Application of ultrasound. What is ultrasound and how is it useful?

Frequencies of 16 - 18000 Hz, which the human hearing aid is capable of perceiving, are usually called sound frequencies, for example, the squeak of a mosquito »10 kHz. But the air, the depths of the seas and the bowels of the earth filled with sounds lying below and above this range - infra and ultrasound. In nature, ultrasound is found as a component of many natural noises: in the noise of wind, waterfalls, rain, sea pebbles rolled by the surf, and in thunderstorms. Many mammals, such as cats and dogs, have the ability to perceive ultrasound with a frequency of up to 100 kHz, and the location abilities of bats, nocturnal insects and marine animals are well known to everyone. The existence of inaudible sounds was discovered with the development of acoustics at the end of the 19th century. At the same time, the first studies of ultrasound began, but the foundations of its use were laid only in the first third of the 20th century.

The lower limit of the ultrasonic range is called elastic vibrations with a frequency of 18 kHz. The upper limit of ultrasound is determined by the nature of elastic waves, which can propagate only under the condition that the wavelength is significantly greater than the free path of molecules (in gases) or interatomic distances (in liquids and gases). In gases upper limit is »106 kHz, in liquids and solids »1010 kHz. As a rule, frequencies up to 106 kHz are called ultrasound. Higher frequencies are commonly called hypersound.

Ultrasonic waves by their nature do not differ from waves in the audible range and are subject to the same physical laws. But ultrasound has specific features, which determined its widespread use in science and technology. Here are the main ones:

• Short wavelength. For the lowest ultrasonic range, the wavelength does not exceed several centimeters in most media. The short wavelength determines the ray nature of the propagation of ultrasonic waves. Near the emitter, ultrasound propagates in the form of beams similar in size to the size of the emitter. When it hits inhomogeneities in the medium, the ultrasonic beam behaves like a light beam, experiencing reflection, refraction, and scattering, which makes it possible to form sound images in optically opaque media using purely optical effects (focusing, diffraction, etc.)
• A short period of oscillation, which makes it possible to emit ultrasound in the form of pulses and carry out precise time selection of propagating signals in the medium.
• Possibility of obtaining high values ​​of vibration energy at low amplitude, because the vibration energy is proportional to the square of the frequency. This makes it possible to create ultrasonic beams and fields with a high level of energy, without requiring large-sized equipment.
• Significant acoustic currents develop in the ultrasonic field. Therefore, the impact of ultrasound on the environment gives rise to specific effects: physical, chemical, biological and medical. Such as cavitation, sonic capillary effect, dispersion, emulsification, degassing, disinfection, local heating and many others.
• Ultrasound is inaudible and does not create discomfort for operating personnel.

History of ultrasound. Who discovered ultrasound?

Attention to acoustics was driven by the needs navy leading powers - England and France, because acoustic is the only type of signal that can travel far in water. In 1826 French scientist Colladon determined the speed of sound in water. Colladon's experiment is considered the birth of modern hydroacoustics. The underwater bell in Lake Geneva was struck while the gunpowder was ignited. The flash from the gunpowder was observed by Colladon at a distance of 10 miles. He also heard the sound of the bell using an underwater auditory tube. By measuring the time interval between these two events, Colladon calculated the speed of sound to be 1435 m/sec. Difference with modern computing only 3 m/sec.

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 underwater, and the receiver was large auditory tubes lowered over the side of the ship. The results of the experiment were disappointing. The sound of the bell (as, indeed, the explosion of gunpowder cartridges in the water) gave too weak an echo, almost inaudible among the other sounds of the sea. It was necessary to go to the region of higher frequencies, allowing the creation of directed sound beams.

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

In 1880 Pierre and Jacques Curie made a discovery that was decisive for ultrasound technology. The Curie brothers noticed that when pressure is applied to quartz crystals, electric charge, directly proportional to the force applied to the crystal. This phenomenon was called "piezoelectricity" from Greek word, meaning "to press". In addition, they demonstrated the inverse piezoelectric effect, which manifested itself when a rapidly changing electric potential applied to a crystal, causing it to vibrate. From now on, it is technically possible to manufacture small-sized ultrasound emitters and receivers.

The death of the Titanic from a collision with an iceberg, the need to combat new weapons - submarines required the rapid development of ultrasonic hydroacoustics. In 1914, French physicist Paul Langevin together with the talented Russian emigrant scientist Konstantin Vasilyevich Shilovsky, they first developed a sonar consisting of an ultrasound emitter and a hydrophone - a receiver of ultrasonic vibrations, based on the piezoelectric effect. Sonar Langevin - Shilovsky, was the first ultrasonic device, used in practice. At the same time, the Russian scientist S.Ya. Sokolov developed the fundamentals of ultrasonic flaw detection in industry. In 1937, the German psychiatrist Karl Dussick, together with his brother Friedrich, a physicist, first used ultrasound to detect brain tumors, but the results they obtained turned out to be unreliable. IN medical practice Ultrasound first began to be used only in the 50s of the 20th century in the USA.

Receiving ultrasound.

Ultrasound emitters can be divided into two large groups:

1) Oscillations are excited by obstacles in the path of a stream of gas or liquid, or by interruption of a stream of gas or liquid. They are used to a limited extent, mainly to obtain powerful ultrasound in a gaseous environment.

2) Oscillations are excited by transformation into mechanical oscillations of current or voltage. Most ultrasonic devices use emitters of this group: piezoelectric and magnetostrictive transducers.

In addition to transducers based on the piezoelectric effect, magnetostrictive transducers are used to produce a powerful ultrasonic beam. Magnetostriction is a change in the size of bodies when they change magnetic state. A core of magnetostrictive material placed in a conductive winding changes its length in accordance with the shape of the current signal passing through the winding. This phenomenon, discovered in 1842 by James Joule, is characteristic of ferromagnets and ferrites. The most commonly used magnetostrictive materials are alloys based on nickel, cobalt, iron and aluminum. The highest intensity of ultrasonic radiation can be achieved by the permendur alloy (49% Co, 2% V, the rest Fe), which is used in powerful ultrasonic emitters. In particular, those produced by our company.

