Strange New Uses of Sound

by HARLAND MANCHESTER

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IN a Chicago laboratory a test tube full of water containing a squirming goldfish was placed for half a minute in a device which produces silent sound waves, pitched far beyond the topmost notes of a violin or piccolo. Restored to his tank, the fish rolled over on his back, stone-dead. The ultrasonic waves, vibrating at the rate of 450,000 times a second, had shattered his blood corpuscles and generally churned up his insides. A research man in Hartford, Connecticut, put some mercury in a tube and added water. Mercury and water don’t readily mix. When bombarded for a few seconds by inaudible sound, they merged in a uniform gray solution. In Russia and in Connecticut, plant seeds stimulated with silent sound have produced sensational yields. And at Columbia University, focused ultrasonic waves have penetrated the skulls of animals to perform experimental knifeless surgery.

Scientists have known for decades that sound waves are far more than a useful vehicle for information and entertainment. All sounds are caused by mechanical vibrations. Few people can hear sounds which vibrate faster than 16,000 times a second, which is about the upper limit of a symphony orchestra, but generators now in use turn out inaudible ultrasound with a vibration rate as high as 12,000,000 a second. Only about 1/750 of this vast keyboard can be detected by the human ear. In this curious region of silent sound strange and wonderful things are happening.

In corporation and university laboratories throughout the world, research men are doing all manner of uncanny tricks with sounds both heard and unheard. Sound has become a tool with great potentialities in science, industry, and medicine. The new tool has already been put to work in a number of practical jobs, and half a dozen firms are rapidly adapting it to an amazing variety of uses. Sound waves of various types will burn your finger, kill bacteria, destroy tissue, homogenize milk, speed chemical reactions, age whiskey, locate submarines, detect flaws in metals, mix paint, precipitate dust particles from smoke, paralyze rabbits, and make you feel as though a mule had kicked you in the belly. These sound vibrations do not create their effects by sheer power; like a dog who shakes a massive bridge by the rhythmic impact of his trot, they get results by repeated small pushes, their timing matched with the special “pushability” of the thing they act upon.

Sound waves travel faster and farther in water than in air. This fact enabled Allied destroyers to locate hundreds of U-boats during the war — a major factor in winning the Battle of the Atlantic. Although the Germans and the Japanese used a similar technique, Admiral Dönitz has stated that his U-boats were “beaten by United States superiority in the field of sound.”

Sonar waves broadcast from a vibrating metal diaphragm attached to the ship’s hull bounced against submarines miles away, and a receiver picked up the echo. The echo was converted into an electric impulse, which flashed a light on a dial to show how far away the submarine was. Some of these sound detectors could not only give the enemy craft’s location, but show whether it was moving, standing still, submerging, or rising to the surface. If the sound is beamed downward, the depth of the water can be measured by timing the echoes from the sea bottom; so sonar is now being used to chart the beds of channels, harbors, and rivers. This is useful both for navigation and for finding spots where fish are likely to abound.

Schools of fish also reflect characteristic echoes, and shrimps go them one better, snapping their claws to broadcast ultrasonic vibrations in the sonar range. During the war this noise was often a nuisance but sometimes was useful as camouflage against Japanese sound detection devices. Now the Submarine Signal Company of Boston has utilized this wartime experience to perfect fishlocating sound equipment, which has been thoroughly tested in boats off the Maine coast. This may supplement or supplant the traditional lookout man aloft, whose watch for surface signs of fish is sometimes complicated by thick weather or dazzling sunlight.

Loud sounds can be transmitted thousands of miles through the ocean, it has been shown by Dr. Maurice Ewing of Columbia University and the Woods Hole Oceanographic Institute. When Dr. Ewing exploded a 4-pound TNt bomb at a 4000foot depth, the sound impulses were picked up 3100 miles away. Since islands and shoals cast “shadows” in the sound beam, he suggested that the method be used for charting unknown waters. By exploding two or more charges at widely separated points, surveyors could determine the exact position of the protuberances by triangulation. If a distressed ship drops a bomb overboard, she can be located within a mile by shore sound-receiving stations.

Silent sound has been used or proposed for many other jobs of detection and communication. Work has been done on a light, portable sound-echo device which would enable the blind to detect obstacles in their path. This is similar to the built-in ultrasonic system which bats use for night navigation. The belief that they find their way about by broadcasting inaudible sound waves and timing the echo has been experimentally confirmed by Dr. Galambos and Dr. Griffin of Harvard.

