I’ve just took this thing out of a microwave oven.
This is called a magnetron and could be very dangerous.
I’m especially afraid of this pink part right here.
These are ceramic insulators but the dangerous part is that they could contain beryllium
oxide.
If you break this ceramic it will turn into dust, and if you inhale dust containing beryllium
oxide you will suffocate or get cancer and there is no cure for that.
Yeah, pretty scary thing, right?
Anyway, the rest of a magnetron are just metal parts and magnets so if you keep them away
from high voltage, they are safe to examine.
And yeah, these components work with thousands of volts so never connect them outside of
the proper shielding of a microwave oven.
In this video I will tear down an old microwave, check what components it has inside 1 by 1,
and then I will try to explain to you how a magnetron works and what is made of.
After that we should be ready to understand how the microwave is capable of heating your
food using waves that you can’t even see.
It should be quite an interesting and fascinating video, so guys, let’s get started.
What's up my friends, welcome back.
This is my old microwave but as you can see inside here, this metal part got a hole in
it and because of that it makes all kind of sparks and doesn’t work properly anymore.
So instead of throwing it away I’ll make a teardown and try to explain you the parts
we have and how the magnetron works.
Once I have the oven open I can take out the parts.
We can see a huge high voltage transformer.
We also have a huge capacitor on the side and the magnetron which is this part here.
I take these 3 parts out.
In a few minutes I have the transformer connected to the huge capacitor and the magnetron.
We also have an AC fan.
If you are interested, apart from the main components you could also get some buttons,
fuses, a light bulb, wires and PCB components, another PCB with a transformer, relays, buzzer
and other components and we also get another AC motor used for the turntable.
But the components we are interested in are these 3 here.
Transformer, capacitor and magnetron.
Basically, these are used to get microwaves which will heat up your food.
Microwaves are a form of electromagnetic radiation with wavelengths ranging from about one meter
to one millimeter corresponding to frequencies between 300 MHz and 300 GHz.
For a microwave oven, those waves will fill this metal cavity and heat up your food, but
how that is done is for the next video.
Because today we want to understand how could we get these microwaves out of a cavity magnetron.
These are the main parts that make such a component.
We start with the RF output antenna.
This is where the microwaves are coming out.
Then we have this pink insulator.
This could contain aluminum oxide which is safe.
But it could also contain beryllium oxide which is very, very, dangerous if inhaled.
So, under no condition you should break this ceramic insulator and create dust from it,
so stay far from this.
By the way, if we open the bottom part we can see yet another insulator like that one
connected to the input wires.
The magnetron has the mounting plate which is this metal part and we can see two permanent
magnets, one on top and one below the tube.
Then we have the radiator used to dissipate heat because this could get quite hot.
Also, to detect when the maximum temperature was reached, on the side we have a thermo-switch.
This component cuts off the current flow when it passes a certain temperature.
Here I have the switch connected to the multimeter and we can hear a beep meaning the switch
is closed.
I heat it up and after we hear a click, the switch is now open That’s how it works.
When it gets cold again, the current flow opens back.
Ok so on the bottom side of the tube we have a conductive noise suppressor filter coil
and the input to the tube.
And in the middle is the most important part, the anode or the resonant cavity.
You see, the magnetron working principle is based on LC oscillation and we’ve seen such
oscillation in many other projects.
Basically, when we have a capacitor in parallel with a coil, we get a so-called LC tank that
will resonate at its resonating frequency creating back and forth movement of electrons.
Here I have a coil in parallel with a capacitor and the oscilloscope it connected as well.
I apply voltage from my supply.
When I remove that voltage, we can see some oscillations and this is the resonating frequency
based on the coil inductance value and the capacitor capacitance value.
When we start, the capacitor is fully charged and we have no current flow.
We remove the power supply.
The charge will start flowing through the coil from one side to the other attracted
by the positive side.
As we all know, this current flow will create a magnetic field around the coil.
When the current flow is over, this magnetic field can’t keep anymore and it will collapse.
This collapse will induce a voltage but in the opposite direction charging up the capacitor
with inverse polarity.
Then when the capacitor is full again it will create a current flow backwards once again
and create another magnetic field.
