The Application of Computational Electromagnetics to EMC

By Paul Duxbury - Flomerics Ltd

Traditionally EMC is considered as a test and measurement discipline, being dealt with at the end of the product development cycle. However, in today’s highly competitive environment, it is becoming more critical to consider EMC much earlier in the design cycle, indeed, while the product is still on the drawing board. Virtual prototyping is now possible, and is becoming a reality in EMC thanks to recent advances which have been made in the field of computational electromagnetic modelling.  While only a few years ago, these tools were the preserve of academic and research environments, they are now becoming more widely available, and used, in the commercial world.  As an example, let’s look at the developments in thermal analysis over the past decade.

In the early 1990’s, the application of computational fluid dynamics (CFD) analysis was taken to a new level.  CFD software packages historically, had always been general purpose tools, but while they were very powerful, they lacked a focus and therefore the necessary pre and post processing for many applications.  Flomerics recognised this and developed a CFD package which specifically addressed the needs of the electronics design industry.  This package, FloTherm, is now the worlds leading tool for the analysis of thermal design issues in the electronics industry.

Despite the advances in computational capabilities and within the field of CEM, there are still many challenges which need to be faced such as being able to represent the complex geometrical designs of today’s electronic systems, fine features such as slots, wires and air vents in a large 3D volume and also the ever-increasing frequencies of interest. All of these issues mean that many of the traditional analysis techniques are starting to struggle and enhancements are needed to make them suitable for modelling these complex problems.

Based around the powerful Transmission Line Matrix (TLM) method for solving Maxwell’s Equations, FLO/EMC is leading an evolution in computational electromagnetics as applied to the EMC issues which are faced by the electronics industry.

TLM Node

TLM is a time domain technique and therefore, it is possible to obtain very wide band frequency data from a single simulation. It is also a volumetric multi-grid technique which makes it possible to accurately represent complex curvilinear geometry.  Unfortunately, this means that the small cells which are required to represent this detailed geometry, can ‘bleed’ across the rest of the workspace. FLO/EMC therefore has the capability to recombine these small cells in areas where they are not required into larger cells, hence reducing the total number of cells in the solution and also therefore the computation time.  This technique known as cell lumping can typically reduce the number of cells in a model by up to 50% and, effectively embeds a fine grid within a coarser one.

Representation of solution mesh before and after cell lumping

Another challenge is that of obtaining the radiated field strengths from a piece of equipment at large distances away from it. Traditionally, to obtain this information it would be necessary to model the volume of space in between the system and the location of the monitor point.  In a test case posed by the University of Missouri-Rolla, it was required to calculate the electric field strength 3m from the front panel of the enclosure. Using the capability in FLO/EMC to place the output points outside of the workspace, it was possible to solve the problem in a matter of a few minutes as opposed to hours.  As can be seen, the results obtained from FLO/EMC match the measured results almost exactly. It is also possible to obtain a cylindrical radiation pattern from the simulation. Both the radius of the cylinder (eg 3 or 10m) and the height range (eg 1 to 4m) are user definable.

Measured and Modelled results for the UMR test case

Cylindrical Field Plot at First Resonance

One of the areas of electronic system design, which affects both the thermal and electromagnetic performance of a system, is that of ventilation panels.  Within FLO/EMC it is possible to model ventilation panels without having to individually model each hole within the panel.  The compact vent representation within the software has been shown to produce results which are comparable with a fully modelled vent, but in a fraction of the time.  This technique of being able to represent detailed geometrical features through the use of compact models can significantly reduce computation times while still maintaining an accurate solution.  An important aspect of compact models, is to ensure that they are self-consistent. This means that they fully interact with, and affect the surrounding electromagnetic fields.

Comparison of a Meshed and Compact Vent

While EM simulation does not negate the need for actual testing, analysis can be used to assess design issues before going to a test chamber, indeed before even building a physical prototype.  Over the next few years, CEM techniques will have to continue to develop to give the design engineer more analysis capabilities. Areas which will be addressed include; the development of more compact models, addition of more EMC specific features and also linkage to MCAD packages and other analysis tools.

Paul Duxbury is a Senior EM Engineer with Flomerics, where he is responsible for providing technical support to Flomerics’ customers within Europe and the Far East. Flomerics produce thermal and electromagnetic analysis software for the electronics industry. He can be contacted by phone on 020 8941 8810 or by email at paul.duxbury@flomerics.co.uk.  www.flomerics.com