What is a MAGNETRON - How Does it Work

hi today we are going to uncover the secrets of the humble magnetron one of the applications for magnetron is something you already know about a microwave so what is a magnetron well the short answer is it's a variation of matter no no no we're worried before you go running to the hills just remember that the radiation emitted by this is 2.4 gigahertz which is relatively low so you're not at risk of developing cancer of anything however it is a kilowatt which means it's very high-powered so it will burn you but how does something produce a kilowatt of 2.4 gigahertz electromagnetic radiation let's find out all right so here's what the inside of a microwave looks like here we see the magnetron which emits waves into the main cavity that's this part over here oh and it's cooled by the span we down here we have a 2 thousand volt transformer and a two thousand volt capacitor it's because of these that you never work on a microwave while it's plugged in I've pulled out this microwave transformer as an example and you can see how the high-voltage oats across the air is super heating it into a plasma so here's how a magnetron works in theory we already know that it needs high voltage in order to operate this is that the electrons can jump off the cathode and move freely around the chamber every magnetron has two powerful permanent magnets inside of it they're there to create a constant magnetic field pointing through the cavity of the magnetron now here's where the physics gets a little weird we need to remember a thing called the right hand rule you hold your fingers in this pose your middle finger points in the direction of the magnetic field your index finger points in the direction of the current or the velocity of a single moving charge and your thumb points in the direction of the voice that that charge will feel now that we've discussed the right-hand rule let's take a look back in of a magnetron as we kind of touched down earlier we know that the electrons are emitted out radially from the center cathode and there's also a magnetic field going bite down the middle of the magnetron cavity so how does this interact with the electrons well using the right-hand rule if we know that an electron is heading straight out from the center then the magnetic field is going into the plane of your computer screen then we know that the poise is going to be accelerating that particle this direction and after a moment the particle will have a new velocity like this and so on and so on inevitably what this electron is going to do is it's going to follow a spiral pattern going outward well we've just described is what physics knows as a cyclotron when you can get charged particles like electrons to cycle around in a spiral pattern when these spiraling electrons finally make their way to the anode block the outside wall of the magnetron cavity they will induce a charge separation a voltage across the anode resonating cavities those are the smaller circles on the periphery that we see why the electrons do this is a lengthy explanation and out of the scope of this video so I'll leave some links in the description for your own study if you're interested now let's take a closer look at one of these vests innate in capitals well we see that across this resonating cavity the base of it where the charge separation is kinda looks like a capacitor and that loop going around the circle kind of looks like an inductor with one tune well let's model it as such and see what happens this capacitor portion at the bottom creates a constant electric field across it thanks to the charge separation and the one turn inductor will create a magnetic field going in and out of the plane of that circle thanks to the rotating current around it essentially it's a really weak electromagnet so all we see is that the electric and magnetic fields are perpendicular to each other and oh my gosh its electromagnetic radiation as evident by the alternating electric and magnetic fields that are perpendicular to one another we can solve for what the resonant frequency is by solving this equation as we can see both the inductance and the capacitance are in the denominator under the boot which means that the smaller they are the higher frequency we're gonna get since will you know that we're talking about a magnetron from microwave we can expect this to be somewhere around 2.4 gigahertz but wait a second these waves aren't very powerful in fact they're incredibly weak so how does a magnetron make them more powerful well let's take a look back inside the magnetron at the electric fields created by this charge separation once more the red lines you see here are the electric fields created inside the main cavity of a magnetron and the arrowhead points in the direction that these fields are going now let's consider an electron as it interacts with these fields well it looks like the electron is occasionally going against the electric field which will cause it to slow down and use energy this is called a retarding the electron and as this happens that energy needs to go somewhere it's absorbed into the RF the radio frequency that's being created by the Vezina tting cavities and this is how a magnetron takes that teeny tiny power of an electromagnetic wave and makes it very powerful there is a lot more we could say about this in fact we could be here all day but if you're interested in learning more I'll include some links and references in the description for your own study if you are interested but for now I think you get the idea so I'm gonna move on in fact let's take a look back at the magnetron I have sitting on the table and see what it looks like now this top piece here is the antenna for the magnetron now you may expect the waves to come straight out as if it was coming out of a gun but that's not actually what it looks like I'll animate this as best I can but the output from the antenna looks something like this these shapes that you see here are the primary lobes this is where you can expect the greatest intensity which means something directly in front of the magnetron would have almost no interaction with it alright now that we know what to expect I think now we're ready to cut this thing up like a Christmas ham and see what it's really made of ok this is very important you see pink band here this is a ceramic insulator that is oftentimes made of beryllium oxide which is extremely dangerous if it's broken and you get particulates either in your mouth oven your lungs you could potentially develop condition called brilli aussies which will have both acute and chronic side effects that'll probably end up killing you oh and it's also close to no genic in fact magnetrons are full of bad news I can't stress enough to wear some proper protection while you work okay it's a little while later and I've made some progress so I've removed some of the outer case of the magnetron let's see what some of these parts are well this one that just fell off this is just a brass reflector prevents waves from bouncing back into the magnetron that's it's not really important so here beneath the antenna and beneath the cover we can take a look at one of these permanent magnets there are two of them once again to make a magnetic field going through the cavity of the magnetron which you can see in there is the cylinder the surrounding it or the heat sinks because this magnetron while it's in operation gets very very hot in fact if you look inside of a microwave oven this is what the fans pointing at across here now in the back first of all we can see more pink danger so I'll cover that up but as soon as I can and we also see these two coils here all right let's see if I can get off one of these permanent magnets so with everything else gone I'm just left now with the resonant cavity of the magnetron it's sort of unbelievable that beyond all the bells and whistles a microwave oven can just be boiled down to this I think I'll bisect it right across here so I can get a cross-sectional view of this inside pattern all right well we see that the inside is made out of copper which is not what I was expecting I thought it would be made out of steel which would be a much toughen material this actually wasn't too bad to cut the Vale here that Center rod right there that's the the filament where the electrons are ejected from that's superheated by the ways that the electrons can migrate away from it into the cavity now I'm I depicted it in the schematic as circles but in this magnetron these triangular regions trapezoidal regions these are the these are the resonant cavities for the electrons now I know that they've been trying to make magnetrons a lot cheaper over the last decade or two I just I never imagined they would simplify it down some now the other one looks pretty much the same once again we got that filament action going through there and this leads up to the antenna well there we have it I think we have fully uncovered what is inside of a magnetron truly and this is just your typical magnetron the kind of thing that you would find in your microwave at home so I think we answered what we set out to do and that was once again to find exactly what a magnetron does and how it works just remember to stay safe and have fun and as always thanks for watching [Music]

Channel: Blueprint

Views: 901,496

Rating: 4.8287845 out of 5

Keywords: dayton aardema, engineering, blueprint, diy, how to, microwave, operation, theory, magnetron, transformer, danger, beryllium, oxide, antenna, cavity, resonating cavity, resonance, LC, capacitor, inductor, electron, charge, chaimber, filiment, cathode, anode, physics, explanation, how does, tutorial, cross, section, cut, saw, open, inside

Id: 5DpYlnHT-0s

Length: 10min 41sec (641 seconds)

Published: Sun Mar 18 2018