Numerical analysis of field coupling to microstrip circuits

The behavior of reradiated fields from PCBs, with the radar cross section being the main parameter of interest is investigated in this work. A rigorous approach to predict radiation from PCBs in a GTEM cell is presented. The analysis is based upon the use of the reciprocity theorem in combination with the method of moment applied to the scattered field. Thus, yielding a generalized impedance matrix, whose determinant represents the characteristic polynomial of the scattering system. The effectiveness of the method is demonstrated by investigating some canonical circuit configurations and structures illustrating sources of fundamental EMI mechanism. The validity and the accuracy of the analysis becomes obvious in view of the one-to- one correlation with measurements. I. INTRODUCTION Printed-Circuits Boards (PCB) are of overriding importance in modern microelectronics where they undergo a continu- ous package complexity. Multilayer structures, split reference planes, various interconnects like bends, vias, etc. and trace circuit configurations in form of rectangular/circular loop, bent wire, linear dipoles, etc., are commonly mounted and present on hihgly integrated PCBs. These structures have led to an upsurge of interest in the analysis of the possible elec- tromagnetic interference (EMI) since they are often sources of unintentional radiated emission which can alter the EMC performance of real PCBs. Especially, in presence of an RLC- circuit, high-speed signals routed on the board may carry over resonances. These resonances tend, on their own, to carry interferences over much longer distances, which can not be predicted by field or gavanic coupling. The behavior of the reradiated field, with the PCB radar cross section (RCS) being the main parameter of interest, is therefore a good figure of merit in diagnosing radiation problems on the board. This paper addresses these particular points. Especially, it provides a rigorous approach to predict radiation from PCBs in a Giagahertz transverse electromagnetic (GTEM) cell. The analysis is based upon the use of the reciprocity theorem in combination with the application of the method of moment (MoM) to the scattered field yielding a generalized impedance matrix, whose determinant represents the characteristic poly- nomial of the scattering systems. After deriving an expression for the RCS in the next section, the generalized impedance matrix is evaluated for arbitrar- ily shaped wire radiating elements with a conducting plane reflector (section III). The real-axis method characterized by Sommerfeld-type integrals and moment-method solutions (1)- (3) is used to calculate elements of the impedance matrices. The effectiveness of the method is demonstrated by inves- tigating some canonical circuit configurations and structures illustrating sources of fundamental EMI mechanism (section IV). The validity and the accuracy of the analysis become ob- vious in view of the one to one correlation with measurements (section V).

Based on the method of moments (MoM), radio frequency (RF) ground voltage drop of any signal return path on printed circuit board (PCB) is modeled numerically. The full-wave treatment provides the flexibility in predicting RF ground voltage drop of non-ideal ground return, such as holes and slots in the ground plane. An example is given to illustrate the application aspect of RF ground voltage prediction for EMC design purposes. I. INTRODUCTION With ever-increasing operating speeds of electronic circuits, the effects of interconnects of printed circuit boards (PCBs) become significant and have to be accounted for in the design. Hence, accurate modeling of interconnects on PCB is gaining more attention in high- speed circuit design. Conventionally, a ground plane of a PCB as return path for signal trace is assumed to be ideal with zero potential difference. Usually, the voltage drop on a signal delivery path (signal and ground conductors) is usually lumped into the signal conductor for circuit analysis purposes. Hence, information on ground voltage drop of any signal delivery path is not readily available. As logic devices switch at very high speed and draw large amount of current during switching (very high di/dt), significant voltage drop in the ground conductor is expected even its inductance is very small (1)-(8). Therefore, additional information on ground voltage drop or ground bounce provides an assessment on the effectiveness of a specific ground design for high-speed circuit so that potential EMI problem can be identified and rectified. Most commercially available full-wave electromagnetic simulation tools are based on either finite element method (FEM) (9), method of moments (MoM) (10) or finite-difference time-domain (FDTD) method (11). These tools usually model interconnects as a two- port network, which is usually good enough for signal integrity analysis purposes but does not provide additional information on ground voltage drop. To predict the RF ground voltage drop of any arbitrary signal delivery path on PCB, full-wave treatment in the modeling is the only way to model it accurately. In this paper, a full-wave approach to model the RF ground voltage drop based on MoM is presented. With

