[Show abstract][Hide abstract] ABSTRACT: Metasheet structures together with bulk composite dielectric layers can be used for antenna radomes, absorbers, and band gap structures. Transmission (T) and reflection (Γ) coefficients for a plane wave incident at any angle upon a metasheet embedded in a dielectric layer are considered. These metasheets are either patch-type or an aperture-type, and they can be either single-layered or multi-layered. To calculate T and Γ for a patch-type metasheet, a concise unified matrix approach is derived using the Generalized Sheet Transition Conditions (GSTC). The Babinet duality principle is utilized to get T and Γ for single-layered aperture-type metasheets (as complementary to the patch-type ones) at an arbitrary angle of incidence. The T-matrix approach is applied to calculate characteristics of multilayered metasheet structures containing a cascade of metasheets and dielectric slabs. In this paper, the minimum distance for neglecting higher-order evanescent mode interactions between the metasheets has been determined. Computed results based on the proposed analytical approach are compared with the full-wave numerical simulations. The analytical results are verified for satisfying the energy balance condition.
Preview · Article · Jan 2012 · Progress In Electromagnetics Research B
[Show abstract][Hide abstract] ABSTRACT: A procedure is developed to predict electromagnetic interference from electronic products using near-field scan data. Measured near-field data are used to define equivalent electric and magnetic current sources characterizing the electromagnetic emissions from an electronic circuit. Reconciliation of the equivalent sources is performed to allow the sources to be accurately applied within full-wave numerical modeling tools like finite-difference time domain (FDTD). Results show that the radiated fields must typically be represented by both electric and magnetic current sources if scattering and multiple-reflections from nearby objects are to be taken into account. The accuracy of the approach is demonstrated by predicting the fields generated by a microstrip trace within and outside of a slotted enclosure, and by predicting the fields generated by the microstrip trace close to a long wire. Values predicted from near-field scan data match those from full-wave simulations or measurements within 6 dB.
No preview · Article · Dec 2011 · IEEE Transactions on Electromagnetic Compatibility
[Show abstract][Hide abstract] ABSTRACT: Near-electric-field and magnetic-field probes are used for a wide variety of applications. Accurate measurement of the fields, however, requires an accurate model of the receiving characteristic of the probe. The receiving characteristic for a reciprocal near-field probe can be calculated from its transmitting characteristic. This receiving characteristic can be used to evaluate the quality of the probe and to compensate for the effect of the probe on the measured field, thereby allowing the electric and magnetic fields to be found accurately from the measurements. In the following paper, methods of evaluating near-field probes using reciprocity are derived and are applied to a typical loop probe in order to compensate near-field measurements over a device under test.
Preview · Article · Mar 2011 · IEEE Transactions on Electromagnetic Compatibility
[Show abstract][Hide abstract] ABSTRACT: A methodology to efficiently design products based on magneto-dielectric (ferrite) materials with desirable frequency responses that satisfy electromagnetic compatibility and signal integrity requirements over RF and microwave bands is presented here. This methodology is based on an analytical model of a composite magneto-dielectric material with both frequency-dispersive permittivity and permeability. A procedure for extracting complex permittivity and permeability of materials from experimental data is based on transmission line measurements. The genetic algorithm is applied for approximating both permittivity and permeability of materials by series of Debye frequency dependencies, so that they are represented as “double-Debye materials” (DDM). The DDM is incorporated in the finite-difference time-domain numerical codes by the auxiliary differential equation approach.
Full-text · Article · Dec 2010 · IEEE Transactions on Electromagnetic Compatibility
[Show abstract][Hide abstract] ABSTRACT: A few scenarios of applying different magneto-dielectric absorbing sheet materials to mitigate electromagnetic inference (EMI) are analyzed in this paper using a full-wave 3D finite-difference time-domain (FDTD) technique. Frequency characteristics of both permittivity and permeability of these magneto-dielectric materials are approximated by the series of the Debye terms suitable for time-domain simulations. This approximation is accomplished using a new curve fitting technique based on the Legendre polynomials and the regression analysis optimization. The results of the numerical simulations are verified by the corresponding experiments, and the good agreement is obtained.
