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2011-08-18 PIER B Vol. 33, 383-407, 2011. doi:10.2528/PIERB11070204

Genetic Algorithm and Finite Element Analysis for Optimum Design of Slotted Torus Axial-Flux Permanent-Magnet Brushless DC Motor

Amin Mahmoudi, Nasrudin Abd Rahim, and Hew Wooi Ping

This paper presents an inside-out axial-flux permanent-magnet brushless DC motor optimized by Finite Element Analysis (FEA) and Genetic Algorithm (GA) that uses sizing equation. The double-sided slotted-stator designed TORUS motor has sinusoidal back EMF waveform and maximum power density. The GA obtained the dimensions that gave the motor its highest power density. Field analysis of the dimensions was then put through FEA, to obtain and re-optimize the motor's characteristics. Possible design parameters were investigated via use of Commercial Vector Field Opera 14.0 software used in three-dimensional FEA simulation and of MATLAB 2010a in GA programming. Techniques such as modifying winding configuration and skewing the permanent magnets were explored to achieve the most-sinusoidal back-EMF waveform and minimized cogging torque. The desired technical specifications were matched by simulation results of the 3D FEA and the GA. The FEA and the GA simulation results comparison of the flux density in different parts of the designed motor at no-load condition agreed well.

2011-08-15 PIER B Vol. 33, 359-382, 2011. doi:10.2528/PIERB11062702

Electromagnetic Analysis of Dispersion and Form Factor Characteristics of a Disc-Loaded Cylindrical Waveguide for a Gyro-TWT Amplifier

Rajiv Kumar Singh

A disc-loaded cylindrical waveguide structure for its potential use in a gyro-TWT amplifier operating in the TE mode is analysed for its electromagnetic behaviour. A modal matching technique is used to develop a dispersion relation in order to study the shape of the dispersion curve for wide device bandwidth. The band-pass characteristic of the structure has also been explored. The structure dispersion characteristic has been numerically plotted over a wide range of structure parameters to appreciate the role of individual parameter on the dispersion behaviour of the structure. It has been found that the disc-hole radius may be decreased and the structure periodicity increased for widening the device bandwidth. To validate the theoretical considerations, the structure is also simulated using commercially available simulation software ``CST Microwave Studio'' in order to observe the penetration of the travelling electric fields in different regions of the disc-loaded structure. A good agreement (<1%) has been achieved between the analytical and simulation results of dispersion characteristics. The analysis is extended further to derive the form factor which plays a very important role in the optimization of the electron-beam position for maximum interaction between RF wave and electron beam. Maximum coupling of the cyclotron wave to the resonant waveguide mode is found to be at the ratio of hollow beam radius to waveguide wall radius (rb/rW=0.44) for TE01, (rb/rW=0.39) for TE02 and (rb/rW=0.35) for TE03 mode. This article has been removed from the website because it has been found to violate plagiarism rule of our journal.

2011-08-14 PIER B Vol. 33, 339-358, 2011. doi:10.2528/PIERB11070701

Peer-to-Peer Localization in Urban and Indoor Environments

Siwen Chen, Soon Yim Tan, and Chee Kiat Seow

This paper presents a novel peer-to-peer or mobile-to-mobile localization scheme for general indoor and outdoor environments. In this scheme, two mobile nodes at arbitrary locations are able to locate each other without the need of Line-of-Sight (LOS) path between the two mobile device, and without the need for any reference devices such as GPS or land base beacons. Existing peer-to-peer localization techniques make use of Time of Arrival (TOA) and Angle of Arrival (AOA) of LOS and single bounce scattering paths to derive line of possible mobile device positions (LPMDs). The intersections of LPMDs are then used to estimate the unknown mobile device position - referred to as the Line Segment Intersection. However, in a heavy multipath environment with many multiple-bounce scattering paths, existing techniques require weighting factors and threshold values which are specifically chosen for that particular environment in order to select the LPMDs that correspond to LOS and single-bounce scattering paths for localization. Large localization error will occur if multiple-bounce scattering paths' LPMDs are mistakenly used for intersections. In addition, existing techniques also do not work well in a multipath environment with high level of TOA and AOA noises especially when the angles between LPMDs are small. The accuracy of the Line Segment Intersection also deteriorates as the distance traveled by multipath signals become comparable to each other. This renders the weighting and threshold values ineffective. This paper presents a novel Gaussian weighting process to remove the abovementioned limitations. The Gaussian weighting process also dramatically improves the accuracy of the localization. Experimental coupled with simulation results show that our proposed localization scheme outperforms existing Peer-to-peer localization technique by a significant margin of up to 83% and 54% in indoor and urban environments respectively especially under severe multipath propagation conditions and high level of TOA and AOA noises.

