With the development of acoustics at the end of the 19th century, ultrasound was discovered, and the first studies of ultrasound began at the same time, but the foundations of its application were laid only in the first third of the 20th century.
Ultrasound and its properties
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.
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.
The main wave parameters are wavelength, frequency and period. Ultrasonic waves 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:
- 1. 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.).
- 2. 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.
The needs of the navy of the leading powers - England and France, for exploring the depths of the sea, aroused the interest of many scientists in the field of acoustics, because This is the only type of signal that can travel far in water. So in 1826, the French scientist Colladon determined the speed of sound in water. 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 results of the experiment were disappointing. The sound of the bell 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.
The first ultrasound generator was made in 1883 by the 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 decisive discovery 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 the talented Russian emigrant scientist Konstantin Vasilyevich Shilovsky, 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.
Waves began more than a hundred years ago; only in the last half century have they become widely used in various fields of human activity. This is due to the active development of both the quantum and nonlinear branches of acoustics, as well as quantum electronics and solid state physics. Today, ultrasound is not just a designation for the high-frequency region of acoustic waves, but an entire scientific direction in modern physics and biology, which is associated with industrial, information and measurement technologies, as well as diagnostic, surgical and therapeutic methods of modern medicine.
What is this?
All sound waves can be divided into those audible by humans - these are frequencies from 16 to 18 thousand Hz, and those that are outside the range of human perception - infra- and ultrasound. Infrasound refers to waves similar to sound waves, but perceptible to the human ear. The upper limit of the infrasound region is considered to be 16 Hz, and the lower limit is 0.001 Hz.
Ultrasound is also sound waves, but only their frequency is higher than the human hearing aid can perceive. As a rule, they mean frequencies from 20 to 106 kHz. Their upper limit depends on the medium in which these waves propagate. Thus, in a gaseous environment the limit is 106 kHz, and in solids and liquids it reaches 1010 kHz. There are ultrasonic components in the sound of rain, wind or waterfalls, thunderstorms and the rustling of pebbles rolled by sea waves. It is thanks to the ability to perceive and analyze ultrasonic waves that whales and dolphins, bats and nocturnal insects navigate in space.
A little history
The first studies were carried out at the beginning of the 19th century by the French scientist F. Savart, who sought to find out the upper frequency limit of audibility of the human hearing aid. Subsequently, such famous scientists as the German V. Wien, the Englishman F. Galton, and the Russian with a group of students studied ultrasonic waves.
In 1916, French physicist P. Langevin, in collaboration with Russian émigré scientist Konstantin Shilovsky, was able to use quartz to receive and emit ultrasound for marine measurements and detect underwater objects, allowing researchers to create the first sonar, consisting of an ultrasound emitter and receiver.
In 1925, the American W. Pierce created a device, today called the Pierce interferometer, which measures with great accuracy the speed and absorption of ultrasound in liquid and gaseous media. In 1928, the Soviet scientist S. Sokolov was the first to use ultrasonic waves to detect various defects in solids, including metal ones.
In the post-war 50-60s, based on the theoretical developments of a team of Soviet scientists headed by L. D. Rosenberg, the widespread use of KM in various industrial and technological fields began. At the same time, thanks to the work of English and American scientists, as well as the research of Soviet researchers such as R.V. Khokhlova, V.A. Krasilnikov and many others, the scientific discipline of nonlinear acoustics is rapidly developing.
Around the same time, the first American attempts to use ultrasound in medicine were made.
Back in the late forties of the last century, the Soviet scientist Sokolov developed a theoretical description of a device designed for visualizing opaque objects - an “ultrasonic” microscope. Based on these works, in the mid-70s, specialists from Stanford University created a prototype of a scanning acoustic microscope.
Peculiarities
Having a common nature, waves in the audible range, as well as ultrasonic ones, obey physical laws. But ultrasound has a number of features that allow it to be widely used in various fields of science, medicine and technology:
1. Short wavelength. For the lowest ultrasonic range it does not exceed several centimeters, causing the radial nature of signal propagation. In this case, the wave is focused and propagated in linear beams.