[Show abstract][Hide abstract] ABSTRACT: Frequency-dependent causal RLGC(f) models are proposed for single-ended and coupled transmission lines. Dielectric loss, dielectric dispersion, and skin-effect loss are taken into account. The dielectric substrate is described by the two-term Debye frequency dependence, and the transmission line conductors are of finite conductivity. In this paper, three frequency-dependent RLGC models are studied. One is the known frequency-dependent analytical RLGC model (RLGC-I), the second is the RLGC( f) model (RLGC-II) proposed in this paper, and the third (RLGC-III) is same as the RLGC -II, but with causality enforced by the Hilbert transform in frequency domain. The causalities of the three RLGC models are corroborated in the time domain by examining the propagation of a well-defined pulse through three different transmission lines: a single-ended stripline, a single-ended microstrip line, and an edge-coupled differential stripline pair. A clear time-domain start point is shown on each received pulse for the RLGC-II model and the RLGC-III model, where their corresponding start points overlap. This indicates that the proposed RLGC(f) model (RLGC-II) is causal. Good agreement of simulated and measured S-parameters has also been achieved in the frequency domain for the three transmission lines by using the proposed frequency-dependent RLGC(f) model.
Full-text · Article · Mar 2010 · IEEE Transactions on Electromagnetic Compatibility
[Show abstract][Hide abstract] ABSTRACT: The paper describes a methodology for an efficient design of novel products based on magneto-dielectric (ferrite) materials with desirable frequency responses that satisfy EMC and SI requirements. The methodology starts from estimating complex permittivity and permeability of these materials. This requires measurement techniques, approximation resultant frequency characteristics for permittivity and permeability using a curve-fitting procedure, and development of a full-wave numerical simulation tool that could deal with frequency-dispersive materials. An example of a ferrite material measurement, constitutive parameters extraction using a genetic algorithm, and corresponding FDTD modeling over the frequency range from 10 to 500 MHz is provided.
[Show abstract][Hide abstract] ABSTRACT: An analytical model of an effective permittivity of a composite taking into account statistically distributed orientations of inclusions in the form of prolate spheroids will be presented. In particular, this paper considers the normal Gaussian distribution for either zenith angle, or azimuth angle, or for both angles describing the orientation of inclusions. The model is an extension of the Maxwell Garnett (MG) mixing rule for multiphase mixtures. The resulting complex permittivity is a tensor in the general case. The formulation presented shows that the parameters of the distribution law for orientation of inclusions affect the frequency characteristics of the composites, and that it is possible to engineer the desirable frequency characteristics, if the distribution law is controlled.
Full-text · Article · Jan 2009 · Progress In Electromagnetics Research
[Show abstract][Hide abstract] ABSTRACT: An effective method for extracting parameters of a Debye or a Lorentzian dispersive medium over a wideband frequency range using a genetic algorithm (GA) and a transmission-line model is presented. Scattering parameters (S-parameters) of the transmission-line sections, including a parallel plate, microstrip, and stripline, are measured. Wave equations for TEM/quasi-TEM mode with a complex propagation constant and a frequency-dependent wave impedance are used to evaluate the corresponding S-parameters in an analytical model. The discrepancy between the modeled and measured S-parameters is defined as the objective function in the GA. The GA is used for search of the dispersive-medium parameters by means of minimizing the objective function over the entire frequency range of interest. The reconstructed Debye or Lorentzian dispersive material parameters are corroborated by comparing the original measurements with the FDTD modeling results. The self-consistency of the proposed method is demonstrated by constructing different test structures with an identical material, i.e., material parameters of a substrate extracted from different transmission-line configurations. The port effects on the material parameter extraction are examined by using through-reflection-line calibration.
[Show abstract][Hide abstract] ABSTRACT: High-frequency currents on the pins of integrated circuits (ICs) and on printed circuit board (PCB) traces are needed to predict and analyze electromagnetic interference in high-speed devices. These currents can, however, be difficult to measure when traces are buried within the PCB or chip-package, especially when several current-carrying traces are in close proximity. Techniques for estimating high-frequency currents from near-field scan data are proposed in this paper. These techniques are applied to find currents on the pins of an IC, on traces buried beneath other traces in a PCB, and on traces over a slot in the ground plane. Methods of dealing with the ill-posed nature of the current-estimation problem are discussed, as are applications to electrically large structures. A study of the sensitivity of the technique to errors in the measured fields, errors in the circuit geometry, and errors in the estimated dielectric constant of the PCB or chip package show that, for reasonable errors in these parameters, currents can be estimated to within an average of 20% (1.6 dB) or less of their correct values.