Application of ultrasound.

The diverse applications of ultrasound can be divided into three areas:

• obtaining information about a substance
• effect on the substance
• signal processing and transmission

Dependence of propagation speed and attenuation 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 chemical reactions, phase transitions, polymerization, etc.
• determination of solution concentration
• determination of strength characteristics and composition of materials
• determination of the presence of impurities
• determination of the flow rate of liquid and gas

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

Ultrasonic gas analyzers monitor the accumulation of hazardous impurities. The dependence of ultrasonic 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 speed and flow rate of blood in clinical studies.

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 foreign bodies in the environment and are used in such areas as:

• sonar
• non-destructive testing and flaw detection
• medical diagnostics
• determination of liquid levels and friable solids in closed containers
• determining product sizes
• visualization of sound fields - sound vision and acoustic holography

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

Measurement methods based on the dependence of resonance parameters oscillatory system on the properties of the medium loading it (impedance), are used for continuous measurement of the viscosity and density of liquids, and for measuring the thickness of parts that can only be accessed from one side. The same principle underlies ultrasonic hardness testers, level gauges, and level switches. Advantages of ultrasonic testing methods: short measurement time, the ability to control explosive, aggressive and toxic environments, no impact of the instrument on the controlled environment and processes.

The effect of ultrasound on a substance.

The effect of ultrasound on a substance, leading to irreversible changes in it, is widely used in industry. At the same time, the mechanisms of influence of ultrasound are different for different environments. In gases, the main operating factor is acoustic currents, which accelerate heat and mass transfer processes. Moreover, the efficiency of ultrasonic mixing is significantly higher than conventional hydrodynamic mixing, because the boundary layer has a smaller thickness and, as a result, a greater temperature or concentration gradient. This effect is used in processes such as:

• ultrasonic drying
• combustion in an ultrasonic field
• aerosol coagulation

In ultrasonic processing of liquids, the main operating factor is cavitation . The following technological processes are based on the cavitation effect:

• ultrasonic cleaning
• metallization and soldering
• sound-capillary effect - penetration of liquids into the smallest pores and cracks. It is used for impregnation of porous materials and occurs during any ultrasonic processing of solids in liquids.
• crystallization
• intensification of electrochemical processes
• obtaining aerosols
• destruction of microorganisms and ultrasonic sterilization of instruments

Acoustic currents- one of the main mechanisms of the effect of ultrasound on matter. It is caused by the absorption of ultrasonic energy in the substance and in boundary layer. Acoustic flows differ from hydrodynamic flows in the small thickness of the boundary layer and the possibility of its thinning with increasing oscillation frequency. This leads to a decrease in the thickness of the temperature or concentration boundary layer and an increase in temperature or concentration gradients that determine the rate of heat or mass transfer. This helps to accelerate the processes of combustion, drying, mixing, distillation, diffusion, extraction, impregnation, sorption, crystallization, dissolution, degassing of liquids and melts. In the stream with high energy the influence of the acoustic wave is carried out due to the energy of the flow itself, by changing its turbulence. In this case, the acoustic energy can be only a fraction of a percent of the flow energy.

When a high-intensity sound wave passes through a liquid, a so-called acoustic cavitation . In an intense sound wave, during half-periods of rarefaction, cavitation bubbles appear, which collapse sharply when moving to an area of ​​​​high pressure. In the cavitation region, powerful hydrodynamic disturbances arise in the form of microshock waves and microflows. In addition, the collapse of bubbles is accompanied by strong local heating of the substance and the release of gas. Such exposure leads to the destruction of even such durable substances as steel and quartz. This effect is used to disperse solids, produce fine emulsions of immiscible liquids, excite and accelerate chemical reactions, destroy microorganisms, extract from animals and plant cells enzymes. Cavitation also determines such effects as a weak glow of a liquid under the influence of ultrasound - sonoluminescence , and abnormally deep penetration of liquid into the capillaries - sonocapillary effect .

Cavitation dispersion of calcium carbonate crystals (scale) is the basis of acoustic anti-scale devices. Under the influence of ultrasound, particles in water split, their average sizes decrease from 10 to 1 micron, their number increases and total area particle surfaces. This leads to the transfer of scale formation from the heat exchange surface directly into the liquid. Ultrasound also affects the formed layer of scale, forming microcracks in it that contribute to the breaking off of pieces of scale from the heat exchange surface.

In ultrasonic cleaning installations, with the help of cavitation and the microflows generated by it, contaminants both rigidly bound to the surface, such as scale, scale, burrs, and soft contaminants, such as greasy films, dirt, etc., are removed. The same effect is used to intensify electrolytic processes.

Under the influence of ultrasound, such a curious effect occurs as acoustic coagulation, i.e. convergence and enlargement of suspended particles in liquid and gas. The physical mechanism of this phenomenon is not yet completely clear. Acoustic coagulation is used for the deposition of industrial dusts, fumes and mists at frequencies low for ultrasound, up to 20 kHz. It is possible that the beneficial effects of ringing church bells based on this effect.

Mechanical processing of solids using ultrasound is based on the following effects:

• reduction of friction between surfaces during ultrasonic vibrations of one of them
• reduction in yield strength or plastic deformation under the influence of ultrasound
• strengthening and reduction of residual stresses in metals under the impact of a tool with ultrasonic frequency
• Combined effects of static compression and ultra sound vibrations used in ultrasonic welding

There are four types of machining using ultrasound:

• dimensional processing of parts made of hard and brittle materials
• cutting difficult-to-cut materials with ultrasonic application on the cutting tool
• deburring in an ultrasonic bath
• grinding of viscous materials with ultrasonic cleaning of the grinding wheel

Effects of ultrasound on biological objects causes a variety of effects and reactions in body tissues, which is widely used in ultrasound therapy and surgery. Ultrasound is a catalyst that accelerates the establishment of an equilibrium, from a physiological point of view, state of the body, i.e. healthy state. Ultrasound has a much greater effect on diseased tissues than on healthy ones. Ultrasonic spraying is also used medicines during inhalation. Ultrasound surgery is based on the following effects: tissue destruction by focused ultrasound itself and the application of ultrasonic vibrations to a cutting surgical instrument.

