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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. Index Terms--Electromagnetic propagation in dispersive media, finite-difference time-domain (FDTD) methods, genetic algorithms (GAs), scattering parameters, transmission lines.

Susceptibility scanning is an increasingly adopted method for root cause analysis of system-level immunity sensitivities. It allows localizing affected nets and integrated circuits (ICs). Further, it can be used to compare the immunity of functionally identical or similar ICs or circuit boards. This paper explains the methodology as applied to electrostatic discharge and provides examples of scan maps and signals probed during immunity scanning. Limitations of present immunity analysis methods are discussed. Index Terms--Electrostatic discharges (ESDs), immunity, scanning, susceptibility.

A statistical cable bundle model is developed to account for the random disturbance of the wire positions along hand-assembled cable bundles. The nonuniform random bundles are modeled as n-cascaded segments of a uniform multiconductor transmission line. At each section, all wire positions are disturbed with random numbers obeying a Gaussian distribution. In addition, a spline interpolation function is used to improve the continuity of wires winding along the bundle. The wire crosstalk and the common-mode (CM) current distribution along the bundle can be calculated with simulation program with integrated circuit emphasis (SPICE)-like solvers. By injecting the CM current along the bundle into a full-wave tool, e.g., finite-difference time domain (FDTD), as impressed current sources, the system-level electromagnetic emissions from the cable bundles can be predicted. The model has been experimentally validated with a controlled laboratory setup. Index Terms--Cable bundles, common-mode (CM) current, crosstalk, electromagnetic interference (EMI), multiconductor transmission line (MTL), statistical.

This paper considers the case of a wide-band Lorentzian (WBL) algorithm in the finite-difference time-domain (FDTD) modeling of dispersive media. It is shown herein that the WBL model is a physically meaningful and practically useful case of the frequency behavior of materials along with the Debye and narrow-band Lorentzian (NBL). The recursive convolution algorithms for the finite-difference time-domain technique for NBL and WBL models differ. The Debye model, which is suitable for comparatively low-frequency dispersive materials, may not have sufficient number of parameters for describing the wide-band material, especially if this material exhibits pronounced absorption at higher frequencies. It is shown that the Debye model can be used, if the Q-factor of the linear circuit analog corresponding to the Lorentzian model of the material is less than approximately 0.8. If the quality factor is in the limits of about 0.8 < Q [less than or equal to] 1, then the WBL model is appropriate. For Q > 1, the NBL model must be applied. The NBL model is suitable for dielectrics exhibiting resonance effects in the microwave frequency range. The WBL model is typical for composites filled with conducting fibers. Index Terms--Debye model, dispersive media, finite-difference time-domain (FDTD) technique, Lorentzian model, recursive convolution.

This paper describes the evaluation of the susceptibility of a cavity with an aperture using the finite-difference time-domain (FDTD) method and experimentally. To reduce the computing time, the FDTD method is used for the radiation from the cavity and the susceptibility is obtained by using the reciprocity theorem. The cavity used here is modeled after a full-tower desktop enclosure with a 3.5-in bay. The susceptibility characteristics are evaluated by measuring outputs of a monopole antenna and transmission lines installed in the cavity. The susceptibility characteristics, using a three-dimensional (3-D) map, are studied from the computed and the measured results by applying slowly rotating electromagnetic fields to the cavity on a turntable. Measured and modeled results are in good agreement, indicating the merits of the proposed approach for susceptibility/immunity evaluation. Moreover, some discussions are made to check the susceptibility mechanism. Index Terms--Electromagnetic coupling, finite-difference time-domain (FDTD) method, reciprocity theorem, rotating fields, three-dimensional (3-D) susceptibility map.