Preview · Article · Dec 2007 · IEEE Transactions on Electromagnetic Compatibility
[Show abstract][Hide abstract] ABSTRACT: This paper provides an approach for predicting the effects of skew and imbalance on radiated emission of cables inside a commercial 19-inch rack-based cabinet. Scattering parameters (S-parameters) for two sets of cable assembly are measured with a four-port vector network analyzer (VNA) and converted into mixed mode S-parameters. Time-domain input signals with different slew rates and different amount of skew are transferred into frequency-domain using fast Fourier transform (FFT). The spectra of radiation emission associated with different inputs are then estimated.
[Show abstract][Hide abstract] ABSTRACT: An analytical model of a composite dielectric presented in this paper is the extension of Maxwell Garnett formulation. It takes into account the simultaneous statistical (Gaussian) distribution of conductivity and aspect ratio of inclusions. The inclusions are randomly oriented elongated conducting spheroids at concentrations below the percolation threshold. The formulation presented herein is limited to microwave frequencies. However, taking subtle frequency- dependent effects that play important part at optical frequencies into account is straightforward. Some results of computations of microwave complex effective permittivity of composites with different input parameters have been obtained using analytical and numerical integration in Maple 10 software. It is shown how the parameters of the distribution laws — mean values and standard deviations of aspect ratio and conductivity — affect the resultant complex effective permittivity. The results of computations demonstrate that the most important factors affecting frequency characteristics of microwave effective permittivity are the mean values of the aspect ratio and conductivity. As for the standard deviations of aspect ratio and conductivity, their effects are the most noticeable in the transition between the static and optical limits of the Debye characteristic for the effective permittivity. There is almost no effect in the static and "optic" regions of the Debye curves.
Full-text · Article · Jan 2007 · Progress In Electromagnetics Research
[Show abstract][Hide abstract] ABSTRACT: From an electromagnetic compatibility perspective, a commercial 19-inch rack-based cabinet of 40U height is comprised of different functional modules housed in well-shielded enclosures. A main source of high-frequency radiated EMI from the cabinet is common-mode current on the cables. This common-mode current is caused by connector systems, printed circuit boards, and cabling systems used in the equipment. Two methodologies, in situ measurements on a functioning cabinet using a spectrum analyzer, and three-port mixed-mode S-parameter measurements with a swept frequency range of 100MHz to 2GHz using a vector network analyzer, are applied to investigate the overall shielding performance of various cabinet features, including the effects on radiated emissions from cable egress through the top of the cabinet, as opposed to the bottom of the cabinet. The results of the in situ measurements on a functioning cabinet show that, by bringing the cables out the top of the cabinet, the resulted radiated levels likely to exceed the EMI regulatory limit at a clock frequency of 627 MHz. The frequency response of the cabinet was further studied using the second methodology. Both approaches show that the cabinet, while not specifically designed to be a high-performance EMI shielded enclosure, does, however, provide about 5 ∼ 10 dBμV/m of overall shielding performance that is important in meeting EMI regulatory requirements with the current system. The swept frequency approach, as proved, can be an effective method in the evaluation of shielding performance of similar equipments.
[Show abstract][Hide abstract] ABSTRACT: Investigation of a dc power delivery network, consisting of a multilayer PCB using area fills for power and return, involves the distributed behavior of the power/ground planes and the parasitics associated with the lumped components mounted on it. Full-wave methods are often employed to study the power integrity problem. While full-wave methods can be accurate, they are time and memory consuming. The cavity model of a rectangular structure has previously been employed to efficiently analyze the simultaneous switching noise (SSN) in the power distribution network. However, a large number of modes in the cavity model are needed to accurately simulate the impedance associated with the vias, leading to computational inefficiency. A fast approach is detailed herein to accelerate calculation of the summation associated with the higher-order modes. Closed-form expressions for the parasitics associated with the interconnects of the decoupling capacitors are also introduced. Combining the fast calculation of the cavity models of regularly shaped planar circuits, a segmentation method, and closed-form expressions for the parasitics, an efficient approach is proposed herein to analyze an arbitrary shaped power distribution network. While it may take many hours for a full-wave method to do a single simulation, the proposed method can generally perform the simulation with good accuracy in several minutes. Another advantage of the proposed method is that a SPICE equivalent circuit of the power distribution network can be derived. This allows both frequency and transient responses to be done with SPICE simulation.
