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The twenty-first century is the century of the atom, the conquest of space, radio electronics and ultrasound. The science of ultrasound is relatively young. The first laboratory works on the study of ultrasound were carried out by a Russian scientist - P.N. Lebedev at the end of the 19th century, and then J.-D. Colladon, J. and P. Curie, F. Galton.

IN modern world ultrasound plays everything big role in scientific research. Theoretical and experimental studies in the field of ultrasonic cavitation and acoustic flows have been successfully carried out, which made it possible to develop new technological processes that occur when exposed to ultrasound in the liquid phase. Currently, a new direction of chemistry is being formed - ultrasonic chemistry, which makes it possible to accelerate many chemical technological processes. Scientific research contributed to the birth of a new branch of acoustics - molecular acoustics, which studies the molecular interaction of sound waves with matter. New fields of application of ultrasound have emerged. Along with theoretical and experimental research in the field of ultrasound, many practical works have been carried out.

When I visited the hospital, I saw devices that work based on ultrasound. Such devices allow detecting various homogeneities or inhomogeneities of substances in human tissues, brain tumors and other formations, pathological conditions of the brain, make it possible to control the rhythm of the heart. I wondered how these devices work with the help of ultrasound, and in general what ultrasound is. In the school physics course, nothing is said about ultrasound and its properties, and I decided to study ultrasound phenomena myself.

Objective: study ultrasound, experimentally investigate its properties, explore the possibilities of using ultrasound in technology.

Tasks:

theoretically consider the reasons for the formation of ultrasound;

get an ultrasonic fountain;

investigate the properties of ultrasonic waves in water;

to investigate the dependence of the height of the fountain on the concentration of the solute for different solutions (viscous and non-viscous);

examine modern applications ultrasound in technology.

Hypothesis:ultra sound waves have the same properties as sound waves (reflection, refraction, interference), but due to the greater penetrating ability in the substance, ultrasound has more possibilities of application in technology; as the concentration of the solution (density of the liquid) increases, the height of the ultrasonic fountain decreases.

Research methods:

Analysis and selection of theoretical information; hypothesis of research; experiment; hypothesis testing.

II. - Theoretical part.

1. The history of the emergence of ultrasound.

The attention to acoustics was caused by the needs of the navies of the leading powers - England and France, since acoustic is the only type of signal that can travel far in water. In 1826, the French scientists J.-D. Colladon and C.-F. The assault was determined by the speed of sound in water. Their experiment is considered the birth of modern hydroacoustics. The blow to the underwater bell in Lake Geneva was accompanied by the simultaneous ignition of gunpowder. The flash from gunpowder was observed by scientists at a distance of 10 miles. The sound of the bell was also heard through the underwater auditory tube. By measuring the time interval between these two events, the speed of sound was calculated - 1435 m / s. The difference with modern calculations is only 3 m / s.

In 1838, in the USA, sound was first used to determine the profile of the seabed for the purpose of laying a telegraph cable. The source of the sound, as in Colladon's experiment, was a bell sounding under water, and the receiver was large auditory tubesdescending overboard the ship. The results of the experiment were disappointing. The sound of the bell (as well as the detonation of gunpowder cartridges in the water) gave too weak an echo, almost inaudible among other sounds of the sea. It was necessary to go to the region of higher frequencies, allowing to create directional sound beams, that is, to switch to ultrasound.

The first ultrasound generator was made in 1883 by the Englishman Francis Galton. The ultrasound was created like a whistle on the tip of a knife when blown on. The role of such a point in Galton's whistle was played by a cylinder with sharp edges. Air or other gas escaping under pressure through an annular nozzle with a diameter the same as the edge of the cylinder ran into the edge, and high-frequency vibrations occurred. By blowing the whistle with hydrogen, it was possible to obtain vibrations up to 170 kHz.

In 1880, Pierre and Jacques Curie made a decisive discovery for ultrasound technology. The Curie brothers noticed that when pressure is applied to quartz crystals, an electric charge is generated that is directly proportional to the force applied to the crystal. This phenomenon was named "piezoelectricity" from the Greek word meaning "to push." In addition, they demonstrated the opposite piezoelectric effect, which manifested itself when a rapidly changing electrical potential was applied to the crystal, causing it to vibrate. This vibration occurred at an ultrasonic frequency. From now on, there is a technical possibility of manufacturing small-sized emitters and ultrasound receivers.

The phenomenon of electrostriction (inverse piezoelectric effect) is caused by the orientation and dense packing of some of the water molecules around the ionic groups of amino acids and is accompanied by a decrease in the heat capacity and compressibility of solutions of bipolar ions. The phenomenon of electrostriction consists in the deformation of a given body in an electric field. Due to the phenomenon of electrostriction, mechanical forces arise inside the dielectric. Although the phenomena of electrostriction are observed in many dielectrics, they are weakly expressed in most crystals. In some crystals, for example Rochelle salt and barium titanate, the phenomenon of electrostriction is very intense.

