Showing papers in "IEEE Transactions on Electromagnetic Compatibility in 2001"

Wideband frequency-domain characterization of FR-4 and time-domain causality

Abstract: FR-4 is one of the most widely used dielectric substrates in the fabrication of printed circuits for fast digital devices. This material exhibits substantial losses and the loss tangent is practically constant over a wide band of frequencies. This paper presents measured data for the complex permittivity of this material from power frequencies up to the microwave region. In addition it gives simple closed-form expressions that approximate the measured data and provide a causal response in the time domain.

Current and electromagnetic field associated with lightning-return strokes to tall towers

Abstract: An analysis of electric and magnetic fields radiated by lightning first and subsequent return strokes to tall towers is presented. The contributions of the various components of the fields, namely, static, induction, and radiation for the electric field, and induction and radiation for the magnetic field are illustrated and discussed. It is shown in particular that the presence of a tower tends, in general, to increase substantially the electric and magnetic field peaks and their derivatives. This increase is mainly caused by the presence of two oppositely propagating current wavefronts originating from the tower top and by the very high propagation velocity of current pulses within the tower, and depends essentially on the wavefront steepness of the channel-base current. Because of the last factor, the increase of the field magnitudes is found to be significantly higher for subsequent return strokes, which are characterized by much faster risetimes compared to first return strokes. The presented results are consistent with experimental observations of current in lightning strokes to the Toronto CN Tower and of the associated electric and magnetic fields measured 2 km away. These findings partially explain the fact that subsequent return strokes characterized by lower current peaks but higher front steepnesses and return stroke speeds may result in higher field peaks. The results obtained have important implications in electromagnetic (EM) compatibility. It is found that lightning strokes to tall metallic objects lead to increased EM field disturbances. Also, subsequent return strokes are to be considered an even more important source of EM interference than first return strokes. Indeed, EM fields from subsequent strokes are characterized by faster fronts and additionally, they may reach greater peaks than first strokes. Lastly, findings of this study emphasize the difficulty of extracting reliable lightning return stroke current information from remote EM field measurements using oversimplified formulae.

Transient response of a tall object to lightning

Abstract: Experimental data showing the transient behavior of tall objects struck by lightning are reviewed. The influence of this transient behavior, illustrated by simple calculations, on measured lightning current and measured remote electromagnetic fields is discussed. The estimated equivalent impedance of the lightning channel at the time of the initial current peak is appreciably higher than the characteristic impedance of an ordinary tall object (a factor of 3 or so for both the Ostankino and Peissenberg towers and about a factor of 2 for the CN tower). The grounding impedance of a tower is typically lower than its characteristic impedance. Thus, the current reflection coefficient is negative at the top and positive at the bottom of the tower. The similarity of the statistical distributions of subsequent-return-stroke peak currents in: 1) natural downward lightning; 2) natural upward (object-initiated) lightning; and 3) rocket-triggered lightning measured at objects with heights ranging from 4.5 to 540 m suggests that current peaks are not significantly influenced by the presence of a tall object, provided that measurements are taken at the top of the object. This inference is consistent with modeling results of Melander (1984) who showed that the current peaks measured in Switzerland and Italy at the top of 70-m and 40-m towers, respectively, are essentially unaffected by the presence of the towers. If lightning current could be represented by an ideal current source, current at the top of the object would be equal to the source current at all times. The peak current measured at the bottom of a tall object is usually more strongly influenced by the transient process in the object than the peak current at the top. For example, peak currents measured in the lower part of the 540-m Ostankino tower are about a factor of two higher than the peak currents measured near the tower top because the current reflection coefficient at the bottom of the tower is near +1. Observations and modeling suggest that a tall metallic strike object replacing the lower part of lightning channel serves to enhance the lightning-radiated electromagnetic fields relative to the fields due to similar lightning discharges attached directly to ground, this effect being more pronounced for the sharper lightning current pulses.

