Electromagnetic design problems usually involve a large number of varying parameters. A designer can use different kinds of models in order to achieve optimum design. Some models, e.g., finite-element model, can be very precise: however, it requires large computational costs (i.e., CPU time). Therefore, the designer should use a screening process to reduce the number of parameters in order to reduce the required computational time. In this paper, using the Design of Experiments (DOE) approach to reduce the number of parameters is explored. The benefits of this technique are tremendous. For example, once researchers realize how much insight and information can be obtained in a relatively short amount of time from a well-designed experiment, DOE would become a regular part of the way they approach their simulation projects. The main objective of this paper is to apply the DOE technique to electromagnetic simulations of different systems and to explore its effectiveness on a new field, namely the magnetic refrigeration systems. The methodology of the DOE is presented to assess the effects of the different variables and their interaction involved in electromagnetic simulations design and optimization processes.
The mathematical approach for the calculation of the membrane functions of a coaxial gyrotron cavity with an arbitrary corrugated inner rod is proposed. It is utilized mainly for two aims. First, it is shown that for typical parameters of the coaxial gyrotron cavity with the corrugated inner conductor the shape of corrugations only slightly influences the eigenvalues of competing eigen-modes. However, it can significantly influence the density of ohmic losses in the inner conductor. In particular, it is shown that the density of ohmic losses can be reduced almost twice by the proper choice of the corrugation shape. Second, it is shown that the usual idealizations of the corrugated surface of the inner conductor (the surface with rectangular grooves, having rounded edges, is approximated by a surface with wedged groves that have sharp edges) are correct. The physical interpretation of the obtained results and their practical meaning are discussed.
The diffraction problem of three-dimensional Gaussian beam on the aperture array of rectangular holes is solved. A new algorithm for calculating scattered fields of the beam is proposed. The conditions under which the distortion of the reflected field pattern and the narrowing of the transmitted field pattern appear are studied.
Super-resolution algorithms used in radar imaging, e.g., MUltiple SIgnal Classification (MUSIC), can help us to get much higher resolution image beyond what is limited by the signal's bandwidth. We focus on MUSIC imaging algorithm in the paper and investigate the uniqueness and effectiveness conditions of the MUSIC algorithm when used in 1-D radar range imaging. Unlike conventional radar resolution analysis, we introduced the concept of resolution threshold from Direction of Arrival (DOA) into the MUSIC radar range imaging, we derive an approximate expression of theoretical resolution threshold for 1-D MUSIC imaging algorithm through the approach of asymptotic and statistical analysis to the null spectrum based on the perturbation theory of algebra and matrix theories. Monte Carlo simulations are presented to verify the work.
The plasmonic effects of a gold prolate nanospheroid on the spontaneous emission of an adjacent emitter, regarded as an oscillating electric dipole, at the excitation and emission stages are studied respectively by using the multiple multipole method. The numerical results show that when an irradiating light is at the longitudinal surface plasmon resonance frequency of the nanospheroid and with a polarization parallel to the long axis, the strongest excitation rate occurs at the proximity of the long-axis vertex. In addition, if the emitter is at this region, and its orientation is also parallel to the long axis, the apparent quantum yield of the emission is the maximum, compared to the other locations and orientations. Therefore, for this case the overall enhancement factor of a nanospheroid on an emitter's spontaneous emission is the maximum. In contrast, the emitter's emission could be quenched, if it is near the short-axis vertex.
A detailed analysis and design of thin planar absorbing structure using Jerusalem cross slot (JCS) is presented in this paper. Based on uniplanar compact high-impedance surface characteristics, the resistance loss material layer can be directly attached to the surface of JCS structure, thus absorbing electromagnetic waves effectively. The improved design is characterized by its wider bandwidth and adjustable range. The absorption frequency band can be flexibly adjusted by the slot parameters. The influences of various structure parameters of JCS, including incident wave polarization and variation of incident angles on the absorption properties, are analyzed to provide guidance on theoretical design for practical application. The loaded resistance can be adjusted to obtain the optimum absorbing performance. The validation and effectiveness of the proposed design are conducted by using X-band waveguide simulation and measurement.
The biosensor design for sensing of biological signals is highly complex for accurate detection. Optimal detection of biological signals is necessary for distinguishing different tissues. This paper proposes a threshold-based detection technique which provides significant improvement in FinFET optical biosensor performance using wavelet coefficients. It uses a simple maximum likelihood (ML) function for detecting the threshold values. In this method, we have considered the different layers of body tissue as a turbid medium. To the best of our knowledge, this method is the first of its kind for classifying different tissues using threshold value of optical signals obtained from the surface potential variations of nanoscale FinFET illuminated by laser source of different wavelengths. By using this method, the point to point variations in tissue composition and structural variations in healthy and diseased tissues could be identified. The results obtained are used to examine the performance of the device for its suitable use as a nanoscale sensor.
