The paper presents analytical solution of nonmagnetic and conductive disc levitation problem. The alternating magnetic field exerts eddy currents in conductive disc and levitation force, subsequently. The electromagnetic field and eddy currents distributions are determined. The force acting upon nonmagnetic disc (Lorentz, Maxwell, coenergy methods) and power losses (Joule volume integral, Poynting surface integral methods) are evaluated. For example, levitation force and power losses versus field frequency are figured out. Additionally, an optimization task for power losses at constant disc volume is solved.
Nowadays it is important to create military and civilian vehicles which would be invisible to radar (or homing precision weapons). Such a task requires using high amount of radio-absorbing materials and high cost of finished samples of re-engineering. So it is very useful to have some methods for mathematical modeling of electromagnetic waves scattering on the object in order to take into account various techniques to reduce the object visibility at the stage of design. After the mathematical modeling for each case (specified wavelength, polarization, background surface, etc.), we obtain the angular RCS dependence. We obtain such dependencies for two different models. Based on the comparison of these two dependencies for different objects, it is very difficult to determine which one of the objects is more detectable. This paper presents a new calculation method which allows characterizing the scattering properties of each object only with a few numbers: specific RCS (same as normalized RCS) and RCS dispersion. The presented method can be simply used to assess the visibility of the objects placed on different background surfaces.
In this paper, a new diode-clamped multilevel inverter for capacitor voltage with inserted inductors is proposed. The key is to solve the voltage unbalance of diode-clamped multilevel inverter (DCMLI), which utilizes fewer switches and adopts a simpler control strategy. In this way, the cost and volume of the DCMLI can be effectively reduced. Firstly, the new five-level inverter topology is analyzed in detail under different operation modes. Then, the proposed topology extended to (2n+1) level inverter is introduced and discussed. Finally, both simulation and experiment results are demonstrated to verify the validity of the proposed topology.
An alternative representation of a Green function for electric fields on surfaces of thin impedance vibrators is proposed. The representation can be applied in software packages for simulation of RF and microwave devices. Advantages of the approach were demonstrated by analyzing the well-known problem of a thin symmetrical horizontal vibrator above a perfectly conducting plane. For a half-wave vibrator, numerical estimates of an effective external induced impedance were made for various distances between the vibrator and the plane. A possibility to realize a distribution of intrinsic impedance on the vibrator capable to compensate of the plane influence was also analyzed.
An electrodeless measurement technique of complex dielectric permittivity of high-K dielectric films is described. The technique is based on a quasi-optic Fabry-Perot resonator and modified for investigation of two-layer dielectric structures --- substrate/K-film. This procedure is destined to be used for providing a simple intermediate control of parameters of high-K films before the following technological process. Regimes of measurements providing the most sensitive conditions for definition of film parameters are considered. The proposed method is tested on two-layer structures with well-known parameters and is used for characterization of ferroelectric (Ba,Sr)TiO3 films in the millimeter wavelength range (~50 GHz).
A study of the Hebron two-way radio tower in Halhul, which is part of the two-way radio network that links Bethlehem tower in the West Bank to Khan Younes tower in Gaza strip, was conducted. Hebron Tower was built over the highest spot in the region, 1027 m above the sea level. Measurements of signal power was conducted for Hebron tower and compared to various other transmitting towers seen from the area. Analysis reveals that power densities of all towers are invariably safe, and their power densities fall below international safe standards. Results show that power densities from Orange cellular tower, 3500 m away and Marah radio tower, 2350 m away from Hebron tower were indeed higher than all others measured, when all power densities were referenced back to 30 m of their respective tower antenna positions. As far as the Hebron tower is concerned, its height of 111m provides a relative safe umbrella, from electromagnetic radiation hazard, away from the main radiation beam, over the area below it.
A highly efficient hybrid method of single integral equation (SIE) and electric/magnetic current combined field integral equation (JMCFIE) is presented, named as SJMCFIE, for analysing scattering from composite conductor and dielectric objects, in which, SIE can reduce one half unknowns in dielectric region. The resultant matrix equation of SJMCFIE can be represented in the iteration form, which makes the computation complexity reduced further, and coupling mechanism of composite model becomes more explicit. For accelerating matrix-vector multiplications (MVMs), Multilevel Fast Multipole Algorithm (MLFMA) is employed to combine SJMCFIE to formulate SJMCFIE-MLFMA at last, which is the extension of SIE-MLFMA in the proposed reference. Finally, some examples verify the new hybrid method on accuracy, memory storage, computation efficiency compared to SIE-MLFMA and JMCFIE-MLFMA. Besides, SJMCFIE-MLFMA can also be used to analyse the complete coated model's scattering.
