New Wave

They convey television signals through the skies and carry the voices of orbiting astronauts back to control stations on earth. They link long-distance telephone systems and bounce off high-flying aircraft, locating them for radar observers. The high-frequency radio waves--or microwaves--that perform these familiar services are now becoming even more versatile.

To keep abreast of the new wave, 215 scientists met at Stanford University last month to consider the current and future capability of microwave technology and its applications.

.HEATING. When microwaves are focused into a narrow beam and directed at substances such as water, organic solvents and salt solutions, they cause them to heat almost instantaneously. Because the molecules of these substances are polarized--containing an uneven distribution of positive and negative charges--they align themselves with the direction of an electric field. Microwave fields reverse themselves rapidly; to keep up with them, the polarized molecules must oscillate constantly. This oscillation produces a rise in temperature. In a microwave oven, for example, the electric field completely permeates a potato, instantly heating the moisture in its center as well as in its skin: it is evenly baked within five minutes. Microwaves have already been put to work precooking chicken before freezing, drying freshly painted surfaces and dehydrating lumber, paper and potato chips.

.KILLING GERMS. The ability to heat also gives microwaves the power to kill microorganisms. Litton Industries Biologist Carl M. Olsen has found that wrapped bread exposed to microwaves just before leaving the bakery remains free of mold for ten days, twice as long as bread treated only with a chemical preservative. Microwaves have also been used to pasteurize milk, beer and wine. Scientists have proposed a mobile microwave source that could be slowly moved across a farm field, generating enough energy to destroy harmful microorganisms before planting.

.TRANSMITTING POWER. Because of the difficulty often involved in stringing power lines through mountains and backwoods areas, other methods of transmitting power have long been sought. Microwaves, which generate a current when they strike an electrical conductor like copper, may provide an answer. Instead of being fed into power lines, electricity produced at a power station could be used to generate microwaves that would be beamed at a moun tain-top radar station or observatory where they would be converted back into electrical energy.

Looking even further into the future, scientists at the Stanford meeting suggested the use of microwaves in mining and even in the launching of space vehicles. In microwave mining, capsules containing water would be inserted into holes drilled in the rock. A powerful microwave beam would then be aimed at the capsule, almost instantly converting the water into steam that would burst the capsule and blast the rock. Powerful microwave beams could also be used to power the first stage of a rocket during launch and at relatively low altitudes, reducing the amount of fuel required for the mission.

A Rensselaer Polytechnic Institute group is investigating the practicality of a subway that would be suspended by compressed air in a cylindrical tube and whip along at 350 m.p.h., driven by a microwave-powered propeller. The microwaves would be generated at stations along the length of the route and transmitted efficiently within the subway tube, which would act as a giant wave guide. And some day, fixed-station helicopters, miles in the air, might be used to beam microwaves hundreds of miles in a straight line to other fixed-station helicopters--instead of from hilltop to nearby hilltop, as is now done. How would such a helicopter fly? By means of an electric engine powered by a microwave beam located directly below on the ground.

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