Accurate solution of square scatterer as benchmark for validationof electromagnetic modeling of plate structures

An infinitesimally thin-square scatterer, of size λ×λ, excited normally by an incident plane wave, which is polarized along a scatterer edge, is analyzed. The accurate solution of its current distribution is found in the form of a double series of basis functions, which automatically satisfy the continuity equation at the plate edges and include the edge effect. The coefficients that multiply basis functions are determined starting from the electric field integral equation by using the Galerkin method. The solution obtained for the order of approximation n=8 is adopted as a benchmark. The corresponding coefficients are tabulated and graphs of such obtained current distribution are given. The solution adopted as a benchmark is applied for comparison of rooftop basis functions and polynomial entire-domain basis functions. The relative error of the mean absolute value of current deviation is used as an error metric     

Reduced sized cells for electromagnetic bandgap structures

Electromagnetic bandgap structures of simple squares are compared to convoluted and interleaved elements to reduce bandgap frequency for fixed periodicity. A reduction of 42% in bandgap frequency is obtained for one (Hilbert) convolution. This frequency reduction increases to 55% when adjacent elements in the structure are interleaved.     

Numerical modeling and electromagnetic resonant modes in complex grating structures and optoelectronic device applications

An extended surface impedance boundary condition algorithm is developed that allows for the optical properties of a wide variety of complex one-dimensional periodic grating structures to be modeled. Wood-Rayleigh anomalies, diffraction, and electromagnetic resonance modes including horizontally oriented surface plasmons and vertical surface resonances are identified and described as well as analyzing their structural and geometrical dependencies. Methods to combine these modes to produce hybrid modes that channel and localize light are described. Application of these modes to metal-semiconductor-metal photodetectors (MSM-PD) is discussed and an example silicon-based MSM-PD with over 30 GHz bandwidth and 0.3 A/W responsivity is described.     

Dual electromagnetic bandgap CPW structures for filter applications

A novel coplanar waveguide (CPW) low pass filter based on electromagnetic bandgaps (EBG) with double periodicity has been designed and fabricated. The device consists on a CPW with T-shaped loading capacitances at periodic positions and slot width modulation. By properly choosing the ratio between the two periods of the structure, a huge band gap (more than five times the bandwidth) is obtained through the suppression of spurious frequencies. The fabricated prototypes also exhibit very sharp cutoff, very low insertion loss in the passband and slow wave effect.     

Physical/electromagnetic pHEMT modeling

An effective technique, which is based only on geometrical and physical data, is presented for the analysis of high-frequency FETs. The intrinsic part of this electron device is described by a quasi-two-dimensional hydrodynamic transport model, coupled to a numerical electromagnetic field time domain solver in three dimensions that analyzes the passive part of the FET. Such an analysis is entirely performed in the time domain, thus allowing linear and nonlinear operations. The obtained data give insights to some parameters affecting the signal distribution through the entire device structure; a comprehensive discussion of these is given for a test device. In order to prove the validity of the approach, the bias-dependent small-signal analysis is compared with the corresponding measurements up to 50 GHz for two 0.3-/spl mu/m gate-length AlGaAs-InGaAs-GaAs pseudomorphic high electron-mobility transistors, each having two gate fingers of 25-/spl mu/m and 100-/spl mu/m width, at bias points ranging from Idss to the pinchoff regime. The accuracy and the efficiency of the approach make it suitable for device optimization.     

An electromagnetic interaction modeling advisor

A knowledge-based approach for the modeling of electromagnetic (EM) interactions in a system is described. The purpose is to determine any unwanted EM effects that could jeopardize the safety and operation of the system. Modeling the interactions in a system requires the examination of the compounded and propagated effects of the EM fields. A useful EM modeling approach is one that is incremental and constraint-based. The approach taken here subdivides the modeling task into two parts: (a) the definition of the related EM topology and (b) the propagation of the EM constraints. A prototype of some of the EM constraints has been implemented in Quintus Prolog under NeWS on a Sun workstation. User interaction is through a topology drawing tool and a stack-based attribute interface similar to the HyperCard interface of the Apple Macintosh computer     

A complete description of a source-type method for modeling planar structures

A source-type method is developed with a view to model microstrip planar circuits. A complete study is made. It allows us to put in a prominent position the arbitrary nature of the source, which is defined on the metal plane. The presence of a coupling two-port network, whose role is fundamental for solving the problem, is demonstrated too. Extended wavelet trial functions are used for modeling the current density in the circuit. This theory is illustrated with results giving the modulus of the transmission coefficient for some elementary discontinuities.     

