Noise is every unwanted sound for a person. As a sound, we perceive the elastic oscillations, propagating the wave-like in solid, liquid or gaseous media. Sound waves occur in disruption of the stationary state of the medium due to the impact on it of any disturbing force. The medium particles at the same time begin to fluctuate relative to the equilibrium position, and the speed of such oscillations (oscillatory speed and) is significantly less than the speed of the wave propagation (sound velocity C).

In a gaseous environment, sound speed

where x is the adiabatic index (for air x \u003d 1.41); PCT and P is pressure and gas density.

Under normal atmospheric conditions (T \u003d 20 ° C and PCT \u003d 760 mm Hg. Art.) The speed of sound with in the air is 344 m / s.

Sound field - this area of \u200b\u200bspace in which audio waves are distributed. At each point of the sound field, the pressure and speed of air particles change over time. The difference between the instantaneous value of full pressure and average pressure, which is observed in a unperturbed medium, is called sound pressure. unit of measurement sound pressure N / m2.

The middle square of the sound pressure acts on the rumor

where the feature means averaging in time, which in the ear of a person occurs for T \u003d 30-100 ms.

In a flat sound wave, i.e., in which the surface passing through points with the same oscillation phase is a plane perpendicular to the direction of fluctuation propagation, the sound pressure ratio to the oscillatory speed does not depend on the amplitude of the oscillations.

It is equal (ns / m3)

p / v \u003d pc,

where RS is a specific acoustic resistance of the medium that is for air, for example, equal to 410 ns / m3, for water 1.5-106, for steel 4.8-107.

When the sound wave is propagated, energy is transferred. The average energy flow at a point of the medium per unit of time, referred to a unit of the surface, normal to the direction of propagation of the wave, is called the intensity of the sound at this point. The intensity of the sound is indicated by the letter / and is measured in watts divided into a square meter (W / m2).

Sound intensity is associated with sound pressure addiction

The magnitudes of the sound pressure and the intensity of the sound with whom have to deal in the practice of combating noise, can vary widely: by pressure up to 108 times, intensity up to 1016 times. Naturally, it is quite uncomfortable to operate with such numbers. The very important thing is that a person's ear can respond to a relative change in intensity, and not to absolute. The sensations of a person arising from different irritations, in particular with noise, are proportional to the logarithm for the amount of energy of the irritant. Therefore, logarithmic values \u200b\u200bwere introduced - levels of sound pressure and intensity expressed in decibels (dB).

Sound intensity level (dB) are determined by the formula

LJ \u003d 10LG (J / J0)

where J0 is the intensity of the sound corresponding to the hearing threshold (J0 \u003d 10-12 W / m2 at a frequency of 1000 Hz).

The magnitude of the sound pressure level (dB)

where the threshold sound pressure P0 is chosen in such a way that under normal atmospheric conditions, sound pressure levels were equal to the levels of intensity, i.e. p0 \u003d 2 * 10-5 n / m2. Sound intensity (W / m2)

J0 \u003d p0 / p0c0, (10)

where P0С0 is the density and speed of sound under normal atmospheric conditions.

The magnitude of the intensity level is used when conducting acoustic calculations, and the sound pressure level is to measure noise and to assess its impact on a person, since the hearing body is not sensitive to intensity, but to the standard pressure. The relationship between the level of intensity and the sound pressure level is obtained by separating the expression (9) to the expression (10) and prologarithming

LJ \u003d L + 101G (P0C0 / PC).

Under normal atmospheric conditions

The reduction of noise is also estimated in decibels:

For example, if the noise of the unit is reduced by intensity in 1000 times, the level of intensity will be reduced by

L1 - L2 \u003d 10 LG 1000 \u003d 30 dB.

In the case when noise from several sources falls into the calculation point, their intensities are folded, but not levels. It believes that sources are incoherent, i.e., the pressure generated by them have arbitrary phases

J \u003d j1 + j2 + ... + jn.

The desired level of intensity (dB), with simultaneous operation of these sources, we obtain, dividing the left and right parts of this expression on J0 and prologarithming:

where L1, L2, ..., Ln is the levels of sound pressure or intensity levels created by each of the sources at the calculation point.

The considered features of the summation of levels are of great practical importance for noisemissions. Thus, with a large number of the same sources, the overthrow of only a few of them practically does not weaken the total noise. If there is noise from different sources from the intensity of sources, it is necessary to reduce the noise of more powerful sources at first.

If there is a n equal sources of noise with the sound pressure level of the Li created by each source, then the total noise (dB)

L \u003d Li + 10LGN.

From this formula, it is clear that two identical sources will jointly create a level of 3 dB greater than each source.

Fig. 38. Curves equal volume of sounds

The logarithmic scale of the Decibel allows you to determine only the physical characteristic of noise. However, it is constructed in such a way that the threshold value of the sound pressure P0 corresponds to the threshold of audibility at a frequency of 1,000 Hz.

