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Design007-July2022

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26 DESIGN007 MAGAZINE I JULY 2022 When I-Connect007 asked me to contribute to this issue on field solvers, I wondered what more could be added to this subject. But as a supplier and developer of field solvers, Polar is still asked some of the same questions—both by experienced customers who are perhaps exposed to a new scenario and, as is most wel- come, by new entrants to the industry. I will start by saying that all field solvers are accurate; they solve Maxwell's equations by one or another of the available mathematical methods. When all are fed with the same data, all should generate very similar results, and any differences observed will be orders of magni- tude less than the variations in the PCB trans- mission lines caused by the composite nature of PCB substrate dielectrics and the variations of the plating and etching processes. However, field solver is a very generic term for a range of tools in this application for pre- dicting the behavior of PCB trans- mission lines. It is important to remember that some areas of field solvers are not actually field solving. Calculating the loss owing to sur- face roughness of copper is a prime example of this. e surface nature of plated copper is so complex that full field solving would be imprac- tical, so most commercial "solvers" will overlay the core field-solving function with empirical techniques: Hammerstad, Groisse, Huray, and Cannonball-Huray, to name just a few. ese empirical extensions Field Solver Finesse for Modelling Transmission Lines extend the capability of the field solver into modelling parameters that are: • Vital to model insertion loss • Impractical to field solve given the complexity of the surface profile and the available compute power in the hands of even the best equipped SI engineers Feeding the solver with the correct dimen- sions is vitally important, as no tool will give an accurate result if fed with incorrect start parameters. Customers frequently ask whether the transmission line structure height should include the trace thickness in the total height. is is easy to answer if you are working "back- ward from a microsection" but if you are imag- ining the finished PCB from a simulation, then it's less obvious. My question in Figure 1 is set as a puzzle as it is one of the most frequently asked items The Pulse Feature Column by Martyn Gaudion, POLAR INSTRUMENTS Figure 1: Does H2 include the copper or not?

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