Magnetron: Who among us knows how does the microwave oven in our kitchen work? Hardly few. Obviously, it seems no less than rocket science producing waves. The microwave ovens have a magnetron inside it that is the heart it. These are almost the same that is what you need on a radar. The magnetrons are a bit complicated but this article will explain to you all about a magnetron in the simplest words. Read the full article to get the knowledge you deserve.
The cavity magnetron is almost outmoded these days. It was developed for the radar services during world war 2, which led to other vacuum devices as well. But we all know that the vacuum tubes are ‘yesteryear’ now. Isn’t it?
I mean, where do you see people watching shows on vacuum tubes? Though it has been replaced by slim LED tv screens that are called solid-state devices, now you will ask, then why do we need to learn about magnetron? So here’s the answer. These are multiple answers to this question. Firstly, it is not like this device is not used now. This machine still has various applications like the larger machines are used in broadcast and radar applications. Secondly, the magnetron has given birth to many other important devices with its concepts like microwave tubes.
Now the next question that arises here is that what is a magnetron, and why is it useful? So to tell you that if you want to make a sandwich in 2 mins or get your flight through lousy weather safely, you need microwaves. This is not the microwave that you use in your house, and it is precisely talking about the radio signals that are super energetic, invisible, and short-wavelength signals. And for making these microwaves, you need a heavy device like cavity magnetron.
These devices can be really complicated. So, to sum it up, its use, a magnetron, is a high voltage vacuum tube. It works as a self-excited oscillator that id capable of producing microwaves. Typically, a magnetron used in ovens produces really short radio waves ranging from 1mm to 30cm and is enough for cooking your food.
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The magnetron was first invented in the 1900s by an American engineer Albert W. Hull.
After that, in 1934, another scientist, Arthur l. Samuel invented the cavity magnetron in his laboratory. Then in 1939, two physicists from the University of Birmingham invented a much better and powerful version of magnetron that can be used in ships and submarines. And then, it was in 1976 when an MIT researcher developed a 90 times more powerful machine than cavity magnetron. The magnetron started as a machine with three levels.
The first layer was an oven on the top. Then in the middle, it was a range in, and at last, was a large microwave along with the calrod elements at the lowest layer. The main use of this appliance at that time was to roast turkeys and other items. A few years later, this appliance was changed into a countertop machine. The first oven that was made in the 1900s. It was at general electric. Louisville from general electric said that GE oven was depended on the metal mesh gasket that had its core made up of elastomer and was used to seal the door. The shielding also used to deteriorate, and there was a significant power loss of microwaves. But now, as times have passed, we are here with the best of technology to produce microwaves.
So now, I hope you would love to know the process of the generation of a microwave. In simple words, the microwave oven in your home has a magnetron generating microwave energy. The microwave signals transverse through the waveguide and is spread all over the metal cavity that you see after opening the microwave. The food absorbs these microwaves produced you keep inside the cavity, exciting the moisture, or you can say the water molecules in the food. The heat generated in this process is then distributed all over the food cooking it.
We all know, microwave oven cooks the food much faster as compared to standard ovens. The only reason behind this is that microwaves penetrate much better into items and can produce heat through inside out. But talking of a conventional oven, it generates heat using the external environment, and this process happens slowly in order to transfer heat.
Working of a magnetron
The cavity magnetron is the main part of a household microwave oven. As mentioned earlier, a magnetron is a microwave oscillator that emits or produces electrons. There is a solid hot rod known as a cathode that produces these electrons. The anode is a ring-like structure that surrounds the cathode. It has cuts or slots in it that are called resonant cavities. Switching on a magnetron would lead to the first step, which is an emission of electrons from the cathode to anode in straight lines but moving all around the surface. This process is almost similar to the basics of a TV set, but two extra things to make this different from TV.
The first difference lies due to the cavities created in the anode. The other difference is of the powerful magnet that is kept under anode along the length of the tube that is parallel to the cathode, to produce high magnetic fields. When these electrons travel from cathode to anode, they experience an electric field and magnetic field simultaneously, one due to cathode to anode transfer and other fields due to the magnet. And like any other charged particle in the field, the electrons move in a circular path whirling in the space between anode and cathode. As soon as the electrons pass the cavities, they tend to radiate, or you can say produce microwave radiations.
Now further, these radiations are coupled with vacuum through a probe. Then these waves that have been produced in this process are taken into a funnel-like structure called the waveguide. Now, this waveguide actually guides these radiations in different places. For example, it may be channeled to the metal cavity that is the cooking compartment in an oven, or else it is sent out into the air through antennas for radar services.
You can also take this device in comparison with a flute where imagine a person blowing electrons into the cavities of the basic structure and producing microwaves instead of sound waves. The magnetron used in radar and microwave ovens is different. Like the radars operate with the help of small but high powered pulses, whereas the magnetron in ovens uses continuous waves.
Now you may ask what governs the frequency of the magnetron? So the answer is the size of the cavity along with its arrangement. This is the most crucial thing and needs to be designed according to the purpose that is to be served. Well, magnetrons also have an adjustment for changes in the size of cavities with a screw but to a small extent. This device is generally not tunable, but few complicated and expensive versions may give you that feature also.
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The magnetrons require an external source of power. Their requirement is of high DC voltage that can go up to 3KV. Now, this device can consider as a converter that precisely converts high DC voltage into the desired 2.45GHz frequency radiation.