Ultrasonic devices are used for conversion and analog processing of electronic signals and for controlling light signals in optics and optoelectronics. Low speed ultrasound is used in delay lines. Control of optical signals is based on the diffraction of light by ultrasound. One of the types of such diffraction, the so-called Bragg diffraction, depends on the wavelength of ultrasound, which makes it possible to isolate a narrow frequency interval from a wide spectrum of light radiation, i.e. filter light.

Ultrasound is an extremely interesting thing and it can be assumed that many of its practical applications are still unknown to mankind. We love and know ultrasound and will be happy to discuss any ideas related to its application.

Where is ultrasound used - summary table

Our company, Koltso-Energo LLC, is engaged in the production and installation of acoustic anti-scale devices "Acoustic-T". The devices produced by our company are distinguished by an exceptionally high level of ultrasonic signal, which allows them to work on boilers without water treatment and steam-water boilers with artesian water. But preventing scale is a very small part of what ultrasound can do. This amazing natural tool has enormous possibilities and we want to tell you about them. Our company's employees have worked for many years at leading Russian enterprises involved in acoustics. We know a lot about ultrasound. And if suddenly the need arises to use ultrasound in your technology,

MINISTRY OF EDUCATION OF THE RYAZAN REGION

Regional State Budgetary

Professional educational institution

"Ryazan teacher training college»

INDIVIDUAL TRAINING PROJECT

In the academic discipline "Physics"

Topic: “Ultrasound and infrasound in human life”

Completed by: Vasilyeva

Alena Nikolaevna

Specialty: 02/44/02 Teaching

IN primary school

Group: 11sh

Head: Galkina

Natalia Evgenievna

Introduction.

I chose the topic “Ultrasound and infrasound in human life” because I find it very interesting and useful.

Infrasounds and ultrasounds are outside the range of frequencies that cause sound sensations.

Infrasounds, or elastic waves with frequencies of 16 Hz and below, occur under a variety of conditions - when blown by wind various items, vibration with sufficient amplitude of machine tools, the body of a moving car, a running aircraft engine, etc. Infrasounds are not perceived by the human hearing organs, but the body as a whole reacts to them, so the need for a detailed study of such vibrations is understandable. Research into infrasound began relatively recently and currently there is no coherent theory for the indicated range of elastic waves. The task of studying infrasound is complicated by the peculiarities of their impact on devices and living organisms. So, internal organs Humans have natural vibration frequencies (resonance frequencies) ranging from 6 to 8 Hz, so exposure to infrasonic vibrations of sufficient amplitude can cause unpleasant and even painful sensations. Therefore, one of the tasks of infrasound research is related to determining the degree of influence of low-frequency vibrations on the nervous, cardiovascular system person, on his performance.

Ultrasound is used to effectively clean surfaces, parts, and mechanical components from various contaminants, traces of corrosion, etc. Thus, with the help of ultrasonic installations, parts are cleaned from oil, traces of scale, and the bottom of the ship is cleaned; moreover, a protective ultrasonic installation prevents the fouling of the bottom of a sea vessel by various marine living and plant organisms, thereby preserving the operational qualities of the ship. With the help of ultrasound, they clean the air from pollution, precipitating impurity particles, use ultrasound to combat fog, etc.

Ultrasound is also widely used in accelerating a number of technological processes, where the use of other methods is difficult. For example, when welding or soldering thin foils or wires, it is ultrasound that makes it possible to obtain high-quality connections. I will tell you more about all this in the main part of the project.

Project goal:

Get acquainted with the concepts of ultrasound and infrasound. Remember where they are used. Find out the effect of ultra and infra sound on the human body.

Project objectives:

1. Study the material on the topic “The influence of ultrasound and infrasound on the human body”

2. Be able to apply the studied material in life.

Ultrasound and infrasound in human life.

The influence of ultrasound.

Ultrasound is sound waves having a frequency higher than those perceived by the human ear; usually, ultrasound means frequencies above 20,000 Hertz.

The specific sensation that we perceive as sound is the result of an effect on the human hearing system. oscillatory motion elastic medium - most often air. However, not all vibrations of the medium reaching the ear cause the sensation of sound. The lower limit of audible sound is vibrations with a frequency of 20 vibrations per second (20 Hz), the upper limit lies between 16,000 and 20,000 Hz. The position of these boundaries is subject to individual changes.

Field of application of ultrasound

Outside the specified frequency range, there are also oscillatory processes that are not physically different from sound vibrations and waves, but are not perceived by the ear as sounds. Fluctuations of the medium with frequencies higher upper limit hearing, on the order of tens and hundreds of thousands of hertz, are usually called ultrasounds.

In recent years, ultrasound has found wide application in national economy, biology and medicine. In the USA, for example, there are currently millions of ultrasonic installations.

Industry uses ultrasound, the frequency of which is billions of times higher than the intensity of the audible sounds around us. Ultrasounds can be focused and create very high local pressure. Ultrasound can crush substances and accelerate chemical reactions. Ultrasound is capable of introducing water into colloids. With the help of ultrasound, the processes of tanning leather, dyeing, bleaching and washing fabrics, producing synthetic fibers, leather substitutes and plastics are significantly accelerated. Ultrasound is used for flaw detection, which makes it possible to determine internal defects in parts, for cleaning boilers from scale, underwater surfaces of ships, for tinning with aluminum, silvering, etc. Ultrasound has found application in blast furnace production, in water transport, in fishing and geology.