An “autosonic” garage door opener is manufactured by a Kansas City firm. Press a button on the dash, and a whistle attached to the windshieldwiper hose emits a silent blast. A small microphone on the garage picks up the vibration and starts a motor which opens the door and turns on the light. A captured German document describes a new microphone which disregards sounds from its carrier plane but detects noise coming from another plane. Engineers state that it would be easy to transmit voice or music by silent sound, modulating carrier sound weaves as radio waves are modulated. The late Professor Reginald Fessenden actually carried on underwater conversations by sound waves in Boston Harbor. However trivial some of these tasks may appear in themselves, the important thing is that sound has been harnessed to perform them. Other possibilities are being explored, and ultrasonics may find a valuable role in tomorrow’s communication and detection systems.

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MEANWHILE, sound is doing practical, moneysaving jobs. In many factories, waves vibrating millions of times a second are “looking” through huge metal castings up to ten feet thick and instantly spotting hidden cracks and flaws which cannot be detected otherwise. Damascus swordmakers once tested their blades by tapping them and listening to the “ping,” and Dr. Floyd Firestone of the University of Michigan found that flawless castings bombarded with silent sound gave off a characteristic echo which could be picked up and amplified. A sour note shows the presence of an imperfection. The exact position of the flaw or crack, or any general imperfection of an alloy, is pictured at once on a screen. X-ray machines have been used by industry to examine metal parts, but they take hours, while ultrasonic waves do it in a second. The new detectors, manufactured by Sperry Products, Inc., the General Electric Company, and other firms, are now widely used in checking marine propeller shafts, locomotive axles, and other big parts, and can be mounted on assembly lines to sampletest metal, plastic, and ceramic products.

Similar sound-making devices are being adopted by various industries to work changes in solid, liquid, and gaseous materials. The vibrating steel diaphragm which beams sound waves through the sea has been converted by the Submarine Signal Company into a simple device which homogenizes milk and kills most of the bacteria in it. A dozen or more dairies are using this method. An electromagnet of the type which rings a doorbell attracts and repels the diaphragm, creating sound vibrations equivalent to F above Middle C. As the milk flows over the diaphragm at the rate of 250 gallons an hour, the fat globules are broken into smaller sizes, which remain in suspension instead of rising later to the top of the bottle. The result is a milk which forms into smaller curds in the stomach, and has been recommended by medical authorities as superior for babies. Sound has also been used for the even and permanent mixing of mayonnaise, peanut butter, face cream, ginger ale ingredients, paint, chemicals, and eggs. Sometime we may have a kitchen mixer which will turn out a smoother waffle batter in the key of F.

Ultrasonic laundering of clothes has been suggested by Sir Edward Appleton, secretary of Great Britain’s Department of Scientific and Industrial Research. High-frequency vibrations would shake dirt from fabrics and help to emulsify it in the suds, he says. Thinking along the same lines, a Chicago inventor has applied for a patent on a sonic vacuum cleaner which would force rug fibers into sympathetic vibration, loosening dirt particles.

Sterilization of foods is one of the great goals of the pioneering young group of sound engineers. In laboratory tests, sound waves have reduced the bacteria count of milk to 8 per cubic centimeter, while a count of 30,000 indicates a high standard of purity for pasteurized milk. An Arden, New York, dairyman reports that when his sound-treated milk was first tested by health authorities, they were suspicious because of the unprecedented low bacteria count and came around to see how he did it. This 99.9 per cent result does not satisfy research men, who point out that by definition, sterilization must be complete or it doesn’t exist. The few remaining bacteria can multiply swiftly, and it’s hard to tell just which bacteria have survived. Yet their almost complete destruction will make milk last several days longer.

Should complete sterilization of foods by sound waves become commercially practical, a revolution in food distribution would be in order. Containers of milk could be shipped anywhere and kept for months on the pantry shelf, and fruits and vegetables could be canned or packaged fresh without heat.

There are a number of ways of generating these working sound waves. The most common laboratory method is to pass high-frequency alternating current through a quartz crystal, making the crystal expand and contract hundreds of thousands of times a second, thus creating the ultrasonic vibrations. They can also be produced by running a coil of wire from an alternating-current generator around a metal bar. As the current changes direction, the bar rapidly becomes longer and shorter by perhaps one-millionth of its length. You cannot see the bar move, but if you touch it, it will “burn” you, and the pointed tip of such a bar will drill a hole through glass or wood. Such devices, made by ihe Submarine Signal Company, Crystal Research Laboratories, Inc., of Hartford, Connecticut, and Televiso Products, Inc., of Chicago, will kill bacteria and will kill or paralyze small animals placed in contact with them. They are also useful for treating small quantities of drugs, chemicals, and many other products, but their vibrations are not strong enough to get results when beamed through the air.

