Jak urządzenia mobilne wykrywają swoje położenie w przestrzeni 3D? (film, 20 min)
Czy kiedykolwiek zastanawiałeś się, jak twój telefon zna swoją lokalizację w przestrzeni? Nie chodzi tu o pozycję na Ziemi, która opiera się na satelitach i GPS. Mowa tu o fizycznej lokalizacji i orientacji, co jest naprawdę niezwykłą zdolnością, ponieważ w telefonach nie ma ruchomych części. W tym wpisie Breaking Taps zagłębia się w to fascynujące zjawisko, pokazując, w jaki sposób ten mały chip wewnątrz telefonu potrafi wykrywać jego ruch. Chociaż na początku mówi się, że nie ma ruchomych części, można je znaleźć w układzie mikroelektromechanicznym (MEMS), który jest odpowiedzialny za funkcje takie jak akcelerometry czy żyroskopy.
Te urządzenia MEMS to małe chipy, które kosztują mniej niż dolar, a ich technologia jest rzeczywiście zaawansowana. Breaking Taps wyjaśnia, że stosowane są różne rodzaje MEMS, jak akcelerometry i żyroskopy. W filmie szczegółowo pokazano, jak autor otwiera chip przy użyciu lasera, pieca i różnych narzędzi mechanicznych, aby zobaczyć, co jest w środku. Ostatecznie udało mu się uzyskać dwa połączone kawałki krzemu, co pozwoliło zrozumieć, jak te niezwykle małe elementy łączą się, aby umożliwić nam pomiar ruchu w trójwymiarowej przestrzeni.
Wszystko, co autor wspomina o akcelerometrach, jest interesujące. Funkcjonują one na zasadzie wykrywania przyspieszeń liniowych w jedno-osiowych kierunkach. Ich działanie jest oparte na zasadzie Newtona, a po rozmowie o tym, jak akcelerometry reagują na ruchy telefonu, Breaking Taps przyciąga uwagę widzów do tego, jak czujniki MEMS pozwalają na tak zaawansowane funkcje w naszych codziennych urządzeniach. Możliwość wykrywania uderzeń i odchyleń w górę i w dół dzięki prostym mechanizmom jest ekscytująca i daje lepszy wgląd w to, jak te urządzenia działają.
Z kolei żyroskopy na urządzeniach MEMS są bardziej skomplikowane. Breaking Taps przybliża ich działanie w kontekście efektu Coriolisa, podkreślając, jak ważne jest, aby czujniki te mogły detektować rotacje i zmiany kierunku. Dzięki ciekawym przykładom i modelem 3D autor sprawia, że temat staje się przystępny, nawet dla laików. Czytelnikom może nie być łatwo zrozumieć wszystkie szczegóły, dlatego Breaking Taps dostarcza pomocne wizualizacje i wyjaśnienia, które upraszczają proces uczenia się o tych nowoczesnych technologiach.
Na koniec warto zwrócić uwagę na dane o widoczności w filmie, który na chwilę obecną ma ponad 1,2 miliona wyświetleń i zdobył 57 tysięcy lajków. To pokazuje, jak wiele osób jest zainteresowanych mechanizmami i technologią, która pozwala na tworzenie zaawansowanych urządzeń, takich jak nasze telefony. Breaking Taps podsumowuje swoje myśli, zachęcając do eksploracji i zainteresowania różnymi rodzajami systemów MEMS, które mogą jeszcze raz zrewolucjonizować nasze życie.
Toggle timeline summary
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Wprowadzenie do tego, jak telefony określają swoje fizyczne położenie.
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Wyjaśnienie, jak telefony śledzą ruch w przestrzeni trójwymiarowej.
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Wprowadzenie do urządzeń MEMS, które ułatwiają to śledzenie.
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Dyskusja na temat funkcjonalności akcelerometrów i żyroskopów.
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Instrukcje dotyczące otwierania układu, który zawiera urządzenia MEMS.
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Szczegóły dotyczące wyzwań, jakie napotykano przy otwieraniu układu MEMS.
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Przegląd komponentów wewnątrz urządzenia MEMS.
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Wyjaśnienie, jak akcelerometry wykrywają przyspieszenia liniowe.
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Demonstracja działania akcelerometrów za pomocą modeli fizycznych.
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Wprowadzenie do różnicy funkcjonowania żyroskopów w porównaniu do akcelerometrów.
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Uproszczone wyjaśnienie, jak efekt Coriolisa wpływa na odczyty żyroskopów.
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Różnice między różnymi rodzajami żyroskopów w urządzeniu MEMS.
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Podsumowanie, jak akcelerometry i żyroskopy współpracują ze sobą.