Ultrasound is used in medicine for diagnostic purposes (detection of foreign bodies), in dentistry (drills), for the production of emulsions of medicinal substances, etc.

Currently, low-intensity ultrasound is widely used for therapeutic purposes.

Ultrasound has a complex and pronounced biological effect, the essence of which has not yet been sufficiently clarified. This action seems to depend mainly on the enormous local pressures created in the tissues and on the local thermal effect associated with energy absorption during vibration damping. Liquids and gases absorb ultrasound, while solids conduct it well. Bones are also good conductors of ultrasound.

The three main areas of application of ultrasound in medicine are ultrasound diagnostics, “ultrasonic scalpel” and ultrasound physiotherapy. Let's start the story with the last two.

The “ultrasonic scalpel” is used primarily where precise and limited exposure is necessary, where every extra millimeter of destroyed tissue can cause severe consequences, as, for example, in the surgical treatment of eye diseases, facial plastic surgery, etc. Focusing ultrasound in a small, specified area makes it possible to influence deep-lying structures of the body. This is especially important when performing neurosurgical operations on the brain, during operations to destroy the accessory pathways of the heart. As the frequency of ultrasound increases, its action becomes extremely localized. For example, at a frequency of 4 MHz, a tissue area with a volume of only 0.05 mm3 can be destroyed, while the surrounding tissue remains undamaged.

For the treatment of eye diseases, ultrasound was first used by doctors at the Odessa Research Institute of Eye Diseases and Tissue Therapy named after. V. P. Filatov, known for the development of a number of new methods for treating corneal opacities, cataracts of traumatic origin, retinal detachment, etc. Low-frequency ultrasound with a frequency of 20-40 kHz was used to expand the lacrimal canal, as well as during operations on the cornea.

Surgery for cataracts (clouding of the lens) is usually performed only after it has matured, when vision has already been completely lost. Under natural conditions, this process sometimes lasts for years. “Sounding” with ultrasound speeds it up to several minutes, which allows the operation to be performed in less time. early dates and with best results. To carry out this operation, an original ultrasonic instrument was developed in the form of a hollow needle 1 mm thick, enclosed in a thin silicone sheath and connected to an ultrasonic generator. Observing the movement of the needle through a microscope, the surgeon brings it close to the lens and turns on the ultrasound. Under the influence of ultrasound, after a few moments the clouded lens liquefies. The resulting liquid is washed out of the capsule with a disinfectant solution entering through the gap between the needle and its case, and is sucked out through the internal channel of the needle. The postoperative period after such an operation is significantly reduced.

Focused ultrasound was used to delay a potentially blinding retinal detachment. Its targeted effect at several points fixes the retina to the underlying tissues. In many cases, ultrasound helps avoid surgery for glaucoma. The main symptom of this disease is increased intraocular pressure. The sclera of the eye is “sounded” with ultrasound at several points, after which the intraocular pressure decreases. According to American doctors, this method is effective in 80% of cases.

The destructive effect of ultrasound is also used to remove blood clots from large vessels. Through a hole made with a special needle, the surgeon inserts a thin ultrasonic waveguide into the vessel and carefully moves it towards the blood clot. After 10-12 seconds of “sounding,” the thrombus ceases to exist, and the resulting liquid contents are washed out of the lumen of the vessel and sucked out through the same needle. The tool is removed and the hole is “sealed” with an ultrasonic weld.

Ultrasound is also used in the surgical treatment of diseases of the ear, nose and throat. Operations to remove swollen tissue from the chronically inflamed nasal mucosa and to correct a deviated nasal septum are performed in most cases using a scalpel, chisel and hammer. Later they developed ultrasound equipment for this operation. The ultrasound instrument made it possible to perform it bloodlessly, almost painlessly and, moreover, many times faster. The same group of Russian doctors developed an ultrasonic scalpel for performing tracheotomy (cutting the trachea). This operation is usually performed for health reasons - in case of sudden onset of suffocation. Every moment is precious here, and the use of ultrasound can save as much as 10 minutes.

According to many doctors, the ultrasound method undoubtedly expands the possibilities surgical treatment patients with various pathologies of the lungs and pleura. Doctors perform chest surgery using ultrasound. An ultrasound instrument cuts and connects the sternum, ribs, bronchi, and bougienates narrowed arteries. Long flexible ultrasonic waveguides for manipulations on the trachea and bronchi, developed for the first time in the world by a group of Soviet scientists, are being introduced into practice. Conducted experimental studies by connecting the tray tissue and closing the bronchial stump using ultrasound.

Scientists have developed and applied an ultrasonic cutting and joining method bone tissue using ultrasonic welding - first in numerous experiments on animals, and later in the clinic. To cut a bone with an ordinary saw, it is necessary to peel off the soft tissue over a fairly large area, but for an ultrasonic saw, a hole in the soft tissue with a diameter of 1 cm is sufficient. This is of particular importance during craniotomy, rib resection, etc.

The method of ultrasonic surfacing of bone tissue consists in the fact that the cavity formed in the bone after removal of the pathological focus is filled with bone chips, which are impregnated with a special filler material and “sounded” with ultrasound. After “sounding,” this entire mass turns into a conglomerate, firmly fused to the bone. Ultrasound is also used to connect tissues of the liver, spleen, and endocrine glands.

For many years, ultrasonic devices have been used in dentistry to remove tartar, and in recent years, also to treat caries and its complications. An abrasive (aluminum oxide, boron, etc. powder suspended in water) is placed between the working end of the ultrasonic vibrator and the tooth. The abrasive particles, hitting the tooth tissue, gradually remove layer by layer from it. The resulting cavity reproduces the shape of the end of the vibrator. Its walls are smoothly polished. The quality of filling is also better, since under the influence of “sounding” the structure changes and the density of the filling material increases. Ultrasound dental treatment is silent. The heat generation, and therefore the heating of the tooth, is weaker than when drilling with a rotating bur. Therefore, pain in most patients is absent or minimal. IN in this case This undoubted advantage of ultrasound turns into its disadvantage. With virtually painless ultrasound treatment of pulpitis, it is difficult for the doctor to determine the moment of approaching the nerve. Therefore, ultrasonic drills can only be used by experienced specialists.