This process repeats over and over creating the so-called LC resonating frequency.
So basically, we would have a magnetic field rising and collapsing over and over again
around the main coil.
So, if we put another coil on the side with an antenna, this magnetic field will induce
current into the second coil and the antenna will radiate electromagnetic waves.
This is the basic theory behind the so-called cavity magnetron.
But this radiation dies out fast due to losses.
So to understand the next part, we need to open the magnetron but be careful with those
ceramic insulators.
To open the main case, we need to bend a few metal parts and the case will just open.
We remove the top metal washer carefully so we could now remove the first magnet.
Then on the bottom side, in order to get the tube out we need to cut the filter wires.
Cut those wires and then if we pull upwards the tube it will get out.
Now carefully remove the heat dissipator, they are just pressed down on top of each
other.
Now we have the main tube made out if copper.
Believe it or not, this could be used as a high voltage diode right now.
This is the anode, the antenna and the main input terminals.
Now the tricky part, open the tube.
Carefully, using a Dremel tool, cut the copper tube.
It is quite thick.
But finally is opened but you will notice the main antenna inside.
Twist it till you can full open it.
And this is what we have inside.
10 electrodes all around.
In the middle we have the filament made out of tungsten and thorium so it could withstand
high temperatures but also have a good source of electrons.
So guys, how dose this work?
We apply a very high voltage between the filament and the copper anode around it.
The filament will get very hot and start shooting electrons out with a process called thermionic
emission just as we have seen in the vacuum tube video.
But without the copper anode, these electrons would stay here.
But since we have the copper anode all around, the electrons, due to the voltage difference
will accelerate twards the copper anode.
As the theory of radiation states, these charges will produce radiation when they are accelerated.
And there we have our radiation, but this is not efficient at all because the electrons
spend a very short time between the filament and the anode.
To make the time longer, we add those permanent magnets, one below and one above.
That will create a magnetic field that will make the electrons spin around.
So now the time from the filament to the anode is a lot longer so the process is more efficient
and this is called a hull magnetron.
To improve the efficiency even more, we add the previously seen LC oscillator.
To achieve that oscillation, the anode is designed with cavities as we’ve seen when
we opened the magnetron tube.
As you can see we have 10 cavities made out of the same copper.
So how could this act as an LC tank, where is the coil and where is the capacitor?
Well for that let’s see this example.
Assume a copper bar with a cavity.
When an electron is passing on the side if it, it will repel all the other electrons
inside the copper bar, right?
But near the cavity, the electrons have no space above them so they will jump to the
other side.
Like that we create a more positive region here and a more negative region here.
And that’s exactly as a capacitor.
So basically we have 10 capacitors all around.
And the interesting part is that the curved part of the copper anode acts as an inductor.
And there we have our LC tank that will resonate.
That means that when the electron from the filament is rotating around these cavities,
it will create positive and negative charged capacitors.
These are connected together through the anode wall which acts as an inductor.
So all the charges will oscillate at the same time.
This huge oscillation is now extracted with an antenna which will create a more efficient
magnetic radiation this time.
We can see that antenna here, that was connected to the copper cavity.
This will emit our microwaves.
By the way, I forgot to mention that the cavity is under vacuum so there are no other particles
inside.
Even more, inside of the cavity, since we now have those capacitors with different polarity,
the spinning electrons will be attracted by the positive charge regions like this, creating
a spoke wheel pattern.
The capacitor charges are oscillating so the spoke wheel will spin like this.
That’s pretty much what’s happening inside of a cavity tube of the magnetron.
Basically, the antenna is now radiating the needed microwaves to heat our food.
Be aware that this is very dangerous if not kept in a metal casing as the microwave oven.
This could melt you from the inside out without you even knowing.
Have in mind this works with thousands of volts out of this huge transformer.
This usually delivers a lethal voltage of around 3000V AC and around 500mA of current.
In a future video I will explain you how these microwaves are able to heat our food and how
the microwave oven works internally to create bouncing waves.
More about that in the next video.
I hope you have learned something new and if so, consider giving me a like or comment
below.
Thanks again and see you alter guys.