A genetic algorithm based method for source identification and far-field radiated emissions prediction from near-field measurements for PCB characterization

Abstract: A new method for predicting the far-field radiated emissions and for finding the radiation sources of a device from near-field measurements is presented. It is based on the substitution of the original device by an equivalent set of elemental dipoles, placed over the main radiating sources, which radiate the same near-field (and therefore, far-field). This equivalent set of elemental dipoles is generated using a genetic algorithm. From the position and type of the equivalent elemental dipoles, the position of the actual radiating sources is determined. Since the field produced by an elemental dipole is known, the far-field radiation of the actual radiating source can be calculated. The new method has been tested using synthetic data and real measurements from the radiation generated by a modem PCB demonstrating its viability and usefulness.

An improved transmission-line model of grounding system

Abstract: This paper presents a time-domain transmission line model of grounding system, which includes the mutual electromagnetic coupling between the parts of the grounding structure and the influence of air-earth interface. The model can be used to simulate the transient behavior of the grounding system under lightning strike. The simulation results are in good agreement with that of the model based on the solution of full Maxwell's equations. The influence of different parameters, such as the soil relative permittivity /spl epsi//sub /spl tau//, the soil resistivity /spl rho/, and the conductivity and diameter of the conductor, on the transient voltage distribution of the grounding system is investigated. It shows that, among the parameters investigated here, the soil resistivity is the most important parameter that affects the transient response of bare buried conductors. The soil permittivity has very little influence on the transient response of the grounding system when the grounding system is buried in the soil with low resistivity, but have moderate influence in the soil with extremely high resistivity. The conductivity of the conductor and skin effect have practically no influence on the peak transient voltage of the grounding system. Increase in conductor diameter tends to decrease the peak transient voltage. The model presented in this paper is simple, but sufficiently accurate and can be used easily in engineering practice. Since the model is in the time domain, it could be easily coupled to the other time-domain models of nonlinear surge-protection components.

Quantifying SMT decoupling capacitor placement in dc power-bus design for multilayer PCBs

Abstract: Noise on a dc power-bus that results from device switching, as well as other potential mechanisms, is a primary source of many signal integrity (SI) and electromagnetic interference (EMI) problems. Surface mount technology (SMT) decoupling capacitors are commonly used to mitigate this power-bus noise. A critical design issue associated with this common practice in high-speed digital designs is placement of the capacitors with respect to the integrated circuits (ICs). Local decoupling, namely, placing SMT capacitors in proximity to ICs, is investigated in this study. Multilayer PCB designs that employ entire layers or area fills for power and ground in a parallel plate structure are considered. The results demonstrate that local decoupling can provide high-frequency benefits for certain PCB geometries through mutual inductive coupling between closely spaced vias. The associated magnetic flux linkage is between the power and ground layers. Numerical modeling using an integral equation formulation with circuit extraction is used to quantify the local decoupling phenomenon. Local decoupling can effectively reduce high-frequency power-bus noise, though placing capacitors adjacent to ICs may limit routing flexibility, and tradeoffs need to be made based on design requirements. Design curves are generated as a function of power-bus layer thickness and SMT capacitor/IC spacing using the modeling approach to quantify the power-bus noise reduction for decoupling capacitors located adjacent to devices. Measurement data is provided to corroborate the modeling approach.

Analysis of power/ground-plane EMI decoupling performance using the partial-element equivalent circuit technique

Abstract: The design of printed circuit (PC) boards with decoupling capacitors has been the subject of debate and different opinions for many years. The design and electrical impact of the capacitors has been difficult to separate from all other electrical interactions occurring on a conventional PC board populated with integrated circuits. This work demonstrates how the partial-element equivalent circuit (PEEC) modeling technique can be used to accurately predict the performance of various decoupling design strategies. Computer modeling using the PEEC approach is very flexible due to the ease of mixing physical geometries with a large number of circuit elements. Also, the compute time for such practical mixed EM and circuit problems are relatively short. Using this technique, the usual iteration between a number of different designs of test boards can be avoided. We show that the change of the voltage across the PC board, or the voltage gradient, can be used as an effective tool for the improvement of the decoupling efficiency.