Higher order hierarchical Legendre basis functions for electromagnetic modeling

This paper presents a new hierarchical basis of arbitrary order for integral equations solved with the method of moments (MoM). The basis is derived from orthogonal Legendre polynomials which are modified to impose continuity of vector quantities between neighboring elements while maintaining most of their desirable features. Expressions are presented for wire, surface, and volume elements but emphasis is given to the surface elements. In this case, the new hierarchical basis leads to a near-orthogonal expansion of the unknown surface current and implicitly an orthogonal expansion of the surface charge. In addition, all higher order terms in the expansion have two vanishing moments. In contrast to existing formulations, these properties allow the use of very high-order basis functions without introducing ill-conditioning of the resulting MoM matrix. Numerical results confirm that the condition number of the MoM matrix obtained with this new basis is much lower than existing higher order interpolatory and hierarchical basis functions. As a consequence of the excellent condition numbers, we demonstrate that even very high-order MoM systems, e.g., tenth order, can be solved efficiently with an iterative solver in relatively few iterations.     

近场电磁散射特点及其对建模要求

介绍了近场电磁散射问题,从电磁散射角度阐释当前对近场特性认识上的分歧,分析近场电磁散射问题中局部照射与探测器及动态过程关联密切等特点.根据近场特点提出了对建模中目标模型、电磁算法以及计算特性类型等的一般要求,同时提出了一种基于基础近场散射问题与探测器去相关的建模方式,并针对典型弹载雷达探测情况,给出了近场动态散射建模中运动模型、天线模型以及动态采样等具体要求.     

Initial results for automated computational modeling ofpatient-specific electromagnetic hyperthermia

Developments in finite-difference time-domain (FD-TD) computational modeling of Maxwell's equations, super-computer technology, and computed tomography (CT) imagery open the possibility of accurate numerical simulation of electromagnetic (EM) wave interactions with specific, complex, biological tissue structures. One application of this technology is in the area of treatment planning for EM hyperthermia. In this paper, we report the first highly automated CT image segmentation and interpolation scheme applied to model patient-specific EM hyperthermia. This novel system is based on sophisticated tools from the artificial intelligence, computer vision, and computer graphics disciplines. It permits CT-based patient-specific hyperthermia models to be constructed without tedious manual contouring on digitizing pads or CRT screens. The system permits in principle near real-time assistance in hyperthermia treatment planning. We apply this system to interpret actual patient CT data, reconstructing a 3-D model of the human thigh from a collection of 29 serial CT images at 10 mm intervals. Then, using FD-TD, we obtain 2-D and 3-D models of EM hyperthermia of this thigh due to a waveguide applicator. We find that different results are obtained from the 2-D and 3-D models, and conclude that full 3-D tissue models are required for future clinical usage.     

Comparative evaluation of DSP techniques coupled with electromagnetic time-domain simulators for the efficient modeling and design of highly resonant RF-MEMS structures

Four digital signal processing (DSP)-based digital predictors [Prony's, covariance, forward-backward (FB), matrix pencil (MP)], that are commonly used to enhance the time-domain modeling and design of highly complex RF MEMS structures, are evaluated in terms of computational efficiency and accuracy as a function of the model order, the decimating factor, and the size of sample train. For a benchmarking case of an RF MEMS tuner, it is found that while covariance method has the best performance in terms of accuracy, MP method confers robustness to computational economies (less numerical effort) and saves more CPU time with a smaller model order that can be selected by easy and efficient criteria.     

Field computations and network representations for open electromagnetic structures

Rigorous network representations for radiating structures are still an open problem. In this contribution the concept of Transition Region for deriving such a network representation of complex structures radiating into free-space is introduced. The space is divided into one or more computational domains which contain the complex geometrical features embedded into a transition region delimited by an outer spherical surface. The introduction of the transition region is expedient to avoid a large computational domain of spherical shape. A theoretical investigation of the computational procedures for deriving the transition region network representation is also presented.     