2. A short period of oscillation, due to which ultrasound can be emitted pulsed.
3. In various environments, ultrasonic vibrations with a wavelength not exceeding 10 mm have properties similar to light rays, which makes it possible to focus vibrations, form directed radiation, that is, not only send energy in the desired direction, but also concentrate it in the required volume.
4. With a small amplitude, it is possible to obtain high values of vibration energy, which makes it possible to create high-energy ultrasonic fields and beams without the use of large-sized equipment.
5. Under the influence of ultrasound on the environment, many specific physical, biological, chemical and medical effects occur, such as:
- dispersing;
- cavitation;
- degassing;
- local heating;
- disinfection and much more. etc.
Kinds
All ultrasonic frequencies are divided into three types:
- ULF - low, with a range from 20 to 100 kHz;
- USCh - mid-frequency - from 0.1 to 10 MHz;
- UHF - high frequency - from 10 to 1000 MHz.
Today, the practical use of ultrasound is primarily the use of low-intensity waves for measuring, monitoring and studying the internal structure of various materials and products. High frequencies are used to actively influence various substances, which makes it possible to change their properties and structure. Diagnosis and treatment of many diseases with ultrasound (using various frequencies) is a separate and actively developing area of modern medicine.
Where is it used?
In recent decades, not only scientific theorists have been interested in ultrasound, but also practitioners who are increasingly actively introducing it into various types of human activity. Today ultrasonic units are used for:
Obtaining information about substances and materials | Events | Frequency in kHz |
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Study of the composition and properties of substances | solids | |||
liquids | ||||
Control of sizes and levels | ||||
Hydrolocation | ||||
Flaw detection | ||||
Medical diagnostics | ||||
Impacts on substances | Soldering and metallization | |||
Plastic deformation | ||||
Mechanical restoration | ||||
Emulsification | ||||
Crystallization | ||||
Spraying | ||||
Aerosol coagulation | ||||
Dispersing | ||||
Chemical processes | ||||
Effect on combustion | ||||
Surgery | ||||
Signal processing and control | Acoustoelectronic converters | |||
Delay lines | ||||
Acousto-optical devices | ||||
In the modern world, ultrasound is an important technological tool in such industrial sectors as:
- metallurgical;
- chemical;
- agricultural;
- textile;
- food;
- pharmacological;
- machine and instrument making;
- petrochemical, refining and others.
In addition, ultrasound is increasingly used in medicine. This is what we will talk about in the next section.
Use in medicine
In modern practical medicine, there are three main areas of use of ultrasound of various frequencies:
1. Diagnostic.
2. Therapeutic.
3. Surgical.
Let's take a closer look at each of these three areas.
Diagnostics
One of the most modern and informative methods of medical diagnostics is ultrasound. Its undoubted advantages are: minimal impact on human tissue and high information content.
As already mentioned, ultrasound is sound waves propagating in a homogeneous medium in a straight line and at a constant speed. If on their path there are areas with different acoustic densities, then part of the vibrations is reflected, and the other part is refracted, while continuing their own. Thus, the greater the difference in the density of the boundary media, the more ultrasonic vibrations are reflected. Modern methods of ultrasound examination can be divided into localization and transmission.
Ultrasonic location
In the process of such research, pulses reflected from the boundaries of media with different acoustic densities are recorded. Using a movable sensor, you can determine the size, location and shape of the object being examined.
Transillumination
This method is based on the fact that different tissues of the human body absorb ultrasound differently. During the examination of an internal organ, a wave with a certain intensity is sent into it, after which the transmitted signal from the reverse side is recorded with a special sensor. The picture of the scanned object is reproduced based on changes in signal intensity at the “input” and “output”. The received information is processed and converted by a computer in the form of an echogram (curve) or sonogram - a two-dimensional image.
Doppler method
This is the most actively developing diagnostic method that uses both pulsed and continuous ultrasound. Doppler ultrasound is widely used in obstetrics, cardiology and oncology, as it allows you to monitor even the most minor changes in capillaries and small blood vessels.