A new and more powerful type of sound-maker has been built by the Ultrasonic Corporation of Cambridge, Massachusetts. Its vibrations are felt hundreds of feet from its giant throat. It is a kind of combination siren and meat-chopper: compressed air goes through a pipe and is sliced by whirling turbine blades to create sound vibrations running all the way from the audible range to 200,000 a second. Stand in its range and you feel no air movement, but you may be overcome by a “sense of impending doom,” and you may feel acutely ill. The acoustic power which it throws into the air is equivalent to 30 h.p. Caperton Horsley, a former X-ray manufacturer, invented it, and the young Cambridge firm is rapidly applying it to industrial uses.

In a big Texas plant where carbon black (lampblack) is made, one of these sound-makers is installed in a flue. The sound vibrations create collisions between carbon particles. They roll up like snowballs and fall, instead of being carried out and wasted. The machine is also being installed in chemical plants to keep fumes from poisoning the countryside. It is being tested to hasten the drying of powdered milk, soap, and drugs. The liquid is now sprayed through the top of a tower and dehydrated by hot air as it falls. Sound agitates the falling particles and secures quicker evaporation. This is one of many projects on which this firm is working in coöperation with a dozen manufacturers. Last winter the firm secured a few pints of new, raw bourbon and gave it the silent sound treatment for a few minutes. It tasted like fine, old whiskey, and chemical tests showed that it had been given the equivalent of four years’ normal aging. Aging in liquor is caused by collisions between certain types of molecule, and the agitation caused by ultrasonic waves greatly increases the rate of collision.

The Ultrasonic Corporation is working with the Navy on a project to clear fog above airports by turning it into rain by means of sound waves. Tests have been made with air-raid sirens, but their noise is highly objectionable. In the firm’s Cambridge laboratory the writer saw artificial fog in a glass tank cleared in one second by high-frequency sound. With a similar device mounted on a truck with a big reflector to beam the waves upward, tests were made recently at Areata, California. The rainmaking machine showed promise, but a stiff wind blew in fog faster than the machine could handle it. A still larger sound-maker, designed to deliver an acoustic punch equivalent to 250 h.p., is now being built, and further tests are under way. If fog can be cleared at will several hundred feet above any airport, radar and other aids can take care of the rest of the job, and aviation will achieve the great goal of safe, all-weather landings.

Bombarding a smoke-filled tube with supersound is another laboratory trick. The tiny suspended particles instantly form into flakes and fall to the bottom of the tube. At its Salt Lake laboratories, the Bureau of Mines has been testing this method with a view to using it in abating the city smoke nuisance, and has been waiting for the arrival of larger and more powerful ultrasonic generators. The new Cambridge sound-chopper may be the answer.

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ANOTHER fascinating use of ultrasonic waves grew out of the Crystal Research Laboratories, Inc., at Hartford, the war-baby industry of S. I. Ward. Before Pearl Harbor, Mr. Ward and his wife ran a home decorating shop, advertising heavily on the radio. Wishing to convert to war work, Mr. Ward heard from his radio friends that the armed forces were short of quartz crystals needed to keep radio transmitters on the beam. So he imported crude quartz from Brazil, turned his loft into a factory, and was soon producing the accurately ground radio crystals at the rate of thousands a month. Peace came and he wondered what to do with his crystal factory. He heard that crystals were used in supersound generators, and that hundreds of laboratories wanted the new equipment. So he found himself launched in the silent sound business.

Then Mr. Ward met a man in Washington who told him that some Russian scientists had treated plant seeds with ultrasonic waves and had reported sensational increases in yield. This research team, O. Istomina and E. Ostrovskij, tell in their papers how they treated potato and pea seeds from two to five minutes with sound vibrating 400,000 times a second. The potatoes flowered a week or so earlier than “control” plants, and they obtained an increase in yield of 40 to 50 per cent. Peas sprouted earlier, produced twice as many pods, and in some cases tripled their crop yield.

Mr. Ward showed these reports to Dr. Raymond H. Wallace, an enterprising botanist at the University of Connecticut, and supplied equipment for further experimentation. For two years Dr. Wallace has been planting sound-treated seeds of various plants and recording their yield. A cautious scientist, Dr. Wallace will say only that he has repeated the work of the Russians and has obtained favorable results. He is continuing the work and expects to make a formal report this fall. The possible effects of this development upon the world’s food production are obvious.