The crushing action of ultrasound can also be used to destroy ureteral stones. The ultrasonic tool crushes the stone in 5-60 seconds, depending on the size and density of the stone.

An ultrasonic scalpel is neither in appearance nor in principle of operation similar to a surgical one. Outwardly, it resembles a miniature two-stage rocket that easily fits in your hand. Its first stage contains an ultrasonic vibrator, the action of which is based on the principle of magnetostriction (from the Latin word “strictio” - compression).

The essence of the magnetostriction phenomenon is that some metals, when exposed to a magnetic field, change their geometric dimensions. If a copper wire is wound around a rod of such a ferromagnetic material and an alternating current is passed through it with a frequency corresponding to ultrasound frequencies, then the rod will change its dimensions at the same frequency. Since the amplitude of changes in the size of the vibrator is very small, an ultrasound concentrator (the second stage of the “rocket”) is designed to amplify it. The concentrator tapers from the base to the top, the range of vibrations of which is tens of times greater than that of the base, which changes position along with the vibrator. The oscillation amplitude of the top of the concentrator reaches 50-60 microns, and the frequency is 25-50 kHz. An ultrasonic scalpel works like a sharp microsaw. Due to the energy of ultrasonic vibrations, it separates the tissue at the boundaries of the contact of cell membranes, almost without damaging the cells themselves, which promotes better and faster healing. By slightly rotating the instrument and thereby changing the direction of the ultrasound beam, you can change the direction of the incision without expanding the surgical approach. When cutting tissue, ultrasound stops capillary bleeding. It is also important that the use of ultrasound significantly reduces the pain of surgical intervention.

Surgical ultrasound technology is now part of the arsenal practical medicine. It is used along with traditional surgical instruments, electrocoagulation, laser and other methods, taking into account the characteristics of the disease, indications and contraindications. As the production of ultrasound equipment for surgical interventions improves and increases, its implementation in practice will expand.

The physical phenomena that arise when ultrasound influences liquids were the basis new technique wound treatment developed by Russian scientists. Solutions of antibiotics or antiseptics are injected into the wound, which are “sounded” using an ultrasonic waveguide. The sounded liquid removes dead tissue, massages the wound surface, and improves blood circulation in it. The diffusion of medicinal substances also improves, pain during dressing is reduced, and bacterial contamination of the wound is reduced, which contributes to faster and smoother healing. The treatment time for such patients in the hospital is noticeably reduced.

A separate area of ​​application of ultrasound in medicine is ultrasound physiotherapy.

The mechanism of the physiological effect of therapeutic ultrasound on the tissue of a living organism has not yet been fully elucidated. It is customary to distinguish three main factors of the influence of ultrasound: mechanical, thermal and physico-chemical. The mechanical effect consists of vibration micromassage of tissues at the cellular and subcellular levels, increasing the permeability of cell membranes and metabolism in the cells and tissues of the body. Thermal effect ultrasound at its low intensities used for therapeutic purposes is insignificant. Heat can accumulate mainly in tissues that absorb ultrasonic energy the most (nervous, bone), as well as at the boundaries of environments with different acoustic resistance (at the boundary of bone and soft tissue) and in places with insufficient blood circulation.

The physicochemical effect of ultrasound is mainly due to the fact that the use of acoustic energy causes mechanical resonance in the substance of living tissues. At the same time, the movement of molecules accelerates, their disintegration into ions increases, the electrical state of cells and pericellular fluid changes, new electric fields are formed, and diffusion through biological membranes, metabolic processes are activated,

When the skin is exposed to ultrasound, its barrier-protective function improves, the activity of the sweat and sebaceous glands increases, and regeneration processes are activated. Interestingly, skin sensitivity various areas body to ultrasound is not the same: in the area of ​​the face and abdomen it is higher than in the area of ​​​​the limbs.

When exposed to ultrasound on the nervous system with a power of 0.5 W/cm2. the speed of excitation along nerve fibers increases, and at higher intensity - 1 W/cm2. - it decreases. Ultrasound of moderate intensity has an antispasmodic effect - it relieves spasms of the bronchi, bile and urinary tract, intestines, and increases urination. Under its influence, vascular tone is normalized, blood supply to tissues is improved, and their absorption of oxygen increases.

Ultrasound is used to treat chronic tonsillitis. The affected tonsils are “sounded” with low-intensity ultrasound, due to which the activity of pathogenic microorganisms is reduced, tissue nutrition is improved, and immunobiological processes are activated. As a result, such outpatient treatment helps preserve the tonsils, which play an important role in defensive reactions body. Rostov doctors have developed an original method of ultrasonic eye massage. After instillation of the anesthetic drug, a ring frame is placed on the patient’s eye and the ultrasound is turned on. After a dozen sessions of such ultrasonic massage in patients with initial form glaucoma, intraocular pressure is normalized.

In gynecology, ultrasound is used to treat cervical erosion. After just two or three ultrasound procedures, carried out at intervals of 1-2 days, the erosion began to heal, and after a month in most patients it completely disappeared.

One of the specializations of ultrasound therapy is the treatment of prostate adenoma. This disease mainly affects older men. Treatment in most cases is surgical. The use of ultrasound therapy for prostate adenoma and prostatitis gives good result: after several procedures, the patients’ pain almost completely disappeared, urination became normal, and their general condition improved. “Sounding” performed after surgery to remove the gland contributes to a better course of the postoperative period.

Ultrasound therapy is most widely used for osteochondrosis, arthrosis, radiculitis and other diseases of the peripheral nervous system and musculoskeletal system.