The auditory apparatus of a person has an unequal sensitivity to the sounds of different frequencies, namely, the greatest sensitivity on medium and high frequencies (800-4000 Hz) and the smallest - on low (20-100 Hz). Therefore, for the physiological assessment of noise, the curves of equal volume are used (Fig. 38), obtained according to the results of the study of the properties of the hearing body to estimate the sounds of different frequencies on a subjective sensation of the volume, that is, to judge which one is stronger or weaker.

Volume levels are measured in the backgrounds. At the frequency of 1000 Hz, the volume levels are taken with equal sound pressure levels.

Any dependence of any value (for example, sound pressure) on time can be represented as the sum of the final or infinite number of sinusoidal oscillations of this value (see ch. 4).

Each such oscillation is characterized by its mean square value of the physical size and frequency F, i.e., the number of oscillations per second (Hz).

The human ear can only perceive the oscillations whose frequencies are in the range from 16-20 to 16,000-20,000 Hz. Below 16 Hz and above 20,000 Hz are respectively the field of infrase and ultrasounds by humans.

The dependence of the mean square values \u200b\u200bof sinusoidal components of noise (or corresponding to them levels in decibels) from the frequency is called the frequency spectrum of noise (or just a spectrum).

The spectra are obtained using noise analyzers - a set of electrical filters that skip the signal in a specific frequency band - bandwidth.

The sound is an object of the auditory. He is estimated by a person subjectively. All subjective characteristics of the auditory are associated with objective (physical) characteristics of the sound wave.

Perceived sounds man distinguishes them timbre, height, volume.

Timbre – « coloring "sound and is determined by its harmonic spectrum. Various acoustic spectra correspond to the different timbre, even if they are the same. The timbre is a qualitative characteristic of sound.

Altaton - Subjective assessment of the sound signal, depending on the frequency of sound and its intensity. The more frequency, mainly the main tone, the greater the height of the perceived sound. The greater the intensity, the lower the height of the perceived sound.

Volume - also a subjective assessment characterizing the level of intensity.

Volume mainly depends on the intensity of the sound. However, the perception of intensity depends on the sound frequency. The sound of greater intensity of one frequency can be perceived as less loud than the sound of a smaller intensity of another frequency.

Experience shows that for each frequency in the field of hearing sounds

(16 - 20. 10 3 Hz) There is a so-called hearing threshold. This is the minimum intensity at which the ear also reacts to sound. In addition, for each frequency there is a so-called threshold of pain, i.e. The value of the intensity of the sound, which causes pain in the ears. The combination of points corresponding to the threshold of hearingness, and points corresponding to the threshold of pain, form two curves on the diagram (L, ν) (Fig. 1), which are extrapolated to intersection.

The threshold curve of hearing (a), the threshold curve of pain (b).

The area bounded by these curves is called the hearing area. From the above diagram, in particular, it can be seen that a less intense sound corresponding to the point A will be perceived loudly than the sound is a more intense corresponding to the point in, since the point and more removed from the threshold of hearingness than Point V.

4. Weber-Fehner Law.

Volume can be estimated quantitatively by comparing auditory sensations from two sources.

The basis of the creation of the volume of volume levels is the psychophysical law of Weber-Ferechner. If you increase irritation in geometric progression (i.e., in the same number of times), the feeling of this irritation increases in arithmetic progression (that is, on the same value).

With applied to the sound, this is formulated as follows: if the intensity of the sound takes a number of consecutive values, for example, and i 0, and 2 i 0,

and 3 i 0, .... (A - some coefficient, a\u003e 1), etc., they correspond to the sensation of sound volume e 0, 2 e 0, 3 e 0 ... .. Mathematically, this means that the level of sound volume Proportional to decimal sound intensity logarithm. If two sound irritants are acting with the intensities I and I 0, with I 0 - the hearing threshold, then according to the Weber-Ferehner's law, the volume E and the intensity I 0 is related to read as follows:

E \u003d k lg (I / I 0),

where k is the proportionality coefficient.

If the coefficient K was constant, then it would be that the logarithmic scale of the intensities of the sound corresponds to the scale of irrigation levels. In this case, the level of sound volume is as well as the intensity would be expressed in Belarus or decibels. However, the strong dependence of K from the frequency and intensity of the sound does not allow the volume to measure the volume to the simple use of the formula: E \u003d k LG (I / I 0).

It is conventionally believed that at the frequency of 1 kHz, the volume of volume levels and intensity of sound completely coincide, i.e. k \u003d 1 and e b \u003d lg (I / I 0). To distinguish the volume scales and the intensity of the sound, the volume of the volume scale is called the backgrounds (background).

