In this paper, the robust optimization shape and drive of switched reluctance motors (SRM) are discussed using robust particle swarm optimization (RPSO). The shape optimum goal of the algorithm was found for maximum torque value and minimum torque ripple, following changing the geometric parameters. The drive optimum aim of the algorithm was found minimum torque ripple, following changing the current profiles. The optimization process was carried out using a combination of RPSO and Finite Element Method (FEM). Fitness value was calculated by FEM analysis using COMSOL4.2, and the RPSO was realized by MATLAB 2011. The proposed method has been applied to two case studies and also compared with seeker optimization algorithm. The results show that the optimized SRM using RPSO has higher torque value, lower torque ripple and higher robustness, indicating the validity of this methodology for SRM design and implementation.
In the paper, we prove two theorems relating to the theory of thin impedance vibrator radiators excited by a lumped voltage generator under rather general conditions. The first theorem proves that influence of external electrodynamic media on the vibrator current distribution is limited and can be estimated using a small natural parameter. The second theorem ascertains that there exists principal possibility to compensate influence of spatial boundaries upon current distributions on a perfectly conductive vibrator by applying to its surface complex impedance with predetermined variation along the vibrator length. Several corollaries disclose a range of the theorems application and their fundamental importance.
The authors present transmission data, taken at Ka (36 GHz) and W (95 GHz) bands in the millimetre-wave region of the electromagnetic spectrum, for various dressing materials used in the treatment and management of burn wounds. The results show that such materials are highly transparent (typically > 90% transmission) and, in their dry state, will permit the sensing of the surface of the skin through the thick layers (> 2 cm) of different dressings typically applied in medical treatment of burn wounds. Furthermore, the authors present emissivity data, taken at the same frequency bands, for different regions of human skin on the arm and for samples of chicken flesh with and without skin and before and after localised heat treatment. In vivo human skin has a lower emissivity than chicken flesh samples, 0.3-0.5 compared to 0.6-0.7. However, changes in surface emissivity of chicken samples caused by the short-term application of heat are observable through dressing materials, indicating the feasibility of a millimetre-wave imaging to map changes in tissue emissivity for monitoring the state of burn wounds (and possibly other wounds) non-invasively and without necessitating the removal of the wound dressings.
This paper diagnosis the effect of the AC current densities induced by the electromagnetic interference between high voltage power line and buried power line on the cathodic protection performance of the X70 steel in simulated soil. First, the induced AC voltage onto the pipeline was calculated for different power line configuration, separation distances between transmission line and pipeline and parallelism lengths. The induced AC current density was calculated function to the induced AC voltage, soil resistivity, and holiday diameter. Then, the electrochemical characters of the X70 steel at various AC current densities are measured using the potentiodynamic method. The electrochemical parameters obtained by the electrochemical tests are used as boundary conditions in the cathodic protection simulation model. The results indicate that, under influence of AC current densities, the X70 steel is more susceptible to corrosion, and the cathodic protection is unable to maintain the protection potential.
The properties of the Finite Olver-Gaussian beams propagating through an uniaxial crystal orthogonal to the optical axis are studied. An analytical expression is developed, and some numerical simulations are performed to investigate the effects of some parameters on intensity distribution and profile of this beams family at the out-put plane of the uniaxial crystal. The results show that the beam exiting the optical system depends on the ratio of the extraordinary refractive index to the ordinary refractive index. Upon propagation in the uniaxial crystal, the Finite Olver-Gaussian beam in two transversal directions accelerates, while the acceleration in the transversal direction orthogonal to the optical axis is far slower than that in the transversal direction along the optical axis.
For the radiation problem of multi-antenna on electrical-large platform, a multi-region MoM-PO (Multi-MoM-PO) is firstly proposed in this paper. The conventional MoM-PO generally treats all the antennas as a whole MoM region, but in the Multi-MoM-PO, each antenna is classified as one MoM region. On the basis of the mutual interaction between each MoM region and PO region, the self-interactions among MoM regions are considered. Numerical examples demonstrate that the multi-region technique can effectively boost the efficiency of impedance matrix filling compared with the conventional MoM-PO. Finally, the dependence of the filling efficiency against the number of antennas on platform is discussed.