The common-mode (CM) current due to a trace near a printed circuit board (PCB) edge, and its suppression by a guard band have been studied experimentally and with finite-difference time-domain (FDTD) modeling. As the guard band, copper tape is connected along the entire edge of the ground plane. First, a PCB electromagnetic interferenc (EMI) coupling path that results from the nonzero impedance of the PCB ground plane is discussed. As the trace is moved closer to the PCB edge, the CM current increases. Then, the effect of the guard band on the CM current is detailed. A guard band parallel to and near a trace is most effective in suppressing the CM current. The cross-sectional magnetic field distribution at center of the PCB with and without the guard band is also calculated with FDTD modeling. The guard band decreases the magnetic field distributed on the reverse side of a PCB. These results indicate the guard band is effective in suppressing CM current. Finally, an empirical formula to quantify the relationship between the position of a trace and CM current for the case with a guard band is proposed. Calculated results using the empirical formula and FDTD modeling are in good agreement, which indicates this empirical formula should be useful for developing EMI design guidelines. Index Terms--Common-mode (CM) current, electromagnetic interference (EMI), finite-difference time-domain (FDTD) method, guard band, printed circuit board (PCB).

Power-plane segmentation is often used for dc power-bus noise isolation in multilayer printed circuit board (PCB) designs. To achieve a desirable noise isolation, different power-plane segmentations can be used. A suitable modeling approach, as well as measurements, were employed in this work to study the noise isolation with several power-plane segmentation designs. The geometries studied include power islands, and totally segmented power planes. The effects of the power-bus noise isolation with different types of power island connections, locations of segmentation, and shapes were analyzed, and compared. The modeled and measured results show that suitable power-plane segmentation can result in significant power-bus noise isolation. Index Terms--DC power-bus design, noise isolation, power island, power-plane segmentation.

Via interconnects in multilayer substrates, such as chip scale packaging, ball grid arrays, multichip modules, and printed circuit boards (PCB) can critically impact system performance. Lumped-circuit models for vias are usually established from their geometries to better understand the physics. This paper presents a procedure to extract these element values from a partial element equivalent circuit type method, denoted by CEMPIE. With a known physics-based circuit prototype, this approach calculates the element values from an extensive circuit net extracted by the CEMPIE method. Via inductances in a PCB power bus, including mutual inductances if multiple vias are present, are extracted in a systematic manner using this approach. A closed-form expression for via self inductance is further derived as a function of power plane dimensions, via diameter, power/ground layer separation, and via location. The expression can be used in practical designs for evaluating via inductance without the necessity of full-wave modeling, and, predicting power-bus impedance as well as effective frequency range of decoupling capacitors. Index Terms--DC power-bus design, decoupling capacitor design, lumped-circuit model extraction, multilayer substrate, via inductance, via interconnects.

The discharge current and the transient fields of an electrostatic discharge (ESD) generator in the contact mode are numerically simulated using the finite-difference time-domain method. At first the static field is established. Then the conductivity of the relay contact is changed, which initiates the discharge process. The simulated data are used to study the effect of design choices on the current and fields. They are compared to measured field and current data using multidecade broadband field and current sensors. The model allows accurate prediction of the fields and currents of ESD generators, thus it can be used to evaluate different design choices. Index Terms--Electrostatic discharge (ESD) generator, field sensors, finite-difference time domain (FDTD), numerical modeling, numerical simulation.

This paper experimentally investigates the effectiveness of embedded capacitance for reducing power-bus noise in high-speed printed circuit board designs. Boards with embedded capacitance employ closely spaced power-return plane pairs separated by a thin layer of dielectric material. In this paper, test boards with four embedded capacitance materials are evaluated. Power-bus input impedance measurements and power-bus noise measurements are presented for boards with various dimensions and layer stack ups. Unlike discrete decoupling capacitors, whose effective frequency range is generally limited to a few hundred megahertz due to interconnect inductance, embedded capacitance was found to efficiently reduce power-bus noise over the entire frequency range evaluated (up to 5 GHz). Index Terms--Conduction loss, decoupling capacitor, embedded capacitance (buried capacitance), power-bus decoupling, power-bus impedance, power-bus noise (delta-I noise, ground bounce noise, simultaneous switch noise), power plane, return plane.