2011-08-12 PIER B Vol. 33, 317-337, 2011. doi:10.2528/PIERB11061004

The E-Pile+Smcg for Scattering from an Object Below 2D Soil Rough Surface

Wei-Jie Ji and Chuang-Ming Tong

A rigorous fast numerical method called E-PILE+SMCG is introduced and then used in a Monte Carlo study of scattering from a three dimensional perfectly electrical conductor (PEC) object below lossy soil rough surface. This method is the three dimensional (3D) extendability of PILE (Propagation-Inside-Layer Expansion) method which is proposed for two dimensional (2D) scattering problem. The rough surface with Gaussian profile is used to emulate the realistic situation of statistically rough surface, while the tapered incident wave is chosen to reduce the truncation error. The 3D angular correlation function (ACF) and bistatic scattering coefficient (BSC) are studied and applied to the detection of a target embedded in the clutter. The ACF is computed by using numerical method with circular azimuthal angle averaging technique. Because of its success in suppressing the clutter scattering, the technique appears attractive in real life implementation.

2011-08-05 PIER B Vol. 33, 291-315, 2011. doi:10.2528/PIERB11052802

Performance Analysis of Antenna Array Beamformers with Mutual Coupling Effects

Ju-Hong Lee and Yen Lin Chen

Antenna array beamformers suffer from performance deterioration in the presence of mutual coupling (MC) between array sensors. In this paper, we present a theoretical analysis in terms of the output signal-to-interference-plus-noise ratio (SINR) for the performance of antenna array beamformers under MC effects. Based on the model of a distortion matrix to encapsulate the MC effects, a closed-form expression for the SINR is derived that is shown to accurately predict the SINR obtained in simulations. This theoretical formula is valid for any distortion matrix estimated from collected measurement data. The SINR formulas provide insights into the influence of the MC effects on the performances of the linearly constrained minimum variance (LCMV) beamformer and the eigenspace-based (ESB) beamformer. It is shown that the ESB beamformer outperforms the LCMV beamformer under MC effects. Moreover, we derive the formulas for computing the eigenvalues of signal correlation matrix under MC effects. Simulation results are presented for confirming the validity of the theoretical results.

2011-08-04 PIER B Vol. 33, 277-289, 2011. doi:10.2528/PIERB11071108

Characterization of Magnetically Loaded Microwave Absorbers

Irena Zivkovic and Axel Murk

This work presents new method, retrieved results and validation for complex and frequency dependent permittivity and permeability parameter extraction of two composite, homogeneous and isotropic magnetically loaded microwave absorbers. Permittivities and permeabilities are extracted from free space transmission measurements for frequencies from 22 up to 140 GHz. For validation of the results reflection measurements (samples with and without metal backing) are performed and are compared with simulations that use extracted models. The proposed new method solves some shortcomings of the popular methods: extracts both permittivity and permeability only from transmission parameter measurements, gives good results even with noisy data, does not need initial guesses of unknown model parameters.

2011-08-04 PIER B Vol. 33, 257-276, 2011. doi:10.2528/PIERB11042910

Formulating a Vector Wave Expression for Polarimetric GNSS Surface Scattering

Robert N. Treuhaft, Stephen T. Lowe, and Estel Cardellach

This paper formulates a simple vector integral expression for electromagnetic waves received after scattering from a surface. The derived expression is an alternative to the Stratton-Chu equation frequently used for polarimetric surface scattering. It is intended for use in polarimetric Global Navigation Satellite System (GNSS) ocean remote sensing, or any type of polarimetric remote sensing from surfaces, when the surface roughness pattern is known from simulation or data. This paper is intended to present a complete accounting of the steps leading to the simpler vector integral expression. It therefore starts with the scalar case, using Maxwell's equations and Green's theorem. It principally treats the case of a transmitter within the integration volume, but discusses how the formalism changes if the transmitter is outside of the integration volume, as with plane waves. It then shows how the scalar expression can be extended to a vector expression for the component of the electric field in an arbitrary receive-polarization direction due to scattering from a rough surface of an incident wave with an arbitrary transmit polarization. It uses the Kirchhoff, or tangent-plane, approximation in which each facet on the ocean is considered to specularly reflect the incoming signal. The derived vector expression is very similar to that for a scalar wave, but it includes all vector properties of the scattering. Equivalence is demonstrated between the Stratton-Chu equation and the derived, simpler expression, which is operationally easier to code than the Stratton-Chu equation in many modeling applications.

