Crossposted at Politicook.net
We have discussed stuff through around 2.8 meters. That is the wavelength that would correspond to the height of a giant person, almost nine feet tall. The next band blends in seamlessly, and I will discuss it presently.
Please remember that there is not any "hard" barrier from one wavelength to another, except our perception visually to see an extremely small portion of the spectrum. As the crowd went crazy, Tommy shouted out "Here we go!" He left the "after the jump part out, but that is OK.
Once wavelengths at this range are reached, transmission properties are even more in line of sight and not ionospheric reflection. Now we consider wavelengths lower than the sort of arbitrary 2.8 meters to those of around 1 millimeter or so. Some use other limits, but in general this is not a bad description.
Microwaves are generated differently than classical radio waves, not with oscillators made from "traditional" components, but rather ones that have more to do with geometry and the interaction of alternating electric fields with cavities, (like the Magnetron in your microwave oven) or other, nonlinear effects. Since I am not an electronics engineer, I will not provide an inadequate discussion of their generation. Rather, I will provide a discussion of a few of their impacts.
Before I continue, I should explain the energy bands in matter (not to be confused with energy bands as used in semiconductor work). There are four basic motions in matter: translational (going from points A to B in more or less a straight line); rotational, where molecules or parts of them spin around on some axis; vibrational, wherein atoms within molecules move to and fro, but no bonds are broken; electronic, where electrons are promoted or demoted into higher or lower energy levels; internal nuclear transitions, where the internal arrangement of nuclei changes.
Except for translational energy, which has to the with the thermodynamic temperature of the environment for the most part, (there are important exceptions, but mostly it is that), each transition is associated with a particular wavelength of electromagnetic energy. For instance, water molecules will spin on the axis described by the line that divides the molecule into two symmetrical halves. It turns out that the rate of rotation is quantized, that is, there are only a few allowed angular velocities for such rotations.
My microwave oven, like most, is a broadband microwave transmitter with a nominal frequency of 2.45 GHz (gigahertz) has a nominal wavelength of 122 mm. That is about right to make water molecules rotate and bump into each other. When they bump into each other, some the rotational energy is turned into translational energy, which makes the mass of foot heat. It turns out that sugars and fats also have some parts of their molecules that are stimulated to rotational excited states by this radiation, and they heat up as well. The reason that fats and sugars seem to heat up more rapidly has to do with another physical property, heat capacity. It takes more heat to raise the temperature of water than any other substance, so fats and sugars have a faster temperature rise because it takes less energy to heat them.
Interestingly, my cordless telephone operates at 2.4 GHz (125 mm), very close to that of my microwave oven. Why does it not heat up my brain when I use it? Likely it does, but my oven outputs 1.10 kw (kilowatts) while my telephone only a few mw (milliwatts) at maximum, a factor of over a million in difference. Still, I wonder.
Other uses for microwaves are radar (used for lots of things). Interestingly, the folks who developed radar for military use, after the war, started the Amana Company. One of the engineers noticed that the chocolate candy bar in his pocket melted whilst he was working near the main transmitter tube. Remember what I said about fats and sugars getting hotter, faster? The Radarange was the first commercial microwave oven, offered by Amana decades ago.
For communications, microwaves act in a similar manner to radio waves in that they are modulated by impressing a signal onto a carrier and decoding the matrix at the receiver. The bells and whistles are different, but the basic ideas are the same as long as we do not consider the dreaded digital signals. Let us crawl before we try to sprint, however, but we will look at the differences at another time.
There has been speculation about a relationship between the use of cellular telephones and brain cancer. With the discussion before about heating by induction of rotation, it is a valid question. Studies are inconsistent, and I certainly do not have a good answer. I will, however, make these observations without comment.
I have personally known two people who have died of brain cancer, and both of them kept a cell phone on the side of their head for years and years. Then there is the case of Johnnie Cochran, who lived with one. This is speculation, but I strongly suspect that Senator Kennedy used one extensively as well. Does that prove anything? No. It does make me to consider seriously hooking up my old corded telephone for common use. Will I completely quit using the cell or the cordless. No. But common sense says to minimize risk.
Perhaps it is a good idea to keep the telephone on the belt or in the purse and run wires for earbuds and a microphone. I am not saying this on any authority, but I have begun to discourage my boys and Mrs. Translator from talking directly into a cellular telephone. The main difference between home cordless and cellular telephones is that home cordless ones use a much lower power level than cellular ones. For a home cordless, we are talking a couple of hundred feet of range. For cellular, sometimes miles of range to the nearest tower. Remember, all electromagnetic radiation follows an inverse square intensity relationship, to to double the range, you have to quadruple the energy. I will stick around a while for questions, comments, and flames. Warmest regards, Doc.