Now acoustics, as a field of physics, considers a wider range of elastic vibrations - from the lowest to the extremely high, up to 1012 - 1013 Hz. Sound waves with frequencies below 16 Hz that are not audible to humans are called infrasound, sound waves with frequencies from 20,000 Hz to 109 Hz are called ultrasound, and vibrations with frequencies higher than 109 Hz are called hypersound.
These inaudible sounds have found many uses.
Ultrasounds and infrasounds play a very important role in the living world. For example, fish and other marine animals sensitively detect infrasonic waves created by storm waves. Thus, they sense the approach of a storm or cyclone in advance, and swim away to a safer place. Infrasound is a component of the sounds of the forest, sea, and atmosphere.
Ultrasounds can be produced and perceived by animals such as dogs, cats, dolphins, ants, bats, etc. Bats make short, high-pitched sounds during flight. In their flight, they are guided by the reflections of these sounds from objects encountered along the way; they can even catch insects, guided only by the echoes of their small prey. Cats and dogs may hear very high-pitched whistling sounds (ultrasounds).
INFRASOUND (from Latin infra - below, under), elastic waves of low frequency (less than 16 Hz) inaudible to the human ear. At large amplitudes, infrasound is felt as pain in the ear. Occurs during earthquakes, underwater and underground explosions, during storms and hurricanes, from tsunami waves, etc. Since infrasound is poorly absorbed, it travels over long distances and can serve as a harbinger of storms, hurricanes, and tsunamis.
In the earth's crust, shocks and vibrations of infrasound frequencies are observed from a wide variety of sources, including from rockfall explosions and transport pathogens.
Infrasound is characterized by low absorption in various media, as a result of which infrasound waves in air, water and in the earth’s crust can propagate over very long distances. This phenomenon has practical applications in determining the location of large explosions or the position of a firing weapon. The propagation of infrasound over long distances in the sea makes it possible to predict a natural disaster - a tsunami. The sounds of explosions, containing a large number of infrasonic frequencies, are used to study the upper layers of the atmosphere and the properties of the aquatic environment.
A person does not hear infrasound, but feels it; it has a destructive effect on the human body. A high level of infrasound causes dysfunction of the vestibular apparatus, predetermining dizziness and headache. Attention and performance decrease. There is a feeling of fear and general malaise. There is an opinion that infrasound greatly influences the human psyche. All mechanisms that operate at rotation speeds less than 20 rps emit infrasound. When a car moves at a speed of more than 100 km/h, it is a source of infrasound, which occurs due to the disruption of the air flow from its surface. In the mechanical engineering industry, infrasound occurs during the operation of fans, compressors of internal combustion engines, and diesel engines. According to current regulatory documents, sound pressure levels in octave bands with geometric mean frequencies 2, 4, 8, 16, Hz should be no more than 105 dB, and for bands with a frequency of 32 Hz no more than 102 dB. Due to its large length, infrasound travels over long distances in the atmosphere. It is almost impossible to stop infrasound with the help of building structures along the path of its propagation. Personal protective equipment is also ineffective. An effective means of protection is to reduce the level of infrasound at the source of its formation. Among such measures, the following can be distinguished: - increasing shaft rotation speeds to 20 or more revolutions per second; - increasing the rigidity of large oscillating structures; - elimination of low-frequency vibrations: - making design changes in the structure of sources, which allows the transition from the region of infrasonic vibrations to the region of sound vibrations; in this case, their reduction can be achieved by using sound insulation and sound absorption.
Main sources of infrasonic waves
The development of industrial production and transport has led to a significant increase in sources of infrasound in the environment and an increase in the intensity of the infrasound level.
The main man-made sources of infrasound vibrations in cities are shown in the table.
Infrasound source Characteristic frequency
infrasound range Infrasound levels
Road transport The entire spectrum of the infrasound range Outside 70-90 dB, inside up to 120 dB
Rail transport and trams 10-16 Hz Indoor and outdoor 85 to 120 dB
Industrial installations of aerodynamic and impact action 8-12 Hz Up to 90-105 dB
Ventilation of industrial installations and premises, the same in the subway 3-20 Hz Up to 75-95 dB
Jet aircraft About 20 Hz Outdoor up to 130 dB
Ultrasound is high-frequency elastic waves, to which special sections of science and technology are devoted. Typically, the ultrasonic range is considered to be a frequency range from 20,000 to several billion hertz. Although scientists have known about the existence of ultrasound for a long time, its practical use in science, technology and industry began relatively recently.
The human ear cannot perceive ultrasound, however, some animals, such as bats, can perceive and produce ultrasound. Rodents, cats, dogs, whales, and dolphins partially perceive ultrasound. Ultrasonic vibrations occur during the operation of car engines, machine tools and rocket engines. In practice, to produce ultrasound, electromechanical ultrasound generators are usually used, the action of which is based on the ability of certain materials to change their dimensions under the influence of a magnetic (magnetostrictive generators) or electric field (piezoelectric generators), while emitting high-frequency sounds. Due to its high frequency (short wavelength), ultrasound has special properties.
It is strongly absorbed by gases and weakly by liquids. In a liquid under the influence of ultrasound, voids are formed in the form of tiny bubbles with a short-term increase in pressure inside them. In addition, ultrasonic waves accelerate the processes of diffusion (interpenetration of two media into each other). significantly affect the solubility of the substance and, in general, the course of chemical reactions. These properties of ultrasound and the peculiarities of its interaction with the environment determine its wide technical and medical use.
For the first time, the idea of the practical use of ultrasound arose, as is known, in the first half of the last century in connection with the development of methods and instruments for detecting various objects in the depths of the sea: submarines, reefs, underwater parts of icebergs, etc. This was caused primarily by the sinking of the Titanic in 1912 and the beginning of the participation of submarines in military operations during the First World War.
Low-frequency ultrasonic vibrations propagate well in the air. The biological effect of their influence on the body depends on the intensity, duration of exposure and the size of the body surface exposed to ultrasound. Long-term systematic influence of ultrasound propagating in the air causes functional disorders of the nervous, cardiovascular and endocrine systems, auditory and vestibular analyzers. Severe asthenia, vascular hypotension, and a decrease in the electrical activity of the heart and brain are noted in those working on ultrasound machines. Changes in the central nervous system in the initial phase are manifested by a violation of the reflex functions of the brain (a feeling of fear in the dark, in a confined space, sudden attacks with increased heart rate, excessive sweating, spasms in the stomach, intestines, gall bladder). The most typical symptoms are vegetative-vascular dystonia with complaints of severe fatigue, headaches and a feeling of pressure in the head, difficulty concentrating, inhibition of the thought process, and insomnia.
The contact effect of high-frequency ultrasound on the hands leads to disruption of capillary blood circulation in the hands, a decrease in pain sensitivity, i.e., peripheral neurological disorders develop. It has been established that ultrasonic vibrations can cause changes in bone structure with a decrease in bone density.
Industrial vibration.
Basic concepts and definitions. The effect of vibration on the human body. Principles of vibration regulation in production
2.1 Scope and general provisions vibration
Measurement and hygienic assessment of vibration, as well as preventive measures, must be carried out in accordance with guideline 2.2.4/2.1.8-96 “Hygienic assessment of physical factors of production and the environment” (under approval).
With the approval of these sanitary standards, “Sanitary standards and rules for working with machines and equipment that create local vibration transmitted to the hands of workers” No. 3041-84, “Sanitary standards for vibration of workplaces” No. 3044-84, “Sanitary standards for permissible vibrations” become invalid in residential buildings" No. 1304-75.
2.2 Terms and definitions
The maximum permissible level (MAL) of vibration is the level of a factor that, during daily (except weekends) work, but not more than 40 hours a week throughout the entire working period, should not cause diseases or health problems detected by modern research methods in in the process of work or in the long term of the life of the present and subsequent generations. Compliance with vibration limits does not exclude health problems in hypersensitive individuals.
The permissible level of vibration in residential and public buildings is the level of the factor that does not cause significant concern in humans and does not cause significant changes in the indicators of the functional state of systems and analyzers that are sensitive to vibration.
The corrected vibration level is a single-numeric vibration characteristic, determined as the result of the energy summation of vibration levels in octave frequency bands, taking into account octave corrections.
An equivalent (energy) corrected level of time-varying vibration is an adjusted level of time-constant vibration that has the same RMS adjusted value of vibration acceleration and/or vibration velocity as the given non-constant vibration during a certain time interval.
2.3 Classification of vibrations affecting humans
According to the method of transmission to humans, they are distinguished:
General vibration transmitted through supporting surfaces to the body of a sitting or standing person;
Local vibration transmitted through human hands.
Note. Vibration transmitted to the legs of a seated person and to the forearms in contact with vibrating surfaces of work tables is referred to as local vibration.