This paper considers a periodic circular cylinder array with additional cylinders and formulates the electromagnetic scattering problem of this imperfectly periodic structure. Generally, the fields in imperfectly periodic structures have continuous spectra, and the spectral-domain approaches require appropriate discretization schemes in many cases. The present formulation is based on the pseudo-periodic Fourier transform and the discretization scheme can be considered only inside the Brillouin zone.
In this paper, a two-dimensional (2D) diffraction tomographic algorithm based on the first order Born approximation is proposed for the imaging of hidden targets behind the wall. The spectral expansion of the three layered background medium Green's function is employed to derive a linear relationship between the spatial Fourier transforms of the image and the received scattered field. Then the image can be efficiently reconstructed with inverse Fast Fourier Transform (IFFT). The linearization of the inversion scheme and the easy implementation of the algorithm with FFT/IFFT make the diffraction tomographic algorithm suitable in through-the-wall radar imaging (TWRI) applications concerning the diagnostics of large probed domain and allow real-time processing. Numerical and experimental results are provided to show the effectiveness and high efficiency of the proposed diffraction tomographic algorithm for TWRI.
Photoinductive (PI) field mapping for eddy-current (EC) probes above a thin metal film was performed by multiphysics analysis with two-dimensional finite element method (FEM). The FEM model of PI method was used to observe how metal film properties affect the field-mapping signals of EC probes. The PI signal was tested for effects of resistivity, temperature coefficient of the resistivity, thermal conductivity, heat capacity, and thin film density The applicability of actual thin film materials for mapping the field of EC probe when using PI method was discussed. Field-mapping signals of EC probe coils with tilt angles of 0o, 5o, 10o, 15o, and 20o were also examined with appropriate metal film material. These experiments showed that the higher-resolution field-mapping signals of EC probes can be obtained by given a titanium thin film The resolution of field-mapping signals of EC probes correlated positively with resistivity, heat capacity, and density of thin film and correlated negatively with its thermal conductivity. Improved understanding of distinct field distribution of EC probes enables selection of optimal probes for EC inspection.
We investigate the propagation characteristics of super-Gaussian beam in highly nonlocal nonlinear media. The optical beam propagation has been modeled by well known nonlocal nonlinear Schrődinger equation. The variational method is employed to find the initial beam propagation parameters and then split step Fourier method is used for numerical simulations. A generalized exact analytical solution of the model is obtained and critical power of soliton is determined. The evolution of super-Gaussian beam has shown oscillatory propagation.
In this paper, the simulation and experimental studies of SAR distribution in a bio-medium situated very close to a rectangular dielectric resonator antenna (RDRA) in C-band of microwave frequencies are reported. The simulation study has been carried out using CST Microwave Studio simulation software. The experimental distribution has been obtained using two 50Ω L-shaped and straight probes and Agilent make 3 Hz-50 GHz spectrum analyzer. The experimental results for SAR distribution are compared with simulated results.
This paper deals with adaptive antenna array beamforming under spatial information uncertainties including steering angle mismatch, random perturbations in array sensor positions, and mutual coupling between antenna array sensors. To make antenna array beamformers robust against the spatial information uncertainties, we present an iterative method to obtain an appropriate estimate of the actual direction vector for each of the desired signals. The proposed method uses only the a posteriori information of the received array data. It invokes an appropriate objective function for estimation and solves the minimization of the objective function by using a gradient based algorithm. The convergence property of the proposed method is investigated. Simulation results are provided for showing the effectiveness of the proposed method.
Space mapping (SM) is one of the most popular surrogate-based optimization techniques in microwave engineering. The most critical component in SM is the low-fidelity (or coarse) model --- a physically-based representation of the structure being optimized (high-fidelity or fine model), typically evaluated using CPU-intensive electromagnetic (EM) simulation. The coarse model should be fast and reasonably accurate. A popular choice for the coarse models are equivalent circuits, which are computationally cheap, but not always accurate, and in many cases even not available, limiting the practical range of applications of SM. Relatively accurate coarse models that are available for all structures can be obtained through coarsely-discretized EM simulations. Unfortunately, such models are typically computationally too expensive to be efficiently used in SM algorithms. Here, a study of SM algorithms with coarsely-discretized EM coarse models is presented. More specifically, novel and efficient parameter extraction and surrogate optimization schemes are proposed that make the use of coarsely-discretized EM models feasible for SM algorithms. Robustness of our approach is demonstrated through the design of three microstrip filters and one double annular ring antenna.