HIRF penetration through apertures: FDTD versus measurements

Abstract: The penetration of high-intensity radiated fields (HIRF) into conducting enclosures via apertures is an EMI issue that is relevant to all aviation. The stories are numerous, of disrupted communications, disabled navigation equipment, etc., due to the effects of EM sources external to the aircraft. Here, the FDTD method is used to predict the shielding effectiveness of conducting enclosures with apertures, and the numerical results are compared with measurements. Several issues related to the FDTD analysis of highly resonant and high-quality factor (high-Q) structures, such as windowing and acceleration techniques, are examined and discussed.

Parasitic modes on printed circuit boards and their effects on EMC and signal integrity

Abstract: In this paper, parasitic modes, such as slotline, parallel plane, and surface wave (SW) modes, commonly found on printed circuit boards (PCBs) are analyzed and their effects on electromagnetic compatibility (EMC) and signal integrity are discussed. The analysis is based on numerical simulations using the finite difference time domain (FDTD) method which is shown to be very well suited for rigorous modeling of parasitic mode effects. The EMC and signal integrity problems discussed include power loss, crosstalk, ground bounce, and free space radiation. Design guidelines for improved EMC and signal integrity are derived from the results obtained. Comprehensive simulation and characterization of SWs using FDTD is presented for the first time.

A study on stray capacitance modeling of inductors by using the finite element method

Abstract: Stray capacitance modeling of an inductor is essential for its RF equivalent circuit modeling and inductor design. Stray capacitance determines an inductor's performance and upper frequency limit. A method has been proposed for modeling the distributed stray capacitance of inductors by the finite element method and a node-to-node lumped capacitance network. The effects of wire insulation layer, ferrite core, number of segments used to model the circumference of a wire cross section, pitch and coil-to-core distances, and the capacitance between nonadjacent turns, etc., an an inductors' self-capacitance and calculation accuracy, have all been considered. The calculated equivalent lumped stray capacitance for a rod inductor with a ferrite core is compared to that estimated from measurement. Good agreement between them has been observed.

Operation of electromagnetic reverberation chambers with wave diffractors at relatively low frequencies

Abstract: The dependence of the modal density on chamber geometry is analyzed, for general unstirred reverberation chambers at relatively low frequencies of operation. An expression for the lowest usable frequency is derived based on the chamber mode density. The use of curved wave diffractors is investigated as a method for increasing the average mode density. The specific effect of corner, edge, surface and volume diffractors on the mode density and quality factor of a nominally rectangular shielded room is analyzed as a function of diffractor size, density, and operating frequency. This paper complements earlier studies on field statistics of undermoded reverberation chambers and the performance of acoustic-type diffusers in electromagnetic reverberation chambers.

EMI mitigation with multilayer power-bus stacks and via stitching of reference planes

Abstract: General methods for reducing printed circuit board (PCB) emissions over a broad band of high frequencies are necessary to meet EMI requirements, as processors become faster and more powerful. One mechanism by which EMI can be coupled off a PCB or multichip module (MCM) structure is from high-frequency fringing electric fields on the DC power and reference planes at the substrate periphery. An approach for EMI mitigation by stitching multiple ground planes together along the periphery of multilayer PCB power-bus stacks with closely spaced vias is reported and quantified in this paper. Power-bus noise induced EMI and coupling from the board edges is the major concern herein. The EMI at 3 m for different via stitch spacing and layer thickness is modeled with the finite-difference time domain (FDTD) method. Design curves and an empirical equation are extracted from a parametric study to summarize the variation of the radiated EMI as a function of layer thickness and stitch spacing.

High-frequency electromagnetic field coupling to long terminated lines

Abstract: We present a theory for the EMC problem of electromagnetic field coupling to a long line with arbitrary terminations The theory is applicable for the high-frequency plane wave electromagnetic field excitations, when the transmission line approximation is no longer valid Analytical expressions are derived for the induced current along the line, and at the two-line terminals The coefficients of these expressions are determined using a procedure based on the exact solutions of the integral equation for two similar line configurations, but having a significantly shorter length The method is, therefore, particularly efficient when considering the electromagnetic field coupling to very long lines The advantage of the proposed approach is that, in contrast with transmission line approximation, it takes into account high-frequency radiation effects Furthermore, it allows a considerable reduction in computation time and storage requirements with respect to conventional numerical solutions based on the thin-wire approximation