According to the source of vibrations, they are distinguished:
Local vibration transmitted to a person from hand-held power tools (with engines), manual controls of machines and equipment;
Local vibration transmitted to a person from hand-held non-mechanized tools (without engines), for example, straightening hammers of various models and workpieces;
General vibration of category 1 - transport vibration affecting a person at the workplace of self-propelled and trailed machines, vehicles when moving across terrain, agricultural backgrounds and roads (including during their construction). Sources of transport vibration include: agricultural and industrial tractors, self-propelled agricultural machines (including combines); trucks (including tractors, scrapers, graders, rollers, etc.); snow plows, self-propelled mining rail transport;
General vibration of category 2 - transport and technological vibration affecting a person at the workplace of machines moving on specially prepared surfaces of production premises, industrial sites, and mine workings. Sources of transport and technological vibration include: excavators (including rotary), industrial and construction cranes, machines for loading (charging) open-hearth furnaces in metallurgical production; mining combines, mine loading machines, self-propelled drilling carriages; track machines, concrete pavers, floor-mounted production vehicles;
General vibration of category 3 - technological vibration that affects people at workplaces of stationary machines or is transmitted to workplaces that do not have vibration sources. Sources of technological vibration include: metal and woodworking machines, forging equipment, foundry machines, electrical machines, stationary electrical installations, pumping units and fans, equipment for drilling wells, drilling rigs, machines for livestock farming, grain cleaning and sorting (in including dryers), equipment for the building materials industry (except for concrete pavers), installations for the chemical and petrochemical industries, etc.
a) at permanent workplaces of industrial premises of enterprises;
b) in workplaces in warehouses, canteens, utility rooms, duty rooms and other industrial premises where there are no machines that generate vibration;
c) at workplaces in plant management premises, design bureaus, laboratories, training centers, computer centers, health centers, office premises, workrooms and other premises for mental workers;
General vibration in residential premises and public buildings from external sources: urban rail transport (shallow and open subway lines, trams, railway transport) and vehicles; industrial enterprises and mobile industrial installations (when operating hydraulic and mechanical presses, planing, cutting and other metalworking mechanisms, piston compressors, concrete mixers, crushers, construction machines, etc.);
General vibration in residential premises and public buildings from internal sources: engineering and technical equipment of buildings and household appliances (elevators, ventilation systems, pumps, vacuum cleaners, refrigerators, washing machines, etc.), as well as built-in retail establishments (refrigeration equipment) , utility service enterprises, boiler houses, etc.
Based on the nature of the vibration spectrum, the following are distinguished:
Narrowband vibrations, in which the controlled parameters in one 1/3 octave frequency band are more than 15 dB higher than the values in the adjacent 1/3 octave bands;
Broadband vibrations - with a continuous spectrum more than one octave wide.
Based on the frequency composition of vibrations, they are divided into:
Low-frequency vibrations (with a predominance of maximum levels in octave frequency bands of 1-4 Hz for general vibrations, 8-16 Hz for local vibrations);
Mid-frequency vibrations (8-16 Hz - for general vibrations, 31.5-63 Hz - for local vibrations);
High-frequency vibrations (31.5-63 Hz - for general vibrations, 125-1000 Hz - for local vibrations).
According to the time characteristics of vibrations, they are divided into:
Constant vibrations, for which the value of the normalized parameters changes no more than 2 times (by 6 dB) during the observation period;
Non-constant vibrations, for which the value of the standardized parameters changes by at least 2 times (by 6 dB) during an observation time of at least 10 minutes when measured with a time constant of 1 s, including:
a) vibrations that fluctuate over time, for which the value of the standardized parameters changes continuously over time;
b) intermittent vibrations, when human contact with vibration is interrupted, and the duration of the intervals during which contact occurs is more than 1 s;
c) pulse vibrations, consisting of one or more vibration impacts (for example, impacts), each lasting less than 1 s.
2.4 Maximum permissible values of standardized parameters
The maximum permissible values of the standardized parameters of industrial local vibration with a duration of vibration exposure of 480 minutes (8 hours) are given in Table. 1.
Table 1
*Maximum permissible values on the axes
Geometric mean frequencies of octave bands, Hz vibration acceleration vibration velocity
m/s dB m/s 10 dB
8 1,4 123 2,8 115
16 1,4 123 1,4 109
31,5 2,8 129 1,4 109
63 5,6 135 1,4 109
125 11,0 141 1,4 109
250 22,0 147 1,4 109
500 45,0 153 1,4 109
1000 89,0 159 1,4 109
Adjusted and equivalent adjusted values and their levels 2.0 126 2.0 112
* Working in conditions of vibration with levels exceeding these sanitary standards by more than 12 dB (4 times) according to the integral assessment or in any octave band is not allowed.
Electrical safety.
The effect of current on the human body. Electrical injuries and their classification.
Types of electric shock.
Passing through a living organism. current produces the effect:
1. Thermal - in burns of certain areas, heating of blood vessels, blood, nerves.
2. Electrolytic - decomposition of blood and other organic liquids.
3. Biological - irritation and excitation of living tissues of the body, which is accompanied by involuntary convulsive contractions of muscles, including the muscles of the heart and lungs.
As a result of all this, various disturbances in the body can occur, up to a complete stop of the heart and lungs.
All this leads to two defeats: electrical injuries and electrical shocks.
Electrical injury is a clearly defined local damage to body tissues caused by exposure to electricity. current or arc. It usually affects the skin, ligaments and bones. In most cases, email. injuries are healed completely or partially. In some cases, death may occur.
The following emails are distinguished: injuries: el. burn, el. marks, metallization of the skin and mechanical damage.
Email burn is the most common electrical injury.
There are two types of burns: current and arc.
Electrical burn occurs when current passes through the body and burns are observed.
An arc burn is the result of exposure to electricity on the body. arc, high temperatures are observed here - up to 3500.
Email signs - marks on the body of gray color - during the passage of electricity. current
Metallization of the skin - penetration into the skin of small particles of metal, molten electricity. arc.
Email shock is the excitation of living tissues during the passage of electricity. current There are four of them according to severity:
Clinical (imaginary) death is a transition period from life to death, occurring from the moment the heart and lungs stop working. A person in a state of clinical death lacks all signs of life. However, the body has not yet died; metabolic processes continue.
Cause of death from electric current - cessation of the work of the heart, lungs, electricity. shock.
Fibrillation is chaotic rapid heart contractions.
Depending on the consequences that arise, electric shocks are divided into four degrees:
I - convulsive muscle contraction without loss of consciousness;
II - convulsive muscle contraction with loss of consciousness, but with preserved breathing and heart function;
III - loss of consciousness and disturbance of cardiac activity or breathing (or both);
IV - state of clinical death.
The main factors influencing the outcome of electric shock.
The amount of current passing through a person is the main factor determining the outcome of the injury. A person begins to feel the passage of an alternating current of industrial frequency (50 Hz) of 0.6-1.5 mA, and a DC current of 5-7 mA - these are the so-called current sensation thresholds. Large currents cause convulsions in humans.
At 10-15 mA, the pain becomes barely bearable, and the convulsions are such that a person cannot overcome them.
The outcome of the injury is greatly influenced by the resistance of the human body. The highest resistance (3...20 kOhm) is found in the upper layer of skin (0.2 mm), consisting of dead keratinized cells, while the resistance of the cerebrospinal fluid is 0.5...0.6 Ohm. The overall resistance of the body due to the resistance of the upper layer of skin is quite high, but as soon as this layer is damaged, its value decreases sharply.
In calculations related to electrical safety, the resistance of the human body is taken to be 1 kOhm.
The duration of the passage of current through the human body affects the outcome of the injury: the longer the current, the greater the likelihood of a severe fatal injury.
The path of current in the victim's body plays a significant role in the outcome of the injury. So if there are vital organs in the path of the current - the heart, lungs, brain, then the danger of damage is very high.
Type of current and frequency direct current is less dangerous than alternating current by about four times, but this is true up to 250-300 V. Increasing frequency leads to increased danger.
The most dangerous current is the passage of current through the heart, lungs and brain.
The degree of damage also depends on the type and frequency of the current. The most dangerous is alternating current with a frequency of 20... 1000 Hz. Alternating current is more dangerous than direct current at voltages up to 300 V. At higher voltages - direct current.
Electrical safety.
Sound waves are characterized by a frequency ranging from 16 Hz to 20 kHz. Elastic waves with frequency v< 16 Гц называются infrasound, and with a frequency v>20 kHz - ultrasound(Fig. 56).
Infrasound. The human ear cannot perceive infrasound waves. Despite this, they are capable of exerting certain physiological effects on humans. These actions are explained by resonance. The internal organs of our body have fairly low natural frequencies: the abdominal cavity and chest - 5-8 Hz, the head - 20-30 Hz. The average resonant frequency for the whole body is 6 Hz. Having frequencies of the same order, infrasound waves cause our organs to vibrate and, at very high intensity, can lead to internal hemorrhages.
Special experiments have shown that irradiating people with sufficiently intense infrasound can cause loss of balance, nausea, involuntary rotation of the eyeballs, etc. For example, at a frequency of 4-8 Hz a person feels the movement of internal organs, and at a frequency of 12 Hz - an attack of seasickness .
They say that one day the American physicist R. Wood (who was known among his colleagues as a great original and a merry fellow) brought a special apparatus emitting infrasonic waves to the theater, and, turning it on, directed it onto the stage. No one heard any sound, but the actress became hysterical.
The resonant effect of low-frequency sounds on the human body also explains the stimulating effect of modern rock music, saturated with repeatedly amplified low frequencies of drums, bass guitars, etc.