Solving electromagnetic field problems using a multiple gridtransmission-line modeling method

A multiple grid technique for solving electromagnetic field problems using the transmission-line modeling (TLM) method is described. The ideal conversion conditions across the interface between fine and coarse mesh regions are described and the implications of making the approximations needed for a practical implementation are discussed. Simulations are presented showing the accuracy of the method and its benefits in terms of reduced storage and run-time     

Harmonics generation in quantum-size structures in a strong electromagnetic field

Harmonics generation in a system of tunneling-coupled quantum wells is investigated by solving numerically the nonstationary Schrödinger equation, without using perturbation theory, in an external electromagnetic field. The time-dependence of the dipole moment is calculated and a method is proposed for calculating the radiation intensity at a fixed frequency. For systems containing three equidistant energy levels, it is shown that the effect of the field on the energy spectrum becomes substantial at intensities of several hundreds V/cm; the system falls out of resonance. The field-dependence of the second harmonic amplitude becomes nonquadratic, in contrast to the dependence predicted by perturbation theory, and the system passes into a stable level. In the quasienergy-crossing regime, it is shown that even-harmonics generation is possible in a symmetric system in a strong field. The amplitude of the harmonics is largely determined by the initial state of the system. It is possible to have a situation where the amplitude of the generated harmonic can even be greater than in structures with a resonance configuration of energy levels (three equidistant levels for the second harmonic).     

Application of subspace projection approaches for reduced-order modeling of electromagnetic systems

Subspace projection approaches, including the Pade/spl acute/ via Lanczos (PVL), Krylov, and rational Krylov algorithms, are used for reduced-order modeling of wide-band electromagnetic systems. The properties of these algorithms are discussed. A frequency segmentation technique has also been used with the Lanczos algorithm to obtain benchmark data of electromagnetic fields and for scattering parameter extraction from the calculated electromagnetic field values. From the various techniques, the combined PVL/frequency segmentation technique is the most promising for efficient and accurate modeling of electromagnetic systems.     

Spectral electromagnetic modeling of a planar integrated structurewith a general grounded anisotropic slab

A formulation for the solution of the electromagnetic field in vertically stratified structures with a general anisotropic grounded slab under planar electric excitation conditions is presented. The development of the solution is obtained by using the two-dimensional Fourier transform applied to the partial differential equations describing the electromagnetic field, which can be expressed in terms of dyadic electric Green's functions. Moreover, a spectral equivalent circuit representation of the solution, separated into its spectral transverse electric (TE) and transverse magnetic (TM) components (with respect to the vertical direction), is given. It is demonstrated that such a spectral circuit representation is always possible when the constitutive ϵ and μ tensors are reduced to their diagonal form. The transmission-line representation for an unbounded gyrotropic medium with vertical preferred axis is presented. This theory is applied to a planar structure with an anisotropic biaxial grounded slab and an electric horizontal point source embedded in it. Numerical examples of evaluation of the radiated pattern and noteworthy information about the radiation on the horizon plane are given     

Analyses of electromagnetic scattering from wire-mesh structures

Various analytical and numerical methods have been developed recently to calculate the interaction of wire-mesh structures with electromagnetic waves. An intercomparison of these methods is reported for the two cases where the wire junctions are bonded and unbonded. In particular, it is found that the average boundary condition method of Kontorovich and Astrakhan appears to give valid results only if the interwire spacing of the mesh is small compared with a wavelength. However, we may safely conclude from both their work and ours that bonding the wire junctions may degrade the shielding performance of such meshes.     

Linear electromagnetic actuator modeling for optimization of mechatronic and adaptronic systems

In active mechanical systems (mechanisms or structures) the possibility of a coupling between active and passive elements at an early stage of the design process is becoming more and more significant. In order to integrate actuators in preliminary design procedures or in a multidisciplinary optimization approach, reliable models of the actuator performance (actuator force and stroke, loading curves, strength limit, volume and mass specific work and power, frequency range, efficiency) as a function of the design parameters and variables (actuator principle, size of the actuator element) are necessary. The present work deals with the formulation of model-based design rules to be used in the conception of optimized mechatronic and adaptronic systems and applies it to linear electromagnetic actuators optimization focusing on the solenoid and moving coil actuators.     

Improved heat transfer modeling of the eye for electromagnetic wave exposures

This study proposed an improved heat transfer model of the eye for exposure to electromagnetic (EM) waves. Particular attention was paid to the difference from the simplified heat transfer model commonly used in this field. From our computational results, the temperature elevation in the eye calculated with the simplified heat transfer model was largely influenced by the EM absorption outside the eyeball, but not when we used our improved model.