Ultrasound treatment is not recommended for acute infectious diseases, angina pectoris, cardiac aneurysm, hypertension stages II B and III, blood diseases, bleeding tendency, and also during pregnancy. Previously, the presence of malignant tumors was also considered a contraindication. But in lately The issue of using ultrasound therapy for their treatment, both separately and in combination with radiotherapy, is being studied.

Sometimes ultrasound is used in combination with various medicinal substances. This method is called phonophoresis, although it would be more correct to call it ultraphonophoresis. The method is based on increasing the permeability of the skin, mucous membranes, cell membranes and improving local microcirculation under the influence of ultrasound. All this helps the introduction of a number of medicinal substances through the skin and mucous membranes.

Currently, phonophoresis of many drugs is used, such as hydrocortisone, analgin, aminazine, interferon, complamin, heparin, aloe extract, FiBS, a number of antibiotics, etc. However, it has been found that some drugs, for example, aminophylline, ascorbic acid acid, thiamine (vitamin B1) and others, when “sounded” by ultrasound, either do not penetrate the body or are destroyed. Sometimes, during phonophoresis, the skin or mucous membrane is first sounded with ultrasound, and then, after removing the contact medium, a medicinal substance is applied in the form of a lotion or ointment. But more often the procedure is performed in the same way as conventional ultrasound irradiation. Medicinal substances are first applied to the surface of the skin or mucous membrane in the form aqueous solution, emulsions or ointments. They also serve as a contact medium during scoring. With phonophoresis, as well as with “sounding” without the use of drugs, two techniques are used: stable and labile. With the first, the vibrator remains motionless during the procedure, with the second, it moves slowly over the surface of the skin or mucous membrane.

In recent years, the possibilities of using ultraphonopuncture, focused ultrasound, biocontrolled and biosynchronized ultrasound have been studied. The scope of ultrasound therapy continues to expand.

Ultrasound - mechanical vibrations, located above the frequency range audible to the human ear (usually 20 kHz). Ultrasonic vibrations travel in waveforms, similar to the propagation of light. However, unlike light waves, which can travel in a vacuum, ultrasound requires an elastic medium such as a gas, liquid or solid.

, (3)

For transverse waves it is determined by the formula

Sound dispersion- addiction phase speed monochromatic sound waves on their frequency. The dispersion of the speed of sound can be determined as physical properties environment, and the presence of foreign inclusions in it and the presence of boundaries of the body in which the sound wave propagates.

Types of ultrasonic waves

Most ultrasound techniques use either longitudinal or shear waves. There are also other forms of ultrasound propagation, including surface waves and Lamb waves.

Longitudinal ultrasonic waves– waves, the direction of propagation of which coincides with the direction of displacements and velocities of particles of the medium.

Transverse ultrasonic waves– waves propagating in a direction perpendicular to the plane in which the directions of displacements and velocities of particles of the body lie, the same as shear waves.

Surface (Rayleigh) ultrasonic waves have elliptical particle motion and spread over the surface of the material. Their speed is approximately 90% of the speed of shear wave propagation, and their penetration into the material is equal to approximately one wavelength.

Lamb wave- an elastic wave propagating in a solid plate (layer) with free boundaries, in which the oscillatory displacement of particles occurs both in the direction of wave propagation and perpendicular to the plane of the plate. Lamb waves are one of the types of normal waves in an elastic waveguide - in a plate with free boundaries. Because these waves must satisfy not only the equations of the theory of elasticity, but also the boundary conditions on the surface of the plate; the pattern of motion in them and their properties are more complex than those of waves in unbounded solids.

Visualization of ultrasonic waves

For a plane sinusoidal traveling wave, the ultrasound intensity I is determined by the formula

, (5)

IN spherical traveling wave Ultrasound intensity is inversely proportional to the square of the distance from the source. IN standing wave I = 0, i.e., there is no flow of sound energy on average. Ultrasound intensity in harmonic plane traveling wave equal to the energy density of the sound wave multiplied by the speed of sound. The flow of sound energy is characterized by the so-called Umov vector- vector of the energy flux density of the sound wave, which can be represented as the product of the ultrasound intensity and the wave normal vector, i.e. unit vector, perpendicular to the wave front. If the sound field is a superposition harmonic waves different frequencies, then for the vector of the average sound energy flux density there is additivity of the components.

For emitters creating a plane wave, they speak of radiation intensity, meaning by this emitter power density, i.e. the radiated sound power per unit area of ​​the radiating surface.

Sound intensity is measured in SI units in W/m2. In ultrasonic technology, the range of changes in ultrasound intensity is very large - from threshold values ​​of ~ 10 -12 W/m2 to hundreds of kW/m2 at the focus of ultrasonic concentrators.

Table 1 - Properties of some common materials

Ultrasound attenuation

One of the main characteristics of ultrasound is its attenuation. Ultrasound attenuation is a decrease in amplitude and, therefore, a sound wave as it propagates. Ultrasound attenuation occurs due to a number of reasons. The main ones are:

The first of these reasons is due to the fact that as a wave propagates from a point or spherical source, the energy emitted by the source is distributed over an ever-increasing surface of the wave front and, accordingly, the energy flow through a unit surface decreases, i.e. . For a spherical wave, wave surface which increases with distance r from the source as r 2 , the amplitude of the wave decreases in proportion to , and for cylindrical wave- proportionally.

The attenuation coefficient is expressed either in decibels per meter (dB/m) or in decibels per meter (Np/m).

For a plane wave, the amplitude attenuation coefficient with distance is determined by the formula

, (6)

The attenuation coefficient versus time is determined

, (7)

The unit dB/m is also used to measure the coefficient, in this case

, (8)

Decibel (dB) – logarithmic unit measurements of energy or power ratios in acoustics.