2011-08-02 PIER B Vol. 33, 239-256, 2011. doi:10.2528/PIERB11061312

Potential Generated by Rotating Charged Cylinders

Tze-Chuen Toh

The potential field generated by two charged cylindrical perfect electrical conductors sandwiching a dielectric plane of finite thickness, and the influence of the dielectric plane on the field, is analysed. In particular, the field profile is examined when the cylinders are (i) rotating at some constant angular velocities, and (ii) surrounded, respectively, by uniform dielectric tubes of finite thickness.

2011-08-02 PIER B Vol. 33, 221-237, 2011. doi:10.2528/PIERB11062111

Calculation of the Mutual Inductance and the Magnetic Force Between a Thick Circular Coil of the Rectangular Cross Section and a Thin Wall Solenoid (Integro-Differential Approach)

Slobodan Babic, Cevdet Akyel, Frederic Sirois, Guy Lemarquand, Romain Ravaud, and Valerie Lemarquand

Systems that employ stimulating and implantable monitoring devices utilize inductive links, such as external and implanted coils. The calculation of the mutual inductance and the magnetic force between these coils is important for optimizing power transfer. This paper deals with an efficient and new approach for determining the mutual inductance and the magnetic force between two coaxial coils in air. The setup is comprised of a thick circular coil of the rectangular cross section and a thin wall solenoid. We use an integro-differential approach to calculate these electrical parameters. The mutual inductance and the magnetic force are obtained using the complete elliptic integrals of the first and second kind, Heuman's Lambda function and one term that has to be solved numerically. All possible regular and singular cases were solved. The results of the presented work have been verified with the filament method and previously published data. The advantage of these proposed formulas for mutual inductance or for the magnetic force is that they give the solution in the analytical and the semi-analytical form either for regular cases or singular cases. It is not case with already known methods in which it is necessary to take particular care of these cases of consideration.

2011-07-30 PIER B Vol. 33, 203-219, 2011. doi:10.2528/PIERB11060505

Numerical Optimization of the Method of Auxiliary Sources by Using Level Set Technique

Afif Bouzidi and Taoufik Aguili

It is well-known that the choice of the auxiliary surface and the arrangement of radiation centers play a decisive role for ensuring accuracy and stability of the method of auxiliary sources (MAS). Using level set technique, a numerical scheme is proposed to determine the optimal location and amplitudes of the auxiliary sources for three-dimensional scattering problems.

2011-07-30 PIER B Vol. 33, 175-202, 2011. doi:10.2528/PIERB11042206

A Negative Refractive Index Metamaterial Based on a Cubic Array of Layered Nonmagnetic Spherical Particles

Edward F. Kuester, Nadja Memic, Simone Shen, Aaron D. Scher, Sung Kim, Kendra Kumley, and Hung Loui

A low-loss passive metamaterial exhibiting negative refractive index or ``double negative'' electromagnetic properties at microwave frequencies is proposed. The metamaterial is a lattice of spherical particles made up of multiple dielectric materials in concentric layers. Because no magnetic constituents (that tend to have higher losses) are involved, the negative-index behavior is possible with very low values of attenuation. A negative-index metamaterial based on dielectric-coated metal spheres is also proposed, and is predicted to have lower attenuation than other structures based on metallic scatterers. Numerical results and design principles are given.

2011-07-29 PIER B Vol. 33, 153-174, 2011. doi:10.2528/PIERB11061609

Refractivity from Clutter by Variational Adjoint Approach

Xiaofeng Zhao and Sixun Huang

Inferring refractivity profiles from radar sea clutter is a complex nonlinear optimization problem. Previous works treat this problem as a model parameter estimation issue by using some idealized refractivity models, such as the Log linear evaporation duct model, bilinear model, and trilinear model, to describe the synoptic structure of the real atmospheric conditions. However, these idealized models can not describe the exact information of the refractivity profile. Rather than estimating a few model parameters, this paper puts forward possibilities of retrieving the refractivity values at each point over height by variational adjoint approach for RFC measurement geometry. The adjoint model is derived from the parabolic equation for a smooth, perfectly conducting surface and horizontal polarization conditions. An evaporation duct profile collected at East China Sea is provided as the true refractive environment. The performance of this approach is determined via simulations and is evaluated as a function of: 1) the initial guess profile; 2) the measurement noise; and 3) the spatial samples.