This paper discusses the application of the so-called thin sheet approximation (TSA) for dielectric coatings to the calculation of the 3D coupling of printed circuit boards (PCBs) using the method of moments (MoM). By extending the TSA to open structures, the volume currents in the dielectric layer can be described by surface currents on the PEC conductor and the problem can be reduced to single current layers. As a consequence, the number of unknowns is reduced drastically. In order to verify the TSA approach and its accuracy and to investigate the influence of the layer and conductor thickness of coated PCBs, comparisons to results obtained by the classical MoM computation and a finite element (FEM) solver are given.

Printed circuit board(PCB) designers require fast and accurate methods of simulating immunity of PCB to electrostatic discharge(ESD) events to adequately predict and analyze ESD issues. An efficient methodology for calculating the electromagnetic field coupling from ESD electromagnetic pulse(EMP) to PCB while fully considering the non-linear circuit elements in the PCB core is proposed in this paper. Voltages and currents within the PCB are found by merging full-wave simulations of ESD EMP with a SPICE model of the PCB and the coupled electromagnetic energy. This method was verified through experiments, results show the promise of the method. This hybrid modelling method can significantly accelerate simulation time compared with traditional modelling techniques and can allow the designers to explore the variation in coupling that occurs with small changes in the test setup better, such as the position and orientation of the EMP and PCB pins.

Electromagnetic disturbances for vehicle-mounted radios can be caused mainly by conducted noise currents flowing out from vehicle-mounted multi-layer printed circuit boards (PCBs) to wire-harnesses. Using actual electronic equipment for vehicles, we previously showed that combining, not separating, the ground layer patterns of a digital circuit and an analog circuit is more advantageous to reduce the noise current outflow, while the mechanism remains unknown. In the present study, based on an idea that this mechanism should generate from a change in the amount of common return currents flowing to the ground, we measured noise current outflows from five types of simple PCBs having different ground patterns, which were validated from simulation with the method of moment. As a result, we could confirm that slits on a ground pattern allow conducted noise currents to flow out from PCBs, while the levels for the symmetric two slits ground types are smaller compared to the case for the asymmetric two slits ground types. The mechanism could be explained qualitatively from balanced conditions of an equivalent bridge circuit.

An innovative approach is described for diagnosing faults in printed circuit boards (PCB) and PCB components through the detection, analysis, and localization of electrical field changes that occur within and around the PCB. This method utilizes electromagnetic emissions (EME) originating from the PCB to determine circuit health. EME from rapidly changing voltages and currents within high-speed logic and other circuits have traditionally been seen as a problematic source of interference that must be eliminated to as great an extent as possible. However, changes within these emissions can be a highly significant indicator that a failure has occurred within a PCB component as well as within adjacent circuit card paths of the board itself. Further, the hardware and software requirements needed to capture and analyze these emissions are relatively simple in comparison to todaypsilas highly complex automatic test equipment. This unique approach involves analyzing electromagnetic emission signatures through automated means, and ascribing failures to the circuit board as a whole, as well as to the individual circuit board components.

The prediction of the radiated electromagnetic field from printed circuit boards and/or parts of electronic systems is dealt with by more and more publications in the recent literature. Numerical techniques such as the method of moments are applied to solve complex mathematical expressions. Such algorithms are nowadays in use e.g. for performing pre-compliance examinations by analysing the emission of electromagnetic fields generated by all clock lines of a printed circuit board. For this purpose, the algorithms used must be able to account for the exact layout geometry including any neighbouring metallised structures which influence the overall radiation characteristics. It has been shown that for simple structures good compliance of simulation and measurement results can be achieved. But it is still in discussion whether these tools are able to analyse real examples of higher complexity without losing a significant part of their quality and exactness. Fortunately, the experience of EMI/EMC-engineer's suggests that more than 90% of the EMI-problems are caused by fewer than 10% of the circuits. It is shown that by identifying and addressing these critical circuits, many EMI problems can be prevented or solved. (5 pages)

Field coupling benefits signal exchange between Colpitts systems

An integrated biohydrometallurgical approach for the extraction of base metals from printed circuit boards

The stress and displacement fields of a piston are calculated with temperature-structure field coupling by The finite element software ANSYS, Contact boundary conditions are employed in using FEM software ANSYS, the results can be provided a reference for improving the design.

