Hybrid Method Of Moments Research Articles

Improved NURBS MOM-PO method for analyzing antenna around electrically large platform

The hybrid method of moments and physical optics (MOM-PO) based on nonuniform rational B-spline (NURBS) modeling represented a suitable approach for dealing with electromagnetic (EM) radiation problems because of its higher efficiency and more accurate modeling than Triangle MOM-PO method.However, the invalidation in existing NURBS MOM-PO method occurs when the distance between antenna and scatterer is less than one wavelength. The reason is analyzed in detail in this article. This article introduces an improved NURBS MOM-PO method to overcome this problem. Ludwig integral combining with stationary phase method is utilized to calculate the integral of PO currents. Thus, both the efficiency and validity are ensured. Numerical results demonstrate that accurate results can be achieved efficiently in electrically large EM radiation problems by using the present method. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2675–2679, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25569

Modeling the oxidation-induced fragmentation of soot aggregates in laminar flames

While the formation and growth of soot particles has received much attention, the subsequent destruction of the particles is less well understood. Soot particles are destroyed though two parallel processes: oxidation and fragmentation. Oxidation is the removal of mass from particles due to chemical reactions with molecular oxygen and hydroxyl radicals. Fragmentation is the break-up of large aggregates into smaller aggregates. Here, a new model for fragmentation inspired by previous experimental investigations is proposed and formulated within the Hybrid Method of Moments (HMOM). With the formulation, the rate of particle loss due to oxidation is closed, resolving a long-standing problem with the Method of Moments. Less important, secondary unclosed terms are introduced, and models for these terms are proposed. The oxidation and fragmentation models are validated using a set of laminar premixed methane flames and then applied to a series of laminar counterflow diffusion acetylene flames. The role of fragmentation is distinctly different in the two flame types. In the premixed flames, fragmentation only occurs in lean flames with a high oxygen concentration. In the diffusion flames, fragmentation is virtually absent, for soot passes through an OH radical layer and is completely oxidized before reaching high oxygen concentrations.

Improved MOM‐PO hybrid method for analyzing antenna around nurbs scatterer

AbstractA new efficient technique for analyzing disturbed pattern of antenna around nonuniform rational B‐spline scatterer is proposed in this article, termed the hybrid method of moments and physical‐optics (MOM‐PO) technique. The integral of PO currents is calculated by using Ludwig integral, which solves the invalidation when the distance between antenna and scatterer is less than one wavelength mentioned in literatures before. The relative pattern obtained using this method is compared with the patterns obtained from the previous solution and MOM. The pattern of the presented method agrees more closely with that of MOM, which demonstrates the accuracy of this approach. The outstanding advantage is that the present approach is applicable without restrictions on the distance between the antenna and the surface. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 2049–2053, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25392

Validation of Hybrid MoM Scheme With Included Equivalent Glass Antenna Model for Handling Automotive EMC Problems

In this paper, based on the refined modified image theory, an equivalent model of the layered glass antenna structure is suggested and validated by comparison with Sommerfeld's traditional solution to Green's function. Using this model, a hybrid method of moments (MoM) scheme is derived to handle the full MoM geometries including finite-sized and curved glass antenna structures. This scheme is validated by comparison of the measured and simulated electromagnetic compatibility (EMC) characteristics of the special simplified models and a full vehicle model with a realistic rear window glass antenna.

An Efficient Simulation Technology for Characterizing the Ultra-Wide Band Signal Propagation in a Wireless Body Area Network

This paper presents an efficient simulation technology to characterize the Ultra-Wide Band signal propagation between the antennas in close proximity to a human body, where the human body works as a Wireless Body Area Network. The first technique is the hybrid Method of Moments and asymptotic Physical Optics in which the formulation is extended for modeling the dielectric body. The second technique combines the modification of the Multilevel Fast Multipole Algorithm with the Impedance Boundary Condition. These two techniques drastically reduce the computational complexity to model and simulate an electrically very large and complex structure including antennas and human body. Numerical examples showing the effects of the human body on the Ultra-Wide Band signal transmission between two antennas are presented to demonstrate the efficiency of our proposed method.

