It is the waveguide that channels the microwaves created into the cooking space within a microwave oven. In radar technology these microwaves are beamed out via the waveguide into the air.
The above is really the simplest explanation I could give for how microwaves are created using a magnetron. How though do these microwaves then cook food in a microwave oven? Again the following is my own understanding of how this works. Feel free to add to this in the comments below. Once the microwaves are passed into the cooking compartment of a microwave oven by the waveguide , they are reflected by the walls inside the microwave oven.
So effectively they bounce around inside the microwave, being constantly reflected by the sides. The waveguide works slightly differently in a flatbed microwave than it does in a regular or solo microwave. Once food is placed inside of the microwave oven it then absorbs the microwaves that bounce around inside of it. Once the microwaves are absorbed by the food they cause the water molecules inside of the food to vibrate extremely quickly. These vibrations then produce heat , and it is this heat that cooks the food.
Any food that is high in water content will be cooked in a microwave extremely quickly. The more water molecules a food is made up of the more molecules there are to vibrate causing more heat at a faster rate. Foods such as vegetables that are high in water particles will cook very quickly in a microwave oven.
As mentioned above, the microwaves cannot be absorbed by metal. This is why they bounce around inside the cooking area of a microwave. For more information about this you can read my post on the advantages and disadvantages of microwave ovens. The kind of magnetron used in modern day microwave ovens is called a Cavity Magnetron. The multi-cavity magnetron used in microwave ovens is attributed to the work of John Randall and Henry Boot.
Randall and Boot were engineers at the University of Birmingham. Way before they were used in microwave ovens, magnetrons had another very important use. The use of magnetrons played a very important role throughout Word War Two. We can trace the origins of the magnetron back to before the work of Randal and Boot. It is widely reported that the first magnetron was conceived and developed by H.
Gerdien in , way before the cavity magnetron in microwave ovens. In a Swiss physicist by the name of Heinrich Greinacher tried to further this work by using a diode tube. The two half cylinders could be charged to the same voltage, in which case the magnetron operated like earlier models. Applying slightly different voltages to the two anodes caused the electrons to be attracted to and flow to the more positively charged plate.
An external oscillator was connected to the two plates. When a strong magnetic field was applied, the electrons followed a looping rather than circular path toward the anodes and the overall output power was greater than in the single-anode magnetron.
A disadvantage, however, was that a portion of the electrons returned to the cathode, which then overheated and released still more electrons initiating an avalanche condition. The resonant cavity magnetron, also known as an electron-resonant magnetron, provides a high-power, high-frequency output, and there is not the overheating problem as in the split-anode model. The oscillation is created by the shape of the anode.
The resonant cavity magnetron consists of a single, solid block drilled through the geometric axis. The entire metal block is the anode. Typically, there are nine preferably an odd number smaller drilled holes spaced evenly around the central hole and each connected to it by means of a narrow slot.
In the central hole are leads running to the heater and cathode, which is coated with an oxide. Through one of the small holes is the output coupling loop, which allows RF energy to be extracted and fed to a waveguide.
The assembly is analogous to an LC oscillator. The capacitors consist of the parallel sides of the connecting slots and the inductors are the round holes. The output frequency is dependent upon the dimensions of these elements. Large amounts of RF energy are generated within the resonating cavities.
Because the cavities are open at one end, they become synched and function as a single oscillator. Upon powering up, oscillation requires slightly varying times, so phase is not preserved. Moreover, from pulse to pulse frequency may drift a slight amount. But this is not a problem for continuous-wave radar and, of course, not for microwave ovens.
The DC field extends radially from adjacent anode segments to the cathode. The AC fields, extending between adjacent segments, are shown at an instant of the maximum magnitude of one alternation of the RF oscillations occurring in the cavities.
In Figure 6 is shown only the assumed high-frequency electrical AC field. This AC field work in addition to the permanently available DC field. Well, the electrons which fly toward the anode segments loaded at the moment more positively are accelerated in addition.
These get a higher tangential speed. On the other hand, the electrons which fly toward the segments loaded at the moment more negatively are slow down. These get consequently a smaller tangential speed. On reason of the different speeds of the electron groups, the velocity modulation leads to a density modulation. The space-charge wheel rotates about the cathode at an angular velocity of 2 poles anode segments per cycle of the AC field. This phase relationship enables the concentration of electrons to continuously deliver energy to sustain the RF oscillations.
One of the spokes just is near an anode segment which is loaded a little more negatively. The electrons are slowed down and pass her energy on to the AC field.
This state isn't static, because both the AC- field and the wire wheel permanently circulate. The tangential speed of the electron spokes and the cycle speed of the wave must be brought in agreement so.
Recall that an electron moving in an E field is accelerated by the field and takes energy from the field. Also, an electron dispenses energy to a field and slows down if it is moving in the same direction as the field positive to negative. The electron spends energy to each cavity as it passes and eventually reaches the anode when its energy is expended.
Thus, the electron has helped sustain oscillations because it has taken energy from the DC field and given it to the ac field. This electron describes the path shown in Figure 5 over a longer time period looked. Due to the multiple decelerations of the electron, its energy is optimally utilized and efficiencies of up to 80 percent are achieved. After switching the anode voltage, there is still no RF field. The single electron moves under the influence of the static electric field of the anode voltage and the effect of the magnetic field as shown in Figure 5 by the red electron path.
Electrons are charge carriers: during the flyby at a gap, they give off a small part of the energy to the cavities. Similar to a flute: A flute produces sound when a stream of air is flowing past an edge of a hole.
The cavity resonator begins to oscillate at its natural resonant frequency. Immediately begins the interaction between this RF field with an initial low power and the electron beam. The electrons are additionally influenced by the alternating field. It begins the process described in the sequence of phase 1 to 4 of the interaction between the RF field and the now velocity-modulated electrons.
Unfortunately, the transient oscillation doesn't begin with a predictable phase. It was believed that the main use of the microwave would be to speed up roasting turkeys and other large items, and thus the Calrod element was needed. Later on the device was changed into the counter-top appliance we know today. Below Mr. Of course, as things developed, users were much more interested in quickly cooking or reheating much smaller items.
The GE oven depended on an elastomer-cored metal mesh gasket for sealing the door. It took only a few food spills to gunk up that gasket whereupon the shielding deteriorated and significant microwave power escaped. That resulted in quite a recall and hastened the demise of that product. Percy Spenser is regarded as the person who came up with the oven concept but since Raytheon had no experience in appliances, they negotiated a deal with Amana and the Radar Range ensued.
He tells us how the microwave works and shows us older magnetrons vs the current magnetron: Above: older magnetrons were more fragile and larger than newer magnetrons. Below is the s era power supply used with the oven on the right.
For use of Edison Tech Center images and videos see our licensing agreement. The cavity magnetron is the main component of a microwave. Vacuum Tubes.
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