Infrasound is not perceived by the human ear, but some animals can hear it. For example, jellyfish confidently perceive infrasound waves with a frequency of 8-13 Hz, which arise during a storm as a result of the interaction of air currents with the crests of sea waves. Reaching the jellyfish, these waves “warn” them in advance (15 hours in advance!) of the approaching storm.
Sources of infrasound can be lightning discharges, gun shots, volcanic eruptions, atomic bomb explosions, earthquakes, operating jet engines, wind flowing over the crests of sea waves, etc.
Infrasound is characterized by low absorption in various media, as a result of which it can propagate over very long distances. This makes it possible to determine the location of strong explosions, the position of the firing gun, monitor underground nuclear explosions, predict tsunamis, etc.
Ultrasound. Ultrasound is also not perceived by the human ear. However, some animals are able to emit and perceive it. For example, thanks to this, dolphins confidently navigate in muddy water. By sending and receiving ultrasonic pulses that return, they are able to detect even a small pellet carefully lowered into water at a distance of 20-30 m. Ultrasound also helps bats that have poor eyesight or cannot see anything at all. By emitting ultrasonic waves (up to 250 times per second) using their hearing aid, they are able to navigate in flight and successfully catch prey even in complete darkness. It is curious that some insects have developed a special defensive reaction in response to this: certain species of moths and beetles also turned out to be able to perceive ultrasounds emitted by bats, and upon hearing them, they immediately fold their wings, fall down and freeze on the ground.
Ultrasonic signals are also used by some toothed whales. These signals allow them to hunt squid in the complete absence of light.
It has also been established that ultrasonic waves with a frequency of more than 25 kHz cause pain in birds. This is used, for example, to repel seagulls from drinking water reservoirs.
Ultrasound is widely used in science and technology, where it is obtained using various mechanical (for example, siren) and electromechanical devices.
Ultrasound sources are installed on ships and submarines. By sending short pulses of ultrasonic waves, you can catch their reflections from the bottom or some other objects. Based on the delay time of the reflected wave, one can judge the distance to the obstacle. The echo sounders and sonars used in this case make it possible to measure the depth of the sea (Fig. 57), solve various navigation problems (swimming near rocks, reefs, etc.), carry out fishing reconnaissance (detect schools of fish), and also solve military problems (search for underwater enemy boats, periscopeless torpedo attacks, etc.).
In the industry, the reflection of ultrasound from cracks in metal castings is used to judge defects in products.
Ultrasounds crush liquid and solid substances, forming various emulsions and suspensions.
Using ultrasound, it is possible to solder aluminum products, which cannot be done using other methods (since there is always a dense layer of oxide film on the surface of aluminum). The tip of the ultrasonic soldering iron not only heats up, but also vibrates at a frequency of about 20 kHz, due to which the oxide film on the aluminum is destroyed.
The conversion of ultrasound into electrical vibrations, and then into light, allows for sound vision. Using sound vision, you can see objects in water that is opaque to light.
In medicine, ultrasound is used to weld broken bones, detect tumors, carry out diagnostic tests in obstetrics, etc. The biological effect of ultrasound (leading to the death of microbes) allows it to be used for the sterilization of milk, medicinal substances, and medical instruments.
1. What is infrasound? 2. Give examples of sources of infrasonic waves. 3. What explains the physiological effect of infrasound on humans? 4. What is ultrasound? 5. Give examples of the use of ultrasonic waves by representatives of the animal world. 6. Where and for what are infra- and ultrasounds used?
Ultrasound:
- What is ultrasound;
- The influence of ultrasound on the human body;
- Use of ultrasound in industry and economy;
- Prospects for the use of ultrasound.
Infrasound:
- What is infrasound;
- The influence of infrasound on the human body;
- Infrasound anomalies;
- Animals using infrasound;
- Prospects for the use of infrasound;
- Conclusion
Ultrasound
1. What is ultrasound?
Recently, technological processes based on the use of ultrasound energy have become increasingly widespread in production. Ultrasound has also found application in medicine. Due to the increase in unit powers and speeds of various units and machines, noise levels are increasing, including in the ultrasonic frequency range.
Ultrasound is the mechanical vibration of an elastic medium with a frequency exceeding the upper limit of audibility -20 kHz. The unit of sound pressure level is dB. The unit of measurement for ultrasound intensity is watt per square centimeter (W/s2). The human ear cannot perceive ultrasound, but some animals, such as bats, can both hear and produce ultrasound. It is partially perceived by rodents, cats, dogs, whales, and dolphins. Ultrasonic vibrations occur during the operation of car engines, machine tools and rocket engines.
Due to its high frequency (short wavelength), ultrasound has special properties. Thus, like light, ultrasonic waves can form strictly directed beams. Reflection and refraction of these beams at the boundary of two media obeys the laws of geometric optics. It is strongly absorbed by gases and weakly by liquids. In a liquid under the influence of ultrasound, voids are formed in the form of tiny bubbles with a short-term increase in pressure inside them. In addition, ultrasonic waves accelerate the diffusion processes.
These properties of ultrasound and the peculiarities of its interaction with the environment determine its wide technical and medical use. Ultrasound is used in medicine and biology for echolocation, for identifying and treating tumors and some defects in body tissues, in surgery and traumatology for cutting soft and bone tissues during various operations, for welding broken bones, for destroying cells (high power ultrasound). In ultrasound therapy, oscillations of 800-900 kHz are used for therapeutic purposes.
2. The effect of ultrasound on the human body
Ultrasound has a mainly local effect on the body, since it is transmitted through direct contact with an ultrasonic instrument, workpieces or environments where ultrasonic vibrations are excited. Ultrasonic vibrations generated by ultrasonic low-frequency industrial equipment have an adverse effect on the human body. Long-term systematic exposure to airborne ultrasound causes changes in the nervous, cardiovascular and endocrine systems, auditory and vestibular analyzers.
In the field of ultrasonic vibrations in living tissues, ultrasound has mechanical, thermal, physicochemical effects (micromassage of cells and tissues). At the same time, metabolic processes are activated and the immune properties of the body are increased.
3. Use of ultrasound in industry and economy
Today, ultrasound is used in a huge number of industries. Among them: medicine, geology, steel industry, military industry, etc. Ultrasound is used extremely intensively in geology; there is a special science - geophysics.
Using ultrasound, geophysicists find deposits of valuable minerals and determine the depth of their location. In the metal foundry industry, ultrasound is used to diagnose the state of the metal crystal lattice. When “listening” to pipes and beams of high-quality products, a certain signal is obtained, but if the product has something different from the norm (density, design defect), the signal will be different, which will indicate to the engineer that it is defective.
Surrounded by enemy ships, a submarine has only one safe way to contact the base - transmit a signal in the water environment. For this, a special conditioned ultrasonic signal of a certain frequency is used - it is almost impossible to intercept such a message, because To do this, you need to know its frequency, exact transmission time and “route”. However, sending a signal from a boat is also a complex procedure - it is necessary to take into account all the depths, water temperature, etc. The base, receiving the signal and knowing its travel time, can calculate the distance to the boat and, as a result, its location. The submarine fleet also uses special short ultrasonic pulses sent by sonar directly from the submarine; the impulse is reflected from objects - rocks, other ships, and with its help the direction and distance to the obstacle is calculated (a technique borrowed from nocturnal predators - bats).
Ultrasonic baths are also used both for disinfection of instruments and for cosmetic purposes - massage of the feet, hands, and face. Ultrasonic air humidifiers and nozzles, as well as rangefinders, are very effective (the well-known traffic police speed radars also use ultrasonic pulses).
4. Prospects for the use of ultrasound
In the future, it is expected that ultrasound pulses will be used more widely for cosmetic purposes - scientists are already using ultrasound to clean pores, refresh, and rejuvenate aging skin - ultrasonic peeling. Work is underway to create ultrasonic weapons, as well as to develop protection systems against them. It is expected that ultrasound will be used more widely in households.
Infrasound
5. What is infrasound?
The development of technology and vehicles, the improvement of technological processes and equipment are accompanied by an increase in the power and dimensions of machines, which determines the tendency for low-frequency components in the spectra to increase and the emergence of infrasound, which is a relatively new, not fully studied factor in the production environment.
Infrasound refers to acoustic vibrations with a frequency below 20 Hz. This frequency range lies below the threshold of audibility and the human ear is not capable of perceiving vibrations of these frequencies. Industrial infrasound occurs due to the same processes as noise of audible frequencies. The greatest intensity of infrasonic vibrations is created by machines and mechanisms that have large surfaces that perform low-frequency mechanical vibrations (infrasound of mechanical origin) or turbulent flows of gases and liquids (infrasound of aerodynamic or hydrodynamic origin). The maximum levels of low-frequency acoustic vibrations from industrial and transport sources reach 100-110 dB.
6. The influence of infrasound on the human body
Studies of the biological effect of infrasound on the body have shown that at levels from 110 to 150 dB or more, it can cause unpleasant subjective sensations and numerous reactive changes in people, which include changes in the central nervous, cardiovascular and respiratory systems, and the vestibular analyzer . There is evidence that infrasound causes hearing loss primarily at low and medium frequencies. The severity of these changes depends on the level of infrasound intensity and the duration of the factor.