Hybrid Method of Moments for modeling soot formation and growth

In this work, a new statistical model for soot formation and growth is developed and presented. The Hybrid Method of Moments (HMOM) seeks to combine the advantages of two moment methods, the Method of Moments with Interpolative Closure (MOMIC) and the Direct Quadrature Method of Moments (DQMOM), in an accurate and consistent formulation. MOMIC is numerically simple and easy to implement but is unable to account for bimodal soot Number Density Functions (NDF). DQMOM is accurate but is numerically ill-posed and difficult to implement. HMOM combines the best of both two methods to capture bimodal NDF while retaining ease of implementation and numerical robustness. The new hybrid method is shown to predict mean quantities nearly as accurately as DQMOM and high-fidelity Monte Carlo simulations. In addition, a model for combining particle coalescence with particle aggregation is presented and shown to accurately reproduce experimental measurements in a variety of sooting flames.

Analysis of Antenna Around NURBS Surface With Hybrid MoM-PO Technique

The hybrid method of moments and physical-optics (MoM-PO) approach is used to calculate the radiation pattern of antenna around arbitrarily shaped structure. The structure is modeled with Non-uniform rational B-spline (NURBS) surfaces. The hybrid MoM-PO approach is implemented by modifying the impedance matrix of the MoM region with PO. Formula for the scattered PO field is deduced for cases of antenna located around NURBS surface. The stationary phase method (SPM) is applied for the integral of the induced current in the PO region. Results obtained from this method and from MoM-PO approach based on triangle facet model agree well while the former is more efficient in execution time

Indoor environments propagation simulation using a hybrid MoM and UTD electromagnetic method

Radio channel observation and characterization is indispensable in mobile communications systems development. Efficient propagation prediction is crucial for rapid and cost-effective systems deployment. On-site measurements, statistical models, propagation prediction and deterministic modeling are widely used for the qualification of radio channels. In this paper, a simulation tool for deterministic channel modeling in indoor environments is evolved. A hybrid combination of the Method-Of-Moments (MoM) and the Uniform Theory of Diffraction (Utd) is used. Statistical characteristics of a simple office room are calculated and the results are in excellent agreement with corresponding results of relative research on the field.

A hybrid FEBI-MLFMM-UTD method for numerical solutions of electromagnetic problems including arbitrarily shaped and electrically large objects

Numerical solutions of electromagnetic scattering and radiation problems including arbitrarily shaped objects are obtained by solving integral equations with the method of moments (MoM). Fast and efficient solution of the integral equation with low computation and memory complexity is provided by the multilevel fast multipole method (MLFMM). The presence of electrically large conducting objects leads to hybrid MoM techniques with high-frequency methods. For ray-based high-frequency methods no discretization of the electrically large objects is needed, resulting into a more efficient numerical treatment of the problem. However, in order to retain low computation and memory complexity, the high-frequency fields must be taken into account in the matrix-vector product computations in the various levels of the MLFMM. In this contribution, a ray-based hybridization of the MLFMM with the uniform geometrical theory of diffraction (UTD) is proposed within a hybrid finite element-boundary integral (FEBI) technique, using the combined field integral equation (CFIE), resulting into a hybrid FEBI-MLFMM-UTD method. The hybridization is performed at the translation procedure on the various levels of the MLFMM, using a far-field approximation of the appropriate translation operator to obtain the high-frequency incident fields at the critical points of the UTD. The formulation of this new hybrid technique is presented and numerical results are shown.

Investigations of polarization purity and specific absorption rate for two dual-band antennas for satellite-mobile handsets

A study of the effects of human proximity on the polarization purity of two types of circularly-polarized handset antennas for personal satellite communications was investigated using the hybrid method of moments (MoM)/finite-difference time-domain technique. Associated with this, assessments of specific absorption rate in the head were made. The method gave stable results, in accordance with physical expectations; good agreement with the pure Method of Moments was shown in simplified cases omitting the head. The quadrifilar spiral antenna (QSA) was shown to be a propitious design for personal satellite communications.

