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> He claims that the way EE is taught is a "lie" The thing is: this is sort of true. Now, all electrical engineers are very familiar with transmission line the

by dkbrk 5y ago

> He claims that the way EE is taught is a "lie" The thing is: this is sort of true. Now, all electrical engineers are very familiar with transmission line theory, that's pretty much their bread and butter. And all EEs know that if you're not working with well-defined transmission lines (like coaxial cables), you need to use a field solver. 2D field solvers are often sufficient, but if not 3D field solvers can and will be used. And then most of those same EEs, despite having just used a field solver which clearly shows that all the power is in the fields, which are in the dielectric space between the conductors, persist in using the mental model that electrical power moves in wires. This isn't just a pedantic quibble. There are real, practical effects. If you're designing a PCB and you have two signal lines with overlapping fields, those signals are going to couple, which will create common mode current, which will cause an EMI problem. You can stop those signals coupling by making them reference different ground planes, which makes the fields no longer overlap. If you route a signal line from one side of a ground plane to the other, you have to provide a path for the fields to get to the other side of the ground plane (i.e. "route" the dielectric, generally with a ground via), because if you don't, they will find their own path anyway and you won't like the results. If you persist in thinking that electrical power flows through wires, these sorts of effects are mysterious and only explicable through the magical black box that is a field solver. If, on the other hand, your mental model is that electrical power is in the fields, then -- surprise! -- the results of a field solver won't be so mysterious any more. And if you have a more accurate mental model, if you can predict more or less how the fields will behave before looking at the results of the field solver, then that means you can design with the fields in mind, rather than just tweaking things until the field solver stops being angry at you, but not actually understanding why the design works in the end. Don't believe me? Here's Rick Hartley, an extraordinarily experienced PCB designer: https://www.youtube.com/watch?v=QG0Apol-oj0&t=1102s https://www.youtube.com/watch?v=QG0Apol-oj0&t=1102s I found the responses from other EEs on youtube like Electroboom and EEVBlog disappointing. You can quibble about details of how he presented it (like, saying 1/c rather than 1m/c), but Maxwell's equations are the correct description of how electricity works, and Veritasium is absolutely correct in his core point which is that power flows outside the wires. Other models, such as lumped-element and transmission lines can suffice for many purposes but are ultimately wrong. Rather than responding towards him with hostility, perhaps they should have considered if their own mental models weren't quite as accurate as they had thought. As a final note, the problem as presented by Veritasium can't be accurately modeled by anything less than Maxwell's equations (i.e. a field solver), but you can get most of the way with transmission line theory and tweaking it with some physical common sense. Closing the switch causes electric and magnetic fields to propagate across the gap between the switch and the light bulb, and down the two transmission lines, at the speed of light (modified by the relative permittivity). The current that will initially flow across the light bulb, once the fields reach it, can be calculated from the characteristic impedance of two parallel wires acting as a transmission line. When the signals reach the end of the transmission lines, they will "see" a short and reflect with opposite voltage; when that opposite-voltage signal reaches the switch and light bulb the transmission lines act like a short and from that point on the light-bulb receives the full current. That 1m/c delay, in particular, isn't accounted for by transmission line theory at all. The way you get that (without a field solver) is by knowing that electrical power is in the fields, which propagate at the speed of light. Since transmission line theory can't accurately model the problem in full, I think Veritasium can be forgiven for not mentioning it (especially since he was targeting a general audience).