, (9)

• where A 1 is the amplitude of the first signal,
• A 2 – amplitude of the second signal

Then the relationship between the units of measurement (dB/m) and (1/m) will be:

Reflection of ultrasound from the interface

When a sound wave falls on the interface, part of the energy will be reflected into the first medium, and the rest of the energy will pass into the second medium. The relationship between the reflected energy and the energy passing into the second medium is determined by the wave impedances of the first and second medium. In the absence of sound speed dispersion characteristic impedance does not depend on the waveform and is expressed by the formula:

The reflection and transmission coefficients will be determined as follows

, (12)

, (13)

• where D is the sound pressure transmission coefficient

It is also worth noting that if the second medium is acoustically “softer”, i.e. Z 1 >Z 2, then upon reflection the phase of the wave changes by 180˚.

The coefficient of energy transmission from one medium to another is determined by the ratio of the intensity of the wave passing into the second medium to the intensity of the incident wave

, (14)

Interference and diffraction of ultrasonic waves

Sound interference- uneven spatial distribution of the amplitude of the resulting sound wave depending on the relationship between the phases of the waves that develop at one point or another in space. When harmonic waves of the same frequency are added, the resulting spatial distribution of amplitudes forms a time-independent interference pattern, which corresponds to a change in the phase difference of the component waves when moving from point to point. For two interfering waves, this pattern on a plane has the form of alternating bands of amplification and attenuation of the amplitude of a value characterizing the sound field (for example, sound pressure). For two plane waves, the stripes are rectilinear with an amplitude that varies across the stripes according to the change in the phase difference. An important special case of interference is the addition of a plane wave with its reflection from a plane boundary; this creates standing wave with planes of nodes and antinodes located parallel to the boundary.

Sound diffraction- deviation of sound behavior from the laws of geometric acoustics, due to the wave nature of sound. The result of sound diffraction is the divergence of ultrasonic beams when moving away from the emitter or after passing through a hole in the screen, the bending of sound waves into the shadow region behind obstacles large compared to the wavelength, the absence of a shadow behind obstacles small compared to the wavelength, etc. n. Sound fields created by diffraction of the original wave on obstacles placed in the medium, on inhomogeneities of the medium itself, as well as on irregularities and inhomogeneities of the boundaries of the medium, are called scattered fields. For objects on which sound diffraction occurs that are large compared to the wavelength, the degree of deviation from the geometric pattern depends on the value of the wave parameter

, (15)

• where D is the diameter of the object (for example, the diameter of an ultrasonic emitter or obstacle),
• r - distance of the observation point from this object

Ultrasound emitters

Ultrasound emitters- devices used to excite ultrasonic vibrations and waves in gaseous, liquid and solid media. Ultrasound emitters convert energy of some other type into energy.

The most widely used ultrasound emitters are electroacoustic transducers. In the vast majority of ultrasound emitters of this type, namely in piezoelectric transducers , magnetostrictive converters, electrodynamic emitters, electromagnetic and electrostatic emitters, electrical energy is converted into vibration energy of any solid(emitting plate, rod, diaphragm, etc.), which emits in environment acoustic waves. All of the listed converters are, as a rule, linear, and, therefore, the oscillations of the radiating system reproduce the exciting electrical signal in shape; Only at very large oscillation amplitudes near the upper limit of the dynamic range of the ultrasound emitter can nonlinear distortions occur.

Converters designed to emit monochromatic waves use the phenomenon resonance: they operate on one of the natural oscillations of a mechanical oscillatory system, to the frequency of which the generator is tuned electrical vibrations, exciting converter. Electroacoustic transducers that do not have a solid-state radiating system are used relatively rarely as ultrasound emitters; these include, for example, ultrasound emitters based on electrical discharge in a liquid or on the electrostriction of a liquid.

Characteristics of the ultrasound emitter

The main characteristics of ultrasound emitters include their frequency spectrum, emitted sound power, radiation directivity. In the case of monofrequency radiation, the main characteristics are operating frequency ultrasound emitter and its frequency band, the boundaries of which are determined by a drop in radiated power by half compared to its value at the frequency of maximum radiation. For resonant electroacoustic transducers, the operating frequency is natural frequency f 0 converter, and bandwidthΔf is determined by its quality factor Q.

Ultrasound emitters (electroacoustic transducers) are characterized by sensitivity, electroacoustic efficiency and their own electrical impedance.

Ultrasound emitter sensitivity- the ratio of sound pressure at the maximum directional characteristic at a certain distance from the emitter (most often at a distance of 1 m) to electrical voltage on it or to the current flowing in it. This characteristic applies to ultrasonic emitters used in audio alarm systems, sonar and other similar devices. For emitters for technological purposes, used, for example, in ultrasonic cleaning, coagulation, and influence on chemical processes, the main characteristic is power. Along with the total radiated power, estimated in W, ultrasound emitters are characterized by specific power, i.e., the average power per unit area of ​​the emitting surface, or the average radiation intensity in the near field, estimated in W/m2.

The efficiency of electroacoustic transducers emitting acoustic energy into the sounded environment is characterized by their magnitude electroacoustic efficiency, which is the ratio of emitted acoustic power to expended electrical power. In acoustoelectronics, to evaluate the efficiency of ultrasound emitters, the so-called electrical loss coefficient is used, equal to the ratio (in dB) of electrical power to acoustic power. The efficiency of ultrasonic tools used in ultrasonic welding, machining and the like is characterized by the so-called efficiency coefficient, which is the ratio of the square of the amplitude of the oscillatory displacement at the working end of the concentrator to the electrical power consumed by the transducer. Sometimes the effective electromechanical coupling coefficient is used to characterize energy conversion in ultrasound emitters.

Emitter sound field

The sound field of the transducer is divided into two zones: near zone and far zone. Near zone this is the area directly in front of the transducer where the amplitude of the echo passes through a series of maxima and minima. The near zone ends at the last maximum, which is located at a distance N from the converter. It is known that the location of the last maximum is the natural focus of the transducer. Far zone This is the area beyond N, where the sound field pressure gradually decreases to zero.