E F \u003d 10 K LG (I / I 0)

Volume at other frequencies can be measured by comparing the audio sound

with a sound frequency of 1 kHz.

Curves equal volume. The loudness dependence on the frequency of oscillations in the system of sound measurements is determined based on the experimental data using graphs (Fig. 2), which are called the curves of equal volume. These curves characterize the dependence of the level of intensity L.from frequency ν Sound at a constant volume level. Curves equal volume are called isofonamim.

The lower isothon corresponds to the threshold of hearingness (e \u003d 0 background). The upper curve shows the upper limit of the ear sensitivity, when the auditory sensation goes into a feeling of pain (E \u003d 120 background).

Each curve corresponds to the same volume, but of different intensity, which at certain frequencies cause the feeling of this volume.

Sound measurements. For a subjective rumor assessment, the method of threshold audiometry is used.

Audiometry- method of measuring the threshold intensity of the perception of sound for different frequencies. On a special device (audiometer), the threshold of the auditory sensation at different frequencies is determined:

L n \u003d 10 lg (I p / i 0),

where I n is the threshold intensity of the sound, which leads to the occurrence of the auditory sensation at the subject. Curves are obtained - audiograms, which reflect the dependence of the threshold of perception from the tone frequency, i.e. this is spectral characteristic Ear on the threshold of hearingness.

Comparing the audiogram of the patient (Fig. 3, 2) with the normal threshold curve of the auditory threshold (Fig. 3, 1), determine the difference in the levels of the intensity ΔL \u003d L 1 -L 2. L 1 - the level of intensity on the threshold of the audibility of normal ear. L 2 - the level of intensity on the threshold of hearing the studied ear. The curve for ΔL (RIS3, 3) is called hearing loss.

The audiogram, depending on the nature of the disease, has a form other than the audiogram of a healthy ear.

Noiseomers- Devices for measuring the volume level. The noiseomer is equipped with a microphone that turns the acoustic signal into an electric. The volume level is recorded by an arrow or digital measuring instrument.

5. Hearing physics: sound conducting and operating parts of the hearing aid. Theories of Helmholtz and Bekeshi.

Hearing physics is associated with the functions of the outer (1.2 Fig.4), the mean (3, 4, 5, 6 Fig.4) and the inner ear (7-13 of Fig. 4).

Schematic representation of the main elements of the human hearing aid: 1 - ear sink, 2 - outer hearing aisle, 3 - drummeal, 4, 5, 6 - bone system, 7 - oval window (inner ear), 8 - vestibular staircase, 9 - round Window, 10 - drum staircase, 11 - Helicotrema, 12 - Sniddle Channel, 13 - Basic (Basilar) membrane.

According to the functions performed in the human hearing apparatus, you can select the sound and sound drives, the main elements of which are presented in Fig. 5.

1 - ear sink, 2 - outer hearing pass, 3 - eardrum, 4- bone system, 5 - snail, 6 - basic (Basilar membrane, 7 - receptors, 8 - branching of auditory nerve.

The main membrane is a very interesting structure, it has the frequency-selective properties. It was still notified by Helmholz, which represented the main membrane similarly to a row of the built piano strings. In Helmholtz, each site of the basilar membrane resonated for a certain frequency. The laureate of the Nobel Prize Bekeshi established the fallacy of this resonant theory. In the works of Bekeshi, it was shown that the main membrane is an inhomogeneous line of transmission of mechanical excitation. When exposed to an acoustic stimulus on the main membrane, the wave is spread. Depending on the frequency, this wave fades in different ways. The smaller the frequency, the farther from the oval window (7 Fig.4) the wave is spreading on the main membrane before it starts to fluff. For example, a wave with a frequency of 300 Hz before the start of attenuation spreads approximately 25 mm from the oval window, and the wave with a frequency of 100 Hz reaches its maximum near 30 mm.

According to modern ideas, the perception of the height of the tone is determined by the position of the maximum of the oscillations of the main membrane. These oscillations, acting on the Cortiyev receptor cells, cause the capabilities of the action that human nervas Transmitted to the bark of the brain. The brain finally processes the incoming signals.

1. Characteristics of the auditory, their connection with physical

sound characteristics. The dependence of the volume from the frequency.

Weber-Ferehner law.

The sound tone is characterized by a frequency (period), a harmonic spectrum, intensity, or sound strength and sound pressure. All these sound characteristics are physical or objective characteristics. However, the sound is the object of the auditory feeling, therefore, it is estimated by a person subjectively, i.e. The sound has both physiological characteristics that are reflected in its physical characteristics. The task of the sound measurement system is to establish this relationship and thus enabler when studying hearing in various people, it is unlikely to compare the subjective assessment of the auditory sensation with the data of objective measurements.

The frequency of oscillations of the sound wave is estimated as the height of the sound (tone height). The greater the frequency of oscillations, the more high the sound is perceived.