This paper analyzes the slope stress analysis of seepage-stress field under the condition of water lifting of reservoir slope, taking a practical reservoir slope project for example, on the basis of investigation and study of the geological environment, the soil geology model of the reservoir slope is established. On the basis of interaction calculation module of the fluid structure in the software Geo-Studio and Biot theory, finite element method of seepage-stress field coupling is applied to study the variation of stress field of the reservoir slope mainly with strong weathering argillaceous sandstone and marl, on the condition that reservoir water level rise and fall. The maximum principal stress is mainly compressive stress, the tensile stress just distributes near the top of the slope; the minimum principal stress is mainly compressive stress.

A hybrid FEM/MOM method was used to solve a canonical printed circuit board (PCB) problem. The PCB is populated with three traces. One is a signal line and the other two are I/O lines that extend beyond the boundary of the board. The finite element method (FEM) was used to model the fields in the volume around the on-board trace. The method of moments (MOM) was employed to model the equivalent surface currents on the board and the current on the off-board traces. The FEM and MOM equations were coupled by forcing the continuity of tangential fields on the dielectric boundary. An efficient meshing strategy was employed to reduce the memory requirements. The major contributors to far fields in different frequency bands and for different polarizations are discussed.

Numerical analysis of crosstalk between two traces in a printed circuit board is presented using the method of moments (MoM). In the high-frequency range, the attenuation constant is neglected in the theory for its very small values. The width of the trace is accurately determined for the trace impedance of 50 ohm from the charge distribution on the traces without using an approximated empirical formula. Line capacitances are determined from the total charge on the conductors and the line potentials. The coupling capacitance and inductance are determined from in-phase and out-of-phase excitations between the traces. Crosstalk interference is calculated from these coupling parameters. Results of crosstalk obtained from the above technique are verified by comparing with those obtained from four other methods: (1) Ansoft HFSS software tool, (2) even mode and odd mode analysis, (3) empirical formulae of parasitic elements, and (4) measurements using a vector network analyser. All the results agreed well. The results obtained by using the method of moment technique are more stable, reliable, and accurate among all the described different methods. This paper shows that the analytical method using MoM is a useful tool for predicting crosstalk interference in PCB without using expensive simulation software.

The crosstalk of two bent transmission lines of arbitrary directions have been analyzed by a circuit concept approach. The results for the circuit concept approach, HFSS and measurements are in very good agreement. The derived equations can be expected to be easily applied them for analyzing crosstalk of a various kind of bent transmission lines in printed circuit board

Electro-magnetic field analysis applications based on the Method of Moments can be used to simulate the emissions for electrical devices such as a printed circuit board, a combination of circuit boards and wire connecting boards, or even a cabinet. At the heart of such applications is a solver, which solves a symmetric indefinite dense linear system of size assembled from the model of the electrical device. The main computational challenges lie in the solver stage, where an computation is required for the direct solution of the linear system about a central frequency . For the direct solution we use a general symmetric matrix factorization algorithm, requiring FLOPs. This algorithm’s efficiency is demonstrated by its parallel speedup of 5 for moderate sized matrices on an 8 node AP3000. Some of this cost can be amortized using the fast frequency stepping method, where the system can be solved for nearby frequencies by iterative methods, using the solution at as a preconditioner. Due to the high parallel efficiency of the direct method, the frequency stepping method reduced parallel solution time by a factor of 2 for moderate-sized matrices, with larger improvements expected for large matrices.