Infrasound is by no means a recently discovered phenomenon. In fact, it has been known to organists for over 250 years. Many cathedrals and churches have organ pipes so long that they produce a sound with a frequency of less than 20 Hz, which is not perceptible to the human ear. But, as British researchers have found, such infrasound can instill in the audience various and not very pleasant feelings - melancholy, a feeling of cold, anxiety, trembling in the spine. People exposed to infrasound experience approximately the same sensations as when visiting places where encounters with ghosts took place.
7. Infrasound anomalies
The North American coastline around Cape Hatteras, the Florida Peninsula and the island of Cuba form a giant reflector. A storm occurring in the Atlantic Ocean generates infrasonic waves, which, reflected from this reflector, are focused in the Bermuda Triangle area. The colossal dimensions of the focusing structure suggest the presence of areas where infrasonic vibrations can reach significant values, which is the cause of the anomalous phenomena occurring here. As is known, strong infrasonic vibrations cause panic fear in a person along with the desire to escape from a confined space. Obviously, this behavior is a consequence of an “instinctive” reaction to infrasound developed in the distant past as a harbinger of an earthquake. It is this reaction that causes the crew and passengers to leave their ship in panic. They can get into boats and swim away from their ship, or run onto the deck and throw themselves overboard. If the intensity of infrasound is very high, they may even die - if it comes into resonance with human biorhythms, infrasound of particularly high intensity can cause instant death.
Infrasound can cause resonant vibrations of ship masts, leading to their breakdown (the impact of infrasound on aircraft structural elements can lead to similar consequences). Low-frequency sound vibrations can cause the appearance of thick ("like milk") fog over the ocean that quickly appears and also quickly disappears. And finally, infrasound with a frequency of 5-7 hertz can resonate with the pendulum of a mechanical, hand-held watch that has the same oscillation period.
Obviously, similar focusing structures exist in other areas of the globe. Apparently, the panic caused by intense infrasonic vibrations in one of these structures served as the “starting point” of the siren myth...
Infrasound can propagate under water, and the focusing structure can be formed by the bottom topography. The source of infrasonic vibrations can be underwater volcanoes and earthquakes. Naturally, the shape of “landscape” reflectors is very far from perfect. Therefore, we should talk about a system of reflective elements, specific for each case. With dimensions commensurate with the wavelength, the structure can be resonant.
8. Animals using infrasound
American scientists have discovered that tigers and elephants use not only growls, purrs or roars and trumpet calls to communicate with each other, but also infrasound, that is, very low frequency sound signals that are inaudible to the human ear. According to scientists, infrasound allows animals to maintain communication at a distance of up to 8 kilometers, since the propagation of infrasound signals is almost insensitive to interference caused by terrain, and depends little on weather and climatic factors such as air humidity.
Now scientists intend to find out whether the frequency spectra of tiger voices have individual characteristics that allow them to identify animals. This would greatly facilitate the accounting of their livestock.
While studying the behavior of a group of elephants at the Portland Zoo in Oregon, a group of researchers “felt” unusual vibrations in the air. Using a sophisticated electronic sound detection system, the researchers discovered that these are infrasonic waves emitted by elephants. While observing free-ranging elephants in Kenya, researchers using the same equipment recorded exactly the same type of waves. Scientists have concluded that animals use low-frequency sounds to communicate with each other over a distance of several kilometers.
Scientists hope in the future, having determined the meaning of infrasound signals, to move on to the most exciting stage of the experiments - establishing contact with elephants with their help.
9. Prospects for the use of infrasound
Now scientists are developing a so-called “infrasonic gun.” Low-frequency sound waves are planned to be used here as a “panic generator”. In this case, infrasound is much more convenient than high-frequency waves, since it itself poses a threat to human health. The frequencies of our nervous system and heart lie in the infrasound range - 6 Hz. Emulation of these frequencies leads to poor health, unreasonable fear, panic, madness, and, finally, death.
10. Conclusion
Having completed this work - collecting, processing and summarizing a large amount of material on this problem, we learned a lot about the nature of sound. About the danger that it can pose to the human body, and about how widely it can be used in the household. The most interesting hypothesis for us was about the nature of “awe,” the awe of people in the temple. We consider research into animal communication methods and, of course, the use of infrasound to predict the location and time of future eruptions and earthquakes very promising.
Ultrasound is a sound in the range above the limit of human audibility, i.e. with a sound wave frequency above 20 kHz.
Infrasound is a sound in the range below the limit of human audibility, i.e. with a sound wave frequency of less than 20 Hz.
Ultrasound, infrasound and humans
Recently, technological processes based on the use of ultrasound energy have become increasingly widespread in production. Ultrasound has also found application in medicine. Due to the increase in unit powers and speeds of various units and machines, noise levels are increasing, including in the ultrasonic frequency range.
Ultrasound is the mechanical vibration of an elastic medium with a frequency exceeding the upper limit of audibility -20 kHz. The unit of sound pressure level is dB. The unit of measurement for ultrasound intensity is watt per square centimeter (W/cm2).
Ultrasound has a mainly local effect on the body, since it is transmitted through direct contact with an ultrasonic instrument, workpieces or environments where ultrasonic vibrations are excited. Ultrasonic vibrations generated by ultrasonic low-frequency industrial equipment have an adverse effect on the human body. Long-term systematic exposure to airborne ultrasound causes changes in the nervous, cardiovascular and endocrine systems, auditory and vestibular analyzers. The most characteristic is the presence of vegetative-vascular dystonia and asthenic syndrome.
The degree of severity of the changes depends on the intensity and duration of exposure to ultrasound and increases in the presence of high-frequency noise in the spectrum, while a pronounced hearing loss is added. If contact with ultrasound continues, these disorders become more persistent.
Under the influence of local ultrasound, phenomena of vegetative polyneuritis of the hands (less often of the legs) of varying degrees of severity occur, up to the development of paresis of the hands and forearms, and vegetative-vascular dysfunction.
The nature of the changes that occur in the body under the influence of ultrasound depends on the dose of exposure.
Small doses - sound level 80-90 dB - give a stimulating effect - micromassage, acceleration of metabolic processes. Large doses - sound levels of 120 dB or more - have a damaging effect.
The basis for preventing the adverse effects of ultrasound on persons servicing ultrasonic installations is hygienic regulation.
In accordance with GOST 12.1.01-89 "Ultrasound. General safety requirements", "Sanitary standards and rules for working on industrial ultrasonic installations" (No. 1733-77) the sound pressure levels in the high-frequency region of audible sounds and ultrasounds at workplaces are limited ( from 80 to 110 dB at geometric mean frequencies of one-third octave bands from 12.5 to 100 kHz).
Ultrasound transmitted by contact is regulated by “Sanitary norms and rules for working with equipment that creates ultrasound transmitted by contact to the hands of workers” No. 2282-80.
Measures to prevent the adverse effects of ultrasound on the body of operators of technological installations and personnel of treatment and diagnostic rooms consist primarily of carrying out measures of a technical nature. These include the creation of automated, remote-controlled ultrasound equipment; using low-power equipment whenever possible, which helps reduce the intensity of noise and ultrasound in the workplace by 20-40 dB; placement of equipment in sound-insulated rooms or remote-controlled rooms; equipment of soundproofing devices, casings, screens made of sheet steel or duralumin, coated with rubber, anti-noise mastic and other materials.
When designing ultrasonic installations, it is advisable to use operating frequencies that are farthest from the audible range - not lower than 22 kHz.
To eliminate exposure to ultrasound when in contact with liquid and solid media, it is necessary to install a system to automatically turn off ultrasonic transducers during operations during which contact is possible (for example, loading and unloading materials). To protect hands from the contact action of ultrasound, it is recommended to use a special working tool with a vibration-isolating handle.
If, for production reasons, it is impossible to reduce the level of noise and ultrasound intensity to acceptable values, it is necessary to use personal protective equipment - noise protection, rubber gloves with cotton lining, etc.
The development of technology and vehicles, the improvement of technological processes and equipment are accompanied by an increase in the power and dimensions of machines, which determines the tendency to increase low-frequency components in the spectra and the emergence of infrasound, which is a relatively new, not fully studied factor in the production environment.
Infrasound is the name given to acoustic vibrations that occur frequently! below 20 Hz. This frequency range lies below the threshold of audibility and the human ear is not capable of perceiving vibrations of these frequencies.
Industrial infrasound occurs due to the same processes as noise of audible frequencies. The greatest intensity of infrasonic vibrations is created by machines and mechanisms that have large surfaces that perform low-frequency mechanical vibrations (infrasound of mechanical origin) or turbulent flows of gases and liquids (infrasound of aerodynamic or hydrodynamic origin).
The maximum levels of low-frequency acoustic vibrations from industrial and transport sources reach 100-110 dB.
Studies of the biological effects of infrasound on the body have shown that at levels from 110 to 150 dB or more, it can cause unpleasant subjective sensations and numerous reactive changes in people, which include changes in the central nervous, cardiovascular and respiratory systems, and the vestibular analyzer . There is evidence that infrasound causes hearing loss primarily at low and medium frequencies. The severity of these changes depends on the level of infrasound intensity and the duration of the factor.