Another physiological characteristic is the timbre, which is determined by the spectral composition of complex sound. The complex tones of the same basic frequencies may differ in the form of oscillations and, accordingly, according to the harmonious spectrum. This difference is perceived as the timbre (sound color). For example, the ear distinguishes the same melody reproduced on different musical instruments.

Volume - another subjective sound assessment, which characterizes the level of the auditory. It depends first of all, from the intensity and frequency of sound.

Consider first the dependence of the ear sensitivity from the frequency. The human ear is not equally sensitive to different frequencies at the same intensity. The frequency range is perceived by them - 16Hz-20kHz. The ability of a person to perceive high-frequency sounds is worsening with age. A young man can hear sounds with a frequency of up to 20,000 Hz, but at the middle age the same person is not able to perceive sounds with a frequency above 12-14 kHz. Within the frequency of 1,000-3,000 Hz, the sensitivity is the largest. It decreases to the frequencies of 16 Hz and 20 kHz. Obviously, the nature of the change in the threshold of hearingness is treated with the change in the sensitivity of the ear, i.e. With increasing frequency from 16 Hz, it is first reduced, in the frequency range 1000-3000 Hz remains almost unchanged, then rises again. This is reflected in the chart of the dependence of the change in the threshold of hearing frequency (see Fig. 1).

The schedule is built in a logarithmic scale. The upper curve on the graph corresponds to the painful threshold. The lower chart is called the threshold volume curve, i.e. J 0 \u003d F (ν).

The volume of the sound depends on its intensity. It is a subjective sound characteristic. These two concepts are unequal. The loudness dependence on the intensity of sound is complex, due to the sensitivity of the ear to the action of sound waves. A person can only approximately estimate the absolute intensity of the sensation. However, it definitely establishes the difference when comparing two sensations of various intensity. It caused the appearance of a comparative volume of volume measurement. In this case, the absolute amount of volume is measured, but its ratio with some other value, which is accepted for the initial or zero volume level.

In addition, it was agreed when comparing the intensity and volume of sound to proceed from the tone, with a frequency of 1,000 Hz, i.e. Read the volume of tone with a frequency of 1,000 Hz benchmark for volume scales. As already mentioned, the comparative method is used and when measuring the intensity (strength) of sound. Therefore, there are two scales: one to measure intensity levels; The second is to measure the volume levels. The creation of the volume of volume levels is the important psychophysical law of Weber-Ferehner. According to this law, if you increase irritation in geometric progression (that is, in the same number of times), the feeling of this irritation increases in arithmetic progression (on the same value). For example, if the audio intensity takes a number of consecutive values: a J 0, A 2 J 0, A 3 J 0 (A\u003e 1 is some coefficient), then the corresponding volume changes to them will be equal to E 0, 2E 0, 3E 0. Mathematically, this means that the sound volume is directly proportional to the logarithm of intensity.

If the sound irritant is acting with the intensity J, then on the basis of the Weber-Fehener law, the volume level E is associated with the level of intensity as follows:

E \u003d Kl \u003d KLG, (1)

where - the relative force of irritation, K, some proportionality coefficient, depending on the frequency and intensity, adopted equal to one for ν \u003d 1000 Hz. Therefore, if we take K \u003d 1 at all frequencies, then in accordance with the formula (1) we obtain the scale of intensity levels; with ≠ 1 - the volume scale, where the unit of measurement will no longer decibel, but background. Given that at the frequency of 1 kHz, the volume and intensity scales coincide, it means that the e f \u003d 10.

The dependence of the volume from the intensity and frequency of oscillations in the sound measurement system is determined based on the experimental data using graphs that are called equal volume curves, i.e. J \u003d f (ν) at e \u003d const. We have built a curve of the zero volume level or the threshold of hearingness. This curve is the main (zero volume level - e f \u003d 0).

If you build similar curves for different levels of louds, for example, steps through 10 backgrounds, then the graph of graphs will be obtained (Fig. 2), which makes it possible to find the dependence of the intensity level from frequency at any volume level. These curves are built on the basis of medium data, which were obtained in people with normal hearing. The lower curve corresponds to the threshold of hearingness, i.e. For all frequencies e f \u003d 0 (for frequency ν \u003d 1 kHz, the intensity J 0 \u003d W / m 2). The study of hearing acuity is called audiometry. With an audio system on a special instrument, an audiometer is determined by the surveyed threshold of the auditory sensation at different frequencies. The resulting schedule is called an audiogram. Hearing loss is determined by comparing it with a normal threshold curve of hearing.

2. Sound research methods in the clinic.

Sound phenomena accompany a number of processes occurring in the body, for example, the work of the heart, breathing, etc. Direct listening to sounds arising inside the body make up one of the most important techniques of clinical research and are called auscultation (listening). This method is known since the 2nd century BC. e. For this purpose, a stethoscope is used - the device in the form of a straight wooden or plastic tube with a small field at one end and a flat base on the other for applying the ear. The sound from the body surface to the ear is carried out both by the pillar of air and the walls of the tube.

