The 21st Century - the Century of Radioelectronics, Atom, Conquestspace and ultrasound. Relatively young in our days the science of ultrasound. At the end of the 19th century, P. N. Lebedev, a Russian physiologist, conducted his first studies. After that, many outstanding scientists began to study ultrasound.
Ultrasound is propagating in wavesoscillatory motion that particles of the medium make. It has its own characteristics, which is different from the sounds of the audible range. It is relatively easy to get directional radiation in the ultrasonic range. In addition, it is well focused, and as a result, the intensity of the vibrations is increased. When propagating in solids, liquids and gases, ultrasound gives rise to interesting phenomena that have found practical application in many areas of engineering and science. This is what ultrasound is, whose role in various areas of life today is very large.
Ultrasound in recent years began to play scientificresearch is an increasing role. Experimental and theoretical studies were successfully carried out in the field of acoustic flows and ultrasonic cavitation, which allowed scientists to develop technological processes that occur when exposed to ultrasound in the liquid phase. It is a powerful method for studying various phenomena in such a field of knowledge as physics. Ultrasound is used, for example, in semiconductor and solid state physics. Today, a separate field of chemistry is being formed, called "ultrasonic chemistry". Its use allows you to speed up many chemical-technological processes. Molecular acoustics was also born - a new section of acoustics that studies molecular interaction with sound wave matter. New fields of application of ultrasound have appeared: holography, introscopy, acoustoelectronics, ultrasonic phasomery, quantum acoustics.
In addition to experimental and theoretical work inIn this area, many practical exercises have been performed today. Special and universal ultrasonic machines, installations that operate under increased static pressure, etc., have been developed. Ultrasonic automatic installations have been introduced into production that are included in production lines, which can significantly increase labor productivity.
We will tell you more about what ultrasound is.We have already said that these are elastic waves and vibrations. The frequency of ultrasound is more than 15-20 kHz. The subjective properties of our hearing is determined by the lower limit of ultrasonic frequencies, which separates it from the frequency of audible sound. This boundary, therefore, is conditional, and each of us differently defines what ultrasound is. The upper boundary is indicated by elastic waves, their physical nature. They are distributed only in the material medium, that is, the wavelength must be substantially larger than the mean free path of the molecules present in the gas or the interatomic distances in solids and liquids. With normal pressure in gases, the upper limit of the frequencies of ultrasonic - 109 Hz, and solids and liquids - 1012-1013 Hz
Ultrasound in nature and as a componentsets of natural noises (waterfall, wind, rain, pebbles, rolled by the surf, as well as sounds accompanying thunder discharges, etc.), and as an integral part of the animal world. Some species of animals use it for orientation in space, detection of obstacles. It is known, moreover, that ultrasound in nature is used by dolphins (mostly frequencies from 80 to 100 kHz). At the same time, the power of the radar signals emitted by them may be very large. It is known that dolphins are able to detect shoals of fish that are up to a kilometer away.
Emitters (sources) of ultrasound are divided by 2large groups. The first is the generators, in which the oscillations are excited due to the presence of obstacles in them, which are set in the path of a constant flow - a jet of liquid or gas. The second group, into which it is possible to combine ultrasound sources, is electroacoustic transducers, which transform given current or electrical voltage fluctuations into mechanical oscillations performed by a solid, emitting acoustic waves into the environment.
Medium and low frequencies receiversultrasound are most often of the piezoelectric type electroacoustic transducers. They can reproduce the form of the received acoustic signal, represented as a time dependence of the sound pressure. Devices can be either broadband or resonant - depending on what conditions of use they are intended for. Thermal receivers are used to obtain time-averaged sound field characteristics. They are thermistors or thermocouples coated with sound absorbing material. Sound pressure and intensity can also be estimated by optical methods such as diffraction of light by ultrasound.
There are many areas of its application, withIt uses various features of ultrasound. These spheres can be divided conditionally into three directions. The first of these is associated with the receipt by means of ultrasonic waves of various information. The second direction is its active influence on the substance. And the third is related to the transmission and processing of signals. Ultrasound of a certain frequency range is used in each case. We will describe only some of the many areas in which it has found its application.
Качество такой очистки нельзя сравнить с другими in ways. When rinsing parts, for example, up to 80% of contaminants remain on the surface, about 55% - with vibration cleaning, about 20% - with manual cleaning, and no more than 0.5% of contaminants remain with ultrasonic cleaning. Parts that have a complex shape can only be cleaned well with ultrasound. An important advantage of its use is high productivity, as well as low costs of physical labor. Moreover, it is possible to replace expensive and flammable organic solvents with cheap and safe aqueous solutions, use liquid freon, etc.