III. - The practical part.

Creation of ultrasonic fountains.

To obtain ultrasound, 2 different ultrasonic installations were used in the work: 1) UD-1 school ultrasonic installation and 2) UD-6 ultrasonic demonstration installation.

To obtain a fountain, a lens cup was taken and placed on top of the emitter so that air bubbles would not form between the bottom of the glass and the piezoelectric element, which greatly interfered with the experiments. For this, the glass was placed by moving the bottom along the emitter cover until the glass hit the emitter ledge. Having installed the lens cup correctly, we began to carry out observations and poured ordinary drinking water into the lens cup.

Approximately one minute after the generator was powered from the mains, an ultrasonic fountain was observed (Appendix 1, Fig. 1), which is adjusted with the frequency control knob and adjusting screws. By rotating the frequency control knob, we got a fountain of such a height that water began to spray over the edge of the glass (Appendix 1, Fig. 3, 12). Again, with a screwdriver, turned the trimmer capacitor, reduced the fountain and continued adjusting the screw to a new maximum of the fountain (maximum fountain height 13-15 cm). Simultaneously with the appearance of the fountain, water fog appeared, which is the result of a cavitation phenomenon (Appendix 1, Fig. 2).

The lowering of the fountain with splashing liquid is explained by the departure of the liquid level plane in the vessel from the focus of the ultrasonic lens, due to the lowering of the level. For long-term observation of the fountain, the latter was placed in a glass tube, along the inner wall of which the gushing liquid flows down, so its level in the vessel does not change. For this, we took a tube 50 cm high with a diameter not exceeding the inner diameter of the lens cup (d \u003d 3 cm). When using a glass tube, liquid was poured into the lens glass 5 mm below the upper edge of the glass to maintain the liquid level due to its splashing on the inner wall of the tube (Appendix 1, Fig. 4, 5, 6).

Observation of ultrasound properties .

In order to obtain the reflection of waves, a flat metal plate was introduced into the cuvette with glycerin and water poured from above and placed at an angle of 45 0 to the water surface. We switched on the generator and achieved the formation of standing waves (Appendix 1, Fig. 10), which are obtained as a result of the reflection of waves from the introduced plate and the wall of the cell. In this experiment, wave interference was simultaneously observed (Appendix 1, Fig. 8, 9). Conducted exactly the same experiment, but poured down a strong solution of potassium permanganate with water (Appendix 1, Fig. 11), then glycerin and water on top. In this experiment, the refraction of waves was also achieved: when ultrasonic waves passed through the interface between two liquids, a change in the length of the standing wave was observed; in glycerin, its wave is greater than in water and manganese dissolved in it, which is explained by the difference in the propagation speed of ultrasound in these liquids. The phenomenon of particle coagulation was also obtained: starch was added to a cuvette with clean water, mixed thoroughly; after turning on the generator, we saw how the particles collect in the nodes of standing waves and after turning off the generator, they fall downward, purifying the water. Thus, in these experiments, we observed reflection, refraction, ultrasound interference and coagulation of particles.

Observation of the dependence of the height of the fountain on the size of the molecule of the solute and the type of solution.

We checked the hypothesis put forward about the dependence of the height of the ultrasonic fountain on the density of the liquid (concentration of the solution) and the size of the molecule. For this, the density was changed by dissolving substances with different molecular sizes (starch, sugar, egg white) in it.

In order to find out how the height of the fountain depends on the density of the solution and the size of the molecule of the solute, the following experiments were carried out. At constant frequency, voltage and volume of the liquid (25 ml), irradiated with ultrasound water, with dissolved starch, sugar, egg white. For each substance, I carried out 4 experiments, with each subsequent one reduced the concentration of substances by 2 times, that is, in the second experiment the concentration is 2 times lower, in the third experiment - 4 times lower, in the fourth - 8 times lower. All observations were recorded and compiled in the table above. There is also a diagram in the appendix, which clearly shows how the concentration of substances decreases (Appendix 2, diagram 1).

Thus, the dependence of the height of the fountain on the concentration of substances was obtained (Appendix 2, diagram 2), and in experiments with egg white and starch, the height of the fountain increased, and in experiments with sugar it decreased.

This is because starch and protein molecules are biological polymers (IUDs are high molecular weight compounds). When dissolved in water, they form colloidal solutions (colloidal particle diameter - 1-100 nm) with high viscosity. Due to the presence of a large number of hydroxo groups (-OH), hydrogen bonds are formed in the molecules of such substances (between the molecules of water and starch, water and protein), which contributes to a more even distribution of particles in solution, which negatively affects the transmission of waves.

Sugar is a dimer (C 12 H 22 O 11) n, its dissolution leads to the formation of a true solution (the size of the solute particles is comparable to the size of the solvent molecules), non-viscous, with a high penetrating ability, this structure of the solution contributes to a stronger transfer of wave energy.

Thus, for viscous liquids, the height of the ultrasonic fountain decreases with an increase in the concentration of the solution, and for nonviscous liquids, the height of the ultrasonic fountain increases with an increase in the concentration of the solution.