Power-supply decoupling on fully populated high-speed digital PCBs

Abstract: The effectiveness of buried capacitance technology, used with discrete surface mounted decoupling capacitors, in reducing circuit malfunctions due to the noise voltage between power/ground planes in a multilayer printed circuit board is investigated. The analysis is carried out on a fully populated multilayer board, where an integrated circuit with very large package provides a lot of digital signals with measured rise/fall times equal to 400 ps. The role of the integrated circuit's package in damping out the resonance peaks at resonance frequencies on the power plane is highlighted. The relations between the power-bus transfer impedance and noise spectrum are also studied, in order to better evaluate the effects of the buried capacitance technology and decoupling capacitors on the power-bus noise filtering.

Model of the electromagnetic fields inside a cuboidal enclosure populated with conducting planes or printed circuit boards

Abstract: We examine the extension of a simple and versatile model of the electromagnetic fields in an equipment enclosure with an aperture to include the effects of loading the enclosure with conducting planes or printed circuit board structures (PCB). Modeling results are compared with experimental measurements of the shielding effectiveness in a cuboidal enclosure loaded with both grounded and ungrounded conducting planes and/or PCBs with a range of grounded and ungrounded tracks. Measurement results are compared with full electromagnetic simulations and the simple model to demonstrate the accuracy and range of validity of the simple model.

Analysis of crosstalk between finite-length microstrip lines: FDTD approach and circuit-concept modeling

Abstract: Two approaches, one based on the circuit concept and the other based on field theory, are used to model the crosstalk between two microstrip lines of finite length and arbitrary orientation. In the circuit-concept modeling, a set of equations for the line voltages and currents has been derived from a modified telegrapher's equation. A four-port network expression is resultantly obtained by solving the equations, thus the crosstalk can be predicted by applying terminal conditions to the network expression. On the other hand, the extended finite-difference time-domain (FDTD) method has been used to model the terminal resistors and the feeding resistive voltage source in the crosstalk analysis. Several physical models have been fabricated and experiments performed. The calculated results are compared to measurements. In our experiment, for microstrip lines of finite length and arbitrary orientation, there are short line-sections or vias at each of the four ports, which should be incorporated into the crosstalk analysis. This effect has been investigated numerically and experimentally.

A simple method for measuring the relative permittivity of printed circuit board materials

Abstract: This paper presents a simple method to measure the relative permittivity of glass-epoxy printed circuit boards (PCBs). In this method, the relative permittivity as a function of frequency is measured using an actual PCB. In order to estimate the relative permittivity, the reflection coefficient is measured with a network analyzer. The relative permittivity is calculated by observing the frequencies of the resonant cavity modes. We show that the relative permittivity of an FR-4 sample decreases from 4.3 to 4.2 at frequencies from 300 MHz to 2 GHz.

Electrical behavior of decoupling capacitors embedded in multilayered PCBs

Abstract: We describe the modeling of prototype capacitors embedded in multilayered printed circuit boards. We present the design of these devices. We also report measurement and characterization results. The emphasis is on the modeling of via hole connections to the embedded capacitor, not on the technology of buried capacitors. Several designs have been compared with respect to their electrical behavior. In particular, several via hole configurations have been studied, because they are the main cause of parasitic behavior. With these buried capacitors, we obtained a reduction of the parasitic inductance of 80% compared to an equivalent discrete capacitor. This work has been carried out under a European Brite-EuRAM funded project COMPRISE (BE 96-3371). The objective of this project was to develop new materials and manufacturing processes to embed passive components (R, L, and C) within printed wiring structures fabricated from laminate materials. This technology enables the manufacture of space efficient and radio frequency (RF) optimal performing types of modules or board assemblies particularly suited to the market domain of portable and handheld communication and information technology products.

