The 21st century is the century of radio electronics, the atom, space exploration and ultrasound. The science of ultrasound is relatively young today. At the end of the 19th century, P. N. Lebedev, a Russian physiologist, conducted his first studies. After that, many eminent scientists began to study ultrasound.
What is ultrasound?
Ultrasound is a propagating undulating oscillatory motion that the particles of the medium make. It has its own characteristics, in which it differs from the sounds of the audible range. It is relatively easy to obtain directed radiation in the ultrasonic range. In addition, it focuses well, and as a result of this, the intensity of the oscillations made increases. When propagating in solids, liquids and gases, ultrasound gives rise to interesting phenomena that have found practical application in many areas of technology and science. This is what ultrasound is, the role of which in various spheres of life today is very large.
The role of ultrasound in science and practice
Ultrasound in recent years began to play in scientific researchan increasingly important role. Experimental and theoretical studies in the field of acoustic flows and ultrasonic cavitation were successfully carried out, 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 branch of chemistry is being formed, called "ultrasonic chemistry". Its application allows accelerating many chemical-technological processes. Molecular acoustics was also born - a new branch of acoustics that studies the molecular interaction of sound waves with matter. New areas of application of ultrasound have appeared: holography, introscopy, acoustoelectronics, ultrasonic phase measurement, quantum acoustics.
In addition to experimental and theoretical work in this area, a lot of practical work has been done today. Special and universal ultrasonic machines, installations that operate under increased static pressure, etc. have been developed. Automatic ultrasonic installations included in production lines have been introduced into production, which can significantly increase labor productivity.
More about ultrasound
Let's talk more about what ultrasound is. We have already said that these are elastic waves and oscillations. The frequency of ultrasound is more than 15-20 kHz. The subjective properties of our hearing determine the lower limit of ultrasonic frequencies, whichseparates it from the frequency of the audible sound. This boundary, therefore, is conditional, and each of us differently defines what ultrasound is. The upper limit is indicated by elastic waves, their physical nature. They propagate only in a material medium, that is, the wavelength must be significantly greater than the mean free path of the molecules present in the gas or the interatomic distances in solids and liquids. At normal pressure in gases, the upper limit of ultrasonic frequencies is 109 Hz, and in solids and liquids - 1012-1013Hz.
Ultrasonic sources
Ultrasound is found in nature both as a component of many natural noises (waterfall, wind, rain, pebbles rolled by the surf, as well as in the sounds accompanying thunderstorms, 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 also known that dolphins use ultrasound in nature (mainly frequencies from 80 to 100 kHz). In this case, the power of the location signals emitted by them can be very large. Dolphins are known to be able to detect schools of fish up to a kilometer away.
Emitters (sources) of ultrasound are divided into 2 large groups. The first is generators, in which oscillations are excited due to the presence of obstacles in them installed in the path of a constant flow - a jet of liquid or gas. The second group into which ultrasound sources can be combined iselectro-acoustic transducers that convert given fluctuations in current or electrical voltage into a mechanical vibration made by a solid body that radiates acoustic waves into the environment.
Ultrasound receivers
At medium and low frequencies, ultrasonic receivers are most often piezoelectric type electro-acoustic 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 the application conditions they are intended for. Thermal receivers are used to obtain time-averaged sound field characteristics. They are thermistors or thermocouples coated with a sound-absorbing substance. Sound pressure and intensity can also be estimated by optical methods, such as the diffraction of light by ultrasound.
Where is ultrasound used?
There are many areas of its application, while using different features of ultrasound. These areas can be roughly divided into three areas. The first of them is connected with obtaining various information by means of ultrasonic waves. The second direction is its active influence on the substance. And the third is connected with the transmission and processing of signals. US of a certain frequency range is used in each case. We will cover only a few of the many areas in which it has found its way.
Ultrasonic cleaning
The quality of this cleaning cannot be compared with other methods. When rinsing parts, for example, up to 80% of contaminants remain on their surface, about 55% - with vibration cleaning, about 20% - with manual cleaning, and with ultrasonic cleaning, no more than 0.5% of contaminants remain. Details that have a complex shape can be cleaned well only with the help of ultrasound. An important advantage of its use is high productivity, as well as low costs of physical labor. Moreover, you can 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 gas outlets, regardless of ambient humidity and temperature. If an ultrasonic emitter is placed in a dust settling chamber, its efficiency will increase hundreds of times. What is the essence of such purification? Dust particles moving randomly in the air hit each other stronger and more often under the influence of ultrasonic vibrations. At the same time, their size increases due to the fact that they merge. Coagulation is the process of particle enlargement. Special filters catch their weighted and enlarged clusters.
