Underwater t. V. Camera
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In recent years underwater television has been introduced as an aid in the study of the ocean and underwater work. Apart from a few special features an underwater camera is based on the principles of ordinary T. V. cameras.
At present there are several types of underwater cameras to be operated chiefly at depths from 650 to 1,000 feet.
Connected to the viewing screen by a long flexible cable, the camera can be easily lowered by a crane and moved about. The cable connects the camera to its control equipment. A special intercommunication system is used for the diver to keep in touch with the control personnel.
The T. V. camera can be used for underwater exploration of marine life, television broadcasting as well as for inspection of canals, dams, turbine blades, and ships.
A tape recording may be made of the television picture for a permanent record. This makes possible underwater photography without film.
TEXT 8 C
Wave motion and sound
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Wave Motion. - One of the most important phenomena in nature is the transmission of energy from one point to another by wave motion. This kind of motion is illustrated in many ways. When a stone is dropped into a pool of still water, the surface of the water is covered with circular wavelets which widen out from the central point where the stone fell. The water does not really move outward from the central point, but it rises and then falls again. That such is the case is seen by observing a floating leaf or piece of wood. It does not move forward but returns again and again to its former position. Hence, the water on which the leaf rests must have this same kind of upward and downward motion rather than a forward motion.
When one end of a rope is fastened to a rigid wall the free end moves up and down rapidly, each jerk travels along the rope, each portion of the rope communicating the jerk to the next portion. Each particle of the rope imparts its upward or downward motion to its neighbors. The jerk moves forward, but the particles of the rope move only up and down. Motions of this kind are wave motions, in all these cases it is evident that there is a vibrating center which produces motions in those portions of the medium immediately in contact with it, and that these portions impart their motions to the neighboring portions.
Nature of Sound. - The source of sound is always in a state of vibration. As the vibration dies down, the intensity of the sound diminishes. If a ringing bell is touched with the fingers, the sound ceases because the vibrations are stopped by the fingers. When a weight falls to the floor, the weight as well as that part of the floor which is struck are set in vibration, and sound waves are produced. If a stretched guitar string is plucked, it gives a musical note owing to the vibrations set up in it. These vibrations take place too fast for the eye to follow them, and the string seems to be drawn out into a ribbon in the middle. In a vibrating tuning fork the prongs alternately approach and recede from each other. These movements of the prongs can be felt by touching the prongs with the fingers. They produce compressions and rarefactions in the surrounding air that travel forward as sound waves.
Velocity of Sound. - The velocity of sound depends on the density and the elasticity of the medium. The greater the elasticity and the less the density, the greater is the velocity. The relation between the velocity, the density, and the elasticity of the medium is expressed by the formula
Where v = the velocity of sound
e = the modulus of elasticity of the medium
p = the density of the medium
The Intensity of Sound. - When sound waves spread out in every direction from a source of sound, the intensity varies inversely as the square of the distance from the source. In this case, the sound waves spread out as spheres. The same amount of energy is transmitted across every spherical surface having its center at the source of sound. The larger the surface of these spheres, the smaller the energy that goes through each square centimeter of surface. The surfaces of these spheres increase as the squares of their radii. Hence, the energy that passes through unit area decreases as the squares of the radii increase.
TEXT 8
SONIC TECHNIQUES FOR INDUSTRY
It is apparent that a new area of technology based on the use of sound waves, is taking shape Tho, term "somci» 'was given to this new technology which incuiaes Tthe analysis, testing, and proofing of materials and products by the^uie of mechanical vibrating energy. All applications of sonics are based on the Stint *physical principles, the particular freque'hdy Thai is best suilea foeimf determined by the special requirements and limitations of the task.
We shall see that the phenomenon of acoustic vibration can,be utilized in many ways With sound waves we can "sonograph"(as with light waves we photograph) the inner structure of bodies that are opaque to light. Sound waves can penetrate many solids and liquids more readily than X-rays or other forms of electromagnetic energy. Thus sound can expose a tiny crack embedded many feet deep in metal, where detection by any other means might be impossible. Similarly ultrasonic pulse techniques are now being used in medicine for the early diagnosis of different diseases.
By acoustic techniques we can measure the elastic constants of solid materials, as well as analyse the residual stresses or structural changes. The molecular arrangements within many organic liquids can be found from measurements of sound velocity or absorption. The rates of energy transfer among gas molecules and the chemical affinity of gaseous mixtures can be determined by using sound waves.
As soon as we can measure a process, we have within reach a means of controlling it Indeed acoustic instrumentation offers extensive but practically unexplored opportunities in the automatic control of industrial processes. The geometry of metal parts, the quality of cast metals and laminated plastics, the temperature in the combustion chamber of gasoline engines, the composition of compounds in liquid or gas, the flow velocity of liquids and gases - these and many other processes may, in time, come under the watchful ear of acoustics.
In the above-mentioned applications, the sound is used as a measuring stick or flashlight - the amounts of power are small and incidental. In another class of applications, large amounts of acoustic power are employed to do useful work. Vibrational energy for example is already used to drill rock and to machine complicated profiles in one single operation. Sound has become a powerful method for the cleaning of precision parts and may find important applications in electrochemistry. Acting on fumes, dusts and smokes, sound can speed up the collection of particles.
Here are some of the technical fields in which the sonic and ultrasonic engineering may find wide application: oil-well drilling, liquid processing, machining, engraving and welding, underwater signalling, cleaning of metal parts, information storage, molecular analysis and some others. The frequency range covered by these applications is extremely wide and their realization therefore involves widely different acoustic engineering practices.
Most of the applications listed have today reached the stage of successful operations, that is, the usefulness to industry of these techniques and instruments has been widely recognized, the development of reliable equipment is more or less completed, and the manufacture and maintenance of the equipment have proved to be economical.
We now come to the other application of sonics - namely, the processing of materials. It has been found that intense vibrations affect colloidal distribution, equalize electrolytic concentrations, and speed up aging processes by absorption in a certain medium, intense vibrations may produce local heating effects, as for example, in the use of ultrasonics in medical therapy.
A particularly powerful phenomenon is cavitation. This is the breakdown of cohesion of a liquid that is exposed to high tensile forces as the sound wave passes through it.
Under the influence of cavitations steel surfaces may be pitted, oxide layers removed, bacteria disintegrated, or high polymers depolymerized. One of the particular successful applications of surface cavitation is in ultrasonic drilling, another is in the soldering of aluminium.
Progress during recent years has been encouraging and still more valuable contributions of sonics to industry may well be expected.