Underground electromagnetic fields generated by the return strokes of lightning flashes

Abstract: In this paper, equations are developed in the time domain to represent lightning generated electromagnetic (EM) fields at different depths below the ground surface. The equations connect underground EM fields to surface fields that can easily be measured or calculated. Numerous examples are given to illustrate how the signature of the electric and magnetic field vary as a function of depth as well as conductivity.

DC power-bus design using FDTD modeling with dispersive media and surface mount technology components

Abstract: DC power-bus modeling in high-speed digital design using the finite-difference time-domain (FDTD) method is demonstrated herein. The dispersive character of the dielectric layers used in printed circuit board substrates is taken into account in this study. In particular, FR-4 is considered. The complex permittivity of the dielectric is approximated by a Debye model. A wide-band frequency response (100 MHz-5 GHz) is obtained through a single FDTD simulation. Good agreement is achieved between the modeled and measured results for a typical dc power-bus structure with multiple surface mount technology (SMT) decoupling capacitors placed on the printed circuit board (PCB). The FDTD method is then applied to investigate some general approaches of power-bus noise decoupling.

An EMI estimate for shielding-enclosure evaluation

Abstract: A relatively simple, closed-form expression has been developed to estimate the EMI from shielding enclosures due to coupling from interior sources through slots and apertures at the enclosure cavity modes. A power-balance method, Bethe's (1944) small-hole theory, and empirically developed formulas for the relation between radiation, and slot length and number of slots, were employed to estimate an upper bound on the radiated EMI from shielding enclosures. Comparisons between measurements and estimated field strengths suitably agree within engineering accuracy.

A SPICE model for incident field coupling to lossy multiconductor transmission lines

Abstract: An efficient time-domain macromodel for incident field coupling to lossy multiconductor transmission lines is presented. The model takes the form of ordinary differential equations and can be easily included in SPICE like simulators for transient analysis. The model is based on the closed-form matrix-rational approximation of the exponential matrix describing telegrapher's equations and semi-analytic rational approximation of forcing functions.

Effect of local stir and spatial averaging on measurement and testing in mode-tuned and mode-stirred reverberation chambers

Abstract: The effect of local averaging in mode-tuned and mode-stirred reverberation chambers is investigated, under the assumption of a wide-sense stationary statistical cavity field. The analysis is based on the characterization of the tuning or stirring process in the spectral spatial domain and in the spectral stir domain. The variance function, scale of fluctuation, optimum sampling rate, and normalized spectral bandwidths are computed for each case, based on the modeled power spectral-density function. This second-order analysis enables the effect of local averaging on the point-interval correlation, mean and standard deviation of the maximum test level, upward threshold crossing frequency, time to first passage and mean excursion length to be quantified. The theoretical results for quantifying EUT reliability are illustrated and compared with measured data. The results provide guidelines for the maximum tolerable sensor aperture and stirrer step sizes for mode tuning, and sampling rate and sampling width for mode stirring in chamber calibration and EMC emissions and susceptibility testing.

Frequency-dependent losses on high-performance interconnections

Abstract: This paper compares the major classes of chip-to-chip and on-chips interconnections used in high-performance computers and communication systems and reviews their electrical characteristics. Measurement results of dielectric loss are shown and the attenuation is compared for printed-circuit-board, glass-ceramic, thin-film, and on-chip wiring. Simulation results are shown with representative driver and receiver circuits, guidelines are given for when losses are significant, and predictions are made for the sustainable bandwidths on useful wiring lengths.

Wavelet packet-based EMI signal processing and source identification

Abstract: Existing techniques for recognizing and identifying disturbed signals waveforms are primarily based on visual inspection. This paper proposes a wavelet packet based technique to perform a feature extraction from the disturbance signal and a classification of the extracted features in order to identify the possible causes of the disturbance. The same wavelet based procedure is applied to signal compression and denoising in order to make the EMC analysis of the data easier.

Power electronic converter EMC analysis through state variable approach techniques

Abstract: A technique based on the state vector approach and a simple switch device model is proposed for electromagnetic compatibility (EMC) analysis in converter design. The conducted noise spectrum is straightforward computed in the frequency domain for hard switching converters with alternating or direct current input sources. The results are compared with PSpice time-domain simulations mixed with the fast Fourier transform, considering a buck converter. The technique proposed in this paper is appropriate for applications where calculation speed is preferred rather than high precision.