2011-07-29 PIER B Vol. 33, 135-151, 2011. doi:10.2528/PIERB11032809

Research on a New Kind of High Directivity End-Fire Antenna Array

Guo-Wei Yao, Zheng-Hui Xue, Wei-Ming Li, Wu Ren, and Jia Cao

In this paper, a new kind of end-fire array was built by employing high directivity plate end-fire antenna as the basic element based on electromagnetic surface wave theory. Being different from normal end-fire array, in the new array, high directivity plate end-fire antenna elements were arranged end to end along the end-fire direction, and the interelement spacing and uniform progressive phase were carefully adjusted to achieve high directivity. The simulations and measurements showed that the whole array achieved 19.2 dB directivity with four elements at 14.7 dB directivity each.

2011-07-28 PIER B Vol. 33, 115-134, 2011. doi:10.2528/PIERB11060209

A Method for Tracking Characteristic Numbers and Vectors

Miloslav Capek, Pavel Hazdra, Pavel Hamouz, and Jan Eichler

A new method for tracking characteristic numbers and vectors appearing in the Characteristic Mode Theory is presented in this paper. The challenge here is that the spectral decomposition of the moment impedance-matrix doesn't always produce well ordered eigenmodes. This issue is addressed particularly to finite numerical accuracy and slight nonsymmetry of the frequency-dependent matrix. At specific frequencies, the decomposition problem might be ill-posed and non-uniquely defined as well. Hence an advanced tracking procedure has been developed to deal with noisy modes, non-continuous behavior of eigenvalues, mode swapping etc. Proposed method has been successfully implemented into our in-house Characteristic Mode software tool for the design of microstrip patch antennas and tested for some interesting examples.

2011-07-28 PIER B Vol. 33, 99-114, 2011. doi:10.2528/PIERB11053002

Analysis and Investigation of a Cantor Set Fractal UWB Antenna with a Notch-Band Characteristic

Yingsong Li, Xiao-Dong Yang, Cheng-Yuan Liu, and Tao Jiang

A coplanar waveguide (CPW) fed ultra-wideband (UWB) antenna with a notch band characteristic is presented in the paper. The radiation patch of the proposed UWB antenna is designed using cantor set fractal technology. The bandwidth is broadened by setting two symmetrical triangular tapered corners at the bottom of the wide slot of the proposed UWB antenna. The notched band characteristic is achieved by employing a T-shaped tuning stub at the top of the wide slot. The notched band can be controlled by adjusting the length and the width of the T-shaped tuning stub to give tunable notched band function. The proposed cantor set fractal wide slot UWB antenna has been designed in details and optimized. Experimental and numerical results show that the proposed antenna, with compact size of 26×21 mm2, has an impedance bandwidth range from 2.8 GHz to 11 GHz for voltage standing-wave ratio (VSWR) less than 2, except the notch band frequency 5.0 GHz-6.3 GHz for HIPERLAN/2 and IEEE 802.11a (5.1 GHz-5.9 GHz).

2011-07-27 PIER B Vol. 33, 83-97, 2011. doi:10.2528/PIERB11062005

Influence of the Pole Number on the Magnetic Noise of Electrical AC Machines

Bertrand Cassoret, Jean-Philippe Lecointe, and Jean-Francois Brudny

This paper deals with the influence of the AC machine pole number on vibrations and noise of electromagnetic origin. First, rules of design of AC machines are reminded, pointing out the influence of the pole number. Then, the origin of magnetic vibrations and noise is explained. Analytical mechanical relations are given, allowing to estimate vibrations and noise of a machine. After that, the influence of the pole number is studied: on the machine radius, on the stator deformations, on the mechanical resonance frequencies and on the noise. The conclusions underline that machines with high pole number have stator vibrations of high amplitude. Calculations compare three machines with different pole number and fed at different frequencies. The conclusion is that, at the same speed and working power, machines with high pole number fed at high frequency are noisier than those with low number of poles fed at low frequency. Practical experiments illustrate these theoretical considerations.