We deal with the problem of determining the profile of a perfectly conducting rough surface from single-frequency and multistatic data. The two fundamental polarizations are investigated, in a two-dimension scattering configuration. Emitting and receiving antennas are positioned on a probing line some wavelengths above the profile. It is shown how the boundary integral equation method can be adapted to the case where the antenna footprint is much wider that the rough part of the profile. The Newton-Kantorovich iterative inversion process is then performed on these synthetic data. Its accuracy and robustness to additive noise are studied in the context of random rough surfaces with correlation length smaller than the wavelength and slope root mean square up to 0.9.
We develop a semi-analytical approach to calculate the polarizability tensors of an arbitrary scatterer. The approach is based on numerical integration from induced charges and currents on the scatterer. By taking the advantages of the present approach, we calculate the polarizability tensors of any arbitrary scatterer in a homogeneous isotropic medium. This approach, in comparison to other reported approaches, is simple, easily implemented, and does not require spherical harmonic expansion or complicated far-eld calculations. We examine the validity of the approach using several examples and compare the results with other approaches.
Compared with traditional monostatic synthetic aperture radar (SAR), bistatic SAR (BiSAR) has stronger advantages in terms of anti-interference and anti-strike abilities. However, the complex system structure of BiSAR brings new difficulties to imaging processing. In order to make the imaging algorithms of traditional monostatic SAR apply to BiSAR imaging as well, this paper proposes an equivalent monostatic model for BiSAR. This model mainly provides two benefits: (1) The equivalent monostatic range history has the form of hyperbolic function; (2) The equivalent monostatic velocity of any scattering point in the observed scene, with respect to the radar platform, is not only the same but also invariant with the equivalent monostatic range. Due to the above benefits, a novel wavenumber domain algorithm (WDA) is further proposed for BiSAR imaging. Finally, the experimental results demonstrate that the proposed algorithm is effective and feasible.
Scattering of light by metal-coated dielectric nanocylinders periodically distributed along a cylindrical surface is investigated both theoretically and numerically. The structure is under the authors' interest because of its practical application in design and fabrication of plasmonic devices such as plasmonic ring resonators, Plasmonic Crystals and THz waveguides. The method is based on the T-matrix approach and the field expansion into the cylindrical Floquet modes. The method is rigorous, straightforward and can be easily applied to various cylindrical configurations with different types and locations of the excitation sources. Scattering cross section and absorption cross section of three and four silver (Ag) coated-dielectric nanocylinders periodically situated along a cylindrical surface are studied. Near field distributions are investigated at particular wavelengths corresponding to the resonance wavelengths in the spectral responses. Special attention is paid to the unique and interesting phenomena characterizing the cylindrical structure composed of the metalcoated nanocylinders such as: a) localization of the field at the outer and inner interfaces of the metal-coated nanocylinders; b) excitement of the field in the gap region between the nanocylinders through the coupled plasmon resonance and c) strong confinement of the field inside the cylindrical structure. Detailed investigations have shown that unique phenomena characterizing the cylindrical configurations of the nanocylinders can be realized using a relatively simple structure composed of three nanocylinders and there is no need to further increase a number of the scatterers (nanocylinders).
This paper mainly deals with the problem of target detection in compound-Gaussian clutter with orthogonal frequency division multiplexing (OFDM) radar. First, the OFDM measurement model is developed to compound-Gaussian clutter by taking advantage of frequency diversity of OFDM radar waveform and we devise a generalized likelihood rate test (GLRT) detector where the target scattering coefficients and clutter covariance matrix are unknown. Then, we propose an adaptive waveform design scheme based on maximizing Mahalanobis distance of the distributions under two hypothesises to improve the detection performance. Finally, the effectiveness of the proposed detector as well as the adaptive waveform design method is demonstrated via numerical examples.