IV. -Technical applications of ultrasound.

The various applications of ultrasound can be roughly divided into three areas:

obtaining information about a substance;

effect on the substance;

signal processing and transmission.

The dependence of the speed of propagation and attenuation of acoustic waves on the properties of matter and the processes occurring in them is used in the following studies:

study of molecular processes in gases, liquids and polymers;

study of the structure of crystals and other solids;

control of the course of chemical reactions, phase transitions, polymerization, etc.;

determination of the concentration of solutions;

determination of strength characteristics and composition of materials;

determination of the presence of impurities;

determination of the flow rate of liquid and gas.

Information about the molecular structure of a substance is given by measuring the speed and absorption coefficient of sound in it. This makes it possible to measure the concentration of solutions and suspensions in pulps and liquids, to control the course of extraction, polymerization, aging, and the kinetics of chemical reactions. The accuracy of determining the composition of substances and the presence of impurities by ultrasound is very high and amounts to a fraction of a percent.

Measuring the speed of sound in solids makes it possible to determine the elastic and strength characteristics of structural materials. Such an indirect method for determining strength is convenient for its simplicity and the possibility of using it in real conditions.

Ultrasonic gas analyzers monitor the accumulation of hazardous impurities. The dependence of ultrasound speed on temperature is used for non-contact thermometry of gases and liquids.

Ultrasonic flow meters operating on the Doppler effect are based on measuring the speed of sound in moving liquids and gases, including inhomogeneous ones (emulsions, suspensions, pulps). Similar equipment is used to determine the rate and flow rate of blood flow in clinical trials.

A large group of measurement methods is based on the reflection and scattering of ultrasound waves at the boundaries between media. These methods allow you to accurately determine the location of bodies foreign to the environment and are used in such areas as:

sonar;

non-destructive testing and flaw detection;

medical diagnostics;

determination of the levels of liquids and bulk solids in closed containers;

determining the size of products;

visualization of sound fields - sound imaging and acoustic holography.

Reflection, refraction and the ability to focus ultrasound are used in ultrasonic flaw detection, in ultrasonic acoustic microscopes, in medical diagnostics, to study macroinhomogeneities of a substance. The presence of irregularities and their coordinates are determined by the reflected signals or by the structure of the shadow.

Measurement methods based on the dependence of the parameters of a resonant oscillatory system on the properties of the medium loading it (impedance) are used for continuous measurement of the viscosity and density of liquids, for measuring the thickness of parts, access to which is possible only from one side. The same principle underlies ultrasonic hardness testers, level gauges, level switches. Advantages of ultrasonic control methods: short measurement time, the ability to control explosive, aggressive and toxic environments, the absence of the instrument's impact on the controlled environment and processes.

V. - Conclusion:

In progress research work I theoretically examined the reasons for the formation of ultrasound; studied modern applications of ultrasound in technology: ultrasound allows you to find out the molecular structure of a substance, determine the elastic and strength characteristics of structural materials, monitor the processes of accumulation of dangerous impurities; It is used in ultrasonic flaw detection, in ultrasonic acoustic microscopes, in medical diagnostics, to study macro-inhomogeneities of a substance, for continuous measurement of the viscosity and density of liquids, for measuring the thickness of parts, access to which is possible only from one side. Experimentally, I received an ultrasonic fountain: I found that the maximum height of the fountain is 13-15 cm, (depending on the water level in the glass, the frequency of ultrasound, the concentration of the solution, the viscosity of the solution). She experimentally investigated the properties of ultrasonic waves in water: she determined that the properties of an ultrasonic wave are the same as those of a sound wave, but all processes, due to the high frequency of ultrasound, occur with a large penetration into the depth of the substance.

The experiments carried out have proved that the ultrasonic fountain can be used to study the properties of solutions, such as concentration, density, transparency, and the size of dissolved particles. This research method is distinguished by its speed and simplicity of implementation, the accuracy of the study, and the ability to easily compare different solutions. Such studies are relevant in the implementation of environmental monitoring. For example, when studying the composition of the tailing dump of mining in the city of Olenegorsk at different depths or for monitoring water at treatment facilities.

Thus, I confirmed my hypothesis that ultrasonic waves have the same properties as sound waves (reflection, refraction, interference), but due to the greater penetrating power in the substance, ultrasound has more possibilities of application in technology. The hypothesis about the dependence of the height of the ultrasonic fountain on the density of the liquid was partially confirmed: when the concentration of the solute changes, the density changes and the height of the fountain changes, but the transmission of ultrasonic wave energy depends to a greater extent on the viscosity of the solution, therefore, for different liquids (viscous and non-viscous), the dependence of the height of the fountain on concentration was different.

Vi. - Bibliographic list:

Myasnikov L.L. Inaudible sound. Leningrad "Shipbuilding", 1967. 140 p.