2011-07-27 PIER B Vol. 33, 69-82, 2011. doi:10.2528/PIERB11040901

A Simple Solution for the Damped Wave Equation with a Special Class of Boundary Conditions Using the Laplace Transform

Namik Yener

It is proven that for the damped wave equation when the Laplace transforms of boundary value functions ψ(0,t) and (∂ψ(z,t)/∂z)z=0 of the solution ψ(z,t) have no essential singularities and no branch points, the solution can be constructed with relative ease. In such a case while computing the inverse Laplace transform, the integrals along the segments on the real line are shown to always cancel. The integrals along the circles Cε and C'-ε about the point s=-σ/ε determined by the coefficient of the time derivative in the differential equation and point s=0 are shown to vanish unless Laplace transforms of mentioned boundary value functions have poles at these points. If such poles do exist, the problem is nevertheless one of integration along circles about these poles and then setting the radii of these circles equal to zero in the limit.

2011-07-25 PIER B Vol. 33, 45-67, 2011. doi:10.2528/PIERB11053005

Nonlinear Interaction of Electromagnetic Radiation at the Cell Membrane Level: Response to Stochastic Fields

Assunta De Vita, Rocco Paolo Croce, Innocenzo Pinto, and Bisceglia Bruno

A general rigorous analytic framework for computing the transmembrane potential shift resulting from the nonlinear voltage-current membrane relationship in response to wideband stochastic electromagnetic radiation is outlined, based on Volterra functional series. The special case of an insulated cylindrical cell with Hodgkin-Huxley membrane in an infinite homogeneous medium is worked out in detail, for the simplest case where the applied electric is normal to the cell axis, and independent from the axial coordinate. Representative computational results for a zero-average stationary band-limited white Gaussian incident field are illustrated and briefly discussed.

2011-07-24 PIER B Vol. 33, 21-44, 2011. doi:10.2528/PIERB11042902

Scalar Radiative Transfer in Discrete Media with Random Oriented Prolate Spheroids Particles

Lu Bai, Zhen-Sen Wu, Hai-Ying Li, and Tuo Li

Monte Carlo scalar radiative transfer simulation of light scattering in plane parallel slab is not a simple problem, especially in the study of angular distribution of light intensity. Approximate phase function such as Henyey-Greenstein is often used to simulate the Mie phase function. But even for sphere particle this function is sometimes a poor approximation of real phase function. For a spheroids particle, the angular scattering characteristics cannot be approximated as H-G phase function with sufficient accuracy. In this paper, we study the transmission characteristics of light in parallel plane layer with randomly oriented prolate spheroids aerosol particles. Instead of using H-G phase function, we use sampling method to simulate real phase function of spheroid directly. A database of phase function with various scattering angle and azimuth angles for given spheroids aerosol particle is developed. The transmission characteristics calculated by scattering phase function sampling method and equivalent volume sphere H-G phase function method are compared. The effect of prolate spheroids particle size and form factor on optical transmission properties is analyzed. It is found that although the construction database of phase function takes a certain amount of computing time, for spheroid particles the sample phase function method, compared with the H-G phase function simulation method, can greatly improve the accuracy of transmittance calculation.

2011-07-24 PIER B Vol. 33, 1-19, 2011. doi:10.2528/PIERB11063009

A Rigorous Forest Scattering Model Validation through Comparison with Indoor Bistatic Scattering Measurements

Sami Bellez, Helene Roussel, C. Dahon, and Jean-Michel Geffrin

In this paper, we present numerical simulations and indoor bistatic scattering measurements on scaled targets. The targets are vertical and/or tilted dielectric parallelepipeds representing the main forest elements (tree-trunks and primary branches) at VHF and low-UHF frequencies. They are placed above an aluminum circular plate to simulate a flat ground. The measurements have been conducted in the anechoic chamber of the ``Centre Commun de Ressources Micro-ondes'' (CCRM) in Marseille, France. A 3D forest scattering model using a Method of Moments (MoM) is deployed to simulate the electric fields scattered by these targets. Two radar geometric, azimuthal and zenithal, bistatic configurations with special attention to the specular direction have been considered. Simulation results and experimental data are confronted for both {VV-} and {HH-}polarizations in order to evaluate the accuracy of our model. We have obtained a very good agreement between theoretical and experimental scattered fields for both the magnitude and phase.