Electromagnetic interference (EMI) filters are often utilized on I/O lines to reduce high-frequency noise from being conducted off the printed circuit board (PCB) and causing EMI problems. The filtering performance is often compromised at high frequencies due to parasitics associated with the filter itself, or the PCB layout and interconnects. Finite difference time domain (FDTD) modeling can be used to quantify the effect of PCB layout and interconnects, as well as filter type, on the EMI performance of I/O line filtering. FDTD modeling of a T-type and [pi]-type filter consisting of surface-mount ferrites and capacitors is considered herein. The FDTD method is applied to model PCB layout and interconnect features, as well as the lumped element components, including the nonlinear characteristics of ferrite surface-mount parts. The EMI filters with ferrites are included in the modeling by incorporating the time-domain Y-parameters of the two-port network into the FDTD time-marching equations. Good agreement between the FDTD modeling and S-parameter measurements supports the new FDTD algorithm for incorporating two-port networks. Index Terms--Finite difference time domain (FDTD) method, generalized pencil-of-function (GPOF), I/O filter, two-port network.

Electromagnetic interference (EMI) coupling associated with inter-board connection is investigated herein. Two experimental techniques, based on |S.sub.21| measurements, including both common-mode current and near-field measurements, are reported. Both methods, as well as finite difference time domain (FDTD) modeling, were used as experimental and numerical tools for inter-printed-circuit-board (inter-PCB) connector evaluation. The EMI performance of a lab-constructed stacked-card connector, and a commercially available module-on-backplane connector were studied. EMI characteristics of the connectors are demonstrated by investigating a few aspects of the design: type of shield/ground blade for signal return, number and length of ground pins, signal pin designation, etc. Good agreement is achieved between the measurements and the FDTD modeled results. Index Terms--Common-mode current, finite-difference time domain (FDTD), inter-printed-circuit-board (inter-PCB) connector, near field, S parameter.

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. Index Terms--DC power-bus, Debye model, dispersive media, finite-difference-time-domain method, power-bus noise decoupling, surface mount technology.

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. Index Terms--DC power-bus design, decoupling capacitor location, high-speed digital design, local decoupling, mutual inductance, SMT decoupling capacitors.

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. Index Terms--DC power bus, EMI mitigation, Finite-difference time domain, fringing electric fields, via stitching.

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 herein. Agreement with measurements demonstrates the effectiveness of the approach. Dielectric losses are included into the calculation of Green's functions, and thus, incorporated into the rigorous first principles formulation. A SPICE model is then extracted from the discretized integral equation. A quasi-static approximation is used for 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. Index Terms--Circuit extraction, dc power-bus design, dielectric losses, mixed-potential integral equation formulation, segmented power plane, surface mount decoupling.

Parasitic inductance in printed circuit board (PCB) geometries can detrimentally impact the electromagnetic interference (EMI) performance and signal integrity of high-speed digital designs. This paper identifies and quantifies the parameters that affect the inductance of some typical PCB geometries. Closed-form expressions are provided for estimating the inductances of simple trace and ground plane configurations. Index Terms - Electromagnetic coupling, electromagnetic interference, inductance

The effectiveness of dc power-bus decoupling is impacted by the inductance associated with interconnect vias in printed circuit boards (PCB's). Adequate characterization of these interconnects is necessary to facilitate modeling and simulation, and to assess the effectiveness of added decoupling. In this study, a measurement procedure is presented for determining the series inductance and resistance of an interconnect with a network analyzer. The validity and limitations of the procedure are discussed. Experimental results of interconnect parameters on an 8 x 10 in ten-layer test-board corroborate those measured with a precision impedance analyzer. The measured interconnect values are used to simulate several cases of power-bus decoupling which show good agreement with two-port swept frequency measurements. Index Terms - Decoupling, interconnect model, multilayer PCB, power bus modeling