For auscultation use a phonenadoscope consisting of a hollow capsule with a membrane applied to the patient's body. There are two rubber tubes from the capsule, which are inserted into the ears of the doctor. The resonance of the air column in the capsule enhances the sound.

To diagnose the state of the cardiovascular system, the method is used - phonocardiography (FKG) - graphic registration of tones and sound noise with the aim of their diagnostic interpretation. The record is made using a phonocardograph consisting of a microphone, amplifier, frequency filter systems and a recorder device.

Excellent from two specified methods is percussion - research method internal organs By tapping on the body surface and the analysis of sounds arising from this. The nature of these sounds depends on the method of tapping and properties (elasticity, density) of fabrics located near the place where the tapping is made. Tapping can be made by a special hammer with a rubber head, a plate of elastic material, called a plaster, or tapping the tip of the bent finger of one hand along the finger phalanner, superimposed on the human body. When the body is impaired, oscillations occur, the frequencies of which have a wide range. Some oscillations will quickly plump, others, due to resonance, will increase and will be heard. According to the tone of the percussion sounds, the condition and topography of the internal organs determine.

3. Ultrasound (UZ), sources of UZ. Features of the propagation of ultrasound waves.

Ultrasound call sound oscillations whose frequency occupies a range of 20 kHz to 10 10 Hz. The upper limit is made quite conditionally from such considerations that the wavelength in substance and tissues for such a frequency is commensurate with intermolecular distances, taking into account the fact that the rate of propagation of ultrasound in water and tissues is the same. The displacement in the bond wave is described by the previously considered wave equation.

Piezoelectric emitters of ultrasound received the greatest distribution both in the technique and in medical practice. Piezoelectric emitters serve as crystals of quartz, barium titanate, segmental salt, and other piezoelectric effect (straight) call the phenomenon of the occurrences of the mentioned crystalline plates opposed on the sign of charges under the action of mechanical deformations (Fig. 3a). After removal of deformation, charges disappear.

There is also a reverse piezoeffect, which has found application and in medical practice for obtaining high-frequency bonds. If there is a variable voltage from the generator on the silver plated edge of the surface of the plates of the piezoelectric elector, then the quartz plate will go to oscillation in the variable voltage of the generator. The amplitude of oscillations will be maximum when the self-frequency of the quartz plate (ν 0) coincides with the generator frequency (ν g), i.e. The resonance will come (ν 0 \u003d ν g). Receiver UZ can be created on the basis of a direct piezoelectric effect. In this case, under the influence of Uz-waves, the crystal deformation occurs, which leads to the appearance of an alternating voltage, which can be measured or recorded on the screen of the electronic oscilloscope after its preinstatement.

Ultrasound can be obtained using devices based on the phenomenon of magnetostriction (for low frequencies), which consists in changing the length (elongation and shortening) of the ferromagnetic rod placed in a high-frequency magnetic field. The ends of this rod will emit low-frequency bonds. In addition to these sources, UZ has mechanical sources (sirens, whistles), in which the mechanical energy is converted into the energy of the oscillations.

By nature, nod, as well as the sound, is a mechanical wave propagating in an elastic environment. The speed of propagation of sound and ultrasonic waves is about the same. However, the wavelength of the UZ is significantly less than sound. This makes it easy to focus the oscillations.

The ultrasonic wave has a much greater intensity than sound, due to the high frequency, it can reach several watts per square centimeter (W / cm 2), and when focusing, it is possible to obtain ultrasound with the intensity of 50 W / cm 2 or more.

The spread of UZ in the medium is different (due to the low wavelength) and another feature of the liquid and solid bodies are good versions of UZ, and the air and gas are bad. So, in water, with other things being equal, the UZ fades 1,000 times weaker than in the air. In the propagation of UZ in an inhomogeneous medium, it is reflected and refracted. The reflection of the bonds on the border of two media depends on the ratio of their wave resistances. If the Uz in medium with W 1 \u003d R 1 j 1 falls perpendicular to the flat surface of the second medium with W 2 \u003d R 2 J 2, then part of the energy will pass through the boundary surface, and the part will reflect. The reflection coefficient will be zero if R 1 j 1 \u003d R 2 J 2 i.e. Uz-energy will not reflect on the boundary of the surface partition, and will move from one medium to another without loss. For the boundaries of the air-liquid, air, liquid-air, solid air and, on the contrary, the reflection coefficient will be equal to almost 100%. This is explained by the fact that the air has very small acoustic resistance.

