Introduction: MICROWAVE RADIATION
I love microwaves, I think they are the coolest thing ever. My science teacher even let me teach a lesson (that I made) on microwaves! On this instructable I will teach you a thing or two about microwave radiation.
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Step 1: History of Micorwaves
Microwaves were first predicted by James Clerk Maxwell (second picture) in 1864 by use of his equations. Later during 1888 Heinrich Hertz (third picture) proved the existence of microwaves by building a device that produced and detected microwave radiation. His device used a horse trough, a wrought iron point spark, Leyden jars, and a length of zinc gutter with a parabolic cross-section that worked as a reflection antenna. In 1894 J. C. Bose (fourth picture) publicly demonstrated radio control of a bell using millimeter wavelengths, and conducted research into the broadcasting of microwaves.
Step 2: Microwaves
Microwaves are a form of electromagnetic waves just below infrared light, with a wavelength ranging from one meter to one millimeter. Microwave frequencies can be as low as 300MhZ and as high as 300GhZ. Microwaves are non-ionizing radiation so according to many beliefs microwaves cannot cause cancer, but can aid in it if exposed for to long. (this guy believes microwaves can cause cancer but is always changing his mind...)
Step 3: Microwave Chemistry
Microwaves react with mobile polarized materials such as water, sugars, and fats. When microwaves pass through a material containing a polarized liquid such as water, the waves alter the polarity causing them to vibrate extremely fast causing friction which heats up the material, this is known as dielectric heating. When placing a light bulb or neon lamp in a microwave you will notice a plasma flame within, this is because the metal parts are acting as an antenna and the microwaves are converted back into electrons which ionize the gases.
Step 4: Producing Microwaves
Microwaves are produced by vacuum tubes devices that operate on the ballistic motion of electron controlled by magnetic or electric fields. Some different kinds of microwave emitters are the cavity magnetron, the klystron, the traveling-wave tube(TWT), the gyrotron and all stars. These devices work in the density modulated mode, instead of current modulated mode, meaning that they work on the basis of clumps of electrons flying ballistically through them, instead of using a constant flow of electrons. Lower power microwaves can me produced by some solid state devices such as the FET (field effect transistor), the tunnel diode, the gunn diode, and the IMPATT diode.
The fist picture is a gunn diode with a waveguide, the second are some different kinds of cavity magnetron's, the third is a gyrotron, the fourth and fifth are klystron tubes, and the last is a traveling wave tube.
Step 5: Microwave Communication
Before fiber optics and such things were invented microwaves were used to carry most long distance calls but now we have fiber optics and such things but still use microwaves as a means of communication. Wireless LAN protocols, such as Bluetooth, use microwaves in the 2.4 GhZ range. Microwaves are also used in broadcasting and telecommunication transmissions because of their short wavelength, highly directional antennas are smaller and therefore more practical than they would be at longer wavelengths. There is also more bandwidth in the microwave spectrum than in the rest of the radio spectrum; the usable bandwidth below 300MhZ is less than 300MhZ while many GhZ can be used above 300 MhZ. Usually microwaves are used in television news to transmit a signal from a remote location to a television station from a van equipped with a microwave transmitter.
Step 6: Making Your Own Microwaves
Want to experiment with microwaves? All you need is a microwave oven to take apart and a bit of metal and follow this instructable and you got yourself some microwave radiation to experiment with (it would be safer if you just left the microwave in tact and used the cooking chamber).
Step 7: Microwaves and You
As much as you may love microwaves they don't love you so you gotta be careful around them! Microwaves do not have enough energy to chemically change substances by ionization because they are below the level of non-ionizing radiation. The word "radiation"only means that energy can radiate. It dose not mean radioactive in this case but it can. It has not been shown conclusively that microwaves have enough adverse biological effects at low levels. Some but not all studies suggest that long-term exposure may have a carcinogenic effect. This is separate from the risks associated with very high intensity exposure, which can cause heating and burns like any heat source, and not a unique property of microwaves specifically.During World War II, it was observed that individuals in the radiation path of radar installations experienced clicks and buzzing sounds in response to microwave radiation. This microwave auditory effect was thought to be caused by the microwaves inducing an electric current in the hearing centers of the brain. Research by NASA in the 1970s has shown this to be caused by thermal expansion in parts of the inner ear. When injury from exposure to microwaves occurs, it usually results from dielectric heating induced in the body. Exposure to microwave radiation can produce cataracts by this mechanism, because the microwave heating denatures proteins in the crystalline lens of the eye faster than the lens can be cooled by surrounding structures. The lens and cornea of the eye are especially vulnerable because they contain no blood vessels that can carry away heat. Exposure to heavy doses of microwave radiation (as from an oven that has been tampered with to allow operation even with the door open) can produce heat damage in other tissues as well, up to and including serious burns which may not be immediately evident because of the tendency for microwaves to heat deeper tissues with higher moisture content. NEVER get inside a microwave and close the door, you can't always get out!