Experimental results show that the transmittance, which is a transmitted power density measured at 50 cm away from the aperture plane, for the parallel resonant apertures is about 7 times (=8.43 dB) higher than that for the single aperture, which agrees well with the simulation.
The electromagnetic characteristics of the aperture located on a PEC (Perfect Electric Conductor) cavity is an important and challenged research in CEM(Computational Electromagnetics) and practical applications. Researches have been done well when the aperture locates on a large flat surface. But the complex slots and apertures are still difficult to analyze, such as a thin long slot. Thin long slots present on different kinds of the structures, such as missiles, aircrafts, handset equipments, and computers. And, most of the surfaces are non-flat. Furthermore, the multiscale characteristic of the structure makes the modeling very difficult in such cases. It becomes an increasing interested research recently. A better result can be obtained by generating much more denser meshes. Because of the complexity of the algorithm and ill-posed matrix problem, It is not an optimized option. In order to get a better use of the aperture theorem in the multiscale problems, a separation technique is developed in this paper. By using readjustment of the equivalence electric and magnetic currents, a simplified model is proposed. Arbitrary shaped aperture can be very well handled through this method, especially the thin long slots.
A hybrid time-domain method combing finite-difference and cell-centered finite-volume method is presented in this paper. This method is applied to solve three dimensional electromagnetic problems which involve media having finite conductivity. The fractional-step technique (FST) for FVTD scheme is applied to solve these problems. Local time-step scheme is used to enhance the efficiency of this method. Numerical results are given and compared with a reliable numerical method, which is used to show the validation of this method.
A problem of electromagnetic waves scattering and radiation by a structure, consisting of a narrow transverse slot in broad wall of rectangular waveguide and a vibrator with variable surface impedance, located inside the waveguide and interacting with one another, is solved. A solution of integral equations for electric current on the vibrator and equivalent magnetic current in the slot is derived by the generalized method of induced electro-magneto-motive forces. Conditions necessary for achievement of maximal slot radiation coefficient are defined. Effectiveness of impedance vibrators application to ensure required level of radiation by vibrator-slot structure in low profile rectangular waveguides is shown. Calculated and experimental plots of energy characteristics of the vibrator-slot structure for different vibrator placement relative to the slot and for various surface impedance dependencies upon the vibrator length are presented.
Magnetic induction tomography (MIT) is a contactless measurement technique of biological tissue conductivity. In this study, the differential induced voltage equations are shown in single layer and n layers models. The paper describes a 16 channels MIT measurement system with working frequency of 1MHz, which can image the plan of low conductivity object. According to physical experiments, the sensitivity is about 0.29°/S·m-1, and the maximum shift of the phase noise is 0.08°. Some preliminary clinical experiments were done, including 2 cases of meningitis and 5 cases of brain normal patients. The comparison of all the measured values shows that all values are smaller than 1.7° in the brain normal cases, but the values of meningitis cases are more than 2°, higher than those of brain normal patients. Therefore, the MIT measurement system has great application prospect in dynamically monitoring the brain diseases.
Using a new combined approach, the effect of the uniaxial anisotropic dielectrics on the resonant frequency and radiation field of an equitriangular patch antenna is presented in this paper. The problem is analysed in the spectral domain using the moment method and an electric field integral equation combined with a mathematical approach. However, the dyadic Green's functions corresponding to the proposed structure are separately developed and the Fourier transform of the basis current components are calculated mathematically using ``the reference element" method. Numerical results show that the change in the resonant frequency and the radiation patterns of the antenna is due primarily to a small disturbance of the substrate's nature. Then the effect of the uniaxial anisotropic materials is a significant parameter and most essential on the microstrip antenna characterization.
In the previous works, based on winding function theory, the calculation of reluctance machine inductances is carried out using numerical integration or inexact analytical equations based on approximated Fourier series expansions of the inverse air gap function. In this paper, development in Fourier series of the inverse air gap function has not been used, but a closed form analytical equation is developed for inductances calculation. This leads to a very precise computation of the inductances of the faulted machine and more accurate results. Moreover, all space harmonics ignored by the Fourier series expansions of the inverse air gap function will be included in the model. Derived comprehensive equation allows calculating time varying inductances of reluctance machines with different static, dynamic and mixed eccentricities in the frame of a single program. Inductances obtained by the proposed method are compared to those obtained from FE results. A satisfactory match was found between them.
Analytic expressions for the scattered magnetic vector potential from an infinitely long DB circular cylinder are presented. An arbitrarily oriented electric dipole is considered as a source of excitation that induces surface currents on the DB circular cylinder. Approximate far field expressions for magnetic vector potential are also derived in this setting. Numerical results of the scattering from the DB cylinder are also presented and compared with those of the PEC cylinder.
In this paper, linearly polarized transmitarray is investigated as to avoid the usage of multilayers for improving the bandwidth of transmitarray. The transmitarray is formed from a single dielectric sheet by perforating selected areas of the material. A perforated dielectric layer is divided into square cell elements. Each cell has four holes with the same diameters. Holes with different diameters in the cell elements are used to allow continuous tuning of the transmitted signal's phase over 360o range with a maximum loss of 3.6 dB at 10 GHz. The transmission coefficient versus the diameter of the holes is calculated by using the finite integration technique. The results are compared with those calculated with transmission line method for verification. The focal-to-diameter ratio of the transmitarray is optimized for lower side lobe level and highest transmitarray gain. A comparison between the transmitarray and the reflectarray with the same aperture area is illustrated.