That is why in all cases of communication of the emitter of bonds with an irradiated medium, for example, with a person's body, it is necessary to strictly monitor so that there is no minimum air layer between the emitters and the cloth (the wave resistance of biological media is 3000 times larger air resistance). To exclude the air layer, the surface of the emitter of the emitter is covered with a layer of oil or it is applied with a thin layer on the surface of the body.

When spreading UZ in the medium, sound pressure arises, which fluctuates, taking a positive value in the compression area and negative in the next region of the discharge. For example, under the intensity of ultrasound 2 W / cm 2 in human tissues, pressure is created in the compression area + 2.6 atm., Which in the next region passes into the discharge - 2.6 atm. (Fig.4). The compression and discharge created by ultrasound leads to the formation of breaks of a solid fluid to form microscopic cavities (cavitation). If this process occurs in fluid, the voids are filled with liquid in pairs or gas dissolved in it. Then, a substance compression site is formed at the cavity site, the cavity slaughters quickly, a significant amount of energy is distinguished in a small volume, which leads to the destruction of the microstructures of the substance.

4. Medico-biological ultrasound use.

The biological effect of the UZ is very diverse. So far, it is impossible to further give an exhaustive explanation of the actions of the bonds on biological objects. It is not always easy to highlight from numerous effects caused by ultrasound, basic. However, it is shown that during the irradiation of bonds of biological objects, it is necessary to be considered mainly with the following actions of UZ:

thermal; mechanical action; indirect, in most cases, physico-chemical action.

The thermal effect of UZ is important, because The process of metabolism in biological objects is characterized by a significant temperature dependence. The thermal effect is determined by the absorbed energy. At the same time, small intensities are used (about 1 W / cm 2). The thermal effect causes extension of tissues, blood vessels As a result, the metabolism increases, an increase in blood flow is observed. Thanks to the thermal effect of the focused ultrasound, it can be used as a scalpel for cutting not only soft tissues, but also bone tissue. Currently, the "welding" method of damaged or transplanted bone tissues has been developed.

Mechanical action. Mechanical oscillations of particles of substance in an ultrasound field can cause a positive biological effect (Micro-massage fabric structures). To this type of impact refers to microvibration at the cellular and sub-bottle level, the destruction of biomacomolecules, the destruction of microorganisms of fungi, viruses, destruction malignant tumors, stones B. bladder bubble and kidneys. Ultrasound is used for crushing substances, for example, in the manufacture of colloidal solutions, highly dispersed medicinal emulsions, aerosols. By the destruction of plant and animal cells, biologically active substances (enzymes, toxins) are distinguished. UZ causes damage and adjustment of cell membranes, changing their permeability.

Physico-chemical action ultrasound. Ultrasound action can be accelerated by some chemical reactions. It is believed that this is due to the activation of the molecules of water, which then disintegrate, forming active radicals H + and it.

Medico-biological application UZ can be divided mainly into two directions: diagnosis and therapy. The first is the location methods using mainly impulse radiation. This is an echohetephalography - determination of tumors and brain swelling.

Located methods are based on reflection of ultrasound from the boundary of the medium-based medium with different density. This method also includes ultrasound cardiography - measurement of heart size in the dynamics. Ultrasound location is used in ophthalmology to determine the size of the eye media. Ultrasonic Doppler effect is used to study the nature of the movement of cardiac valves and blood flow velocities.

A very large future of ultrasound holographic methods for obtaining an image of such organs as a kidneys, heart, stomach, etc.

The second direction includes ultrasound therapy. Ultrasounds are usually used with a frequency of 800 kHz and the intensity of 1 W / cm 2 and less. Moreover, the primary mechanisms of action are mechanical and thermal effect on the fabric. For ultrasound therapy purposes, the device UTP-ZM, etc.

5. Infrasound (from), the features of its distribution.

The effect of infrasounds on biological objects.

Infrasound (from) call sound oscillations, the upper range of which does not exceed 16 - 20 Hz. Lower range of 10 -3 Hz. Of great interest are from the frequency of 0.1 and even 0.01 Hz. From the noise. Sources from are movement (storm) marine or river water, forest noise, wind, thunderstorms, earthquakes and ribs, oscillations of buildings, machine tools, roads from moving transport. From occurs during the vibrations of the mechanisms, when blowing the wind buildings, trees, pillars, when man and animal movement.

The characteristic property of its small absorption of media. Therefore, it spreads over long distances. It is well propagated in the tissue of the human body, especially in bone tissue. The speed of the waves in the air is 1200 km / h, in water 6000 km / h.

The small absorption of it allows to spread it in the earth's crust to detect explosions and earthquakes at a large distance from the source. According to the measured from oscillations, the tsunami is predicted. Currently, sensitive receivers are developed from which, for example, it is possible to predict a storm for many hours before its offensive.

From oscillations have biological activity, which is explained by the coincidence of their frequency with alpha rhythm of the brain.