In accordance with the Hygienic Standards for Infrasound in Workplaces (No. 2274-80), based on the nature of the spectrum, infrasound is divided into broadband and harmonic. The harmonic nature of the spectrum is established in octave frequency bands by the excess of the level in one band over neighboring ones by at least 10 dB.
According to its temporal characteristics, infrasound is divided into constant and non-constant.
The normalized characteristics of infrasound in workplaces are sound pressure levels in decibels in octave frequency bands with geometric mean frequencies of 2, 4, 8, 16 Hz.
Acceptable sound pressure levels are 105 dB in the octave bands of 2, 4, 8, 16 Hz and 102 dB in the octave band of 31.5 Hz. In this case, the total sound pressure level should not exceed 110 dB Lin.
For non-constant infrasound, the normalized characteristic is the overall sound pressure level.
The most effective and practically the only means of combating infrasound is to reduce it at the source. When choosing designs, preference should be given to small-sized machines with high rigidity, since in structures with flat surfaces of large area and low rigidity, conditions are created for the generation of infrasound. The fight against infrasound at its source must be carried out in the direction of changing the operating mode of technological equipment - increasing its speed (for example, increasing the number of working strokes of forging and pressing machines, so that the main frequency of power pulses lies outside the infrasound range).
Measures must be taken to reduce the intensity of aerodynamic processes - limiting vehicle speeds, reducing the flow rates of liquids (aircraft and rocket engines, internal combustion engines, steam discharge systems of thermal power plants, etc.).
In the fight against infrasound along the propagation paths, interference-type jammers have a certain effect, usually in the presence of discrete components in the infrasound spectrum.
The recent theoretical substantiation of the flow of nonlinear processes in resonant-type absorbers opens up real ways to design sound-absorbing panels and casings that are effective in the low-frequency region.
As personal protective equipment, it is recommended to use headphones and earplugs that protect the ear from the adverse effects of accompanying noise.
Organizational preventive measures should include compliance with the work and rest schedule and the prohibition of overtime work. When in contact with ultrasound for more than 50% of the working time, breaks of 15 minutes are recommended every 1.5 hours of work. A significant effect is achieved by a complex of physiotherapeutic procedures - massage, UT-irradiation, water procedures, vitaminization, etc.
Dolphin sonar.
The fact that dolphins have unusually developed hearing has been known for decades. The volumes of those parts of the brain that manage auditory functions are tens (!) times greater than in humans (despite the fact that the total volume of the brain is approximately the same). The dolphin is capable of perceiving frequencies of sound vibrations 10 times higher (up to 150 kHz) than humans (up to 15-18 kHz), and hears sounds whose power is 10-30 times lower than that of sounds accessible to human hearing, such as No matter how good a dolphin’s vision is, its capabilities are limited due to the low transparency of the water. Therefore, the dolphin receives basic information about its surroundings through hearing. At the same time, he uses active location: he listens to the echo that occurs when the sounds he makes are reflected from surrounding objects. The echo gives him accurate information not only about the position of objects, but also about their size, shape, and material. In other words, hearing allows the dolphin to perceive the world around it no worse or even better than vision.
1. Ultrasound emitters and receivers.
2. Absorption of ultrasound in a substance. Acoustic flows and cavitation.
3. Ultrasound reflection. Sound vision.
4. Biophysical effect of ultrasound.
5. Use of ultrasound in medicine: therapy, surgery, diagnostics.
6. Infrasound and its sources.
7. Impact of infrasound on humans. Use of infrasound in medicine.
8. Basic concepts and formulas. Tables.
9. Tasks.
Ultrasound - elastic vibrations and waves with frequencies from approximately 20x10 3 Hz (20 kHz) to 10 9 Hz (1 GHz). The ultrasound frequency range from 1 to 1000 GHz is commonly called hypersound. Ultrasonic frequencies are divided into three ranges:
ULF - low frequency ultrasound (20-100 kHz);
USCh - mid-frequency ultrasound (0.1-10 MHz);
UHF - high frequency ultrasound (10-1000 MHz).
Each range has its own characteristics of medical use.
5.1. Ultrasound emitters and receivers
Electromechanical emitters And ultrasound receivers use the phenomenon of the piezoelectric effect, the essence of which is illustrated in Fig. 5.1.
Crystalline dielectrics such as quartz, Rochelle salt, etc. have pronounced piezoelectric properties.
Ultrasound emitters
Electromechanical Ultrasound emitter uses the phenomenon of the inverse piezoelectric effect and consists of the following elements (Fig. 5.2):
Rice. 5.1. A - direct piezoelectric effect: compression and stretching of the piezoelectric plate leads to the emergence of a potential difference of the corresponding sign;
b - reverse piezoelectric effect: depending on the sign of the potential difference applied to the piezoelectric plate, it is compressed or stretched
Rice. 5.2. Ultrasonic emitter
1 - plates made of a substance with piezoelectric properties;
2 - electrodes deposited on its surface in the form of conductive layers;
3 - a generator that supplies alternating voltage of the required frequency to the electrodes.
When alternating voltage is applied to the electrodes (2) from the generator (3), the plate (1) experiences periodic stretching and compression. Forced oscillations occur, the frequency of which is equal to the frequency of voltage changes. These vibrations are transmitted to particles of the environment, creating a mechanical wave with the corresponding frequency. The amplitude of oscillations of the particles of the medium near the emitter is equal to the amplitude of oscillations of the plate.
The features of ultrasound include the possibility of obtaining waves of high intensity even with relatively small vibration amplitudes, since at a given amplitude the density
Rice. 5.3. Focusing an ultrasonic beam in water with a plano-concave plexiglass lens (ultrasound frequency 8 MHz)
energy flow is proportional squared frequency(see formula 2.6). The maximum intensity of ultrasound radiation is determined by the properties of the material of the emitters, as well as the characteristics of the conditions of their use. The intensity range for US generation in the USF region is extremely wide: from 10 -14 W/cm 2 to 0.1 W/cm 2 .
For many purposes, significantly higher intensities are required than those that can be obtained from the surface of the emitter. In these cases, you can use focusing. Figure 5.3 shows the focusing of ultrasound using a plexiglass lens. For getting very large ultrasound intensities use more complex focusing methods. Thus, at the focus of a paraboloid, the inner walls of which are made of a mosaic of quartz plates or piezoceramics of barium titanite, at a frequency of 0.5 MHz it is possible to obtain ultrasound intensities of up to 10 5 W/cm 2 in water.
Ultrasound receivers
Electromechanical Ultrasound receivers(Fig. 5.4) use the phenomenon of the direct piezoelectric effect. In this case, under the influence of an ultrasonic wave, vibrations of the crystal plate (1) occur,
Rice. 5.4. Ultrasound receiver
as a result of which an alternating voltage appears on the electrodes (2), which is recorded by the recording system (3).
In most medical devices, an ultrasonic wave generator is also used as a receiver.
5.2. Absorption of ultrasound in a substance. Acoustic flows and cavitation
In its physical essence, ultrasound does not differ from sound and is a mechanical wave. As it spreads, alternating areas of condensation and rarefaction of particles of the medium are formed. The speed of propagation of ultrasound and sound in media is the same (in air ~ 340 m/s, in water and soft tissues ~ 1500 m/s). However, the high intensity and short length of ultrasonic waves give rise to a number of specific features.
When ultrasound propagates in a substance, an irreversible transition of the energy of the sound wave occurs into other types of energy, mainly into heat. This phenomenon is called absorption of sound. The decrease in the amplitude of particle vibrations and the intensity of ultrasound due to absorption is exponential:
where A, A 0 are the amplitudes of vibrations of particles of the medium at the surface of the substance and at a depth h; I, I 0 - corresponding intensities of the ultrasonic wave; α - absorption coefficient, depending on the frequency of the ultrasonic wave, temperature and properties of the medium.
Absorption coefficient - the reciprocal of the distance at which the amplitude of the sound wave decreases by a factor of “e”.
The higher the absorption coefficient, the more strongly the medium absorbs ultrasound.
The absorption coefficient (α) increases with increasing ultrasound frequency. Therefore, the attenuation of ultrasound in a medium is many times higher than the attenuation of audible sound.
Along with absorption coefficient, Ultrasound absorption is also used as a characteristic half-absorption depth(H), which is related to it by an inverse relationship (H = 0.347/α).
Half-absorption depth(H) is the depth at which the intensity of the ultrasound wave is halved.
The values of the absorption coefficient and half-absorption depth in various tissues are presented in table. 5.1.
In gases and, in particular, in air, ultrasound propagates with high attenuation. Liquids and solids (especially single crystals) are, as a rule, good conductors of ultrasound, and the attenuation in them is much less. For example, in water, the attenuation of ultrasound, other things being equal, is approximately 1000 times less than in air. Therefore, the areas of use of ultrasonic frequency and ultrasonic frequency refer almost exclusively to liquids and solids, and in air and gases only ultrasonic frequency is used.
Heat release and chemical reactions
The absorption of ultrasound by a substance is accompanied by the transition of mechanical energy into the internal energy of the substance, which leads to its heating. The most intense heating occurs in areas adjacent to the interfaces, when the reflection coefficient is close to unity (100%). This is due to the fact that as a result of reflection, the intensity of the wave near the boundary increases and, accordingly, the amount of absorbed energy increases. This can be verified experimentally. You need to attach the ultrasound emitter to your wet hand. Soon, a sensation (similar to pain from a burn) appears on the opposite side of the palm, caused by ultrasound reflected from the skin-air interface.