DC power-bus modeling and design with a mixed-potential integral-equation formulation and circuit extraction

Abstract: The application of a circuit extraction approach based on a mixed-potential integral equation formulation (CEMPIE) for DC power-bus modeling in high-speed digital designs is detailed. Agreement with measurements demonstrates the effectiveness of the approach. Dielectric losses are included into the calculation of the Green's functions, and thus, incorporated into the rigorous first principles formulation. A SPICE model is then extracted from the discretized integral equation. A quasistatic approximation is used for the Green's functions to keep the extracted circuit elements frequency independent. Previous work has established a necessary meshing criterion in order to ensure accuracy for a given substrate thickness and dielectric constant to a desired frequency. Several power-bus design issues, such as surface mount decoupling and power-plane segmentation, were investigated using the modeling approach. The results and discussions illustrate the application of the method to DC power-bus design for printed circuit and multi-chip module substrates.

A probabilistic model for the response of an electrically short two-conductor transmission line driven by a random plane wave field

Abstract: A probabilistic approach for the characterization of wiring-harness susceptibility to external interference is presented. The problem of field-coupling onto a uniform, lossless, electrically-short two-conductor transmission line loaded by terminal resistances is considered. The external field is modeled as a plane wave with random parameters. By virtue of the low-frequency assumption, the statistical properties of the induced current magnitude in one of the line loads are derived, for different characterizations of the external wave. Investigated configurations include: waves with random amplitude, waves with random amplitude and polarization, waves with random amplitude and direction of incidence, and waves with random amplitude, polarization and direction of incidence. Analytical expressions for the probability density function of the current (voltage) induced in one of the line loads are derived. The proposed model allows the computation of statistical parameters of interest, such as expected values, variances, and confidence intervals of the currents (voltages) in the line loads.

An equivalent transmission-line model containing dispersion for high-speed digital lines-with an FDTD implementation

Abstract: The increase in processor speeds in the last few years has created a growing need for the accurate characterization of waveform propagation on lossy printed-circuit-board (PCB) transmission lines. Due to the dispersive nature of pulse propagation on lossy transmission lines, approximations of the classic transmission-line model can fail in this application (i.e., lossless or DC losses approximations). This paper shows how an equivalent transmission-line model can be used to analyze dispersive transmission lines for high-speed digital applications. The equivalent-circuit elements of this transmission-line model incorporate the frequency dependence of the per unit length impedance and admittance caused by the finite conductivity of the conductors as well as the dielectric losses. We show that these equivalent circuit elements can be readily implemented into finite-difference time-domain (FDTD) transmission-line codes, and we present such a FDTD implementation. S-parameters and pulsed waveforms for a circular wire, coplanar waveguides (CPW) and microstrip lines are shown. Finally, we present approximate expressions for analytically obtaining the resistance and inductance per length of a microstrip line.

Electromagnetic coupling between wires inside a rectangular cavity using multiple-mode-analogous-transmission-line circuit theory

Abstract: This paper examines the coupling between two arbitrarily positioned wire segments inside a rectangular enclosure. The enclosure is treated as a superposition of analogous transmission lines which have been short circuited at two positions on the propagation axis. Each analogous transmission line is associated with a particular waveguide mode in the cavity. Previous work has used this analogy to predict the coupling between two monopoles inside a small box using the dominant TE/sub 10/ mode. This paper considers the general case of high-frequency coupling between two wire monopoles in a large rectangular cavity, where several higher order modes are active. By taking into account higher order modes, and the mutual coupling between the modes, a simple equivalent circuit is presented which can give a prediction for the coupling between the monopoles. Experimental results for various monopole pair positions are shown, which indicate the success of the multimode theory. The technique requires far less computer resources than traditional methods for solving such a problem (e.g., MoM, TLM or FDTD), with solution times of less than a second on an average PC. In addition, considerable insight into the coupling process can be gained by including or excluding particular waveguide modes. This is not possible with numerical methods.