Passport Demonstration ultrasonic unit UD-76 3.836.000 PS

Horbenko I.G. Sound, ultrasound, infrasound. M., "Knowledge", 1978.160 p. (Science and progress)

Attachment 1

Appendix 2

Diagram 1

If in a continuous medium - gases, liquids or solids, the particles of the medium turn out to be removed from the equilibrium position, then the elastic forces acting on them from other particles will return them to the equilibrium position. In this case, the particles will perform oscillatory motion. The propagation of elastic vibrations in a continuous medium is a wave-like process.
Vibrations with a frequency from units of Hertz (Hz) to 20 Hertz are called infrasonic, at a frequency from 20 Hz to 16 ... 20 kHz, oscillations create audible sounds. Ultrasonic vibrations correspond to frequencies from 16 ... 20 kHz to 10 8 Hz, and oscillations with a frequency of more than 10 8 Hz are called hypersounds . Figure 1.1 shows the logarithmic frequency scale based on the expression lg 2 f \u003d 1, 2, 3 ..., n, Where 1, 2, 3 ..., n - octave numbers.

Figure 1.1 - Ranges of elastic vibrations in material media

The physical nature of elastic vibrations is the same in the entire frequency range. To understand the nature of elastic vibrations, let us consider their properties.
Waveform is the shape of the wavefront, i.e. a collection of points with the same phase. Vibrations of the plane create a plane sound wave, if a cylinder serves as the emitter, which periodically contracts and expands in the direction of its radius, then a cylindrical wave arises. A point emitter, or a pulsating ball, whose dimensions are small in comparison with the length of the emitted wave, produces a spherical wave.

Sound waves are classified according to type of waves : they can be longitudinal, transverse, bending, torsional - depending on the conditions of excitation and propagation. In liquids and gases, only longitudinal waves propagate; in solids, transverse and other of the listed types of waves can also occur. In a longitudinal wave, the direction of particle oscillations coincides with the direction of wave propagation (Figure 1.2, and), the shear wave propagates perpendicular to the direction of particle vibration (Figure 1.2, b) .

a) the movement of particles of the medium during the propagation of a longitudinal wave; b) movement of particles of the medium during the propagation of a transverse wave.

Figure 1.2 - Particle motion during wave propagation

Any wave, as an oscillation propagating in time and space, can be characterized by frequency , wavelength and amplitude (Figure 3). In this case, the wavelength λ is related to the frequency f through the speed of propagation of a wave in a given material c: λ = c / f.

Figure 1.3 - Characteristics of the oscillatory process

1.6 Practical application of low-energy ultrasonic vibrations

The field of application of ultrasonic vibrations of low intensity (conventionally up to 1 W / cm 2) is very extensive and we will consider in turn several main applications of ultrasonic vibrations of low intensity.
1. Ultrasonic devices for control of chemical characteristics various materials and environments. All of them are based on the change in the speed of ultrasonic vibrations in the medium and allow:
- determine the concentration of binary mixtures;
- density of solutions;
- degree of polymerisation;
- presence of impurities, gas bubbles in solutions;
- determine the rate of occurrence of chemical reactions;
- fat content of milk, cream, sour cream;
- dispersion in heterogeneous systems, etc.
The resolution of modern ultrasonic devices is 0.05%, the accuracy of measuring the propagation velocity on specimens 1 m long is 0.5-1 m / s (the velocity in the metal is more than 5000 m / s). Almost all measurements are carried out by comparison with a standard.
2. Devices for control of physical and chemical characteristicsbased on measurement of ultrasound attenuation. Such devices allow measuring viscosity, measuring density, composition, content of impurities, gases, etc. The techniques used are also based on benchmarking methods.
3. Ultrasonic flow meters for liquids in pipelines... Their action is also based on measuring the speed of propagation of ultrasonic vibrations along the flow of the liquid and upstream. Comparison of the two speeds allows you to determine the flow rate, and with a known cross section of the pipeline, the flow rate. An example of one of the flow meters (No. 15183 in the State Register of Measuring Instruments) is shown in Figure 1.4.

Figure 1.4 - Stationary ultrasonic flowmeter "AKRON"