Simple design maxims to restrict slot dimensions in enclosure designs below a half-wave length are not always adequate for minimizing electromagnetic interference (EMI). Complex interactions between cavity modes, sources, and slots can result in appreciable radiation through non-resonant length slots. The finite-difference time-domain (FDTD) method can be employed to pursue these issues with adequate modeling of thin slots. Subcellular FDTD algorithms for modeling thin slots in conductors have previously been developed. One algorithm based on a quasistatic approximation has been shown to agree well with experimental results for thin slots in planes. This FDTD thin-slot algorithm is compared herein with two-dimensional (2-D) moment method results for thin slots near corners and plane-wave excitation. FDTD simulations are also compared with measurements for slots near an edge of a cavity with an internal source. Index Terms - EMI, FDTD, shielding enclosures, slots.

Subcellular modeling of thin slots in the finite-difference time-domain (FDTD) method is investigated. Two sub-cellular algorithms for modeling thin slots with the FDTD method are compared for application to shielding enclosures in electromagnetic compatibility (EMC). The stability of the algorithms is investigated, and comparisons between the two methods for slots in planes, and slots in loaded cavities are made. Results for scattering from a finite-length slot in an infinite plane employing one of the algorithms are shown to agree well with published experimental results, and power delivered to an enclosure with a slot agree well with results measured for this study. Index Terms - FDTD, slot.

Fundamental EMI source mechanisms leading to common-mode radiation from printed circuit boards with attached cables are presented in this paper. Two primary EMI source mechanisms have been identified: one associated with a differential-mode voltage and another associated with a differential-mode current, both of which result in a common-mode current on an attached cable. These mechanisms can be used to relate printed circuit layout geometries to EMI sources. The two mechanisms are demonstrated through numerical and experimental results, and an example from a production printed-circuit design is presented.

Radiation from cables attached to printed circuit boards and shielding enclosures is among the primary concerns in meeting FCC Class A and B limits. The finite-difference time-domain (FDTD) method can be employed to model radiation from printed circuit boards and shielding enclosures with complex geometries, but difficulties in modeling wires and cables of arbitrary radii are encountered. Modeling the wire by setting the axial component of the electric field to zero in the FDTD method results in an effective wire radius that is determined by the mesh discretization. Neglecting the wire radius in applications, such as electromagnetic interference (EMI) or printed circuit board modeling, may result in gross errors because near-field quantities are typically sensitive to wire thickness. Taflove et al. have developed a subcellular FDTD algorithm for modeling wires that has been shown to work well for plane wave scattering. The method uses a quasistatic field approximation to model wires with a well defined radius independent of the mesh dimensions. The wire model is reviewed and investigated for application to common-mode radiation from cables attached to printed circuit boards, where the source is often a noise voltage at the connector. Also investigated is energy coupling to attached cables through enclosure apertures resulting in common-mode radiation from the cable. The input impedance for a center-fed dipole antenna, as well as a monopole connected to a conducting half-sheet, is computed with FDTD methods and compared to moment method input impedance results. A simulation of a shielding enclosure with an attached cable demonstrates the utility of FDTD analysis in modeling common-mode radiation.

Guidelines for the selection and placement of decoupling capacitors that work well for one-sided or two-sided printed circuit boards are not appropriate for multilayer boards with power and ground planes. Boards without internal planes take advantage of the power bus inductance to help decouple components at the higher frequencies. An effective decoupling strategy for multilayer boards must account for the low inductance and relatively high capacitance of the power bus.

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 enclosure cavity modes. A power-balance method, Bethe's 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. Index Terms--Apertures, cavities, diffraction, electrical equipment enclosures, shielding.