A serious problem is air pollution with soot,smoke, dust, metal oxides, etc. You can use the ultrasonic method of cleaning air and gas in the gas outlet, regardless of the humidity of the environment and temperature. If the ultrasound emitter is placed in a dust collector chamber, its effectiveness will increase by a hundred times. What is the essence of such a cleaning? Specks of randomly moving dust in the air hit harder and more often under the action of ultrasonic vibrations. At the same time their size increases due to the fact that they merge. Coagulation is the process of enlarging particles. Special filters capture their weighted and enlarged clusters.
If you enter between the workpiece andworking surface of the instrument that uses ultrasound, abrasive material, the particles of the abrasive when the emitter works will affect the surface of this part. In this case, the material is destroyed and removed, being subjected to processing under the action of a multitude of directed micro-blows. The kinematics of processing consists of the main movement - cutting, that is, the longitudinal oscillations performed by the tool, and the auxiliary - feed movement, which the apparatus performs.
Ultrasound can do various jobs.For abrasive grains, the energy source is longitudinal vibrations. They destroy the processed material. The feed movement (auxiliary) can be circular, transverse and longitudinal. Ultrasound processing is more accurate. Depending on what kind of grit has an abrasive, it ranges from 50 to 1 micron. Using tools of various shapes, it is possible to make not only holes, but also complex cuts, curved axes, to engrave, grind, fabricate dies, and even drill a diamond. Used as an abrasive materials - corundum, diamond, quartz sand, flint.
Ultrasound technology is often used in the field ofradio electronics. In this area it is often necessary to delay the electrical signal relative to some other. Scientists have found a good solution by proposing the use of ultrasonic delay lines (abbreviated as LZ). Their action is based on the fact that electrical impulses are converted into ultrasonic mechanical vibrations. How does this happen? The fact is that the speed of ultrasound is significantly less than that developed by electromagnetic oscillations. The voltage pulse after reverse conversion into electrical mechanical oscillations will be delayed at the line output relative to the input pulse.
Piezoelectric and MagnetostrictiveConverters are used to convert electrical oscillations into mechanical and vice versa. LZ, respectively, are divided into piezoelectric and magnetostriction.
Различные виды ультразвука применяются для effects on living organisms. In medical practice, its use is now very popular. It is based on the effects that occur in biological tissues when ultrasound passes through them. Waves cause fluctuations of the particles of the medium, which creates a kind of micromassage of tissues. And the absorption of ultrasound leads to their local heating. At the same time, certain physical and chemical transformations occur in biological media. In the case of moderate intensity of sound, these phenomena do not cause irreversible damage. They only improve the metabolism, and hence contribute to the vital activity of the organism subject to it. Such phenomena are used in ultrasound therapy.
Кавитация и сильное нагревание при больших intensities lead to the destruction of tissues. This effect is used today in surgery. Focal ultrasound is used for surgical operations, which allows for local destruction in the deepest structures (for example, the brain), without damaging the surrounding. In surgery, ultrasound instruments are also used, in which the working end has the form of a file, scalpel, needle. The fluctuations imposed on them give new qualities to these instruments. The required effort is significantly reduced, therefore, the injury of the operation decreases. In addition, the analgesic and hemostatic effect. Exposure to blunt instrument with the use of ultrasound is used to destroy the appearance of certain types of tumors in the body.
The impact on biological tissues is carried out to destroy microorganisms and is used in the sterilization of medicines and medical instruments.
This is mainly a study of abdominalcavities. For this purpose a special apparatus is used. Ultrasound can be used to locate and recognize various tissue anomalies and anatomical structures. The task is often as follows: there is a suspicion of the presence of a malignant formation and it is required to distinguish it from the formation of a benign or infectious.
Ultrasound is useful in examining the liver and forsolving other problems, which include the detection of obstruction and diseases of the bile ducts, as well as the study of the gallbladder to detect the presence of stones and other pathologies in it. In addition, the study of cirrhosis and other diffuse benign liver diseases can be applied.
In the field of gynecology, mainlyanalysis of the ovaries and uterus, the use of ultrasound is for a long time, the main direction in which it is carried out particularly successfully. Often, differentiation of benign and malignant tumors is also needed here, which usually requires the best contrast and spatial resolution. Such conclusions may be useful in the study of many other internal organs.
Ultrasound also found its use indentistry, where it is used to remove tartar. It allows you to quickly remove blood and stone plaque without pain. At the same time, the oral mucosa is not injured, and the "pockets" of the cavity are decontaminated. Instead of pain, the patient experiences a sensation of warmth.
