This paper presents an improvement of the calculation of the magnetic field components created by ring permanent magnets. The three-dimensional approach taken is based on the Coulombian Model. Moreover, the magnetic field components are calculated without using the vector potential or the scalar potential. It is noted that all the expressions given in this paper take into account the magnetic pole volume density for ring permanent magnets radially magnetized. We show that this volume density must be taken into account for calculating precisely the magnetic field components in the near-field or the far-field. Then, this paper presents the component switch theorem that can be used between infinite parallelepiped magnets whose cross-section is a square. This theorem implies that the magnetic field components created by an infinite parallelepiped magnet can be deducted from the ones created by the same parallelepiped magnet with a perpendicular magnetization. Then, we discuss the validity of this theorem for axisymmetric problems (ring permanent magnets). Indeed, axisymmetric problems dealing with ring permanent magnets are often treated with a 2D approach. The results presented in this paper clearly show that the two-dimensional studies dealing with the optimization of ring permanent magnet dimensions cannot be treated with the same precisions as 3D studies.
Light extraction efficiency of light-emitting diodes (LEDs) based on various photonic crystal (PhC) structures was investigated in this study. By using the plane wave method and the finite element method, the influence of several factors on the enhancement of light extraction was discussed, including lattice type, density of states from a photonic band diagram, ratio of cylinder radius and lattice constant, and thickness of a photonic crystal pattern. Some rules are given for the practical implementation of an optimized PhC-based LED with higher light extraction efficiency. In the simulation results, the maximum enhancement of the extraction efficiency could be found to be by a factor of approximately 2.8 for the optimized Archimedean tiling pattern in the LED device emitting at the center wavelength of 530 nm. However, with the use of optimized PhC structures, the square and triangular lattices reveal enhancements of ~1.7 and ~1.5, respectively. The extraction efficiency of the Archimedean PhC LED is much greater than that of the regular lattice PhC LED.
A novel artificial transmission line with right/left-handed behavior is presented in this paper. The unit cell of the new artificial line consists of one series and one shunt wire bonded interdigital capacitors. When wire bonded interdigital capacitors are used, the artificial line has a wider frequency band of operation. A combined analytical-graphical design method of the proposed artificial transmission line is also presented. The method has been assessed with the help of an electromagnetic solver based on the method of moments, and experimental work.
The adjoint variable method is applied for the first time to perform sensitivity analysis with transmission line modelingexploiting rubber cells. Rubber cells allow for the conformal modelingof off-grid boundaries in the transmission line modeling computational domain usingmo dified tensor properties. The scatteringmatrix of the rubber cell is analytically dependent on the dimensions of the modeled discontinuities. Usingthis property, an exact adjoint system is derived. The original and adjoint systems supply the necessary field information for the rubber cell based sensitivity calculations. Our technique is illustrated through sensitivity analysis of waveguide filters. The estimated sensitivities are used for fast gradient-based optimization and tolerance analysis.
An ultra wideband radar system based on a coherent emission of an Ultra-Wideband antenna array using photoconductive switching devices is proposed. The triggering process is obtained by excitation of semiconductor samples in linear mode using a picosecond laser source. The emitting antenna system and the receiving antenna developed by the research Institute XLIM, present some specific qualities suitable for radiation and measurement of ultra-short pulses. The optical control of the sources allows to sum the radiated power and to steer the transient radiation beam accurately. The experiments realized with this optoelectronic array validate these two concepts. An other way of improvement of these systems is proposed. It consists by using bipolar pulse generators.
Uncertainties in biological tissue properties are weighed in the case of a hyperthermia problem. Statistic methods, experimental design and kriging technique, and stochastic methods, spectral and collocation approaches, are applied to analyze the impact of these uncertainties on the distribution of the electromagnetic power absorbed inside the body of a patient. The sensitivity and uncertainty analyses made with the different methods show that experimental designs are not suitable in this kind of problem and that the spectral stochastic method is the most efficient method only when using an adaptative algorithm.
In this paper, a new Yagi-Uda substrate is proposed to obtain radar cross section (RCS) reduction. The Yagi-Uda substrate on which three kinds of metal microstrip lines are etched is put directly on the top of a patch antenna and can reduce RCS sharply by steering the direction of reflecting wave at resonant frequencies. Using a reconfiguration technique, the antenna can radiate without the substrate's effects. When the antenna does not need to work, the Yagi-Uda substrate works to reduce the RCS of the antenna. Besides, the resonant frequencies can be shifted by reconfiguring the Yagi-Uda substrate, so the RCS can be reduced in a broad frequency band.
In this paper, winding function method (WFM), applied to a faulted synchronous generator, is modified and is used for on-line diagnosis of mixed eccentricity fault. For the first time, the static and mixed eccentricities are modeled in synchronous generators. A modified winding function (MWF) method introduced here is more precise compared with previous methods. This MWF enables to compute the air gap magnetic permeance accurately. Here, two or three terms of the infinity permeance series has not been used, but a closed form equation is employed for permeance evaluation. This leads to a very precise computation of the inductances of the faulted machine. Self inductances of the stator and rotor, mutual inductance of two stator phases and the mutual inductance of rotor and stator are obtained. Meanwhile, it is shown that static, dynamic and mixed eccentricities lead to the increase of the amplitude and occurrence of the distortion in the aforementioned inductances. Since calculation of inductances is the most important step for fault diagnosis of the machine, the proposed method improves the on-line diagnosis of the fault. Meanwhile, the spectrum analysis of stator current, obtained from experimental results, is illustrated.
