Modeling of the electromagnetic radiation from shielded enclosures with apertures and attached wires in a real-world environment

A hybrid modeling technique using the Finite-Difference Time-Domain (FDTD) approach in conjunction with the Method of Moments (MoM) approach was developed to allow simulation of electromagnetic interference (EMI) emissions through apertures due to sources within a shielded enclosure. These apertures can include air ventilation openings, option card slots, mating cover seams, or any other opening in the metal shielded enclosure. Modeled emission results can now be directly compared to U.S. and other countries\u27 regulations to allow engineers to predict compliance before hardware prototypes are built. The effects of the test environment, including ground plane and specified measurement distance, as well as configuration requirements, such as long attached wires, are included and result in more accurate models of the real-world environment than previously possible. The first stage of the hybrid technique uses the FDTD approach to model the source within the shielded enclosure and to find the electric fields within the aperture or apertures. The sources within the enclosure include printed circuit board traces, internal wires and cables, and discrete devices, such as integrated circuits and heatsinks. Errors in the aperture fields at low frequencies due to limitations in the FDTD absorbing boundary conditions are then corrected using an extrapolation technique. Once the electric fields within the aperture are known, they become the source for the second stage of the hybrid technique. This second stage uses MoM to find the external fields while including the effects of long attached wires, ground planes, and a distant receive location. The results from the second stage can then be compared to the various regulatory agency requirements

Applying the Method of Moments and the Partial Element Equivalent Circuit Modeling Techniques to a Special Challenge Problem of a PC Board with Long Wires Attached

This paper investigates a canonical printed circuit board (PCB) problem using both a method of moments (MoM) and a partial element equivalent circuit (PEEC) modeling technique. The problem consists of a PCB populated with three traces. One trace is a signal line and the other two are I/O lines that couple to the signal line and extend beyond the boundary of the board. Although the MoM code was a frequency domain code and the PEEC code was a time-domain code, good agreement was achieved in both the time-domain and the frequency-domai

Challenge Problem Update: PEEC and MOM Analysis of a PC Board with Long Wires Attached

At the 2000 IEEE International Symposium on EMC, a paper was presented by Y. Ji et al. (paper appears in 2001 proceedings) that compared the application of PEEC and MOM techniques to the analysis of one of the EMC Society/Applied Computational Electromagnetics Society special challenge problems. Good agreement was obtained between the two codes at 2 out of the 3 measurement ports. At that time, no definite explanation was provided for the discrepancy at the third port. This paper shows that the problem was (at least partly) related to assumptions made about the signal sourc

Estimating DC Power Bus Noise

Simultaneous switching noise (SSN) resulting from IC devices can result in significant power bus noise, as well as radiation problems. An approach for estimating the power bus noise spectrum is presented in this paper. The power bus noise caused by digital circuits injecting high-frequency noise onto the DC buses feeding digital devices is calculated. The transient current drawn by an IC device is modeled using the load current and the shoot-through current through the power dissipation capacitance. Modeling and experimental results for several digital chips are shown. The modeling agrees well with the experimental results

EMI Resulting from a Signal Via Transition Through DC Power Bus-Effectiveness of Focal SMT Decoupling

Signal vias are commonly used in multilayer printed circuit board (PCB) design. For a signal via transitioning through the internal power and ground planes, the return current has to jump from one reference plane to another reference plane. The discontinuity of the return current at the via excites the power and ground planes, and results in power bus noise, and can produce an EMI problem as well. Numerical methods, such as finite-difference time-domain (FDTD), moment methods (MoM), and partial element equivalent circuit (PEEC), were employed herein to study this problem. The modeled results were supported by the measurements. In addition, the EMI mitigation approach of adding decoupling capacitors was investigated with the FDTD method

Link Path Design on a Block-by-Block Basis

In high-speed data communication systems, the complexity of link path between transmitters and receivers present a challenge for designers to maintain an acceptable bit error rate. An approach is presented in this paper to design the link path on a block-by-block basis. The unique advantage of this approach lies on the physics-based model of each block, which relates performance to geometry and makes design improvement and optimization possible. An example link path involving a backpanel is investigated using the approach. The via stubs and the dielectric materials in the backpanel are demonstrated to be critical factors for link performance in certain situations

Modeling EMI Resulting from a Signal Via Transition Through Power/Ground Layers

Signal transitioning through layers on vias are very common in multi-layer printed circuit board (PCB) design. For a signal via transitioning through the internal power and ground planes, the return current must switch from one reference plane to another reference plane. The discontinuity of the return current at the via excites the power and ground planes, and results in noise on the power bus that can lead to signal integrity, as well as EMI problems. Numerical methods, such as the finite-difference time-domain (FDTD), Moment of Methods (MoM), and partial element equivalent circuit (PEEC) method, were employed herein to study this problem. The modeled results are supported by measurements. In addition, a common EMI mitigation approach of adding a decoupling capacitor was investigated with the FDTD method

Large Scale Signal and Interconnect FDTD Modeling for BGA Package

This paper introduces a Finite-Difference Time-Domain (FDTD) approach to modeling portions of Ball Grid Array (BGA) package interconnect circuits. A fullwave circuit model including vias, trace segments, and ground vias was generated, using a computer gridding tool, and fed into the FDTD (Taflove and Hagness, 2005) program. The simulated results were correlated with TDR measurements

Engineering of Composite Media for Shields at Microwave Frequencies

Analytical and numerical modeling of composites with an isotropic dielectric base and multiphase conducting inclusions for the development of wideband microwave shields is considered. The model uses Maxwell Garnett formalism for multiphase mixtures. Such composites are required in many engineering applications, including electromagnetic compatibility

Numerical Modeling of Periodic Composite Media for Electromagnetic Shielding Application

This paper describes a methodology to extract effective electrical properties for periodic composite medium. The extraction algorithm is based on a periodic finite-difference time-domain (FDTD) method. The results are compared with conventional mixing theories and 3D Fourier series expansion methods. Two results show satisfactory agreement. With the extracted effective permittivity and conductivity, one can readily use these parameters to study electrical properties of composite materials with arbitrary micro-geometry and the shielding effects of using composite materials