Tissues with a complex structure (lungs) are more sensitive to ultrasound heating than homogeneous tissues (liver). Relatively much heat is generated at the interface between soft tissue and bone.
Local heating of tissues by a fraction of a degree promotes the vital activity of biological objects and increases the intensity of metabolic processes. However, prolonged exposure may cause overheating.
In some cases, focused ultrasound is used to locally influence individual structures of the body. This effect makes it possible to achieve controlled hyperthermia, i.e. heating to 41-44 °C without overheating adjacent tissues.
The increase in temperature and large pressure drops that accompany the passage of ultrasound can lead to the formation of ions and radicals that can interact with molecules. In this case, chemical reactions can occur that are not feasible under normal conditions. The chemical effect of ultrasound is manifested, in particular, in the splitting of a water molecule into H + and OH - radicals, followed by the formation of hydrogen peroxide H 2 O 2.
Acoustic flows and cavitation
Ultrasonic waves of high intensity are accompanied by a number of specific effects. Thus, the propagation of ultrasonic waves in gases and liquids is accompanied by the movement of the medium, which is called acoustic flow (Fig. 5.5, A). At frequencies in the ultrasonic frequency range in an ultrasonic field with an intensity of several W/cm2, liquid gushing may occur (Fig. 5.5, b) and spraying it to form a very fine mist. This feature of ultrasound propagation is used in ultrasonic inhalers.
Among the important phenomena that arise when intense ultrasound propagates in liquids is acoustic cavitation - growth of bubbles from existing ones in an ultrasonic field
Rice. 5.5. a) acoustic flow that occurs when ultrasound propagates at a frequency of 5 MHz in benzene; b) a fountain of liquid formed when an ultrasonic beam falls from inside the liquid onto its surface (ultrasound frequency 1.5 MHz, intensity 15 W/cm2)
submicroscopic nuclei of gas or vapor in liquids up to a fraction of a mm in size, which begin to pulsate at an ultrasonic frequency and collapse in the positive pressure phase. When gas bubbles collapse, large local pressures of the order of thousand atmospheres spherical shock waves. Such an intense mechanical effect on particles contained in a liquid can lead to a variety of effects, including destructive ones, even without the influence of the thermal effect of ultrasound. Mechanical effects are especially significant when exposed to focused ultrasound.
Another consequence of the collapse of cavitation bubbles is the strong heating of their contents (up to a temperature of about 10,000 °C), accompanied by ionization and dissociation of molecules.
The phenomenon of cavitation is accompanied by erosion of the working surfaces of the emitters, damage to cells, etc. However, this phenomenon also leads to a number of beneficial effects. For example, in the area of cavitation, increased mixing of the substance occurs, which is used to prepare emulsions.
5.3. Ultrasound reflection. Sound vision
Like all types of waves, ultrasound is characterized by the phenomena of reflection and refraction. However, these phenomena are noticeable only when the size of the inhomogeneities is comparable to the wavelength. The length of the ultrasonic wave is significantly less than the length of the sound wave (λ = v/v). Thus, the lengths of sound and ultrasonic waves in soft tissues at frequencies of 1 kHz and 1 MHz are respectively equal: λ = 1500/1000 = 1.5 m;
1500/1,000,000 = 1.5x10 -3 m = 1.5 mm. In accordance with the above, a body with a size of 10 cm practically does not reflect sound with a wavelength of λ = 1.5 m, but is a reflector for an ultrasonic wave with λ = 1.5 mm.
The reflection efficiency is determined not only by geometric relationships, but also by the reflection coefficient r, which depends on the ratio wave resistance of the media x(see formulas 3.8, 3.9):
For values of x close to 0, the reflection is almost complete. This is an obstacle to the transfer of ultrasound from air to soft tissues (x = 3x10 -4, r= 99.88%). If an ultrasound emitter is applied directly to a person’s skin, the ultrasound will not penetrate inside, but will be reflected from a thin layer of air between the emitter and the skin. In this case, small values X play a negative role. To eliminate the air layer, the surface of the skin is covered with a layer of appropriate lubricant (water jelly), which acts as a transition medium that reduces reflection. On the contrary, to detect inhomogeneities in the medium, small values X are a positive factor.
The values of the reflection coefficient at the boundaries of various tissues are given in table. 5.2.
The intensity of the received reflected signal depends not only on the magnitude of the reflection coefficient, but also on the degree of absorption of ultrasound by the medium in which it propagates. Absorption of an ultrasonic wave leads to the fact that the echo signal reflected from a structure located in depth is much weaker than that formed when reflected from a similar structure located near the surface.
Based on the reflection of ultrasonic waves from inhomogeneities sound vision, used in medical ultrasound examinations (ultrasound). In this case, ultrasound reflected from inhomogeneities (individual organs, tumors) is converted into electrical vibrations, and the latter into light, which allows you to see certain objects on the screen in an environment opaque to light. Figure 5.6 shows an image
Rice. 5.6. Image of a 17-week-old human fetus obtained using 5 MHz ultrasound
human fetus aged 17 weeks, obtained using ultrasound.
An ultrasonic microscope has been created at frequencies in the ultrasonic range - a device similar to a conventional microscope, the advantage of which over an optical microscope is that for biological research no preliminary staining of the object is required. Figure 5.7 shows photographs of red blood cells obtained with optical and ultrasound microscopes.
Rice. 5.7. Photographs of red blood cells obtained by optical (a) and ultrasound (b) microscopes
As the frequency of ultrasonic waves increases, the resolution increases (smaller inhomogeneities can be detected), but their penetrating ability decreases, i.e. the depth at which structures of interest can be examined decreases. Therefore, the ultrasound frequency is chosen so as to combine sufficient resolution with the required depth of investigation. Thus, for ultrasound examination of the thyroid gland, located directly under the skin, waves of a frequency of 7.5 MHz are used, and for examination of the abdominal organs, a frequency of 3.5-5.5 MHz is used. In addition, the thickness of the fat layer is also taken into account: for thin children, a frequency of 5.5 MHz is used, and for overweight children and adults, a frequency of 3.5 MHz is used.
5.4. Biophysical effect of ultrasound
When ultrasound acts on biological objects in irradiated organs and tissues at distances equal to half the wavelength, pressure differences from units to tens of atmospheres can arise. Such intense impacts lead to a variety of biological effects, the physical nature of which is determined by the combined action of mechanical, thermal and physicochemical phenomena accompanying the propagation of ultrasound in the environment.
General effects of ultrasound on tissues and the body as a whole
The biological effect of ultrasound, i.e. changes caused in the life activity and structures of biological objects when exposed to ultrasound are determined mainly by its intensity and duration of irradiation and can have both positive and negative effects on the life activity of organisms. Thus, mechanical vibrations of particles that occur at relatively low ultrasound intensities (up to 1.5 W/cm 2) produce a kind of micromassage of tissues, promoting better metabolism and a better supply of tissues with blood and lymph. Local heating of tissues by fractions and units of degrees, as a rule, promotes the vital activity of biological objects, increasing the intensity of metabolic processes. Ultrasonic waves small And average intensities cause positive biological effects in living tissues, stimulating the occurrence of normal physiological processes.
The successful use of ultrasound at these intensities is used in neurology for the rehabilitation of diseases such as chronic radiculitis, polyarthritis, neuritis, and neuralgia. Ultrasound is used in the treatment of diseases of the spine and joints (destruction of salt deposits in joints and cavities); in the treatment of various complications after damage to joints, ligaments, tendons, etc.
High-intensity ultrasound (3-10 W/cm2) has a harmful effect on individual organs and the human body as a whole. High ultrasound intensity can cause
in biological environments of acoustic cavitation, accompanied by mechanical destruction of cells and tissues. Long-term intense exposure to ultrasound can lead to overheating of biological structures and their destruction (denaturation of proteins, etc.). Exposure to intense ultrasound can also have long-term consequences. For example, with prolonged exposure to ultrasound with a frequency of 20-30 kHz, which occurs in some industrial conditions, a person develops nervous system disorders, fatigue increases, the temperature rises significantly, and hearing impairment occurs.
Very intense ultrasound is fatal to humans. Thus, in Spain, 80 volunteers were exposed to ultrasonic turbulent engines. The results of this barbaric experiment were disastrous: 28 people died, the rest were completely or partially paralyzed.
The thermal effect produced by high-intensity ultrasound can be very significant: with ultrasound irradiation at a power of 4 W/cm2 for 20 s, the temperature of body tissues at a depth of 2-5 cm increases by 5-6 °C.
In order to prevent occupational diseases among people working on ultrasonic installations, when contact with sources of ultrasonic vibrations is possible, it is necessary to use 2 pairs of gloves to protect hands: outer rubber and inner cotton.
