EMC SOLUTIONS

Using 64-Bit Architecture in EMC Simulation

David Johns and Rachid Aitmehdi

New software technology pushes EMC simulations to higher frequencies and delivers results in less time than current simulation techniques.

Electromagnetic compatibility (EMC) problems have become extremely complex in recent years. Today's digital electronics switch so fast that the signal spectrum extends well into the microwave band. At the same time, wireless devices, such as Bluetooth (2.45 GHz) antennas, are being integrated directly into electronic systems.

The digital electronics spectrum and wireless spectrum are overlapping. To make matters even worse, EMC regulations have become tighter in both the United States and Europe, and compliance testing is required over an extended frequency band stretching up to 40 GHz. The need to virtually prototype products with more-complex electromagnetic (EM) interactions and over widening frequency bands is fast approaching the limits that 32-bit architecture can handle.

A new era in 3-D EM simulation is now possible with the advent of 64-bit parallel-processor versions of EM simulation tools. The advances in technology are already presenting exciting results.

The move to 64-bit architecture is necessary. Even with the efficiency of transmission-line matrix (TLM) EM solvers, modeling typical electronics systems to frequencies as high as 40 GHz is resulting in problem sizes that require greater than 2 Gbyte of RAM, the technical limit for 32-bit architecture. Simply stated, the models are too large to be simulated using the finite resources offered by the 2 Gbyte maximum RAM available in a 32-bit architecture.

The only solution available to engineers to date was either to simplify the model or to carry out a series of simulations on smaller models, which assumes that the separate analyses are electromagnetically decoupled. This partitioning of the problem is not always a valid approach. The theoretical limit of 64-bit architecture, more than 9 million terabytes, offers an effectively limitless simulation environment provided that the hardware is available to support the solution.

Figure 1. Computer RAM versus frequency to stimulate a 1-m3 volume of space.

Figure 1 illustrates how the total number of cells required to model EM fields in a 1-m3 volume increases with frequency. A fundamental law of numerical EM analysis states: Thou shalt sample EM fields using a minimum of 10 cells per wavelength. This law is necessary to ensure that the analyses accurately follow the sinusoidal field variation over space. As frequency increases, wavelength decreases; consequently, the mesh must be made correspondingly finer. Full-wave electromagnetic solvers typically require 100 bytes per cell to solve the electromagnetic field equations and to store the field vectors. Putting all of these factors together, the limit on a 32-bit machine is reached at around 8 GHz.

Telecommunications and High-Speed Computing

New simulation software has already shown potential in the telecommunications and defense industries. In one case, a manufacturer has a 64-bit machine containing 128 processors. With immense computing power, full-scale EM investigations of electronics enclosures are achievable within acceptable time limits.

Rather than simply recompiling 32-bit code to be compatible with 64-bit platforms, special routines in the software take advantage of the new architecture, namely 64-bit data flow and arithmetic. These enhancements allow processors to calculate certain aspects of the solution significantly faster.

The telecommunications and computing industries will be the first to realize the gains of this new technology. By removing model-size limitations, such software brings to bear sufficient computing power to simulate high-frequency EMC issues in telecom modules, shelves, and even full-size racks. One of the major challenges faced by telecom engineers lies in the integration of third-party subsystems such as optical transceivers.

EMC issues for optical transceivers must be considered at two levels. For the transceiver itself, high-frequency radiation can leak from holes, gaps, and seams that are inherent features of transceivers. This in itself is not a problem because subsystems are not subject to emissions standards. However, problems emerge when electromagnetically hot trans-ceivers are placed into systems that are bound by emissions limits. Radiating transceivers couple to the air vents, cavities, seams, and holes that are built-in features of systems.

Transceivers are often mounted externally on a system. Such mounting breaks the integrity of the enclosure shield and causes the transceivers to effectively behave like antennas, amplifying energy generated inside systems, and then transmitting it to the outside world. Both effects are common. Accurate analysis of the transceivers themselves and their
effect on a system could mean the difference between passing or failing FCC (U.S.) and CE (EU) emissions compliance tests.

Figure 2. Electromagnetic emissions from a telecom module.

Figure 2 shows the high-frequency leakage from a telecom system. The main printed circuit board (PCB) is electrically floating. The chassis and ground-plane resonance results in high current flowing around open tabs in the base of the enclosure. The electric field is plotted in a plane just below the system, and hot spots can be seen where the tabs are located.

Defense and Space

Other early adopters of 64-bit technology include the defense and space industries. The military already runs single simulations that can take more than two weeks to complete using 32-bit simulation technology. For the military, 64-bit software can provide accurate EM simulation to determine a system's immunity to EM emissions from a variety of sources such as radar, lightning, and EM weapons.

Powerful 64-bit electromagnetic analysis allows engineers to include important details such as environmental gaskets, wire-mesh gaskets, fasteners, and gaps between metal plates and other apertures such as honeycomb vents.

In safety-critical and military applications, the seams of an enclosure are sometimes designed to present a tortuous path to electromagnetic threats. This design characteristic provides inherent shielding in the mechanical structure, reducing the dependency on gaskets and low-resistance contacts.

Recently, 64-bit electromagnetic analysis has enabled the space industry to assess the electromagnetic shielding performance of an optical interferometer, part of a metrology system to be installed on a future satellite. The primary concern in this case was the immunity of the interferometer's electronics to a high-power microwave field. The field was radiated by a downlink communications transmitter located nearby on the craft.

The complete interferometer structure was simulated during the concept phase of the design process. The electromagnetic analysis pointed to the need for several modifications in the design, including the addition of below-cutoff waveguide baffles to shield the optical beam injection apertures.

Figure 3. Enclosure radiated with microwave field.

The design improvements were implemented in the first physical prototype, and a greater margin in the EMC performance of the system was achieved well before EMC testing. The benefits of this kind of virtual prototyping are clear. Electromagnetic simulation is not intended to replace EMC tests, but it helps reduce the risk of noncompliance and helps minimize the number of design iterations.

Figure 3 shows the electric field distribution and surface currents induced in an enclosure designed to house data-processing electronics. In the analysis, the system is subjected to an external microwave field incident from the left side. The electric field diffuses through the seams and excites a resonance in a slotted partition. This resonance raises the internal field strength and, consequently, reduces the shielding effectiveness of the enclosure.

Conclusion

The new 64-bit architecture extends the realm of electromagnetic design. The model setup procedure within a 64-bit environment is identical to that of the more widespread 32-bit software. The 64-bit technology, however, eliminates the concerns about overall model size.

Results are limited only by the imagination, hardware, and time available for the simulation. Virtual prototyping is certainly less costly than building and testing full prototypes. Such cost savings will likely drive even-more-ambitious simulation projects using 64-bit architecture in the future.

David Johns, PhD, is vice president of electromagnetic engineering at Flomerics Inc. (Southborough, MA). He can be reached via e-mail at david.johns@flomerics.com. Rachid Aitmehdi, PhD, is head of electromagnetics at Flomerics Ltd. (Hampton Court, UK).