This paper investigates the use of the guard traces to improve the Time-Domain Transmission (TDT) waveform and eye diagram for a flat spiral delay line. Two types of guard trace are adopted to implement and analysis in microstrip line and stripline structures. One is Two Grounded Vias type Guard Trace (TGVGT) and the other is Open-Stub type Guard Trace (OSGT). The time-domain analysis results by HSPICE and the associated simple circuit modeling is presented. According to the simulation results, the original TDT crosstalk noises can be reduced by about 80% when using TGVGTs or OSGTs in a stripline structure and by about 60% when using TGVGTs in a microstrip line structure. Additionally, the eye diagrams also can obtain improvement. The crosstalk noise cancelation mechanisms of the flat spiral routing scheme on TGVGTs and OSGTs are investigated by graphic method. In addition, how the degradation for the OSGT inserted into the flat spiral delay line in microstrip structure is clearly investigated. A flat spiral delay line inserted into TGVGTs and OSGTs both can obtain good improvements of the TDT waveform and eye diagram in a stripline structure. Moreover, adding OSGTs to the flat spiral routing scheme is easily accomplished due to the open end of OSGTs. Finally, HSPICE simulation and time-domain measurements of crosstalk noises of TDT waveforms, and eye diagrams are use to validate the proposed structure and analysis.
This paper presents a novel time-harmonic electromagnetic model for determining the current distribution on conductor grids in horizontally stratified multilayer medium. This model could be seen as a basis of the wider electromagnetic model for the frequency-domain transient analysis of conductor grids in multilayer medium. The total number of layers and the total number of conductors are completely arbitrary. The model is based on applying the finite element technique to an integral equation formulation. Each conductor is subdivided into segments with satisfying the thin-wire approximation. Complete electromagnetic coupling between segments is taken into account. The computation of Sommerfeld integrals is avoided through an effective approximation of the attenuation and propagation effects. Computation procedure for the horizontally stratified multilayer medium is based on the successful application of numerical approximations of two kernel functions of the integral expression for the potential distribution within a single layer, which is caused by a point source of harmonic current. Extension from the point source to a segment of the earthing grid conductors is accomplished through integrating the potential contribution due to the line of harmonic current source along the segments axis.
This work examines reflection of a light from a semi-infinite medium which is modified with an ordered monolayer of spherical nanoparticles placed on or under its surface. We derive analytical expressions for the electric fields within and outside such structures and verify them with help of strict numerical simulations. We show that nanoparticles layer acts as an imaginary zero-thickness surface having complicated non-Fresnel reflection coefficients with wavelength dependent phase shift. It is shown that such monolayers may reduce reflection relative to reflection from a pure substrate surface. We derive and analyse a zero-reflection condition in the simple intuitive form. It is shown that a single layer of nanocavities near the medium-vacuum interface may increase the transparency of a dielectric medium to values close to 100% in a wide wavelength range.
The reconfigurable design problem is to find the element that will result in a sector pattern main beam with side lobes. The same excitation amplitudes apply to the array with zero-phase that should be in a high directivity, low side lobe pencil shaped main beam. Multi-beam antenna arrays have important applications in communications and radar. This paper presents a new method of designing a reconfigurable antenna array with quantized phase excitations using a new evolutionary algorithm called differential evolution (DE). In order to reduce the effect of mutual coupling among the antenna-array elements, the dynamic range ratio is minimized. Additionally, compared with the continuous realization and subsequent quantization, experimental results indicate better performance of the discrete realization of the phase-excitation value of the proposed algorithm.
The estimation of d- and q-axis parameters is highly desirable, because they are fundamental parameters to many vector control algorithms in the d-q reference frame for fast and accurate responses. Using the finite element method (FEM) for the determination of the interior permanent magnet synchronous motor (IPM) reactance provides an accurate means of determining the field distribution. However, this method might be time consuming. The magnetic circuit modelling approach has been successfully used to model a variety of electrical machine such as IPM motors. This paper deals with the inverse problem methodology for the identification of d- and q-axis synchronous reactance of an IPM motor. The proposed method uses a measured electromotive force (EMF) to compute the objective function. The machine parameters identified by the proposed approach are compared to experimental results.
In this paper we will report on the optical performances of submicron planar lensless pixels arranged in the 2 x 2 Bayer cell configuration, the basic element of CMOS colour image sensors. The 2D microlens array placed in front of each pixel in commercial devices has been replaced by a 2D array of submicron holes realised on a thin metal film. Each pixel has been designed to present a lightpipe inside its structure acting as an optical waveguide that confines the light up to photodiode surface. This pixel design is fully compatible with large scale industry production since its fabrication involves only standard lithographic and etching procedures. Simulations of the light propagation inside the lensless pixel has been performed by using full 3D electromagnetic analysis. In this way it was possible to determine the optical performances of the Bayer cell in terms of the normalized optical efficiency and crosstalk effects between adjacent pixels that result to be up to 30% and a factor 10, respectively, better than those ones obtained for the microlens counterpart. The significant increase of the achievable values of the normalized optical efficiency and crosstalk can foresee the possibility to reduce the pixel size down to 1 μm, i.e., beyond the limit imposed by the diffraction effects arising in microlens equipped pixel.