A benchmarking procedure for sparse linear array synthesis methods is proposed. Our approach is based on the comparison of the performance of the array synthesis algorithm under test with the performance of a reference equispaced array. The benchmark procedure is discussed considering some examples regarding sparse synthesis method proposed in literature. Guidelines for the correct comparison of synthesis methods and some ``tough problems'' for the test of new sparse synthesis algorithms are also provided.
The corrosion and anti-corrosion current of a ship modulated by the shaft can be equivalent to a time-harmonic current. Based on Maxwell's equations and boundary conditions of electromagnetic field, the Helmholtz equation of magnetic vector potential and the magnetic field expressions of the time-harmonic current in air are deduced. Then, the fast Hankel transform filtering algorithm is applied to solve the equations which contain Bessel integral. The theoretic calculation indicates that the magnetic induction intensity and its attenuation rate decrease along with the increase of distance. The three components of magnetic field have different distribution. At last, it is verified that the shaft-rate magnetic field can be observed by the experiments of carbon electrodes and ship model carried in a sea pool.
A ternary composite, based on the M-type hexagonal barium ferrite, BaFe12O19, conducting polymer, polyaniline (PANI), carbon allotrope, and multi-walled carbon nanotube (MWCNT), was prepared through a facile in-situ polymerization process. The structural properties of the synthesized composite were characterized through XRD and FESEM analysis. PANI particles were found to be able to coat on BaFe12O19 and MWCNT surfaces. The increased MWCNT wt% loading within the composite resulted in the increase of the electrical conductivity with values as high as 2.0320 S/m for sample PBM5 (25wt% MWCNT). The composite inherited the salient properties of its respective components to achieve optimum values of shielding effectiveness. The highest value of SEA recorded was 42.37 dB at 17.60 GHz. The significantly larger magnitudes of SEA than SER suggest that the mechanism of shielding for all synthesized composites are through absorption.
Hybrid pattern recognition is used to predict the types of insulation materials used inside wall systems of building envelopes. The hybrid pattern recognition features vector is built using the characteristics of UWB signals. UWB signals can penetrate objects, resulting in scattered signals based on the object's dielectric properties. The object's dielectric properties and structure have a signature within the scattered signals. This paper demonstrates that proper hybrid pattern recognition can be used to experimentally detect the existence and the type of insulation material inside wall systems with a high success rate.
This paper analyzes the extremely low frequency electromagnetic wave excited by a horizontal electric dipole immersed in the sea. Analytical solutions in the air from HED underwater are deduced using a three-layer model. The effect of the sea-air interface is studied along two perpendicular directions. The electric field is inversely proportional to the square of r while the magnetic field is inversely proportional to the cube of r along the interface. By decomposing the total response into direct, up-going and down-going components, contributions of each component are discussed, indicating that interference cancellation effect occurs among the arrival electromagnetic signals from multi-paths at specific offsets and frequencies.
An electromagnetic interference (EMI) shielding material based on the composite of BaFe12O19, polyaniline (PANI) and multi-walled carbon nanotube (MWCNT) was proposed. The constituents of the composite were brought together through mechanical mixing and the in-situ polymerization of aniline on the BaFe12O19 and MWCNT surfaces. A series of composite with different MWCNT wt% loadings (0, 5, 10, 15, 20 and 25wt%) was prepared, and its effect on the EMI shielding performance was investigated. X-ray diffraction analysis was performed on all synthesized composites to confirm the phase formations. FESEM micrographs reveal the PANI particle formation on both BaFe12O19 and MWCNT surfaces. Electromagnetic measurements were done by using a rectangular waveguide connected to a network analyser to obtain the permeability, μr, permittivity, εr, and shielding effectiveness (SEA and SER). The increase in the MWCNT loading results in the enhancement of the composite's shielding performance to a certain limit. Optimum EMI shielding performance are shown by sample PBM4 (20wt% MWCNT) with SER and SEA values of 5.14 dB at 8.2 GHz and 36.41 dB at 12.4 GHz, respectively. influence of different MWCNT loadings (0, 5, 10, 15, 20 and 25wt%) on the EMI shielding performance of a composite consisting of BaFe12O19, polyaniline (PANI) and multi-walled carbon nanotube (MWCNT) were investigated.
In this work linear random arrays are studied. It is shown that random symmetric linear arrays can be more easily characterised (with respect to the asymmetric ones) in terms of the first and second order statistics of the array factor magnitude. In particular, the non-stationarity of the array factor can be taken into account while studying the array response. Accordingly, this leads to more accurate predictions as far as the side-lobe level is concerned.