Machining brittle and super hard materials
If you enter between the workpiece and the working surface of the tool using ultrasound, abrasive material, then the abrasive particles during operationemitter will affect the surface of this part. In this case, the material is destroyed and removed, subjected to processing under the action of a plurality of directed micro-shocks. The kinematics of processing consists of the main movement - cutting, that is, the longitudinal vibrations made by the tool, and the auxiliary - the feed movement that the machine performs.
Ultrasound can do various jobs. For abrasive grains, the source of energy is longitudinal vibrations. They destroy the processed material. The feed movement (auxiliary) can be circular, transverse and longitudinal. Ultrasonic processing is more precise. Depending on the grain size of the abrasive, it ranges from 50 to 1 micron. Using tools of various shapes, you can make not only holes, but also complex cuts, curved axes, engrave, grind, make matrices and even drill a diamond. Materials used as an abrasive - corundum, diamond, quartz sand, flint.
Ultrasound in radio electronics
Ultrasound in technology is often used in the field of radio electronics. In this area, it often becomes necessary to delay an electrical signal relative to some other one. Scientists have found a good solution by suggesting the use of ultrasonic delay lines (LZ for short). Their action is based on the fact that electrical impulses are converted into ultrasonic mechanical vibrations. How does it happen? The fact is that the speed of ultrasound is significantly less than that developed by electromagnetic oscillations. Pulsevoltage after the reverse transformation into electrical mechanical vibrations will be delayed at the output of the line relative to the input pulse.
Piezoelectric and magnetostrictive transducers are used to convert electrical vibrations into mechanical and vice versa. LZ, respectively, are divided into piezoelectric and magnetostrictive.
Ultrasound in medicine
Different types of ultrasound are used to influence 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. The waves cause fluctuations in the particles of the medium, which creates a kind of tissue micromassage. And the absorption of ultrasound leads to their local heating. At the same time, certain physicochemical transformations occur in biological media. These phenomena do not cause irreversible damage in the case of moderate sound intensity. They only improve the metabolism, and therefore contribute to the vital activity of the body exposed to them. Such phenomena are used in ultrasound therapy.
Ultrasound in surgery
Cavitation and strong heating at high intensities lead to tissue destruction. This effect is used today in surgery. Focused ultrasound is used for surgical operations, which allows local destruction in the deepest structures (for example, the brain), without damaging the surrounding ones. Ultrasound is also used in surgerytools in which the working end looks like a file, scalpel, needle. The vibrations imposed on them give new qualities to these devices. The required force is significantly reduced, therefore, the traumatism of the operation is reduced. In addition, an analgesic and hemostatic effect is manifested. Impact with a blunt instrument using ultrasound is used to destroy certain types of neoplasms that have appeared in the body.
Impact on biological tissues is carried out to destroy microorganisms and is used in the processes of sterilization of medicines and medical instruments.
Research of internal organs
Mainly we are talking about the study of the abdominal cavity. For this purpose, a special apparatus is used. Ultrasound can be used to find and recognize various tissue and anatomical anomalies. The challenge is often as follows: a malignancy is suspected and needs to be distinguished from a benign or infectious lesion.
Ultrasound is useful in examining the liver and for other tasks, which include the detection of obstructions and diseases of the bile ducts, as well as the examination of the gallbladder to detect the presence of stones and other pathologies in it. In addition, testing for cirrhosis and other diffuse benign liver diseases may be used.
In the field of gynecology, mainly in the analysis of the ovaries and uterus, the use of ultrasound is a long timethe main direction in which it is carried out especially successfully. Often, differentiation of benign and malignant formations is also needed here, which usually requires the best contrast and spatial resolution. Similar conclusions can be useful in the study of many other internal organs.
The use of ultrasound in dentistry
Ultrasound has also found its way into dentistry, where it is used to remove tartar. It allows you to quickly, bloodlessly and painlessly remove plaque and stone. In this case, the oral mucosa is not injured, and the "pockets" of the cavity are disinfected. Instead of pain, the patient experiences a sensation of warmth.