Such a flow meter measures the volumetric flow rate and the total volume (amount) of liquids flowing in pressure pipelines of water supply, sewerage and petroleum product supply systems without a tie-in into an operating pipeline. The principle of operation of the flow meter is to measure the difference in the transit time of an ultrasonic wave along the flow and against the flow of the controlled liquid, recalculating it into an instantaneous flow rate with subsequent integration.
The instrument error is 2% of the upper measurement limit. The upper and lower measurement limits are set by the operator. The flow meter includes a sensor unit (consists of two ultrasonic sensors and a device for their attachment to a pipe) and an electronic unit, connected by an RF cable up to 50 m long (10 m as standard). The sensors are installed on a straight section of the pipeline on the outer surface, free from dirt, paint and rust. The condition for correct installation of the sensors is the presence of a straight pipe section of at least 10 pipe diameters - in front of, and 5 diameters - after the sensors.
4. Level indicators
The principle of operation is based on the location of the level of liquid or bulk materials by ultrasonic pulses passing through a gas medium, and on the phenomenon of reflection of these pulses from the "gas - controlled medium" interface. In this case, the measure of the level is the propagation time of sound vibrations from the emitter to the controlled interface between the media and back to the receiver. The measurement result is displayed on a personal computer, where all measurements are memorized, with the subsequent possibility of viewing and analyzing them, as well as connecting to the automated data collection and processing system. The level gauge as part of the system can include state machines, pumps, and other devices at a level above the maximum and below the minimum value, which makes it possible to automate the technological process. Additionally, a current output (0.5 mA, 0-20 mA) is generated for recorders.
The level switch allows you to monitor the temperature of the medium in the tanks. The main output format is the distance from the top of the tank to the surface of the substance it contains. At the request of the customer, upon providing the necessary information, it is possible to modify the device for displaying the height, mass or volume of a substance in the tank.
5. Ultrasonic analyzers of gas composition are based on the use of the dependence of the velocity of ultrasound in a mixture of gases on the velocities in each of the gases that make up this mixture.
6. Security ultrasonic devices based on the measurement of various parameters of ultrasonic fields (vibration amplitudes when the space between the emitter and the receiver overlaps, the frequency changes when reflected from a moving object, etc.).
7. Gas temperature meters and fire alarms based on the change in the propagation speed when the temperature of the environment changes or smoke appears.
8. Ultrasonic non-destructive testing devices. Non-destructive testing is one of the main technological methods for ensuring the quality of materials and products. More than one product should not be operated without testing. You can check by testing, but you can test 1-10 products, but you cannot check 100% of all products, because to check - it means to spoil all the products. Therefore, it is necessary to check without destroying it.
One of the cheapest, simplest and most sensitive is the ultrasonic method of non-destructive testing. The main advantages over other non-destructive testing methods are:

- detection of defects located deep inside the material, which became possible due to improved penetrating ability. Ultrasound examination is carried out to a depth of several meters. Various products are subject to inspection, for example: long steel rods, rotary stampings, etc .;
- high sensitivity when detecting extremely small defects several millimeters long;
- precise determination of the location of internal defects, assessment of their size, characteristics of direction, shape and nature;
- sufficiency of access to only one side of the product;
- process control by electronic means, which provides almost instant detection of defects;
- volumetric scanning, which allows examining the volume of material;
- no requirement for health-related precautions;
- equipment portability.

1.7 Practical application of high-intensity ultrasonic vibrations

Today, the main processes implemented and intensified by high-energy ultrasonic vibrations are usually divided into three main subgroups, depending on the type of environment in which they are implemented (Figure 1.5).

Figure 1.5 - Application of high-energy ultrasonic vibrations

Depending on the type of environment, processes are conventionally divided into processes in liquid, solid and thermoplastic materials and gaseous (air) media. In the following sections, the processes and apparatuses for intensifying processes in liquid, solid and thermoplastic materials, and gaseous media will be considered in more detail.
Next, we will consider examples of the main technologies implemented using high-energy ultrasonic vibrations.
1. Dimensional processing.