Full-text · Article · Jun 2006 · IEEE Transactions on Advanced Packaging
[Show abstract][Hide abstract] ABSTRACT: An analytical model for a shielding structure containing both bulk composite layers and planar metafilms (MFs) made of perfect electric conductors is presented, allowing for synthesis of shielding structures using the genetic algorithm (GA) optimization. MFs can be of two different types: patch or aperture. The frequency response, specifically, transmission (T) and reflection ( ) coefficients in a plane-wave formulation, of any MF is calculated based on polarizabilities determined by the particular pattern geometry. T and of a patch-type MF are derived using the generalized sheet transition conditions (GSTC) and the Babinet's duality principle is used for aperture-type MF to map the results from the complementary problem. T and for a single- layered MF are represented in a unified matrix form for any angle of incidence. T-matrix approach is used for getting T and for a multilayered structure. Any MF buried in a host dielectric can be decomposed into three types of basic elements: a host composite slab, interface between media, and an MF inside the homogeneous host medium. Each basic element is described by a corresponding T-matrix, and the total T-matrix of the stack is the sequential product of the each individual T-matrix. T and of the stack can be easily derived from the total T-matrix. If there are two or more MFs, the distance between them justifies the condition of neglecting higher-order evanescent mode interactions. Then the GA is applied to engineer a structure with the desired frequency response. It helps to choose the best geometry of MF patterns, thickness of layers, and appropriate constitutive parameters of each composite layer.
[Show abstract][Hide abstract] ABSTRACT: A numerical technique to analyze shielding effectiveness of sandwiched FSS-composite structures is proposed. This technique is based on using a dispersive FDTD method in conjuncture with a novel periodic boundary condition to model sandwiched FSS-composite elements. Results show that by inserting single or multilayered FSS elements into composite materials, better shielding effectiveness can be achieved. Keyword FDTD, Z-transform, dispersive medium, debye model, periodic structure, periodic boundary condtion
[Show abstract][Hide abstract] ABSTRACT: A procedure is proposed for predicting TEM cell measurements from near field scans by modeling near-field scan data using equivalent sources. The first step in this procedure is to measure the tangential electric and magnetic fields over the circuit. Electric and magnetic fields are estimated from probe measurements by compensating for the characteristics of the probe. An equivalent magnetic and electric current model representing emissions is then generated from the compensated fields. These equivalent sources are used as an impressed source in an analytical formula or full wave simulation to predict measurements within the TEM cell. Experimental verification of the procedure using a microstrip trace and clock buffer show that values measured in the TEM cell and calculated from near field scan data agree within a few decibels from 1 MHz to 1 GHz.
[Show abstract][Hide abstract] ABSTRACT: An analytical model of composites made of a dielectric base and randomly oriented metal inclusions in the form of nanorods is presented. This model is based on the generalized Maxwell Garnett (MG) mixing rule. In this model, the nanorod particles are modeled as prolate spheroids with a statistically normal distribution of their aspect ratios. It is shown that parameters of the distribution laws affect the frequency characteristics of the composites both at microwave and optical frequencies. The results of computations are represented.
Full-text · Article · Jan 2006 · Progress In Electromagnetics Research
[Show abstract][Hide abstract] ABSTRACT: Dielectric properties and losses are two critical issues in signal link-path characterization. To obtain the substrate dielectric properties for a planar transmission line, an analytical solution is derived and validated based on a stripline structure and measured scattering parameters with TRL de-embedding. The characterized dielectric property is used to evaluate dielectric loss and conductor loss. The total loss is thereby found from their summation. The calculated total loss is compared to the measured total loss, and the conductor loss and dielectric loss are then quantifiable. Since the conventional description using the loss tangent and dielectric constant to represent material properties is usually insufficient as the frequency reaches 20 GHz, a Debye model is proposed. The second order Debye parameters are subsequently extracted using a genetic algorithm. A full wave simulation is implemented to verify the determination of two-term Debye model parameters.
Full-text · Article · Jan 2006 · IEEE International Symposium on Electromagnetic Compatibility
[Show abstract][Hide abstract] ABSTRACT: Mathematical modeling of composites made of a dielectric base and randomly oriented metal inclusions is considered. Different sources of frequency-dependent metal conductivity at optical frequen- cies are taken into account. These include the skin-effect, dimensional (length-size) resonance of metal particles, and the Drude model. Also, the mean free path of electrons in metals can be smaller than the char- acteristic sizes of nanoparticles, and this leads to the decrease in con- ductivity of the metal inclusions. These effects are incorporated in the Maxwell Garnett mixing formulation, and give degrees of freedom for forming desirable optical frequency characteristics of composite media containing conducting particles.
Full-text · Article · Jan 2006 · Progress In Electromagnetics Research