The increased number of electronic systems in today's car designs requires that each system is EMC compliant prior to vehicle assembly. Each system or component auto supplier is mandated to perform system level EMC testing according to the car manufacturer standards. To ensure high functional integrity of these systems, EMC modeling and simulation are used as a tool. This paper provides an EMC model of a general automotive electrical system. The purpose is to measure, model, and simulate radiated emissions of a test-setup that consists of an electronic control unit ECU, harness, and a load. The model then can be used to optimize the overall system design to achieve EMC compliance or provide a directional improvement to obtain an optimum performance to save cost. Lab measurements are conducted and EMC model is developed according to CISPR25 standards. The model of the printed circuit board PCB and cable harness is accomplished using modeling tools with built-in modeling techniques such as 2D MoM and 3D PEEC. IBIS wave models and SPICE models are connected to simulate circuits and harnesses in time or frequency domain. During simulation, the geometric and electric data are stored together for radiation analysis.
We have studied the problem of diffraction of plane waves by a finite slit in an infinitely long soft-hard plane. Analysis is based on the Fourier transform, the Wiener-Hopf technique and the method of steepest descent. The boundary value problem is reduced to a matrix Wiener-Hopf equation which is solved by using the factorization of the kernel matrix. The diffracted field, calculated in the far-field approximation, is shown to be the sum of the fields (separated and interaction fields) produced by the two edges of the slit. Some graphs showing the effects of slit width on the diffracted field produced by two edges of the slit are also plotted.
Abstract-Radiation characteristics of a probe-excited rectangular ring antenna are investigated by using the dyadic Green function approach. The radiation characteristics, such as radiation pattern, beam-peak direction, half-power beamwidth and directivity, are analyzed. For the specified operating frequency, the ring width and ring height are selected as the same crosssectional dimension of rectangular waveguide operated at the dominant mode. The effects of the excited probe and rectangular ring to the modal distributions are described. For the desired modal distribution, the directivity primarily depends on the ring lengths. For compact size of the proposed antenna, the ring length of 0.4λ is chosen to provide a bidirectional pattern with the calculated half-power beamwidth in E-plane and H-plane of 100 and 69 degrees respectively, and directivity of 4.43 dBi. Furthermore, the prototype antenna was fabricated and measured. The coincided results between the theory and the experiment are obtained.
The transverse electric (TE) field patterns and characteristics are considered for a cylinder with N infinite axialsl ots of arbitrary opening size and position. The cylinder is a thin circular conductor and covered by an eccentric material. Radiations are determined by applying the boundary conditions to the cylindrical wave functions of the fields. The addition theorem of Bessel functions is employed to find an infinite-series solution in Fourier-Bessel series form. Results are achieved by reducing the produced infinite series to a finite number of terms and judged against other published data. Numerical and graphical results for different values are also presented and discussed for small eccentricities.
Kelvin-Helmoholtz instability by parallel flow velocity shear in presence of inhomogeneous d.c. electric field and perpendicular density temperature magnetic field gradient has been studied by using method of characteristic solution and kinetic approach. Effect of in homogeneity of d.c. electric field and gradient have been discussed in result. The growth rates have been calculated for different effects and showing in stabilizing and destabilizing of instability.
With development of communication with integration technology, size reduction of microstrip antennas is becoming an important design consideration for practical applications. Here a new microstrip antenna with Koch shaped fractal defects on the patch surface is presented. Using this method, the overall electric length of the antenna is increased largely and hence the size of antenna is reduced to 85%, compared to an ordinary microstrip antenna with the same resonance frequency. Antenna is simulated using high frequency structure simulator (HFSS) V.10 which is based on finite element modeling (FEM). Finally antenna is fabricated on RO4003 substrate. Measurement results are in good agreement with simulated results.
A technique to characterize the fields generated by a cell phone, and projected into an area inside a TEM cell for possible biological interaction studies is described. A double-ended monopole antenna is proposed as the lead signal inducer between the inside and the outside areas of the TEM cell. The coupling voltage at the TEM cell ports and the field distribution within the area under test (AUT) were found to be a function of the phone position, polarization, and dialing type. The measurements for a GSM 850MHz cellular phone showed that the optimum setup is achievable when the phone is placed outside the TEM cell and co-polarized with the signal leader. An improvement of the field uniformity is possible with the use of a shorter signal leader but at the cost of decreased field strength. The proposed setup can be utilized in studies and experiments related to the radio frequency effects on biological cells and organs.
In this paper, we present an adaptive beamforming scheme for smart antenna arrays in the presence of several desired and interfering signals, and additive white Gaussian noise. As compared with standard schemes, the proposed algorithm minimizes the noise and interference contributions, but enforces magnitude-only constraints, and exploits the array-factor phases in the desired-signal directions as further optimization parameters. The arising nonlinearly-constrained optimization problem is recast, via the Lagrange method, in the unconstrained optimization of a non-quadratic cost function, for which an iterative technique is proposed. The implementation via artificial neural networks is addressed, and results are compared with those obtained via standard schemes.