Ultrasonic vibrations are used to process fragile and extra hard materials and metals.
The main technological processes intensified by ultrasonic vibrations are drilling, countersinking, threading, wire drawing, polishing, grinding, drilling of complex holes. The intensification of these technological processes occurs due to the imposition of ultrasonic vibrations on the instrument.
2. Ultrasonic cleaning.
Today there are many ways to clean surfaces from various contaminants. Ultrasonic cleaning is faster, provides high quality and washes hard-to-reach areas. This ensures the replacement of highly toxic, flammable and expensive solvents with plain water.
Using high-frequency ultrasonic vibrations, car carburetors and injectors are cleaned in a few minutes.
The reason for the acceleration of cleaning is in cavitation, a special phenomenon in which tiny gas bubbles are formed in the liquid. These bubbles burst (explode) and create powerful water currents that wash away all the dirt. This is the principle that washing machines and small washing machines exist today. The features of the implementation of the cavitation process and its potential capabilities will be considered separately. UZ cleans metals from polishing pastes, rolled products from scale, precious stones from polishing places. Cleaning of printing plates, washing of fabrics, washing of ampoules. Cleaning of complex pipelines. In addition to cleaning, ultrasound is capable of removing small burrs and polishing.
Ultrasonic action in liquid media destroys microorganisms and therefore is widely used in medicine and microbiology.
Another implementation of ultrasonic cleaning is also possible.
- purification of smoke from solid particles in the air. For this, ultrasonic action on fog and smoke is also used. Particles in the ultrasonic field begin to move actively, collide and stick together, and are deposited on the walls. This phenomenon is called ultrasonic coagulation and is used to combat fog on airfields, roads and seaports.
3. Ultrasonic welding.
Currently, using high intensity ultrasonic vibrations, polymer thermoplastic materials are welded. Welding of polyethylene tubes, boxes, cans provides excellent tightness. Unlike other methods, contaminated plastics, liquid tubes, etc. can be cooked with ultrasound. In this case, the contents are sterilized.
Ultrasonic welding is used to weld the thinnest foil or wire to a metal part. Moreover, ultrasonic welding is cold welding, since the seam is formed at a temperature below the melting temperature. Thus, aluminum, tantalum, zirconium, niobium, molybdenum, etc. are joined by welding.
Currently, ultrasonic welding has found the greatest application for high-speed packaging processes and the production of polymer packaging materials.
4. Soldering and tinning
High-frequency ultrasonic vibrations are used to solder aluminum. With the help of ultrasound, it is possible to tin and then solder ceramics, glass, which was previously impossible. Ferrites, soldering semiconductor crystals to gold-plated cases are realized today using ultrasonic technology.
5. Ultrasound in modern chemistry
At present, as follows from literary sources, a new direction in chemistry has been formed - ultrasonic chemistry. By studying the chemical transformations that occur under the influence of ultrasound, scientists have found that ultrasound not only accelerates oxidation, but in some cases provides a reducing effect. Thus, iron is reduced from oxides and salts.
Good positive results were obtained on the intensification of ultrasound of the following chemical-technological processes:
- electrodeposition, polymerization, depolymerization, oxidation, reduction, dispersion, emulsification, aerosol coagulation, homogenization, impregnation, dissolution, spraying, drying, combustion, tanning, etc.
Electrodeposition - the deposited metal acquires a fine-crystalline structure, the porosity decreases. Thus, copper plating, tinning, silvering is carried out. The process is faster and the quality of the coating is higher than in conventional technologies.
Getting emulsions: water and fat, water and essential oils, water and mercury. The immiscibility barrier is overcome by US.
Polymerization (combination of molecules into one) - the degree of polymerization is regulated by the frequency of ultrasound.
Dispersion - obtaining superfine pigments to obtain dyes.
Drying - without heating biologically active substances... In the food, pharmaceutical industry.
Spraying liquids and melts. Intensification of processes in spray dryers. Obtaining metal powder from melts. These spray devices eliminate rotating and rubbing parts.
Ultrasonic enhances the combustion efficiency by 20 times of liquid and solid fuels.
Impregnation. Liquid passes hundreds of times faster through the capillaries of the impregnated material. Used in the production of roofing material, sleepers, cement slabs, textolite, getinax, impregnation of wood with modified resins
6. Ultrasound in metallurgy.
- It is known that when melting, metals absorb gases of aluminum and its alloys. 80% of all gases in molten metal are H2. This leads to a deterioration in the quality of the metal. Gases can be removed using ultrasound, which made it possible in our country to create a special technological cycle and widely use it in the production of metals.
- Ultrasonic helps to harden metals
- In powder metallurgy, ultrasound promotes adhesion of particles of the produced material. This eliminates the need for high pressure sealing.
7. UZ in mining.
The use of ultrasound makes it possible to implement the following technologies:
- Removal of paraffin from the walls of oil wells;
- Elimination of methane explosions in mines due to its spraying;
- Ultrasonic enrichment of ores (flotation method using ultrasonic).
8. KM in agriculture.
Ultrasonic vibrations of the boon have a pleasant effect on seeds and grains before planting them. So, the treatment of tomato seeds before planting provides an increase in the number of fruits, reduces the ripening time and an increase in the amount of vitamins.
Ultrasonic treatment of melon and corn seeds leads to an increase in yield by 40%.
When processing ultrasonic seeds, it is possible to ensure disinfection and introduce the necessary trace elements from the liquid
9. Food industry.
In practice, the following technologies are already being implemented today:
- Milk processing for homogenization sterilization;
- Processing to increase the shelf life and quality of frozen milk
- Getting high quality powdered milk;
- Getting emulsions for baking;
- Processing yeast by 15% increases its fermentation power;
- Obtaining aromatic substances, puree, extraction of fat from the liver;
- Allocation of tartar;
- Extraction of plant and animal raw materials;
- Perfume production (6 ... 8 hours instead of a year).
10. Ultrasound in biology.
- Large doses of ultrasound kill microorganisms (staphylococci, streptococci, viruses);
- Low intensities of ultrasonic exposure promote the growth of colonies of microorganisms;
11. Influence on a person.
Ultrasonic exposure with an intensity of up to 0.1 ... 0.4 W / cm has a therapeutic effect. In America, exposure to an intensity of up to 0.8 W / cm is considered curative.
12. In medicine.
Ultrasonic scalpels, devices for external and internal liposuction, laparoscopic instruments, inhalers, massagers are widely used and can treat various diseases.
The following course of lectures is intended for preliminary acquaintance of students, postgraduates, engineers and technologists of various industries with the basics of ultrasonic technologies and is intended to give fundamental knowledge on the theory of the formation of ultrasonic vibrations and the practice of using ultrasonic vibrations of high intensity.