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Promocja na wirtualne wydarzenie Keysight i jego znaczenie dla elektroniki.
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Ostateczne przemyślenia na temat piękna i złożoności urządzeń MEMS.
Transcription
Have you ever wondered how your phone seems to know its location in space? Not it's like position on earth. That's done through satellites and GPS and that's a different story, but it's actual like physical location and orientation. A lot of phones you can just flip over to turn them on to silent mode, or you can use star tracking apps to look through your phone up at the night sky and it tracks the movement of the phone in three dimensional space. And when you think about it, it's a pretty remarkable capability because there's no moving parts inside your phone. You know, it's a screen, a battery, and a bunch of microchips. So how does it actually do that? This capability is accomplished using a small chip inside your phone, often costing less than a dollar. But inside that chip is a huge amount of really interesting technology. Today we're going to take one of these chips, break it open, and take a look inside to see how this works. This video is sponsored by Keysight and they're live from the lab virtual event. More on that at the end, but spoiler, they're giving away a lot of cool stuff. These devices are known as micro electromechanical systems or MEMS devices for short. And I lied to you a little bit at the beginning, they do actually have moving parts inside the chip, which is what allows them to track your phone throughout space. But because it's done using semiconductor technology, the same thing to make actual chips. They're very, very small micro systems that are moving around. There are a whole bunch of different kinds of MEMS devices, gears and turbines and little pop-up flexures and different kinds of sensors. The device we're looking at today is an accelerometer gyroscope combination chip, features a three axis accelerometer and a three axis gyroscope. Now first we have to get inside of the chip. This can be a little tricky to get open. I had a few different chips, so I tried different methods, including etching it with a laser, turning it out in a furnace, etching it with a different laser, mechanically scraping it with knives and tweezers. And eventually you're left with two pieces of silicon that are bonded face to face. Inside of this double silicon package is the MEMS device. These two wafer bits are bonded together and the bond is fairly permanent. So there's not a great way to open it other than just kind of cracking it open with a sharp razor. Each time you do this, you're liable to damage the insides and the mechanical bits are very delicate. And so I basically destroyed a couple different chips and took images of all of them to make a composite final diagram of the device. As you can see, there are six discrete components inside this device. Each one of these corresponds to either an accelerometer or a gyroscope, and each one is dedicated to one direction of movement, either X, Y or Z. So I know it's challenging to really visualize how small these devices are. The scale is kind of hard to think about. So the entire chip is only two millimeters wide, and these really fine comb features on the side of some of the devices, you can fit several of those onto a single human hair, just to give you a little bit of context. And this isn't really helpful, but it's kind of fun to think about. An average size bacteria could fit comfortably on top of one of those combs. I don't know about you, but I have a hard time mentally visualizing how all these different mechanisms work without, I don't know, just tracing all the pieces by hand. But that'd be crazy, right? I mean, that would take a long time. Hit it! That's what I'm talking about! Wait! Okay, now. From the beginning. Hit it, boys. It took a week. You're welcome. These are 3D printed replicas of all of the mechanisms, and we'll use them to help describe how everything works, because sometimes it's easier just to see how the pieces move, kind of in the real life, rather than just looking at it on a microscope. And we won't really talk about this too much, but I just want to mention it because it's such a cool property of MEMS devices that I want you to keep it in mind for the rest of the video. The pictures you're seeing now, they're all made out of silicon. This is a single crystal of silicon that's been microfabricated in this really complex shape and it's been done in a way that allows the silicon to move and flex to accomplish its goal. And so it's just, I don't know, it's really interesting that we can fabricate these amazingly complex devices out of a material that's basically like glass. It's a really brittle, hard material in a way that lets us detect accelerations and torques and spins. So just a really cool property of MEMS devices and one of the reasons I find them infinitely fascinating. Okay, so let's talk about the accelerometers first, because they are much simpler devices than the gyroscopes. There are three accelerometers and they're laid out at the top of the device. The ordering, best I can tell, is X, Y, and Z. The job of an accelerometer is to detect linear accelerations in one axis. So if you're holding your phone and you drop it, the phone will feel an acceleration in the negative Z direction, which will be picked up by one of the accelerometers. This is the Z accelerometer for the device. So when you drop your phone, this is what's recording the acceleration downward. It looks complicated, but ultimately there's really only two pieces here. So there's a bottom half and a top half. And they function basically the same. So we'll look at the bottom half first. It's connected to the base with these four posts, and that's what keeps it rigidly attached. And you can see that the rigid outer sections are connected to this middle intersection by a very thin flexure joint, and this allows the outer section to pivot. Accelerometers work by having a large test or proof mass, which is allowed to move on its own. And it's decoupled from the device through these flexure joints. So when you drop your device and there's a downwards