4 ms·

Does that handle the enclosure the board goes into at all? I haven't been in the game for awhile and am curious. We always had different behavior with our enclo

Does that handle the enclosure the board goes into at all? I haven't been in the game for awhile and am curious. We always had different behavior with our enclosure and of course when the sometimes poorly designed enclosure caused strain on the board that added a whole new layer.

jacquesm 3y ago
That's a very interesting question. There are a ton of specialized tools for EMC/EMI simulation, I think they all work on the basic principle of assuming that a portion of your board will be exposed and that that part will be causing some radiation and will receive some from outside. After that it's decisions that will affect cost that will likely drive how far you want to strive for perfection, you could encase everything in grounded copper and it would be as close to perfection as you can manage or you can stick your board in plastic and live with the consequences. Usually, depending on how critical the application is some interference is acceptable as long as the device continues to operate. But on radiated power there are some very strict limits and for say a motor controller any malfunction could cause serious trouble so you will want to be extra careful there. The hardest to control for me: wiring, connectors, density of carbon sprayed inside plastic, anything using inductors (including what orientation to put them in, you want them at right angles to the surface of the board for mechanical stability and lack of coupling between inductors on the same board, but you want them parallel to the board to minimize radiated power and susceptibility to EMI). Apart from shielding and carefully modeling your board (especially the ground plane, supply and any connections that carry a significant fraction of inbound power) you will always end up testing for compliance and that's the gold standard. I think simulation is very useful and can cut down on the number of physical test runs significantly but I've yet to see a design that did exactly what was predicted. Wiring, what happens just outside of the board enclosure, environmental factors, it all adds up. I see simulation as a way to be more efficient, not as a silver bullet to be able to guarantee certification is a one-shot, but possibly others have better experience. There are a couple of very simple tricks to test for EMI sensitivity (a handful of coins, an old fashioned piezo based stove lighter and the oldest cell phone you can get in close proximity to the board), as well as a simple field strength meter. Between those you can probably identify and eliminate the worst and after that it's trial run time at the certification authorities if you are making a device that is to be used in a regulated market. Especially the piezo lighter is interesting, I've had circuits that required substantial redesign just to get them to the point that they would not lock up hard. What's interesting about this stuff is how un-intuitive some of it is. Note that this field is continuously in development and that new tools and techniques are brought to market all the time. Look the other way for a few years and you feel like a dinosaur.
krasin 3y ago
> Does that handle the enclosure the board goes into at all? It might. For example, Lukas Henkel is designing an open source laptop and heavily relying on simulation for that. In the post ([1]), he provides visualization of antenna performance for different placements inside the laptop case. I quote, in case, if LinkedIn wants people to log in to view the post: >I want to optimize the antenna positioning in my laptop design using open-source tools. >The shown simulation is a 3D electromagnetic field simulation performed with the open-source tool Elmer FEM. The aluminum laptop case will have a large impact on the antenna gain and directionality. For correctly iterating on a good antenna positioning, it is necessary to integrate the complex 3D geometry of the laptop case into the simulation. >I´m currently exploring three possible locations for the antenna. There may also be one option to make the laptop case itself as a part of a cavity antenna. >The tools used for the shown simulation are all free and open source: >Mesh generation: Salome_Meca >Solver: Elmer FEM >Visualization: Paraview 1. https://www.linkedin.com/posts/lukas-henkel-ovt_opensource-design-visualization-activity-7058254211846696960-dEty?utm_source=share&utm_medium=member_desktop https://www.linkedin.com/posts/lukas-henkel-ovt_opensource-d...

jacquesm 3y ago

That's a very interesting question. There are a ton of specialized tools for EMC/EMI simulation, I think they all work on the basic principle of assuming that a portion of your board will be exposed and that that part will be causing some radiation and will receive some from outside. After that it's decisions that will affect cost that will likely drive how far you want to strive for perfection, you could encase everything in grounded copper and it would be as close to perfection as you can manage or you can stick your board in plastic and live with the consequences. Usually, depending on how critical the application is some interference is acceptable as long as the device continues to operate. But on radiated power there are some very strict limits and for say a motor controller any malfunction could cause serious trouble so you will want to be extra careful there. The hardest to control for me: wiring, connectors, density of carbon sprayed inside plastic, anything using inductors (including what orientation to put them in, you want them at right angles to the surface of the board for mechanical stability and lack of coupling between inductors on the same board, but you want them parallel to the board to minimize radiated power and susceptibility to EMI). Apart from shielding and carefully modeling your board (especially the ground plane, supply and any connections that carry a significant fraction of inbound power) you will always end up testing for compliance and that's the gold standard. I think simulation is very useful and can cut down on the number of physical test runs significantly but I've yet to see a design that did exactly what was predicted. Wiring, what happens just outside of the board enclosure, environmental factors, it all adds up. I see simulation as a way to be more efficient, not as a silver bullet to be able to guarantee certification is a one-shot, but possibly others have better experience. There are a couple of very simple tricks to test for EMI sensitivity (a handful of coins, an old fashioned piezo based stove lighter and the oldest cell phone you can get in close proximity to the board), as well as a simple field strength meter. Between those you can probably identify and eliminate the worst and after that it's trial run time at the certification authorities if you are making a device that is to be used in a regulated market. Especially the piezo lighter is interesting, I've had circuits that required substantial redesign just to get them to the point that they would not lock up hard. What's interesting about this stuff is how un-intuitive some of it is. Note that this field is continuously in development and that new tools and techniques are brought to market all the time. Look the other way for a few years and you feel like a dinosaur.

krasin 3y ago

> Does that handle the enclosure the board goes into at all? It might. For example, Lukas Henkel is designing an open source laptop and heavily relying on simulation for that. In the post ([1]), he provides visualization of antenna performance for different placements inside the laptop case. I quote, in case, if LinkedIn wants people to log in to view the post: >I want to optimize the antenna positioning in my laptop design using open-source tools. >The shown simulation is a 3D electromagnetic field simulation performed with the open-source tool Elmer FEM. The aluminum laptop case will have a large impact on the antenna gain and directionality. For correctly iterating on a good antenna positioning, it is necessary to integrate the complex 3D geometry of the laptop case into the simulation. >I´m currently exploring three possible locations for the antenna. There may also be one option to make the laptop case itself as a part of a cavity antenna. >The tools used for the shown simulation are all free and open source: >Mesh generation: Salome_Meca >Solver: Elmer FEM >Visualization: Paraview 1. https://www.linkedin.com/posts/lukas-henkel-ovt_opensource-design-visualization-activity-7058254211846696960-dEty?utm_source=share&utm_medium=member_desktop https://www.linkedin.com/posts/lukas-henkel-ovt_opensource-d...