gcommer 5y ago
Is there really an epidemic of EE's who know how to use a field solver, but don't know to consider coupling between signal lines? My intuition is the opposite of yours: most EEs actually know the ideas from the Veritasium video. Therefore, the way EE is taught is not a lie, since it includes that knowledge. (For completeness, the alternate take is that Veritasium was claiming "the way _elementary_ EE is taught is a lie" -- but that still leaves Veritasium having left out critical context for such an audience) > I found the responses from other EEs on youtube like Electroboom and EEVBlog disappointing. [...] Rather than responding towards him with hostility, perhaps they should have considered if their own mental models weren't quite as accurate as they had thought. Personally, I didn't get hostility from any of their videos. They were just injecting some engineering sensibility to bridge the gap between most people's EE knowledge and Derek saying "everything you've been taught is a lie." Also, to my recollection they both absolutely attested that yes Maxwell's equations are the correct description which supports Derek's results (modulo Electroboom's callout about the bulb actually always being on)
- dkbrk 5y ago
  > Is there really an epidemic of EE's who know how to use a field solver, but don't know to consider coupling between signal lines? Now, I'm not an EE myself, just someone who took undergraduate electrodynamics, decided to read up the subject, and found some truly excellent videos on youtube. But, at 1:00:23 in that same video I linked before (https://youtu.be/QG0Apol-oj0?t=3623 https://youtu.be/QG0Apol-oj0?t=3623), Rick Hartley says this: > I spend most of my consulting time solving EMI problems because most of the engineers I meet have no clue about any of this. My job is so easy and I make such a ridiculous amount of money doing it. It's just unbelievable; I solve most EMI problems by simply adding returned vias to boards or changing the positions of decoupling caps, I mean the things are so simple and ridiculous it's amazing and if these guys would educate themselves they wouldn't need to hire me. So I gather that there is a problem. It's not that EEs don't know to consider coupling between signal lines, but because most of them persist in thinking that signals travel in wires, rather than in the fields, they don't understand when coupling will occur and when it won't. Sure, they can look at the result of the field solver and realize they have a problem, but without thinking in terms of fields they don't know how to solve it. So, they fix it either with trial-and-error until the field solver is happy, or by following design patterns that are passed down as an oral tradition, but without actually understanding why it works or what the problem was in the first place. Here's an example: https://youtu.be/52fxuRGifLU?t=1719 https://youtu.be/52fxuRGifLU?t=1719 That's simple to understand if you think in terms of fields. Even worse, if you have signal lines that are parallel and on top of one another (on different planes), referencing the same ground plane from the same side, then it doesn't matter how far apart those planes are, they're going to couple strongly since the fields overlap. You can have two traces right next to each other that have virtually zero coupling because they're stripline, or, if you have a stackup with a single ground plane on the bottom layer, a signal line on top of that, and a signal line on layer one parallel and on top of the bottom trace, they're virtually on opposite sides of the board and yet they'll couple strongly. And if you don't think in terms of fields, you'll observe that, whether in simulation or on a circuit board, and have no idea why it happens or how to fix it. Here's Rick talking about the state of the industry in the 1980s and 1990s: https://youtu.be/ZYUYOXmo9UU?t=4295 https://youtu.be/ZYUYOXmo9UU?t=4295. It's clear that no, EEs weren't taught this, they didn't understand it. The situation has, I believe, improved somewhat, but only perhaps in the last decade or two. I would guess that even today, most EEs still don't really understand this (or Rick wouldn't be making so much money consulting). > Personally, I didn't get hostility from any of their videos. Perhaps "hostility" is the wrong word. I think on reflection "dismissiveness" is better. Like, "Yes, we know that Maxwell's Equations are the ground truth. We were all taught that and understand it. But that's not the way practicing engineers work -- we use models like transmission lines and lumped-element. It's technically correct, but more of a curiosity than anything. It's not something we really need to think about, and certainly not useful for a general audience -- more likely to confuse them than anything." That's the general impression I got. And I think, that not only was Veritasium technically correct, but that model is useful, and most EEs don't use it when they probably should. Most of us here on hn are software developers. I think that most would probably agree that on the whole, we're all pretty terrible at it. Why would you think Electrical Engineering would be different? Because they're "real" engineers, whereas we just sometimes call ourselves "software engineers" (knowing that's pretty much a lie)? Here's a presentation by Eric Bogatin that reminded me more than a little of the sort of cargo-cult design patterns that pervade software engineering: https://www.youtube.com/watch?v=y4REmZlE7Jg https://www.youtube.com/watch?v=y4REmZlE7Jg