Effective electromagnetic parameters (EEPs) of periodic structures fabricated mainly by carbonyl iron powders are calculated in this paper. A method of inverting the scattering parameters obtained from simulation software was used. The effect of the absorbent volume ratio and the cycle length on EEPs was studied and analyzed. The correlation of the shapes with EEPs was also researched. The empirical formulas were proposed to calculate EEPs, in which the interaction between two adjacent cells was considered. By using this method, any material could be designed as a periodic structure with controlled EEPs, and the values of EEPs were located between the electromagnetic parameter (EP) of air and that of the original material by a specific rule. The EEPs can be used to design new absorbers as the fundamental data of electromagnetic property of some fresh materials.
Brain stroke incidences have arisen at an alarming rate over the past few decades. These strokes are not only life threatening, but also bring with them a very poor prognosis. There is a need to investigate the onset of stroke symptoms in a matter of few hours by the doctor. To address this, Electromagnetic Impedance Tomography (EMIT) employing microwave imaging technique is an emerging, cost-effective and portable brain stroke diagnostic modality. It has the potential for rapid stroke detection, classification and continuous brain monitoring. EMIT can supplement current brain imaging and diagnostic tools (CT, MRI or PET) due to its safe, non-ionizing and non-invasive features. It relies on the significant contrast between dielectric properties of the normal and abnormal brain tissues. In this paper, a comparison of microwave signals scattering from an anatomically realistic human head model in the presence and absence of brain stroke is presented. The head model also incorporates the heterogenic and frequency-dispersive behavior of brain tissues for the simulation setup. To study the interaction between microwave signals and the multilayer structure of head, a forward model has been formulated and evaluated using Finite Element Method (FEM). Specific Absorption Rate (SAR) analysis is also performed to comply with safety limits of the transmitted signals for minimum ionizing effects to brain tissues, while ensuring maximum signal penetration into the head.
Low-Loss resonators with high Q factor have special importance in modern microwave telecommunications systems. In this paper, a modern dual-band CSRR with high Q factor is first examined using SIW technology on a surface waveguide. It should be noted that the proposed structure paves suitable way for emitting and propagating wave in two passing bands (approx. 4.7 and 5.3 GHz) below cutoff frequency waveguide. High Q factor and its high small sized percentage is the salient specification of this structure as compared to other similar planar resonators proposed in various references. At the end of this paper, three applications of this resonator are studied in designing a small multi-band filter with high Q factor, a small multi band diplexer with low passage bandwidth and a planar oscillator with low-phase noise. According to the scientific literature, the proposed oscillator was found to enjoy the best performance at low phase noise for planar microwave oscillators.
The phase and group refractive indexes of microwaves in the ionosphere region of the earth atmosphere are very important for both the researching theoretical problems and practical problems in wireless information transmission (WIT) and wireless power transmission (WPT). So far, there have been many attempts devoted to discuss and to determine the refractive indexes concerning their velocities in ionized region, unfortunately due tothe complicated features of the ionosphere region leading to research task facing with many challenges. Up to recent, there is still a lack of systematic numerical data of complex refractive index by altitude depending on high frequencies of the electromagnetic waves in the ionosphere region. This paper outlines and discusses some theoretical aspects of the complex refractive index in atmosphere's ionized region. Based on complex relative permittivity and conductivities by altitude determined numerically, the numerical estimated data of complex refractive indexes by the altitude from 100 km up to 1000 km at the different frequencies arealso shown and discussed.
In this paper, a novel resistance network node potential measurement technique based on 16-channel cycle method is presented, and a grounding grids corrosion diagnosis measurement system with 16 channels is built from this method. Through this measurement system, 1,680 valid potential data and 1,560 effective branch voltage data can be collected in one measurement by only 16 accessible node downleads on the grounding grid. The stability error of the excitation current source is less than 0.15%, and the error of the applicable acquisition data is about 1% according to system data tests. Built on the measurements, an underdetermined sensitivity equation for solving the increasing multiple of branch resistance is put in place to determine the corrosion status of grounding grids. The experimental results show that the plenty of data is necessary when solving the underdetermined equation and also show that the system is under a high stability, high accuracy, and can comply with the requirements of corrosion diagnosis for grounding grids.
Toward an engineering optimization for photonic band-gap structures in waveguide filter, this paper presents an effective optimization method using Kriging surrogate model combing with semi-analytical spectral element method to maximize photonic band-gaps. Photonic crystals are assumed to be finite periodic structures composed of two dielectric materials with different permittivities. Kriging surrogate model is used to build an approximate function relationship between the photonic band-gaps and the design parameters of photonic crystals, replacing the expensive reanalysis for electromagnetic simulations of 3D periodic structure. The semi-analytical spectral element method is used to calculate the photonic band-gaps at different sampling points. Numerical results demonstrate that the proposed optimization method can effectively obtain maximum photonic band-gaps.