From the frequency of 1-7 Hz with an intensity of 70 dB for 8-10 minutes. Exposures cause: dizziness, nausea, difficulty breathing, feeling of oppression, headache, suffocity. All these factors are enhanced by re-exposure from. From a certain frequency may result in death.

Vibrations of mechanisms are the source of. Due to the unfavorable effect of vibration and from the human body, a vibrational disease occurs (WB). WB occurs with the long-term effects of these factors on a certain portion of tissue or human body and leads to fatigue not only separate organs, but also the whole body of a person. It first leads to the atrophing of the muscles of the hands and other organs, to a decrease in sensitivity to mechanical vibrations, to the appearance of cramps of the fingers, legs and other organs.

It is assumed that the primary mechanism of action from the body has a resonant nature. Internal human organs have their own oscillation frequency. When exposed to a frequency equal to own, a resonance arises, which causes the specified unpleasant sensations, and in some cases it can lead to difficult consequences: stopping the heart or breaking blood vessels.

The frequency of human fluctuations in the body is lying - (3 - 4 Hz), standing - (5 - 12 Hz), chest - (5 -8 Hz), abdominal cavity - (3 - 4 Hz) and other organs correspond to the frequency of.

Sounds bring vital information to a person - with their help we communicate, listen to music, find out by the voice of familiar people. The world of surrounding sounds is diverse and complicated, however, we easily focus on it and can unmistakably distinguish the singing of birds from the noise of the city street.

• Sound wave - Elastic longitudinal wave, causing auditory people in humans. The oscillations of the sound source (for example, strings or voice ligaments) cause the appearance of a longitudinal wave. Having reached the human ear, the sound waves force drumpatch Make forced oscillations with a frequency equal to the frequency of source oscillations. Over 20 thousand filamentous receptor endings in inner earTransform mechanical oscillations into electrical impulses. When transferring pulses by nerve fibers in the human brain, a person arises certain auditory sensations.

Thus, in the process of propagation of the sound wave, such characteristics of the medium are changing as pressure and density.

Sound waves perceived by hearing organs cause sound sensations.

Sound waves are classified by frequency as follows:

• infrase (ν < 16 Гц);
• man audible sound (16 Hz< ν < 20000 Гц);
• ultrasound (ν\u003e 2000 Hz);
• hyperzvuk (10 9 Hz< ν < 10 12 -10 13 Гц).

A person does not hear infrasound, but somehow these sounds perceives. Since, for example, experiments have shown that infraser causes unpleasant disturbing sensations.

Many animals can perceive ultracellular frequencies. For example, dogs can hear sounds up to 50,000 Hz, and bats are up to 100,000 Hz. Infrasevuk, spreading in water for hundreds of kilometers, helps whales and many other marine animals to navigate in the thickness of the water.

Physical characteristics of sound

One of the most important characteristics of sound waves is a spectrum.

• Spectrum A set of different frequencies forming this beep is called. The spectrum can be solid or discrete.

Solid spectrum This means that in this set there are waves, the frequencies of which are filled with the entire specified spectral range.

Discrete spectrum Indicates the presence of a finite number of waves with certain frequencies and amplitudes that form the signal under review.

By the type of spectrum, the sounds are divided into noise and musical tones.

• Noise - a set of many diverse short-term sounds (crunch, rustling, rustling, knock, etc.) - is an overlap of a large number of oscillations with close amplitudes, but different frequencies (has a solid spectrum). With the development of the industry, a new problem has appeared - the fight against noise. Even the new concept of "noise pollution" of habitat appeared. Noise, especially big intensity, not just bored and tired - he can and seriously undermine health.

• Musical tone Created by periodic oscillations of the sounding body (tankboard, string) and is a harmonic oscillation of one frequency.

With the help of musical tones, a musical alphabet is created - notes (to, re, mi, fa, salt, la, si), which allow you to reproduce the same melody on various musical instruments.

• Musical sound (consonance) - the result of the imposition of several simultaneously sounding musical tones, from which the main tone can be distinguished corresponding to the lowest frequency. The main tone is also called the first harmonic. All other tones are called overtones. Opertones are called harmonic if the frequencies of overtones are multiplicated by the frequency of the main tone. Thus, the musical sound has a discrete spectrum.

Any sound, in addition to the frequency, is characterized by intensity. So the jet aircraft can create sound intensity of about 10 3 W / m 2, powerful amplifiers at a concert in a closed room - up to 1 W / m 2, the metro train is about 10 -2 W / m 2.

To cause sound sensations, the wave should have some minimum intensity called the hearing threshold. The intensity of the sound waves, in which there is a feeling of grace pain, is called the threshold painful feeling or painful threshold.

The intensity of the sound, captured by the Human Eh, lies widely: from 10 -12 W / m 2 (hearing threshold) to 1 W / m 2 (threshold of pain). A person can hear more intense sounds, but at the same time he will experience pain.