The position of the last maximum N on the acoustic axis, in turn, depends on the diameter and wavelength and for a circular disk emitter is expressed by the formula

, (17)

However, since D is usually much larger, the equation can be simplified to the form

The characteristics of the sound field are determined by the design of the ultrasonic transducer. Consequently, the propagation of sound in the area under study and the sensitivity of the sensor depend on its shape.

Ultrasound Applications

The diverse applications of ultrasound, in which its various features are used, can be divided into three areas. is associated with obtaining information through ultrasonic waves, - with active influence on matter, and - with the processing and transmission of signals (the directions are listed in the order of their historical formation). For each specific application, ultrasound of a certain frequency range is used.

Frequencies of 16 Hz-20 kHz, which the human hearing aid can perceive, are usually called sound or acoustic, for example, the squeak of a mosquito “10 kHz.” But the air, the depths of the seas and the bowels of the earth are filled with sounds that lie outside this range - infra and ultrasound. In nature, ultrasound is found as a component of many natural noises, in the noise of wind, waterfalls, rain, sea pebbles rolled by the surf, and in lightning discharges. Many mammals, such as cats and dogs, have the ability to perceive ultrasound with a frequency of up to 100 kHz, and the location abilities of bats, nocturnal insects and marine animals are well known to everyone. The existence of such sounds was discovered with the development of acoustics only at the end of the 19th century. At the same time, the first studies of ultrasound began, but the foundations of its application were laid only in the first third of the 20th century.

What is ultrasound

Ultrasonic waves (inaudible sound) by their nature do not differ from waves in the audible range and obey the same physical laws. But ultrasound has specific features that have determined its widespread use in science and technology.

Here are the main ones:

• Short wavelength. For the lowest ultrasonic range, the wavelength does not exceed several centimeters in most media. The short wavelength determines the ray nature of the propagation of ultrasonic waves. Near the emitter, ultrasound propagates in the form of beams, similar in size to the size of the emitter. When it hits inhomogeneities in the medium, the ultrasonic beam behaves like a light beam experiencing reflection, refraction, and scattering, which makes it possible to form sound images in optically opaque media using purely optical effects (focusing, diffraction, etc.)
• A short period of oscillation, which makes it possible to emit ultrasound in the form of pulses and carry out precise time selection of propagating signals in the medium.
• Possibility of obtaining high values ​​of oscillation intensity at low amplitude, because the vibration energy is proportional to the square of the frequency. This makes it possible to create ultrasonic beams and fields with a high level of energy, without requiring large-sized equipment.
• Significant acoustic currents develop in the ultrasonic field, so the effect of ultrasound on the environment gives rise to specific physical, chemical, biological and medical effects, such as cavitation, capillary effect, dispersion, emulsification, degassing, disinfection, local heating and many others.

History of ultrasound

Attention to acoustics was caused by the needs of the navy of the leading powers - England and France, because. acoustic is the only type of signal that can travel far in water. In 1826, the French scientist Colladon determined the speed of sound in water. Colladon's experiment is considered the birth of modern hydroacoustics. The underwater bell in Lake Geneva was struck while the gunpowder was ignited. The flash from the gunpowder was observed by Colladon at a distance of 10 miles. He also heard the sound of the bell using an underwater auditory tube. By measuring the time interval between these two events, Colladon calculated the speed of sound to be 1435 m/sec. The difference with modern calculations is only 3 m/sec.

In 1838, in the USA, sound was first used to determine the profile of the seabed. The source of the sound, as in Colladon’s experiment, was a bell sounding underwater, and the receiver was large auditory tubes lowered overboard. The results of the experiment were disappointing - the sound of the bell, as well as the explosion 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 the creation of directed sound beams.

The first ultrasound generator was made in 1883 by the Englishman Galton. The ultrasound was created similar to the high-pitched sound on the edge of a knife when a stream of air hits it. The role of such a tip in Galton's whistle was played by a cylinder with sharp edges. Air (or other gas), coming out under pressure through an annular nozzle with a diameter the same as the edge of the cylinder, ran into it and high-frequency oscillations arose. By blowing the whistle with hydrogen, it was possible to obtain oscillations of up to 170 kHz.

In 1880, Pierre and Jacques Curie made a discovery that was decisive for ultrasound technology. The Curie brothers noticed that when pressure was applied to quartz crystals, an electrical charge was generated that was directly proportional to the force applied to the crystal. This phenomenon was called "piezoelectricity" from the Greek word meaning "to press". They also demonstrated the inverse piezoelectric effect, which occurred when a rapidly changing electrical potential was applied to the crystal, causing it to vibrate. From now on, it is technically possible to manufacture small-sized ultrasound emitters and receivers.

The death of the Titanic from a collision with an iceberg and the need to combat new weapons—submarines—required the rapid development of ultrasonic hydroacoustics. In 1914, the French physicist Paul Langevin, together with a Russian scientist who lived in Switzerland, Konstantin Shilovsky, first developed a sonar consisting of an ultrasound emitter and a hydrophone - a receiver of ultrasonic vibrations, based on the piezoelectric effect. The Langevin-Shilovsky sonar was the first ultrasonic device used in practice. Also at the beginning of the century, the Russian scientist S.Ya. Sokolov developed the fundamentals of ultrasonic flaw detection in industry. In 1937, the German psychiatrist Karl Dussick, together with his brother Friedrich, a physicist, first used ultrasound to detect brain tumors, but the results they obtained turned out to be unreliable. In medical diagnostics, ultrasound began to be used only in the 50s of the 20th century in the USA.

Ultrasound Applications

The diverse applications of ultrasound can be divided into three areas:

1. obtaining information via ultrasound
2. influence on a substance, being
3. 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 for:

• control of chemical reactions, phase transitions, polymerization, etc.
• determination of strength characteristics and composition of materials,
• determining the presence of impurities,
• determining the flow rate of liquid and gas

With the help of ultrasound, you can wash clothes, repel rodents, use them in medicine, check various materials for defects, and much more interesting things.