The effect of ultrasound at the cellular level
The biological effect of ultrasound may also be based on secondary physicochemical effects. Thus, during the formation of acoustic flows, mixing of intracellular structures can occur. Cavitation leads to the breaking of molecular bonds in biopolymers and other vital compounds and to the development of redox reactions. Ultrasound increases the permeability of biological membranes, as a result of which metabolic processes are accelerated due to diffusion. A change in the flow of various substances through the cytoplasmic membrane leads to a change in the composition of the intracellular environment and the cell microenvironment. This affects the rate of biochemical reactions involving enzymes that are sensitive to the content of certain or
other ions. In some cases, a change in the composition of the environment inside a cell can lead to an acceleration of enzymatic reactions, which is observed when cells are exposed to low-intensity ultrasound.
Many intracellular enzymes are activated by potassium ions. Therefore, with increasing ultrasound intensity, the effect of suppressing enzymatic reactions in the cell becomes more likely, since as a result of depolarization of cell membranes, the concentration of potassium ions in the intracellular environment decreases.
The effect of ultrasound on cells can be accompanied by the following phenomena:
Violation of the microenvironment of cell membranes in the form of changes in the concentration gradients of various substances near the membranes, changes in the viscosity of the environment inside and outside the cell;
Changes in the permeability of cell membranes in the form of acceleration of normal and facilitated diffusion, changes in the efficiency of active transport, disruption of membrane structure;
Violation of the composition of the intracellular environment in the form of changes in the concentration of various substances in the cell, changes in viscosity;
Changes in the rates of enzymatic reactions in the cell due to changes in the optimal concentrations of substances necessary for the functioning of enzymes.
A change in the permeability of cell membranes is a universal response to ultrasound exposure, regardless of which of the ultrasound factors acting on the cell dominates in a particular case.
At a sufficiently high intensity of ultrasound, membrane destruction occurs. However, different cells have different resistance: some cells are destroyed at an intensity of 0.1 W/cm 2, others at 25 W/cm 2.
In a certain intensity range, the observed biological effects of ultrasound are reversible. The upper limit of this interval of 0.1 W/cm 2 at a frequency of 0.8-2 MHz is accepted as the threshold. Exceeding this limit leads to pronounced destructive changes in cells.
Destruction of microorganisms
Ultrasound irradiation with an intensity exceeding the cavitation threshold is used to destroy bacteria and viruses present in the liquid.
5.5. Use of ultrasound in medicine: therapy, surgery, diagnostics
Deformations under the influence of ultrasound are used when grinding or dispersing media.
The phenomenon of cavitation is used to obtain emulsions of immiscible liquids and to clean metals from scale and fatty films.
Ultrasound therapy
The therapeutic effect of ultrasound is determined by mechanical, thermal, and chemical factors. Their combined action improves membrane permeability, dilates blood vessels, improves metabolism, which helps restore the body’s equilibrium state. A dosed ultrasound beam can be used to perform a gentle massage of the heart, lungs and other organs and tissues.
In otolaryngology, ultrasound affects the eardrum and nasal mucosa. In this way, rehabilitation of chronic runny nose and diseases of the maxillary cavities is carried out.
PHONOPHORESIS - introduction of medicinal substances into tissues through the pores of the skin using ultrasound. This method is similar to electrophoresis, however, unlike an electric field, an ultrasonic field moves not only ions, but also uncharged particles. Under the influence of ultrasound, the permeability of cell membranes increases, which facilitates the penetration of drugs into the cell, whereas with electrophoresis, drugs are concentrated mainly between the cells.
AUTOHEMOTHERAPY - intramuscular injection of a person's own blood taken from a vein. This procedure turns out to be more effective if the blood taken is irradiated with ultrasound before infusion.
Ultrasound irradiation increases the sensitivity of cells to the effects of chemicals. This allows you to create less harmful
vaccines, since in their manufacture chemical reagents of lower concentration can be used.
Preliminary exposure to ultrasound enhances the effect of γ- and microwave irradiation on tumors.
In the pharmaceutical industry, ultrasound is used to produce emulsions and aerosols of certain medicinal substances.
In physiotherapy, ultrasound is used for local impact, carried out using an appropriate emitter, applied contactally through an ointment base to a specific area of the body.
Ultrasound surgery
Ultrasound surgery is divided into two types, one of which is associated with the effect of sound vibrations on tissue, the second with the application of ultrasonic vibrations to a surgical instrument.
Destruction of tumors. Several emitters mounted on the patient's body emit ultrasound beams that focus on the tumor. The intensity of each beam is not sufficient to damage healthy tissue, but in the place where the beams converge, the intensity increases and the tumor is destroyed by cavitation and heat.
In urology, using the mechanical action of ultrasound, they crush stones in the urinary tract and thereby save patients from operations.
Welding soft tissues. If you put two cut blood vessels together and press them together, a weld will form after irradiation.
Welding bones(ultrasonic osteosynthesis). The fracture area is filled with crushed bone tissue mixed with a liquid polymer (cyacrine), which quickly polymerizes under the influence of ultrasound. After irradiation, a strong weld is formed, which gradually dissolves and is replaced by bone tissue.
Application of ultrasonic vibrations to surgical instruments(scalpels, files, needles) significantly reduces cutting forces, reduces pain, and has hemostatic and sterilizing effects. The vibration amplitude of the cutting tool at a frequency of 20-50 kHz is 10-50 microns. Ultrasonic scalpels make it possible to perform operations in the respiratory organs without opening the chest,
operations in the esophagus and blood vessels. By inserting a long and thin ultrasonic scalpel into a vein, cholesterol thickenings in the vessel can be destroyed.
Sterilization. The destructive effect of ultrasound on microorganisms is used to sterilize surgical instruments.
In some cases, ultrasound is used in combination with other physical influences, for example cryogenic, for surgical treatment of hemangiomas and scars.
Ultrasound diagnostics
Ultrasound diagnostics is a set of methods for studying a healthy and sick human body, based on the use of ultrasound. The physical basis of ultrasound diagnostics is the dependence of the parameters of sound propagation in biological tissues (sound speed, attenuation coefficient, wave impedance) on the type of tissue and its condition. Ultrasound methods make it possible to visualize the internal structures of the body, as well as to study the movement of biological objects inside the body. The main feature of ultrasound diagnostics is the ability to obtain information about soft tissues that vary slightly in density or elasticity. The ultrasound examination method is highly sensitive, can be used to detect formations that are not detected by x-ray, does not require the use of contrast agents, is painless and has no contraindications.
For diagnostic purposes, ultrasound frequency from 0.8 to 15 MHz is used. Low frequencies are used when studying deeply located objects or when studying through bone tissue, high frequencies - for visualizing objects located close to the surface of the body, for diagnostics in ophthalmology, when studying superficially located vessels.
The most widely used in ultrasound diagnostics are echolocation methods based on the reflection or scattering of pulsed ultrasound signals. Depending on the method of obtaining and the nature of presentation of information, devices for ultrasound diagnostics are divided into 3 groups: one-dimensional devices with type A indication; one-dimensional instruments with type M indication; two-dimensional devices with type B indication.
During ultrasound diagnostics using a type A device, a radiator emitting short (lasting about 10 -6 s) ultrasound pulses is applied to the area of the body being examined through a contact substance. In the pauses between pulses, the device receives pulses reflected from various inhomogeneities in the tissues. After amplification, these pulses are observed on the screen of the cathode ray tube in the form of beam deviations from the horizontal line. The complete pattern of reflected pulses is called one-dimensional echogram type A. Figure 5.8 shows an echogram obtained during echoscopy of the eye.
Rice. 5.8. Echoscopy of the eye using the A-method:
1 - echo from the anterior surface of the cornea; 2, 3 - echoes from the anterior and posterior surfaces of the lens; 4 - echo from the retina and structures of the posterior pole of the eyeball
Echograms of tissues of various types differ from each other in the number of pulses and their amplitude. Analysis of a type A echogram in many cases allows one to obtain additional information about the condition, depth and extent of the pathological area.
One-dimensional devices with type A indication are used in neurology, neurosurgery, oncology, obstetrics, ophthalmology and other fields of medicine.
In devices with type M indication, reflected pulses, after amplification, are fed to the modulating electrode of the cathode ray tube and are presented in the form of dashes, the brightness of which is related to the amplitude of the pulse, and the width is related to its duration. The development of these lines in time gives a picture of individual reflecting structures. This type of indication is widely used in cardiography. An ultrasound cardiogram can be recorded using a cathode ray tube with memory or on a paper tape recorder. This method records the movements of the heart elements, which makes it possible to determine mitral valve stenosis, congenital heart defects, etc.
When using type A and M recording methods, the transducer is in a fixed position on the patient's body.
In the case of type B indication, the transducer moves (scans) along the surface of the body, and a two-dimensional echogram is recorded on the screen of the cathode ray tube, reproducing the cross section of the examined area of the body.
A variation of method B is multiscanning, in which the mechanical movement of the sensor is replaced by sequential electrical switching of a number of elements located on the same line. Multiscanning allows you to observe the sections under study in almost real time. Another variation of method B is sector scanning, in which there is no movement of the echo probe, but the angle of insertion of the ultrasound beam changes.
Ultrasound devices with type B indication are used in oncology, obstetrics and gynecology, urology, otolaryngology, ophthalmology, etc. Modifications of type B devices with multiscanning and sector scanning are used in cardiology.