Diagnostic Applications
Today, ultrasound imaging and measurement methods are most widely used in such areas of medicine as:
- obstetrics;
- ophthalmology;
- cardiology;
- neurology of newborns and infants;
- examination of internal organs:
Kidney ultrasound;
Gallbladder and ducts;
Female reproductive system;
- diagnostics of external and subsurface organs (thyroid and mammary glands).
Use in therapy
The main therapeutic effect of ultrasound is due to its ability to penetrate human tissue, heat and warm them, and perform micromassage of individual areas. Ultrasound can be used for both direct and indirect effects on the source of pain. In addition, under certain conditions, these waves have bactericidal, anti-inflammatory, analgesic and antispasmodic effects. Ultrasound used for therapeutic purposes is conventionally divided into high- and low-intensity vibrations.
It is low intensity waves that are most widely used to stimulate physiological reactions or mild, non-damaging heat. Ultrasound treatment has yielded positive results for diseases such as:
- arthrosis;
- arthritis;
- myalgia;
- spondylitis;
- neuralgia;
- varicose and trophic ulcers;
- Bekhterev's disease;
- obliterating endarteritis.
Research is being conducted in which ultrasound is used to treat Meniere's disease, duodenal and gastric ulcers, bronchial asthma, and otosclerosis.
Ultrasound surgery
Modern surgery using ultrasound waves is divided into two areas:
Selectively destroying tissue areas with special controlled high-intensity ultrasonic waves with frequencies from 10 6 to 10 7 Hz;
Using a surgical instrument with superimposed ultrasonic vibrations from 20 to 75 kHz.
An example of selective ultrasound surgery is the crushing of kidney stones with ultrasound. During this non-invasive operation, an ultrasonic wave acts on the stone through the skin, that is, from outside the human body.
Unfortunately, this surgical method has a number of limitations. Ultrasonic crushing should not be used in the following cases:
Pregnant women at any stage;
If the diameter of the stones is more than two centimeters;
For any infectious diseases;
In the presence of diseases that interfere with normal blood clotting;
In case of severe damage to bone tissue.
Despite the fact that ultrasound removal of kidney stones is carried out without surgical incisions, it is quite painful and is performed under general or local anesthesia.
Surgical ultrasound instruments are used not only to cut bone and soft tissue less painfully, but also to reduce blood loss.
Let's turn our attention to dentistry. Ultrasound removes dental stones less painfully, and all other doctor’s manipulations are much easier to tolerate. In addition, in traumatology and orthopedic practice, ultrasound is used to restore the integrity of broken bones. During such operations, the space between bone fragments is filled with a special composition consisting of bone chips and special liquid plastic, and then exposed to ultrasound, due to which all components are firmly connected. Those who have undergone surgical interventions during which ultrasound was used leave different reviews - both positive and negative. However, it should be noted that there are still more satisfied patients!
Recently, the use of ultrasound has become widespread in various fields of science, technology and medicine.
What is it? Where are ultrasonic vibrations used? What benefits can they bring to humans?
Ultrasound is called wave-like oscillatory movements with a frequency of more than 15-20 kilohertz, arising under the influence of the environment and inaudible to the human ear. Ultrasonic waves are easily focused, which increases the intensity of vibrations.
Ultrasound sources
In nature, ultrasound accompanies various natural noises: rain, thunderstorm, wind, waterfall, sea surf. Some animals (dolphins, bats) can produce it, which helps them detect obstacles and navigate in space.
All existing artificial ultrasound sources are divided into 2 groups:
- generators - vibrations occur as a result of overcoming obstacles in the form of a gas or liquid jet.
- electroacoustic transducers - transform electrical voltage into mechanical vibrations, which leads to the emission of acoustic waves into the environment.
Ultrasound receivers
Low and medium frequencies of ultrasonic vibrations are mainly perceived by electroacoustic transducers of the piezoelectric type. Depending on the conditions of use, resonant and broadband devices are distinguished.
To obtain the characteristics of the sound field, which are averaged over time, thermal receivers are used, represented by thermocouples or thermistors, which are coated with a substance with sound-absorbing properties.
Optical methods, including light diffraction, can estimate ultrasound intensity and sound pressure.
Where are ultrasonic waves used?
Ultrasonic waves have found application in a variety of fields.