Specific design criteria are proposed to mitigate radiated emissions from a resonant enclosure excited by a heat sink acting as a microstrip patch antenna source. In this particular application, the EMI mechanism is assumed to be due to coupling from the dominant [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] mode to one or more resonant modes associated with the enclosure dimensions. The enclosure is then presumed to radiate, at the enclosure resonance frequencies, through one or more apertures, slots, or seams. The EMI-reduction strategy consists of shifting the resonant frequency of the dominant-patch antenna mode by dielectrically loading the patch antenna with thermal-gasket material having a specified electric permittivity. Specific formulas and graphs will be presented showing how to select the electric permittivity of the thermal-gasket material in order to obtain a given frequency shift. A comparison of experimental measurements with the predictions of the design criteria indicates that frequency shifts of up to approximately three times the bandwidth of the patch resonance can be predicted with reasonable accuracy. In at least two different commercial products that we are aware of, changing the electrically insulating heat sink gasket materials has solved specific radiated EMI problems. Index Terms--Electromagnetic interference, resonance, microstrip antenna.

Stacked-card and modules-on-backplane printed circuit-board geometries are advantageous for conserving real-estate in many designs. Unfortunately, at high frequencies, electromagnetic interference (EMI) resulting from the nonnegligible impedance of the signal return at the connector may occur. This effective EMI coupling path results in the daughtercard being driven against the motherboard and attached cables, resulting in common-mode radiation. The connector geometry can be modified to minimize the EMI coupling path when high frequencies are routed between the motherboard and daughtercard. Current speeds and printed circuit board (PCB) sizes result in geometries that are of significant dimensions in terms of a wavelength at the upper frequency end of the signal spectrum. The PCB geometries are then of sufficient electrical extent to be effective EMI antennas. The resonant lengths of the EMI antennas may, however, be quite removed from the typical half-wavelength dipole resonances. The finite-difference time-domain method can be used to numerically analyze the printed circuit-board geometries, determine antenna resonances, and investigate EMI coupling paths. EMI resulting from the stacked-card configuration has been investigated experimentally and numerically to ascertain the EMI coupling path at the bus connector, and EMI antennas. Index Terms--Electromagnetic coupling, electromagnetic interference (EMI), finite difference time domain (FDTD) methods, impedance measurement, poles, printed circuit layout, zeros.

Aperture arrays designed to provide airflow through shielding enclosures can provide part of the coupling path from interior sources to external electromagnetic interference (EMI). In this work, radiation through aperture arrays is investigated numerically and experimentally. FDTD modeling is compared with measurements on aperture arrays in a test enclosure. The method of moments (MoM) is also utilized to study radiation from apertures and to investigate the mutual coupling between apertures in an infinite conducting plane. A simple design equation for the relation between aperture size and number and shielding effectiveness is proposed. Index Terms--Apertures, FDTD methods, moment methods, mutual coupling, shielding.

Airflow perforations in shielding enclosures can act as apertures facilitating the coupling from internal sources to external electromagnetic interference (EMI). This EMI radiation for single- and dual-screen configurations was studied herein experimentally and with finite-difference time-domain (FDTD) modeling. A general EMI reduction of more than 20 dB was achieved for dual-perforated screens spaced 1 cm apart when compared to EMI for a single perforated screen. However, in the dual-screen case, the space between the screens can act as a thin cavity, which, in turn, can lead to significant radiation at distinct angles. Damping the resonances by loading the space between the screens with lossy material mitigates this problem and achieves more than 20-dB reduction over a single screen. Index Terms--Aperture, FDTD, shielding enclosure.

Implementing ferrites in finite-difference time-domain (FDTD) modeling requires special care because of the complex nature of the ferrite impedance. Considerable computational resources and time are required to directly implement a ferrite in the FDTD method. Fitting the ferrite impedance to an exponential series with the generalized-pencil-of-function (GPOF) method and using recursive convolution is an approach that minimizes the additional computational burden. An FDTD algorithm for a lumped ferrite using GPOF and recursive convolution is presented herein. Two different ferrite impedances in a test enclosure were studied experimentally to demonstrate the FDTD modeling approach. The agreement is generally good. Index Terms--FDTD, ferrite, GPOF.