All echolocation methods of ultrasound diagnostics make it possible, in one way or another, to register the boundaries of areas with different wave impedances inside the body.
A new method of ultrasound diagnostics - reconstructive (or computational) tomography - gives the spatial distribution of sound propagation parameters: attenuation coefficient (attenuation modification of the method) or sound speed (refractive modification). In this method, the section of the object under study is sounded repeatedly in different directions. Information about the coordinates of the sound and the response signals is processed on a computer, as a result of which a reconstructed tomogram is displayed on the display.
Recently, the method has begun to be introduced elastometry for the study of liver tissue both normally and at various stages of microsis. The essence of the method is this. The sensor is installed perpendicular to the body surface. Using a vibrator built into the sensor, a low-frequency sound mechanical wave is created (ν = 50 Hz, A = 1 mm), the speed of propagation of which through the underlying liver tissue is assessed using ultrasound with a frequency of ν = 3.5 MHz (in essence, echolocation is carried out ). Using
modulus E (elasticity) of the fabric. A series of measurements (at least 10) are taken for the patient in the intercostal spaces in the projection of the position of the liver. All data is analyzed automatically; the device provides a quantitative assessment of elasticity (density), which is presented both numerically and in color.
To obtain information about the moving structures of the body, methods and instruments are used, the operation of which is based on the Doppler effect. Such devices usually contain two piezoelements: an ultrasonic emitter operating in continuous mode and a receiver of reflected signals. By measuring the Doppler frequency shift of an ultrasonic wave reflected from a moving object (for example, from the wall of a vessel), the speed of movement of the reflecting object is determined (see formula 2.9). The most advanced devices of this type use a pulse-Doppler (coherent) location method, which makes it possible to isolate a signal from a certain point in space.
Devices using the Doppler effect are used to diagnose diseases of the cardiovascular system (determination
movements of parts of the heart and the walls of blood vessels), in obstetrics (study of the fetal heartbeat), for studying blood flow, etc.
The organs are examined through the esophagus, with which they border.
Comparison of ultrasonic and x-ray “candling”
In some cases, ultrasonic scanning has an advantage over x-ray. This is due to the fact that X-rays provide a clear image of “hard” tissue against a background of “soft” tissue. For example, bones are clearly visible against the background of soft tissue. To obtain an X-ray image of soft tissues against the background of other soft tissues (for example, a blood vessel against the background of muscles), the vessel must be filled with a substance that absorbs X-ray radiation well (contrast agent). Ultrasonic transillumination, thanks to the already mentioned features, provides an image in this case without the use of contrast agents.
X-ray examination differentiates the density difference up to 10%, and ultrasound – up to 1%.
5.6. Infrasound and its sources
Infrasound- elastic vibrations and waves with frequencies lying below the range of frequencies audible to humans. Typically, 16-20 Hz is taken as the upper limit of the infrasound range. This definition is conditional, since with sufficient intensity, auditory perception also occurs at frequencies of a few Hz, although in this case the tonal nature of the sensation disappears and only individual cycles of oscillations become distinguishable. The lower frequency limit of infrasound is uncertain; its current area of study extends down to about 0.001 Hz.
Infrasonic waves propagate in air and water, as well as in the earth's crust (seismic waves). The main feature of infrasound, due to its low frequency, is low absorption. When propagating in the deep sea and in the atmosphere at ground level, infrasonic waves with a frequency of 10-20 Hz attenuate at a distance of 1000 km by no more than a few decibels. It is known that sounds
Volcanic eruptions and atomic explosions can circle the globe many times. Due to the long wavelength, infrasound scattering is also low. In natural environments, noticeable scattering is created only by very large objects - hills, mountains, tall buildings.
Natural sources of infrasound are meteorological, seismic and volcanic phenomena. Infrasound is generated by atmospheric and oceanic turbulent pressure fluctuations, wind, sea waves (including tidal waves), waterfalls, earthquakes, and landslides.
Sources of infrasound associated with human activity are explosions, gun shots, shock waves from supersonic aircraft, impacts of piledrivers, the operation of jet engines, etc. Infrasound is contained in the noise of engines and technological equipment. Vibrations of buildings created by industrial and domestic pathogens, as a rule, contain infrasonic components. Transport noise makes a significant contribution to infrasonic pollution of the environment. For example, passenger cars at a speed of 100 km/h create infrasound with an intensity level of up to 100 dB. In the engine compartment of large ships, infrasonic vibrations created by operating engines have been recorded with a frequency of 7-13 Hz and an intensity level of 115 dB. On the upper floors of high-rise buildings, especially in strong winds, the infrasound intensity level reaches
Infrasound is almost impossible to isolate - at low frequencies, all sound-absorbing materials almost completely lose their effectiveness.
5.7. Impact of infrasound on humans. Use of infrasound in medicine
Infrasound, as a rule, has a negative effect on humans: it causes a depressed mood, fatigue, headache, and irritation. A person exposed to low-intensity infrasound experiences symptoms of seasickness, nausea, and dizziness. A headache appears, fatigue increases, and hearing weakens. At a frequency of 2-5 Hz
and an intensity level of 100-125 dB, the subjective reaction is reduced to a feeling of pressure in the ear, difficulty swallowing, forced modulation of the voice and difficulty speaking. Exposure to infrasound negatively affects vision: visual functions deteriorate, visual acuity decreases, the field of vision narrows, accommodative ability is weakened, and the stability of the eye’s fixation of the observed object is impaired.
Noise at a frequency of 2-15 Hz at an intensity level of 100 dB leads to an increase in the tracking error of the dial indicators. Convulsive twitching of the eyeball and dysfunction of the balance organs appear.
Pilots and cosmonauts exposed to infrasound during training were slower in solving even simple arithmetic problems.
There is an assumption that various anomalies in the condition of people in bad weather, explained by climatic conditions, are actually a consequence of the influence of infrasonic waves.
At moderate intensity (140-155 dB), fainting and temporary loss of vision may occur. At high intensities (about 180 dB), paralysis can occur with a fatal outcome.
It is believed that the negative impact of infrasound is due to the fact that the natural vibration frequencies of some organs and parts of the human body lie in the infrasound region. This causes unwanted resonance phenomena. Let us indicate some frequencies of natural oscillations for humans:
Human body in a lying position - (3-4) Hz;
Chest - (5-8) Hz;
Abdomen - (3-4) Hz;
Eyes - (12-27) Hz.
The effects of infrasound on the heart are especially harmful. With sufficient power, forced oscillations of the heart muscle occur. At resonance (6-7 Hz), their amplitude increases, which can lead to hemorrhage.
Use of infrasound in medicine
In recent years, infrasound has become widely used in medical practice. Thus, in ophthalmology, infrasound waves
with frequencies up to 12 Hz are used in the treatment of myopia. In the treatment of eyelid diseases, infrasound is used for phonophoresis (Fig. 5.9), as well as for cleansing wound surfaces, improving hemodynamics and regeneration in the eyelids, massage (Fig. 5.10), etc.
Figure 5.9 shows the use of infrasound to treat lacrimal duct abnormalities in newborns.
At one stage of treatment, massage of the lacrimal sac is performed. In this case, the infrasound generator creates excess pressure in the lacrimal sac, which contributes to the rupture of embryonic tissue in the lacrimal canal.
Rice. 5.9. Scheme of infrasound phonophoresis
Rice. 5.10. Massage of the lacrimal sac
5.8. Basic concepts and formulas. Tables
Table 5.1. Absorption coefficient and half-absorption depth at a frequency of 1 MHz
Table 5.2. Reflection coefficient at the boundaries of different tissues
5.9. Tasks
1. The reflection of waves from small inhomogeneities becomes noticeable when their sizes exceed the wavelength. Estimate the minimum size d of a kidney stone that can be detected by ultrasound diagnostics at a frequency ν = 5 MHz. Ultrasound wave speed v= 1500 m/s.
Solution
Let's find the wavelength: λ = v/ν = 1500/(5*10 6) = 0.0003 m = 0.3 mm. d > λ.
Answer: d > 0.3 mm.
2. Some physiotherapeutic procedures use ultrasound with frequency ν = 800 kHz and intensity I = 1 W/cm2. Find the vibration amplitude of soft tissue molecules.
Solution
The intensity of mechanical waves is determined by formula (2.6)
The density of soft tissues is ρ « 1000 kg/m 3 .
circular frequency ω = 2πν ≈ 2x3.14x800x10 3 ≈ 5x10 6 s -1 ;
ultrasound speed in soft tissues ν ≈ 1500 m/s.
It is necessary to convert the intensity to SI: I = 1 W/cm 2 = 10 4 W/m 2 .
Substituting numerical values into the last formula, we find:
Such a small displacement of molecules during the passage of ultrasound indicates that its effect is manifested at the cellular level. Answer: A = 0.023 µm.
3. Steel parts are checked for quality using an ultrasonic flaw detector. At what depth h in the part was a crack detected and what is the thickness d of the part if, after emitting an ultrasonic signal, two reflected signals were received at 0.1 ms and 0.2 ms? The speed of propagation of an ultrasonic wave in steel is equal to v= 5200 m/s.
Solution
2h = tv →h = tv/2. Answer: h = 26 cm; d = 52 cm.