The PMCHWT-IE-FFT-BURA is applied to the wideband analysis of electromagnetic scattering property of homogeneous targets. Over the broad frequency band, the fast computation is achieved by the Maehly expansion on the basis of the Chebyshev approximation of the electric and magnetic currents. On the Chebyshev sampling points, PMCHWT-IE-FFT greatly reduces the memory requirement by sparsely storing the impedance matrix and decreases the computational time to the greatest degree by block acceleration of the matrix-vector product. Finally, numerical results show that the proposed method can make efficient analysis of wideband property of homogeneous targets without sacrificing accuracy much.
The generalized Fibonacci multiferroic superlattices (GFMS) are composed of single-phase multiferroic domains with simultaneous polarization and magnetization and are defined by the binary substitutional rule (B → BmA, A → B, m = 2, 3). We propose to construct a nonreciprocal multi-channel bandstop filter by the GFMS. The couplings between electromagnetic waves and lattice vibration of multiferroic material with ferroelectric and ferromagnetic (or antiferromagnetic) orders can be invoked either through piezoelectric or piezomagnetic effects and can lead to the creation of the polaritonic band structure. The plane wave expansion method with first-order approximation predicts the existence of multiple band gaps, and electromagnetic waves lying within the band gaps are prohibited, and the band gaps with respect to forward electromagnetic waves (FEWs) and backward electromagnetic waves (BEWs) are asymmetric. The forbidden band structures with FEWs and BEWs are calculated by the transfer matrix method and multiple frequency channels with unidirectional transmission of electromagnetic waves can be further confirmed. Nine and twenty transmission dips in transmission spectra for the BEWs in the frequency range of ω = 0.4 − 0.6 (17.06 GHz-25.59 GHz) are found in the GFMS with m = 2 and 3, respectively, in which the BEWs are prohibited while the FEWs can travel. Thus, the GFMS has all the conditions for the nonreciprocal multi-channel bandstop filter. Besides, the GFMS can also be applied to construct compact multi-channel one-way electromagnetic waveguides.
In this paper, the mathematical analysis of a single-walled carbon nanotube composite material (SWCNT-composite) is presented in order to estimate its effective conductivity model and other important parameters. This composite material consists of SWCNT coated by other different materials. The effects of the radius of SWCNT and average thickness of coating layer on this effective conductivity model are investigated. The effects of using different types of coating materials with different radii of SWCNTs on the behavior of this composite material are also presented. An investigation of electromagnetic properties of SWCNT-composite material was carried out based on designing and implementing the dipole antenna configuration using a common electromagnetic engineering tool solver CST (MWS). The results obtained from comparisons between SWCNT and SWCNT-composite materials are presented based on their electromagnetic properties are also described in this paper.
Left-handed metamaterial (LHM) lenses allow the focusing of microwave radiation at specific positions within a medium, depending on its refractive index. A suitable approach needs to consider the reflections between the LHM lens and the adjacent media. This work faces the challenge of focusing the microwave radiation within a medium with arbitrary positive refractive index and characteristic impedance using LHM lenses as imaging-forming systems. To find a right lens formula, a full wave method is presented in theory. The results we achieved show that the characteristic flat shape of conformal-four lens configuration has a spot size of 0.53 x 0.34λeff2 at -3 dB if the different media are perfectly matched. Otherwise, a noteworthy aberration affects the focusing, but it can be mitigated using a conformal circular LHM lens with a spot size of ~0.4 x 0.4λeff2 at -3 dB.