Guided-wave characteristics of waveguide based periodic structures loaded with various FSS strip layers

In this paper, frequency-dependent guided-wave characteristics of waveguide based periodic structures loaded with transversal strip layers of frequency selective surfaces (FSS) are extensively studied in terms of per-unit-length transmission parameters, i.e., complex propagation constant and complex wave impedance. Such a periodic structure with various FSS strip layers are in theory characterized using the hybrid method of moments (MoM)-immittance approach so as to derive these two per-unit-length parameters over a wide frequency range. At first, the extracted phase constant of a simple periodic waveguide, loaded with rectangular patch layer, is compared with the available analytical results, thus validating the approach utilized here. Next, the three novel periodic waveguides, loaded with plus, square loop and Jerusalem cross FSS strip layers, are investigated. It is observed that there is slow-wave behavior in the lower passband for the first two whereas the third one exhibits both fast-wave and slow-wave propagation behaviors in the lower passband. Besides, the third one shows the attractive backward wave propagation within the partial passband, thus introducing a novel waveguide-based artificial negative refractive index metamaterial (NRIM).

A simple iterative method for considering multibounce in PO region of MoM‐PO

AbstractIt has been shown that the hybrid method of moments physical‐optics (MoM‐PO) approach is an efficient tool to model the electromagnetic behavior of antennas with 3D perfectly conducting bodies of arbitrary shape. In this paper, a simple and effective iterative method is proposed to consider multi‐bounce in the PO region of MoM‐PO. Some numerical results are presented and compared with a reference MoM and conventional MoM‐PO solutions in order to illustrate the high accuracy and efficiency of the proposed approach. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 110–112, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11299

A hybrid MoM solution of scattering from finite arrays of cylindrical cavities in a ground plane

In this paper, we propose a novel hybrid space/spectral-domain method-of-moments (MoM) calculation of canonical plane-wave scattering from finite periodic structures comprised of dissimilar cylindrical cavities in an infinite ground plane, covered by a dielectric superstrate. We take full advantage of analyzing this particular type of problem (comprised of a canonical geometry) by employing a set of entire-domain basis functions (waveguide modes), which truly span the Hilbert space in which the desired solution resides. The convergence behavior of a solution using said functions is quite robust. Results show that typically only a few basis functions are required to adequately represent the aperture fields with fidelity. We have also reformulated the conventional magnetic field integral equation in a hybrid fashion, whereby the exterior (unbounded half space) MoM interaction terms have been cast in the spectral domain and the interior (cavity) interactions cast in the space domain directly. The spectral representation allows us to trivially include a superstrate layer in the geometry and additionally leads to an efficient evaluation of the interaction integrals due to an overall reduction in the spatial dimensionality. The interior interactions are readily handled in the space domain, where we take advantage of the orthogonality property of waveguide modes. Most importantly, the technique is significantly more accurate than purely numerical methods, i.e., those in which a discretization of the geometry is necessary.

FFT-based analysis of periodic structures in microacoustic devices

Periodic structures utilized as transducer or reflector elements play an important role in microacoustic wave devices. Such structures can be described using approximate analytical models. However, to obtain the accuracy required for reliable device simulation, numerical methods have to be employed. In this contribution, we present an efficient numerical approach to calculate the dispersion curves associated with microacoustic modes propagating in periodic structures; the method is demonstrated for the case of Love wave modes. The computational efficiency is related to the utilization of the FFT algorithm in a hybrid Method of Moments (MoM)/Mode-Matching analysis. From the obtained dispersion curves, characteristic parameters such as the stopband width can be obtained which can be used in a coupling-of-modes (COM) model of the structure.

Radiation and scattering from infinite periodic printed antennas with inhomogeneous media

The hybrid method of moments (MoM)/Green's function method technique is applied to infinite periodic printed antenna arrays containing dielectric inhomogeneities. The solution uses an integral equation for an infinite periodic printed array on or over a homogeneous dielectric substrate, coupled with equivalent volume polarization currents for dielectric inhomogeneities on top of the homogeneous substrate. Volume pulse-basis functions were used to expand the volume polarization currents. A hybrid MoM/Green's function method solution was then obtained through the matrix form of the problem. The two-dimensional (2-D) solution of plane wave scattering from a grounded dielectric slab was used to validate the reaction impedance of the dielectric inhomogeneity. Several infinite periodic printed dipole arrays with dielectric supports and overlays were studied with this solution and good agreement was observed between the hybrid MoM/Green's function method and waveguide simulator experiments.