No one knows why ultrasound waves should increase plant yield, but Dr. Wallace and other research men have pointed out that apparently, like some drugs, they can either st imulate or destroy, depending on dosage, power, wave length, and the method of treatment.

Medical researchers are doing pioneer work in the use of supersound. In Germany, Pohlman, Richter, and Parow treated fourteen severe cases of sciatica and plexus neuralgia by beaming ultrasonic waves into the affected parts. All but two were benefited, and a number of apparent cures were reported where all other methods of treatment had failed.

The use of ultrasonic waves to perform knifeless surgery has been explored by Dr. John G. Lynn and Dr. Tracy J. Putnam at the Department of Neurology, Columbia University, and a similar project is under way at the Institute of Living at Hartford, Connecticut. Dr. Lynn and Dr. Putnam performed brain operations of various sorts, without opening the skull, on thirty-seven cats, dogs, and monkeys. Waves far up in the ultrasonic scale, with a vibration rate of 800,000 per second, were reflected by a curved crystal, which focused them to a sharp point, as a burning glass bunches the rays of the sun. By this method, the scientists found that they could stimulate temporarily, or destroy, a selected bit of brain tissue. Waves focused briefly on a dog’s motor area caused him to kick, and treatment of a cat’s visual area made him extremely sensitive to light hours later. So many expensive crystals were broken in this work that Dr. Lynn is continuing the project with a different type of apparatus, which focuses a single shock wave on the part of the brain he wishes to treat.

This work is still in its early experimental stage, but it suggests interesting possibilities of knifeless surgery on the human brain. Prefrontal lobotomy, a drastic operation in which the frontal lobes are cut off from the rest of the brain, has been used as a last resort to relieve some 2000 incurable mental patients in the United States. With further refinement of the new technique, such an operation might eventually be performed in a few seconds by sound or shock waves. Dr. Lynn also suggests the possibility of treating delusions and hallucinations by discovering and depressing the brain areas where they originate. Already much is known about the geography of our central brain switchboard. In the course of brain operations performed under local anesthesia, surgeons have been able, by touching certain areas, to produce in conscious patients illusions of loud noises, flashes of light, or formed apparitions. Perhaps sometime in the future, ogres of the mind wall be exorcised by silent sound.

Other scientists have been attempting to use sound as a weapon capable of killing or disabling men. Colonel Leslie E. Simon of the Aberdeen Proving Grounds found such a weapon in a small experiment station near Lofer, Germany, where sonic guns of various types had been built during the war by Dr. Richard Wallauschek. In the latest and best design, sound in the audible range was generated by the rhythmic explosion of gas in a siren-like metal tube, and the waves were focused on the target by a big, parabolic reflector. The operator wore a soundproof helmet. No battle tests had been conducted, but it was estimated that at 60 meters the bunched waves would kill a man in 30 to 40 seconds, and that at 300 meters the effect would be very painful and would probably disable a man for some time. Vision would be affected, and points of light would look like lines. Colonel Simon sees no great future in this gun as a military weapon, but believes that the idea is worth further investigation. Meanwhile, Daniel von Jenef, president of Televiso Products, Inc., of Chicago, has been testing an ultrasonic pistol in which a blast of compressed gas goes through a whistle opening and silent sound waves are beamed through the barrel at the target. The inventor reports that he has killed and disabled small animals.

One of the great goals of post-war military aviation is the production of airplanes which will travel faster than the speed of sound. Designers are confident that such planes can be built, but no one knows what effect the ultrasonic vibrations will have on the pilot. It is reported in England that high-frequency vibrations from turbo-jet motors have made factory workers dizzy and weak. Sonic generators now in use at the Aero Medical Center at Wright Field may supply the answer. Tests are being made on animals and people to determine their physical and mental reactions to supersound waves of various frequencies. Then newly designed planes will be tested to show whether they broadcast the same sound weaves. By this method the Army may discover what a pilot is up against at speeds of 600 m.p.h. or better.

Many other experiments are under way. The young science of ultrasonics is now in that exciting stage when its exponents are bursting with ideas and are eagerly exploring every new possibility. In widely separated laboratories, detached groups and individuals are testing its potentialities. The literature of the subject is meager and dated, and there is little exchange of current information. As a result many ambitious experimenters are hampered. They have far to go, for they have only penetrated the frontier of the new domain. The unknown land beyond them is an alluring challenge to the scientists and technologists of tomorrow.