Microwaves—How Do They Work?
YOU cannot see it or smell it or touch it, but it is all around you. Some environmentalists call it “electronic smog,” and one United States government agency warned that the levels Americans are exposed to every day without even being aware of it may be dangerous. It is not a local problem.
According to a U.S. government report, man may be entering “an era of energy pollution of the environment comparable to the chemical pollution of today.” It warns that the “consequences of undervaluing or misjudging the biological effects of long-term, low-level exposure could become a critical problem for the public health, especially if genetic effects are involved.”
What they are warning about is microwave radiation. But what are microwaves? How do they work? What can they do to you? How dangerous are they?
What They Are
Microwaves are a form of electromagnetic energy, or radiation. In frequency (rate of vibration) and wavelength, microwaves fall in the electromagnetic spectrum between infrared rays and radio waves.
There are two kinds of electromagnetic radiation: ionizing and nonionizing. Ionizing radiation includes, at one end of the spectrum, X rays and gamma rays. Nonionizing radiation, which makes up the rest of the spectrum, includes ultraviolet light, visible light, infrared rays and radio waves. (And it is between the latter two that we find “microwaves.”) The terms ionizing and nonionizing denote an important difference.
Ionizing radiation is capable of dislodging electrons from atoms, creating electrically charged, highly unstable, and chemically reactive atoms called ions. In other words, ionizing radiation invariably damages cells of living tissue and can cause genetic mutations. Any exposure to this kind of radiation, however slight, involves some degree of risk.
Microwaves, on the other hand, are nonionizing energy. They are much less powerful in effect and do not have sufficient energy to dislodge electrons from atoms, which is why man has felt relatively free to utilize this form of energy for its beneficial advantages.
What They Are Used For
About 50 years ago there were no man-generated microwaves. Only small amounts of microwave radiation from the sun and other sources in earth’s galaxy found their way into our atmosphere. But then, prior to World War II, radar was developed. Thus microwaves first came to public notice, since radar uses microwaves. In recent years, man’s ability to generate and harness microwaves has resulted in such a proliferation of devices using microwaves that today virtually everyone on the earth is affected by them to some degree.
Particularly in some urban areas, microwave radiation and related high-frequency radio-wave radiation is estimated to be up to a billion times or more as great as that which naturally exists in the environment. And sources of this kind of radiation are increasing rapidly in many places.
Almost all airports now have radar navigational systems, which use microwaves. Also, police radar operates on microwave frequencies. But in addition to radar, ultrahigh-frequency television signals are also transmitted by microwaves. Long-distance phone calls can go from city to city as microwave radiation. Microwave ovens are increasingly popular. Computers in one city are able to transmit data to computers in another city via microwaves. Broadcasting, surveillance, and communications satellite systems utilize microwaves, as do some air-pollution-monitoring systems. Motorist-aid call boxes along highways work because of microwaves. Many burglar-alarm systems use them, as do some automatic garage-door openers.
The military, by far the largest users of microwave devices in today’s world of electronic warfare, employ microwaves for such things as tracking and scanning radar, guidance systems for nuclear missiles and antimissile missiles, range finders for tanks, and for eavesdropping.
The medical world has its own uses for microwaves: for sterilization, for experimental use in cancer treatment, to retard tumor growth, and in diathermy machines, which heat body tissues for treatment of such ailments as bursitis, arthritis, and muscle aches and sprains. An estimated two million people in the U.S. alone are treated with these machines annually.
Industry uses microwaves to dry potato chips, to roast nuts, beans and coffee, to raise bread and doughnuts, and to precook bacon. They are also used to dry yarn, wood, paints, paper, leather, tobacco, pencils, textiles, match heads, and to cure rubber, nylon, urethane, and rayon. Many companies, such as banks, newspapers, and airlines, now use cathode-ray-tube video display units, called VDT’s, which employ microwaves.
Projected uses of microwaves include a vast outer-space satellite power station to collect solar energy, convert it to microwaves, and beam them to the earth. Here on earth the microwaves would be converted into electricity. Another projected use is in a radar braking system for cars, which could beam microwave radiation ahead of a vehicle, sense an imminent collision, and activate brakes automatically.
Truly microwaves have a tremendous impact on our lives, and yet very few of us really know how they do what they do.
How Do Microwaves Work?
Since microwaves are basically just energy, their uses are varied. With radar, for example, microwaves are focused into highly directional beams and aimed at a target in short bursts or pulses. Microwaves are reflected by electrical conductors such as metal, so the microwaves beamed at the target, say, an airplane, are bounced back to the sender. The time lapse between the sending of the signal and its return makes it possible to measure the distance to the target, remembering that microwaves travel at the speed of light. Comparison of the time lag at two different heights makes it possible to calculate the altitude of the target.
The reason the energy can be used in microwave ovens to cook food is simple: though metals reflect microwaves, foods absorb them. So a metal box, the oven, reflects the beams of microwaves, which bounce around inside the oven until they hit the food. Then they are absorbed into the food and cause the moisture molecules of the food to vibrate rapidly, at two and a half billion times a second. This friction results in heat, and this heat does the cooking. In effect, the food produces its own heat.
In a microwave oven very little of the energy goes to waste heating the oven or the air within it, as happens in conventional cooking. Also, very little goes to waste heating the cooking containers because in microwave cooking you use glass, paper, or plastic, all of which simply allow microwaves to pass through them, neither absorbing nor reflecting them. So when a small amount of food receives the full brunt of the microwaves’ power, it cooks very quickly.
For example, in a conventional oven, a baked potato might require from 45 to 60 minutes to cook. In a microwave oven, one potato might be cooked in approximately 2 1/2 to 6 minutes, depending on the size of the potato and the make and model of the oven. If two potatoes are cooked, it may increase the cooking time to 5 to 12 minutes. The increase in cooking time is due to the microwave energy being divided two ways instead of the full amount being absorbed by one potato. This marked speedup of cooking times when using microwave ovens represents their principal appeal.
There are many millions of these ovens in use in the United States. In 1975, for the first time, sales of microwave ovens exceeded the number of gas ovens sold. It is predicted that one half of all homes in the U.S. will be cooking with microwaves by 1985. In Japan, their popularity is even greater; 17 percent of all homes there did their cooking by microwaves as reported for the year 1976, compared with 4 percent of the homes in the U.S. the same year.
Microwave ovens were first marketed to the general public in the U.S. in 1967, with only 10,000 ovens sold that first year. But sales have skyrocketed phenomenally since then. It is a growth, some say, that has burst on the scene without a complete understanding of the effects microwaves can have on the human system.
Because of this growing concern, in the mid-1970’s the U.S. began extensive research studies into the potential risks involved in exposure to low-level microwave radiation and the validity of current Western safety standards. The results of some of this research are beginning to become available, and some scientists have begun expressing serious concern. Why? What are they discovering? These are questions we will examine in a future issue of Awake!
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Airports now have navigational systems that use microwaves