ULTRASONIC VIBRATIONS, vibrations having such a high frequency that sounds from them are not perceived by the ear. The frequencies of ultrasonic vibrations start from 15000-20000 Hz. The existence of ultrasonic vibrations has been known for a long time, and after the appearance in 1883 of Galton's whistle, which emitted inaudible sounds, their demonstration entered the teaching practice. However, until recently, ultrasonic vibrations had no practical value, since there were no sufficiently powerful sources of ultrasonic vibrations. The beginning of the revival of research on ultrasonic vibrations should be considered 1917-19, when Langevin in Paris managed to use quartz to obtain powerful ultrasonic waves in water. In particular, research on ultrasonic vibrations revived after Cady's work, which began in 1922; this revival continues at this time.

Methods for obtaining ultrasonic vibrations very diverse; almost all methods of obtaining vibrations are suitable for ultrasonic vibrations. Not too powerful sounds are most easily obtained with a Galton whistle (Fig. 1), representing an air resonator, the natural frequency of which can vary from 10,000 to 30,000 Hz and against the opening of which a stream of air is directed. The power of such a whistle is low, and in all the methods described below, the source of ultrasonic frequency energy is an alternating electric current, usually obtained from self-oscillating electric circuits with an electronic lamp; the only exception is the singing arc, with which Neklepaev in 1911 obtained ultrasonic vibrations and waves with frequencies up to 3,500,000 Hz, which corresponds to a wavelength of about 0.1 mm. The waves were received in the air, and it turned out that the latter absorbs them quite strongly. The first powerful source of ultrasonic vibrations was the Langevin piezoelectric transmitter, designed for work in water. The main part of the Langevin transmitter is a quartz plate Q (Fig. 2), cut perpendicular to the electric axis and equipped with plates A, A tightly glued to it. alternating current. With a suitable choice of frequency, when the natural vibrations of the transmitter are in resonance with the current, they become very powerful and emit large ultrasonic energy.

In the Langevin underwater transmitter, only one plate A is in contact with the water, while the other is enclosed in the housing shown in FIG. 2 schematically with a dotted line. Such transmitters are usually built at frequencies around 30,000-40,000 Hz.

Wood and Loomis used for their experiments plates with very thin plates, which practically did not affect the natural frequency of the plate. Since the total thickness of the transmitter was much less for them, the frequency of ultrasonic vibrations was much higher, namely of the order of 5 · 10 5 Hz. Myasnikov managed to reach frequencies of 10 6 -10 7 Hz; the transmitters in both cases were placed in an oil bath, where ultrasonic waves propagated. There are successful attempts to obtain ultrasonic vibrations of sufficient power and by using magnetostrictive vibrations. Gaines received very strong ultrasounds by exciting magnetostrictive oscillations in a nickel tube, on lower part which, in the air, was acted upon by an alternating magnetic field, and the upper, located in the liquid, emitted sound. An electrical spark also gives unsatisfactory results. The Langevin method is currently the best practical method for producing powerful ultrasonic transmitters. Experiments on obtaining ultrasonic waves in air in the same way have shown that the recoil of transmitters of this type in air is very insignificant.

Propagation of ultrasonic waves in gases and liquids generally obeys the same laws as ordinary sound waves, however, there are some peculiarities. Ultrasonic waves in air and gases are very significantly absorbed and the stronger, the higher the frequency of ultrasonic waves. The shortest of them, investigated by Neklepaev, are weakened by a factor of 100, having already passed 6 mm. Waves 8 times longer are attenuated by the same amount after traveling 40 cm, etc. In addition, some dispersion of ultrasonic waves is noticed. At high powers of ultrasonic transmitters, in addition to ultrasonic radiation, there is a "wind" from them, first discovered by Meissner on quartz plates, which is also observed in underwater transmitters. If, as in the experiments of Wood and Lumis, ultrasonic waves fall on the border of two media (in their experiments oil - air and oil - water), then the surface of their contact is greatly distorted due to the so-called. sound pressure, whole fountains of the smallest splashes are formed, and in experiments with oil and water, an emulsion of oil in water is formed; ultrasonic waves propagating along the glass rod cause a burning sensation when touched, although the thermometer shows only a slight increase in temperature. Physiology and the action of powerful ultrasonic waves are also significant: animal and plant cells and bacteria die in the field of ultrasonic waves, so it turned out to be possible to sterilize milk using this method; fishes were dying in the vicinity of Langevin's transmitters. Perhaps with further development, ultrasonic waves will gain therapeutic value. Due to the extremely small wavelength in the field of ultrasonic waves, diffraction of light waves is observed, as in diffraction gratings (Debye and Sears). Built (Pierce) interferometers for ultrasonic waves, used to determine the speed of sound in gases and liquids. Various applications of ultrasonic vibrations in technology, and almost all are based on the properties of precisely quartz resonators. Since the damping in oscillating quartz rods, plates and, in particular, rings is much less than in electrical circuits, the latter are replaced by the first in all cases when a pronounced resonance is required. So they became widespread quartz stabilizers for; the property of quartz to glow when vibrating, since electric charges appear on it, is used in wave indicators (Gibet). The frequency of oscillation given by the quartz rings is so constant that Morrison used them for an electric clock that surpassed all previously known in its accuracy, since quartz is currently the best frequency standard.