In this paper, we investigate the diffraction of complex structures applying a new hybridization between generalized PO (Physical Optic) and MoM-GEC method. The proposed approach is developed to speed up convergence, alleviate calculation and then provide a considerable gain in requirements (processing time and memory storage) because it is based on a single test function instead of numerous sinusoidal or polynomial ones. Based on this approach, each metallic pattern is modeled by a current trial function that consists of two parts. The first part is called modal current, and it is decomposed on Hankel functions for modeling metal edges. However, the second part concerns the middle of metallic patterns, and it is modeled by PO method and called generalized PO current. Based on this approach, we study the diffraction of unidimensional structures, then we generalize our approach to take bidimensional ones. For validation purpose, we investigate 1D and 2D reflectarrays to prove the new approach's benefits. The obtained results show good accuracy with the method of moments. Moreover, we prove the considerable improvements in CPU time and memory storage achieved by the hybrid approach when studying these structures.
The open rectangular grating with step-loaded slow-wave structure (SWS), a type of all-metal SWS for high power wide band mm-wave wave traveling wave tubes (TWT) is presented in this paper. By using the jumping conditions at the interface of two neighboring steps and single-mode approximation (SMA) field matching theory, the dispersion equation and coupling impedance of this SWS were obtained. Then the obtained complex dispersion equation was numerically calculated, and the slow-wave characteristics of the fundamental wave of this structure were discussed. Moreover, the calculation results by our theory were accordant with the simulation data obtained by the 3-D electromagnetic simulation software HFSS, The numerical calculation results show that the dispersion characteristics and coupling impedance are notably improved by loading the steps. And the working bandwidth may be the widest when the thickness of the step is about equal to the thickness of the groove depth. The proper design parameters can be optimized to meet the needs of high frequency characteristics with wide bandwidth and high output power. The present study will be useful for further research and design of this kind of high frequency system.
A fast finite difference delay modeling (FDDM)-based scheme is presented for analyzing transient electromagnetic scattering from lossy inhomogeneous dielectric objects. The proposed scheme is formulated in the region of the scatterers by expressing the total field as the sum of the incident field and the radiated field due to both the polarization and conduction current density. The current density is discretized in space by Schaubert-Wilton-Glisson basis functions and in time by finite differences. Furthermore, the scheme is accelerated by the fast Fourier transform (FFT) algorithm, which can reduce the memory requirement and computational complexity significantly. Numerical results are presented to illustrate the accuracy and efficiency of the proposed method.
The results of experimental measurements of the complex dielectric permittivity (CDP) of powders of quartz granules with different sizes saturated with water and salt solution of weak concentration are given in the frequency band from 20 kHz to 1 GHz. It is shown that at values of saturation level from 0.6 to 0.9 the relaxation phenomena caused by interfacial polarization on the water-air bound can be observed. The result shows considerable reduction of attenuation in gradually saturated rocks, which allows for deeper sensing during georadar mapping. It is determined that in the dielectric relaxation band and at frequencies below it the hysteresis of the real part of the CDP and equivalent specific conductivity can be observed. Its character significantly depends on the sizes of granules. It is shown that the behavior of CDP and attenuation of an electromagnetic wave at frequencies from 0.1 to 10 MHz complicatedly depends on the sizes of granules, saturation level, salinity of the saturating solution and saturation history.
The electromagnetic (EM) fields inside a rotating circular hollow dielectric cylinder were numerically calculated in two dimensions, and the numerical results were presented in this paper. The simulation was carried out by using the method of characteristics (MOC) for the solutions of the time-domain Maxwell equations with the application of the passing center swing back grids (PCSBG) technique in the modified O-type grid system. To illustrate the effects of the rotating hollow dielectric cylinder on the EM fields inside the cylinder, the cylinder may be set to rotate at impractically, extremely high angular frequencies. The use of PCSBG is to overcome the difficulty of the deformed grid cells resulting from the rotating object while the modified O-type grid system satisfies the requirement of minimum number of grid within the shortest wavelength of interest in the larger radius regions where the regular O-type grid fails. A Gaussian EM pulse is utilized as excitation source and set to illuminate the hollow cylinder which is made of either non-magnetic or impedance matching materials. For clear examinations the numerical results of EM fields at and around the cylinder center are exhibited. Several electric field distributions are also shown.