Conventionally, the areas of use of ultrasound can be divided into 3 groups:
- receiving the information;
- active influence;
- signal processing and transmission.
In each case, a specific frequency range is used.
Ultrasonic cleaning
Ultrasonic exposure ensures high-quality cleaning of parts. With simple rinsing of parts, up to 80% of the dirt remains on them, with vibration cleaning - close to 55%, with manual cleaning - about 20%, and with ultrasonic cleaning - less than 0.5%.
Parts with complex shapes can only be removed from contamination using ultrasound.
Ultrasonic waves are also used to purify air and gases. An ultrasonic emitter placed in a dust-sedimentation chamber increases its effectiveness hundreds of times.
Mechanical processing of brittle and ultra-hard materials
Thanks to ultrasound, ultra-precise processing of materials has become possible. It is used to make cuts of various shapes, matrices, grind, engrave and even drill diamonds.
Application of ultrasound in radio electronics
In radio electronics, there is often a need to delay an electrical signal in relation to some other signal. For this purpose, they began to use ultrasonic delay lines, the action of which is based on the conversion of electrical impulses into ultrasonic waves. They are also capable of converting mechanical vibrations into electrical ones. Accordingly, the delay lines can be magnetostrictive and piezoelectric.
Use of ultrasound in medicine
The use of ultrasonic vibrations in medical practice is based on the effects that occur in biological tissues during the passage of ultrasound through them. Oscillatory movements have a massaging effect on the tissue, and when ultrasound is absorbed, they are locally heated. At the same time, various physical and chemical processes are observed in the body that do not cause irreversible changes. As a result, metabolic processes are accelerated, which has a beneficial effect on the functioning of the entire body.
Application of ultrasound in surgery
The intense action of ultrasound causes strong heating and cavitation, which has found application in surgery. The use of focal ultrasound during operations makes it possible to carry out a local destructive effect in the deep parts of the body, including in the brain area, without causing harm to nearby tissues.
In their work, surgeons use instruments with a working end in the form of a needle, scalpel or saw. In this case, the surgeon does not need to exert any effort, which reduces the traumatic nature of the procedure. At the same time, ultrasound has an analgesic and hemostatic effect.
Ultrasound exposure is prescribed when a malignant neoplasm is detected in the body, which contributes to its destruction.
Ultrasonic waves also have an antibacterial effect. Therefore, they are used to sterilize instruments and medicines.
Examination of internal organs
Ultrasound is used to perform a diagnostic examination of organs located in the abdominal cavity. A special apparatus is used for this.
During an ultrasound examination, it is possible to detect various pathologies and abnormal structures, distinguish benign from malignant neoplasms, and detect infection.
Ultrasound vibrations are used in liver diagnostics. They allow you to identify diseases of the bile flow, examine the gallbladder for the presence of stones and pathological changes, and identify cirrhosis and benign liver diseases.
Ultrasound examination has found wide application in the field of gynecology, especially in the diagnosis of the uterus and ovaries. It helps to detect gynecological diseases and differentiate between malignant and benign tumors.
Ultrasound waves are also used to examine other internal organs.
Application of ultrasound in dentistry
In dentistry, dental plaque and tartar are removed using ultrasound. Thanks to it, the layers are removed quickly and painlessly, without damaging the mucous membrane. At the same time, the oral cavity is disinfected.
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 with the simultaneous ignition of gunpowder. 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 vibrations 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 decisive discovery 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:
- obtaining information via ultrasound
- influence on a substance, being
- 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.
ULTRASONIC VIBRATIONS, vibrations that have such a high frequency that the 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 produced inaudible sounds, their demonstration became part of teaching practice. However, until recently, ultrasonic vibrations did not have any practical significance, since there were no sufficiently powerful sources of ultrasonic vibrations. The beginning of the revival of research into ultrasonic vibrations should be considered 1917-19, when Langevin in Paris managed to use quartz to produce powerful ultrasonic waves in water. In particular, research into ultrasonic vibrations was revived after Cady’s work, which began in 1922; this revival continues to this day.