acceleration, the frame of the MEMS device will move down. But because the center mass is decoupled from the rest of it, it will attempt to stay where it is by moving upwards. And this is just Newton's first law of motion. An object at rest will attempt to stay at rest until it's acted on by an outside force. So because of this very loose coupling, the proof mass tries to stay where it is, which in effect moves it upwards in relation to the rest of the device. This upwards movement is then detected by the device using capacitive sensors kind of scattered around. What's cool is we can actually demonstrate this physically using these models and a high speed camera. I'll play it sped up first just so you can get a kind of general feeling of how the device moves. I've put dots on the moving actuator and the static base so that it's a little easier to keep track of the movement in relation to each other. So right at the beginning, you can see the static base begins to move downwards. But the test mass remains motionless for a small amount of time before it too starts moving downwards. If we track these points and graph it, you can actually see the difference or this lag period between the base of the device and the test mass. As it decelerates towards its stopping point at the bottom, the test mass continues to kind of lag behind and overshoots the point that the base ends up at. This is very apparent when it reverses and begins moving back upwards. The test mass is lagging behind and sinks very far into the device before it kind of reverses course and starts traveling back up itself. This forms a characteristic pattern on the position chart where the test mass line is either above or below the baseline as it's either lagging on the upward or downward portion. We can see this a little more clearly if we actually take the difference between the two. So kind of normalize it out, subtract them from each other to see the relative distance between the test mass and the base. And you get a much more dramatic looking curve showing how they differ from each other. If there was no change, this would be a flat line at zero, meaning that there's no deviation between the test mass and the base. You can actually see that we've picked up a bit of an oscillation both in the video and in the charts. This is mainly because it's just a 3D print that's been bolted onto a machine to do this test so it's nothing fancy. We can also transform this position data into velocity charts, which makes some of the trends a little easier to see. The test mass achieves a higher peak velocity at the extents of the travel before it reverses course and you can see the oscillation in the velocity chart a lot more clearly as well. An important thing to note is that this device is only detecting accelerations in the up and down, the Z direction. If you move it left or right or forward and back, nothing really happens. It's designed to be stiff in those two directions, so the only changes you see are when you move up and down and that allows these to rotate. The X and Y accelerometers work very similarly, they're just laid out in a different manner. So this is detecting X direction, this is detecting in Y direction. So the anchor point is here on both sides and then there's this large flexure that goes out through a flexure over here and it comes back to the center sections. And the center sections here are the proof masses. So these are the large masses that are meant to move. If you look very closely, you can see that the whole thing is allowed to flex back and forth in the X direction. So when there's an acceleration in X this way, the mass attempts not to move and will move backwards relative to the rest of the device. The displacement of this mass when there's a movement is detected by this red section. This is called a sensing comb and effectively it forms a capacitor between the red section here and the teal section here. So as this distance changes, the capacitance changes which is then detected by the device. The Y device is effectively the same layout just in a different direction. You can see it's the same general arrangement. The anchoring point is here in the middle. There's the flexure that goes out through the serpentine flexure and then two large proof masses. The whole thing is allowed to move back and forth in the Y direction. You've got the red sensing combs and then there's also this yellow sensing comb. Or at least I think it's a sensing comb over here. I think this extra sensing comb is just to help improve the sensitivity of this device because the motion here in Y is shorter than the motion here in X. It will be intrinsically a little less sensitive because there's less space for things to move. So I think this extra comb here is just to recover some of the sensitivity that X has so they're comparable readouts. So while accelerometers are passive devices, they're just waiting for a force to act on them and then recording changes to distances of all the components. These gyroscopes actually have actively driven components on the mechanism. In the case of this one, there's a section here and a section here which are made to vibrate in resonance with each other. So you can see those go back and forth kind of in plane. And the reason it does this is to mimic a tuning fork and what's known as the Coriolis effect. And I had tried to explain how all this works using, you know, models and little diagrams and I took slow motion capture of a tuning fork to see if we could demonstrate this physically. This is all very complicated and difficult to understand. So this is the CliffNotes version. When you strike a tuning fork, when you strike a tuning fork, it makes a tone at its kind of natural frequency and that's the frequency the tuning fork is resonating back and forth. If you were to apply a rotation to that tuning fork kind of down the axis of the vibration, so it's rotating this way, there's what's known as a Coriolis force. And this is a force that is perpendicular to both the rotation and the vibration. So this is a kind of diagram of the forces involved here. The tuning force is vibrating back and forth. There's a rotation counterclockwise down kind of the barrel of it. And the force that