by dkbrk 5y ago

gcommer 5y ago

Is there really an epidemic of EE's who know how to use a field solver, but don't know to consider coupling between signal lines? My intuition is the opposite of yours: most EEs actually know the ideas from the Veritasium video. Therefore, the way EE is taught is not a lie, since it includes that knowledge. (For completeness, the alternate take is that Veritasium was claiming "the way _elementary_ EE is taught is a lie" -- but that still leaves Veritasium having left out critical context for such an audience) > I found the responses from other EEs on youtube like Electroboom and EEVBlog disappointing. [...] Rather than responding towards him with hostility, perhaps they should have considered if their own mental models weren't quite as accurate as they had thought. Personally, I didn't get hostility from any of their videos. They were just injecting some engineering sensibility to bridge the gap between most people's EE knowledge and Derek saying "everything you've been taught is a lie." Also, to my recollection they both absolutely attested that yes Maxwell's equations are the correct description which supports Derek's results (modulo Electroboom's callout about the bulb actually always being on)

dkbrk 5y ago
> Is there really an epidemic of EE's who know how to use a field solver, but don't know to consider coupling between signal lines? Now, I'm not an EE myself, just someone who took undergraduate electrodynamics, decided to read up the subject, and found some truly excellent videos on youtube. But, at 1:00:23 in that same video I linked before (https://youtu.be/QG0Apol-oj0?t=3623 https://youtu.be/QG0Apol-oj0?t=3623), Rick Hartley says this: > I spend most of my consulting time solving EMI problems because most of the engineers I meet have no clue about any of this. My job is so easy and I make such a ridiculous amount of money doing it. It's just unbelievable; I solve most EMI problems by simply adding returned vias to boards or changing the positions of decoupling caps, I mean the things are so simple and ridiculous it's amazing and if these guys would educate themselves they wouldn't need to hire me. So I gather that there is a problem. It's not that EEs don't know to consider coupling between signal lines, but because most of them persist in thinking that signals travel in wires, rather than in the fields, they don't understand when coupling will occur and when it won't. Sure, they can look at the result of the field solver and realize they have a problem, but without thinking in terms of fields they don't know how to solve it. So, they fix it either with trial-and-error until the field solver is happy, or by following design patterns that are passed down as an oral tradition, but without actually understanding why it works or what the problem was in the first place. Here's an example: https://youtu.be/52fxuRGifLU?t=1719 https://youtu.be/52fxuRGifLU?t=1719 That's simple to understand if you think in terms of fields. Even worse, if you have signal lines that are parallel and on top of one another (on different planes), referencing the same ground plane from the same side, then it doesn't matter how far apart those planes are, they're going to couple strongly since the fields overlap. You can have two traces right next to each other that have virtually zero coupling because they're stripline, or, if you have a stackup with a single ground plane on the bottom layer, a signal line on top of that, and a signal line on layer one parallel and on top of the bottom trace, they're virtually on opposite sides of the board and yet they'll couple strongly. And if you don't think in terms of fields, you'll observe that, whether in simulation or on a circuit board, and have no idea why it happens or how to fix it. Here's Rick talking about the state of the industry in the 1980s and 1990s: https://youtu.be/ZYUYOXmo9UU?t=4295 https://youtu.be/ZYUYOXmo9UU?t=4295. It's clear that no, EEs weren't taught this, they didn't understand it. The situation has, I believe, improved somewhat, but only perhaps in the last decade or two. I would guess that even today, most EEs still don't really understand this (or Rick wouldn't be making so much money consulting). > Personally, I didn't get hostility from any of their videos. Perhaps "hostility" is the wrong word. I think on reflection "dismissiveness" is better. Like, "Yes, we know that Maxwell's Equations are the ground truth. We were all taught that and understand it. But that's not the way practicing engineers work -- we use models like transmission lines and lumped-element. It's technically correct, but more of a curiosity than anything. It's not something we really need to think about, and certainly not useful for a general audience -- more likely to confuse them than anything." That's the general impression I got. And I think, that not only was Veritasium technically correct, but that model is useful, and most EEs don't use it when they probably should. Most of us here on hn are software developers. I think that most would probably agree that on the whole, we're all pretty terrible at it. Why would you think Electrical Engineering would be different? Because they're "real" engineers, whereas we just sometimes call ourselves "software engineers" (knowing that's pretty much a lie)? Here's a presentation by Eric Bogatin that reminded me more than a little of the sort of cargo-cult design patterns that pervade software engineering: https://www.youtube.com/watch?v=y4REmZlE7Jg https://www.youtube.com/watch?v=y4REmZlE7Jg