Methods for producing ultrasonic vibrations very diverse; Almost all methods for producing vibrations are also suitable for ultrasonic vibrations. Not too powerful sounds are most easily produced by a Galton whistle (Fig. 1), which is an air resonator, the natural frequency of which can vary from 10,000 to 30,000 Hz and a stream of air is directed against the hole. The power of such a whistle is small, and in all the methods described below, the source of ultrasonic frequency energy is an alternating electric current, usually obtained from self-oscillating electrical circuits with an electron tube; 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 very strongly. The first powerful source of ultrasonic vibrations was a piezoelectric Langevin transmitter designed for work in water. The main part of the Langevin transmitter is a quartz plate Q (Fig. 2), cut perpendicular to the electrical axis and equipped with plates A, A tightly glued to it. If an alternating current is supplied to them, then due to the piezoelectric effect, the quartz plate expands and contracts with a frequency equal to the frequency 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 water, while the other is enclosed in the housing shown in Fig. 2 schematically dotted line. Such transmitters are usually built at frequencies of about 30,000-40,000 Hz.
Wood and Lumis used for their experiments plates with very thin linings, which had virtually no effect on the plate’s natural frequency. Since the total thickness of the transmitter was much smaller, the frequency of ultrasonic vibrations was much higher, namely about 5·10 5 Hz. Myasnikov managed to reach frequencies of 10 6 -10 7 Hz; In both cases, the transmitters were placed in an oil bath, where ultrasonic waves propagated. There are successful attempts to obtain ultrasonic vibrations of sufficient power by using magnetostrictive vibrations. Gaines obtained very strong ultrasounds by exciting magnetostrictive oscillations in a nickel tube, the lower part of which, located in the air, was subject to an alternating magnetic field, and the upper part, located in the liquid, emitted sound. An electric spark also produces unsatisfactory results. Currently, the best practical method for producing high-power ultrasonic transmitters is the Langevin method. Experiments on producing ultrasonic waves in air using the same method have shown that the impact of transmitters of this type in air is very insignificant.
Propagation of ultrasonic waves in gases and liquids in general, it obeys the same laws as ordinary sound waves, but there are some peculiarities. Ultrasonic waves in air and gases are absorbed very significantly, and the higher the frequency of ultrasonic waves, the more strongly they are absorbed. The shortest of them, studied by Neklepaev, weaken 100 times, 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, a “wind” comes 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 boundary 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, entire fountains of tiny splashes are formed, and in experiments with oil and water, an emulsion of oil in water is formed; Ultrasonic waves propagating along a glass rod cause a burning sensation when touched, although the thermometer shows only a slight increase in temperature. Physiology and the effects 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 in this way; Fish died near Langevin's transmitters. Perhaps, with further development, ultrasonic waves will gain therapeutic value. Due to the extremely short wavelength in the field of ultrasonic waves, diffraction of light waves is observed, as in diffraction gratings (Debye and Sears). Interferometers for ultrasonic waves were built (Pierce), which were 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 quartz resonators. Since the attenuation in oscillating quartz rods, plates and especially rings is much less than in electrical circuits, the latter are replaced by the former in all cases where a pronounced resonance is necessary. 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 (Giebe). The frequency of oscillation given by quartz rings is so constant that Morrison used them for electric clocks, which surpassed in their accuracy all previously known ones, and quartz is now the best frequency standard.
Underwater quartz transmitters for ultrasonic vibrations are still slightly widespread, but due to their high frequency they have two advantages compared to electromagnetic underwater transmitters: they have, firstly; high directivity, allowing the beam of rays emanating from them to be concentrated 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 beam of sound emanating from the transmitter is directed towards the bottom; reflected from it, returns to the same transmitter that receives it; The recording unit records the travel time of the sound from the transmitter to the bottom and back, from where the depth is calculated. Ultrasonic transmitters are used for telegraphy from ship to ship, among other things, and for submarines, for which sound communication is almost the only possible one; in this case, the ultrasonic transmitter is also a receiver. There have been attempts to use ultrasonic rays to open submarines and ice mountains (Boyle and Reid, 1926), to illuminate defects in metals (S. Sokolov), but results have not yet been obtained sufficiently reliable for the corresponding installations to be put into practice.