Underwater quartz transmitters for ultrasonic vibrations, they are still not widely used, however, due to their high frequency, they have two advantages over electromagnetic underwater transmitters: they have, first,; high directivity, allowing you to focus the beam of rays emanating from them in a narrow solid angle; secondly, they have (with a good design, which has not yet been fully achieved) high efficiency. First of all, they were used as instruments for determining depths in the so-called. echo sounders. The sound beam emanating from the transmitter is directed to the bottom; reflected from it, returns to the same transmitter that receives it; the recording installation registers the travel time of sound from the transmitter to the bottom and back, from where the depth is calculated. Ultrasonic transmitters are used for wiring from ship to ship, among other things, and for submarines, for which sound communication is almost the only possible one; the ultrasonic transmitter is also the receiver. There have been attempts to use ultrasonic beams to open submarines and ice mountains (Boyle and Reid, 1926), to transilluminate defects in metals (S. Sokolov), but the results here have not yet been obtained sufficiently reliable for the corresponding installations to be put into practice.

Ultrasound - these are elastic mechanical vibrations with a frequency exceeding 18 kHz, which is the upper threshold of hearing human ear... Due to the increased frequency, ultrasonic vibrations (UZK) have a number of specific features (the ability to focus and directivity of radiation), which makes it possible to concentrate acoustic energy on small areas of the radiated surface.

From a source of oscillations, ultrasound is transmitted in the medium in the form of elastic waves and can be represented in the form of a wave equation for a longitudinal plane wave:

where L - displacement of the oscillating particle; t- time; x- distance from the source of vibration; with is the speed of sound in the medium.

The speed of sound is different for each medium and depends on its density and elasticity. Particular forms of the wave equation allow one to describe wave propagation for many practical cases.

Ultrasonic waveform

Ultrasonic waves from a source of vibrations propagate in all directions. Near each particle of the medium there are other particles vibrating with it in the same phase. A set of points with the same oscillation phase is called wave surface.

The distance over which the wave propagates in a time equal to the oscillation period of the particles of the medium is called wavelength.

where T - oscillation period; / - vibration frequency.

By the front of the wave is called a set of points to which fluctuations reach a certain point in time. At each moment of time, there is only one wave front, and it moves all the time, but the wave surfaces remain stationary.

Depending on the shape of the wave surface, plane, cylindrical and spherical waves are distinguished. In the simplest case, the wave surfaces are flat and the waves are called flat, and the source of their excitement is the plane. Cylindrical waves are called, whose wave surfaces are concentric cylinders. The sources of excitation of such waves appear in the form of a straight line or a cylinder. Spherical waves are created by point or spherical sources, whose radii are much smaller than the wavelength. If the radius exceeds the wavelength, then it can be considered flat.

Equation of a plane wave propagating along the axis X,if the excitation source performs harmonic oscillations with an angular frequency ω and an amplitude A 0, has the form

The initial phase of a wave is determined by the choice of the origin of the coordinate x and time t.

When analyzing the passage of one wave, the origin is usually chosen in such a way that and \u003d 0. Then equation (3.2) can be written in the form

The last equation describes a traveling wave propagating towards increasing (+) or decreasing (-) values. It is one of the solutions of the wave equation (3.1) for a plane wave.

Depending on the direction of vibration of the particles of the medium relative to the direction of wave propagation, several types of ultrasonic waves are distinguished (Fig. 3.1).

If the particles of the medium vibrate along a line coinciding with the direction of propagation of the wave, then such waves are called longitudinal (fig. 3.1, and). When the displacement of the particles of the medium occurs in a direction perpendicular to the direction of propagation of the wave, the waves are called transverse (fig. 3.1, b).

Fig. 3.1. Scheme of vibrational displacements of medium particles for different types of waves: and - longitudinal; b - transverse; in - bending

In liquids and gases, only longitudinal waves can propagate, since elastic deformations in them arise during compression and do not arise during shear. Both longitudinal and transverse waves can propagate in solids, since solids have shape elasticity, i.e. strive to maintain their shape when exposed to mechanical forces. Elastic deformations and stresses arise in them not only during compression, but also during shear.

In small solids, such as rods, plates, the pattern of wave propagation is more complex. In such bodies, waves appear, which are a combination of two main types: torsional, bending, surface.

The type of wave in a solid depends on the nature of the excitation of oscillations, the shape of the solid, its dimensions in relation to the wavelength, and under certain conditions several types of waves can exist simultaneously. A schematic representation of a flexural wave is shown in Fig. 3.1, c. As you can see, the displacement of the particles of the medium occurs both perpendicular to the direction of wave propagation, and along it. Thus, a flexural wave has common features of both P and S waves.