comes out is perpendicular going up and down to each of these two times. And so the long story short, without getting too bogged down in the math and the details about how this really works, when the tuning fork is vibrating this way, and there's a counterclockwise rotation, the fork tines will move outwards from the vibration and then distort. So they kind of bend out of plane like that. And so this Coriolis force, the part that's making it bend this way, is what's detected by these gyroscope mechanisms to determine that there's been a rotation in that axis. So if we look at one of the gyroscopes on the device, well, it doesn't really look like a tuning fork, does it? But I promise it's functioning like a tuning fork. So there are two sections, one here and one here, which are designed to vibrate in resonance with each other. So for this device, it moves back and forth like this. Using our little visual aid here, when there is a force going back and forth on these sections, and then a rotation around this axis, it'll cause an upward force and a downwards force. So it'll pivot these two sections here. And conveniently, underneath these two sections are two little trenches to give more movement to this device so that the inner mechanism doesn't hit the base. Now it gets a little more complicated, but the high-level details is that when these two sections move out of plane, it alters the resonant properties of these two pieces. So say these are resonating at, I don't know, 100 kilohertz. When there's a rotation and these two pieces move out of plane, this resonant frequency might change to 98 kilohertz or 105 kilohertz. It isn't altered in some way. And this slight alteration is picked up by this outer frame and these sensing combs on the outside. So you'll notice that there are a ton of these little capacitive comb fingers that are intermeshed with each other. And as the frame distorts ever so slightly, the distance between all these combs changes and it can pick up the alteration in the resonant frequency here. So the same applies to the other gyroscope. This is essentially a carbon copy of this one, just rotated 90 degrees. So while this one is vibrating in this manner, back and forth, this one is vibrating up and down, but effectively is the same. It has the same pivoting mechanism here in the middle, has the combs on the outside to detect the changes, just like this one. And then we come to the final gyroscope, which looks a lot different. So this gyroscope is designed to detect rotations kind of coming out of the plane of the device, which is why it's not just a rotation like these two. But the principle is the same. We've got a vibrating mass here in the middle, vibrating this way. There's a rotation, which allows the center section to pivot. And that pivot is picked up on the outside by the sensing combs. Unlike these two devices, there's no trench underneath the base of this device because it doesn't need anything to rock or pivot out of plane. Everything is staying kind of in plane, X and Y. And that is, in effect, a very high-level overview of how this 6-axis accelerometer gyroscope MEMS device works. Now I definitely glossed over some details here, like why you need a tuning fork model to begin with, or how some of these devices are driven or sensed. But this should give you a pretty good high-level overview of how this type of device works at a microscopic level. In effect, you've got a heavy mass that doesn't want to move, and you've got a tuning fork that's vibrating. And that's really all there is to it. Long-time viewers of this channel will know my electronics skills are maybe a bit basic, which is why I'm excited to talk about the sponsor for today's video, Keysight, and their virtual event for electrical engineers, or, you know, just general science enthusiasts like me. This free event will have demonstrations, design and test tips, Q&A with industry experts, and they're running a giveaway for tons of test gear, including an 8-channel 6GHz oscilloscope, which really makes my scope look like a dinosaur. The next installment of this bi-monthly livestream will be March 14th, where they're talking about all the things that I should probably learn about. Circuit board, rules of thumb, modern simulation tools, current return pads, ground plane arrangements, you know, like, electrical stuff. Since this is a material science channel, what caught my eye is the liquid nitrogen demonstration, where Keysight is going to show how the extreme cold affects the performance of a 50-ohm trace. Honestly, unrelated to the sponsorship, I'm really excited for one of their summer livestreams. Keysight will be touring some quantum computing labs and talking about the technology and some of the engineering challenges involved. Quantum computing is this really neat mix of material science, optics, and electronics, so I think it'll just be a really fascinating event. If you sign up using my link down below, you'll get an extra entry into the Keysight Test Gear Giveaway, and hopefully you can pick up some cool stuff. Definitely check it out, and I'll see you there. I hope you found that as interesting as I did. I personally love these MEMS devices. They are just infinitely interesting to look at. I mean, you open them up, and they're aesthetically just very beautiful devices with these very regular geometric patterns and serpentine traces, but they're also just really clever devices. You know, they're straddling that micro-to-macro scale, utilizing the properties of a really difficult material like silicon to make a tiny little moving device that you can embed into a cell phone. It's just such a cool field, and I always find them super interesting to look at. There are a lot of different kinds of MEMS devices out there, so if you have a favorite that you would like to see on this channel, leave me a comment down below, and I'll try to find some to pop open. Accelerometers and gyros are definitely the most common, you know, because they're used in cell phones, but there's a lot of other kinds of devices, too, that I think would be interesting to look at someday. I think that's all I've got for you today. Thanks for watching, and I'll see you next time. Bye. Bye. Bye. Bye. Bye.