Full-wave EMI and thermal simulations cut time-to-market by 20 percent

April 1, 2005
A full-wave electromagnetic-interference (EMI) simulation coupled with thermal simulation saved Barco about 20 percent of development time in the design of a ruggedized computer for defense and avionics.

A full-wave electromagnetic-interference (EMI) simulation coupled with thermal simulation saved Barco about 20 percent of development time in the design of a ruggedized computer for defense and avionics.

In the past, Barco had to build several prototypes during the development process to manage EMI environments. On the latest project, we used the first 3-D, full-wave analysis software designed specifically to simulate electromagnetic compatibility (EMC) issues prior to prototyping.

Analysis of a previous and a new design helped our engineers understand how various design parameters affected EMC, for example, showing them that internal mechanical components had a greater-than-expected shielding effect in some places. The previous design was compliant to EMC requirements and the goal of the simulation was to compare the previous and the new version.

The understanding gained during the simulation allowed us to concentrate design efforts only on the areas that required attention, which made it possible to improve the design to meet EMC specifications without increasing manufacturing costs. The new software for designers rather than for analytical specialists made it possible to focus on the design itself rather than think about Maxwell’s equations that underlie EMC phenomena.

Thermal management

Barco received an order for a custom computer that was specially designed for a defense and security application. The computer required several additional components with the result that it dissipates considerably more power than the company’s standard products.

I addressed the thermal management issues first by modeling the new design using Flotherm software from Flomerics. I selected the various components in the design from libraries and located them on the device’s six printed circuit boards, avoiding the need to model them from scratch. The model was solved to generate thermal performance parameters including junction-to-ambient thermal resistance, junction-to-board thermal resistance, and junction-to-case thermal resistance, as well as temperature profiles within the package under various conditions.

The first solution showed that the initial design resulted in excessive junction temperatures. The application has strict acoustical requirements so I was not able to add a more powerful fan. Instead, I looked at ways to increase airflow with the existing fan by reducing pressure drop. Additional simulations showed that it would be possible to reduce junction temperatures to acceptable levels by increasing the size of the inlet and outlet on the panel of the computer.

This design change solved the thermal-management problem but the larger openings raised EMC concerns. In previous designs, Barco engineers had used a long and expensive build-and-test process to address EMC concerns. They would perform some hand calculations initially, but these were typically only able to account for one dimension, so they were of limited use in a design of this complexity. The designers then typically built several prototypes during the early, middle, and late stages of the design process.

The manufacturing, test, and redesign costs of producing and testing an EMC prototype with representative structure and PCBs for a ruggedized computer are very expensive, which often put the design process on hold during that prototype period because management did not want to expend additional resources on a design whose EMC performance had not been validated.

I had considered the possibility of addressing EMI design issues using simulation just as I was already doing thermal management, but was not aware of any software capable of doing the job.

Simulating EMC

Then Flomerics introduced FLO/EMC, which provides an analysis environment for simulating electromagnetic interactions in and around electronic equipment to generate quick solutions to tough design problems. FLO/EMC makes it possible to identify EMC design issues early in the design cycle, well before building physical prototypes.

FLO/EMC differs from general-purpose electromagnetic-simulation software in that it uses the Transmission Line Matrix (TLM) method for solving Maxwell’s equations, which provides major advantages when performing EMC simulations. The TLM method solves for all frequencies of interest in one calculation and therefore captures the full broadband response of the system in one simulation cycle. This is particularly advantageous for EMC analysis because potential resonance and emissions vary over a wide frequency spectrum.

Second, the TLM method creates a matrix of equivalent transmission lines and solves for voltage and current on these lines directly. This uses less memory and CPU time than solving for E and H fields on a conventional computational grid.

I have used Flomerics software for electronics cooling for more than a decade, and have had very good results. I also agree with the Flomerics philosophy of providing practical commercial tools that design engineers can use directly without requiring the specialized theoretical knowledge often needed to run other software. I was hopeful that FLO/EMC would also let me solve EMC problems without having to think about Maxwell’s equations, and I wasn’t disappointed. I was easily able to learn the software in a one-week training class.

Thermal and EMC requirements

Once I returned from the training class, I created an EMC model of the design using the same method that I used for the thermal model, except that I selected components from a different library designed for EMC. Since that time, Flomerics introduced a new version of FLO/EMC that makes it possible to conduct cooling and EMI simulation simultaneously on the same model.

Users can transfer information between the two packages in real time and efficiently assess the impact of design changes on cooling and EMC. I began by modeling the original product, which was in production and had been tested for EMI. In discussions with Flomerics technical support, I determined that it was not necessary to create a detailed model of the PCBs, which made it possible to reduce simulation time without affecting accuracy.

The solution to the initial model showed that the larger openings had less impact than expected on EMI because of the larger-than-expected shielding provided by some of the internal components. The first simulation helped us understand the problem. The EMC simulation sampled electric and magnetic fields using a cylindrical scan around the system on a 1m radius, mimicking a common MIL test standard. The scan showed a high level of radiation emanating from the enlarged openings. Seeing how the waves were emanating from the box made it clear that EMI was not escaping uniformly from the openings but rather that certain locations were much more critical. We used this information to change the shape of the openings, providing shielding in the most sensitive areas while opening up others that were less critical. Over a few iterations, we were able to generate a design that met our EMC requirements in terms of shielding effectiveness, without reducing airflow.

The ability to simulate EMC without a prototype is substantially improving our design process. We are now able to validate equipment layout and mechanical design before building a prototype, and optimize the product for EMI requirements and structural shielding effectiveness.

We can now predict the three-dimensional electromagnetic leakages in a structure where we have known EMI sources in a certain frequency band. Then we can perform “virtual” EMC design, minimizing modifications to decrease leakages and acting only on the relevant mechanical parts, thus optimizing the overall cost impact.

Simulations help our designers optimize our products from an EMC perspective to a level that wasn’t possible in the past; we can evaluate more designs than we could ever prototype. We are also reducing the number of prototypes required, which saves time and money.

The simulations are also sometimes used as part of the proposal process, which helps to differentiate our products from competitors. The key to these improvements is the fact that the user-friendliness and modeling speed of the software makes it ideal for use by design engineers.

For more information about FLO/EMC and other software from Flomerics, contact Flomerics online at www.flomerics.com. Contact BarcoView online at www.barcoview.com.

Jean-Philippe Tigneres heads the Environmental R&D department at the Barco Group in Toulouse, France. He has more than 15 years experience in electronic packaging activities related to thermal management, vibration, and shock design and EMC management.

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