Sound intensity level L. Determine the scale, the unit of which is white (b) or, which is much more often, decibel (dB) (one tenth). 1 b - the weakest sound that perceives our ear. This unit is named after the inventor of the telephone of Alexander Bella. Measuring the level of intensity in decibels is simpler and therefore accepted in physics and technology.

Level of intensity L. Any sound in decibels is calculated through the intensity of the sound by the formula

\\ (L \u003d 10 \\ CDOT LG \\ LEFT (\\ FRAC (I) (I_0) \\ RIGHT), \\)

where I. - the intensity of this sound, I. 0 - the intensity corresponding to the threshold of hearingness.

Table 1 shows the level of intensity of various sounds. Those who are exposed to noise over 100 dB, should be used by headphones.

Table 1

Intensity level ( L.) Sounds

Physiological characteristics of sound

The physical characteristics of the sound correspond to certain physiological (subjective) characteristics associated with the perception of its specific person. This is due to the fact that the perception of sound is the process not only physical, but also physiological. The human ear perceives the sound fluctuations of certain frequencies and intensities (these are objective, independent characteristics of the sound) in different ways, depending on the "receiver characteristics" (the subjective individual features of each person are influenced here).

The main subjective characteristics of the sound can be considered the volume, height and timbre.

• Volume (The degree of audio hearing) is defined as the intensity of sound (amplitude of oscillations in a sound wave) and various sensitivity of the human ear at different frequencies. The Human Ear has the greatest sensitivity in the frequency range from 1000 to 5000 Hz. With an increase in the intensity of 10 times the volume level increases by 10 dB. As a result, the sound of 50 dB turns 100 times more intense sound of 30 dB.

• Sound height Determined by the frequency of sound oscillations with the greatest intensity in the spectrum.

• Timbre (Tint of sound) depends on how many overtones are attached to the main tone and what is their intensity and frequency. We are easily distinguished by the sounds of violin and piano, flutes and guitars, voices of people (Table 2).

table 2

Frequency ν oscillations of various sound sources

Sound speed

The speed of the sound depends on the elastic properties, density and temperature of the medium. The more elastic strength, the faster the oscillations of particles are transmitted to neighboring particles and the faster the wave is spread. Therefore, the speed of sound in gases is less than in liquids, and in liquids, as a rule, less than in solids (Table 3). In vacuum, sound waves, like any mechanical waves, do not apply, since there are no elastic interactions between the particles of the medium.

Table 3.

Sound speed in various environments

The speed of sound in ideal gases with increasing temperature is growing proportional to \\ (\\ sqrt (t), \\) where T. - absolute temperature. In the air, the speed of sound υ \u003d 331 m / s at a temperature t. \u003d 0 ° C and υ \u003d 343 m / s at temperatures t. \u003d 20 ° C. In liquids and metals, the sound speed, as a rule, decreases with increasing temperature (exception - water).

For the first time, the speed of propagation of sound in the air was determined in 1640 by the French physicist Marreen Merced. It measured the time interval between the moments of the appearance of the flash and sound with a rifle shot. Mersenn determined that the speed of sound in the air is 414 m / s.

Application of sound

The infrasound in the technique has not yet been applied. But widespread use received ultrasound.

• Method of orientation or study of surrounding objects based on radiation of ultrasound pulses, followed by perception of reflected pulses (echo) from various objects, is called echolocation, and appropriate devices - echolokators.

Well known animals with ability to echolocation - bats and dolphins. In terms of its perfection, echolokators of these animals are not inferior, and in many respects and are superior (in terms of reliability, accuracy, energy efficiency) modern echolokators created by man.

The echolokators used under water are called hydrocolocators or sonars (Sonar name is formed from the initial letters of three English words: Sound - sound; Navigation - navigation; Range - range). Sonoras are indispensable in research of the seabed (its profile, depth), to detect and study various objects moving deep under water. With their help, they can be easily found both separate large objects or animals and flocks of small fish or mollusks.

Ultrasound frequency waves are widely used in medicine for diagnostic purposes. Ultrasound scanners allow you to explore the internal organs of a person. Ultrasound radiation, in contrast to X-ray, harmlessly for humans.

Literature

1. Zhilko, V.V. Physics: studies. Manual for grade 11 general formation. shk. with rus. Yaz. Learning / V.V. Zhilko, L.G. Markovich. - Minsk: Nar. Asveta, 2009. - P. 57-58.
2. Kasyanov V.A. Physics. 10 cl.: Education. For general education. institutions. - M.: Drop, 2004. - P. 338-344.
3. Myakyshev G.Ya., Sinyakov A.Z. Physics: oscillations and waves. 11 CL: student. For in-depth study of physics. - M.: Drop, 2002. - P. 184-198.

Noise - This is a combination of sounds of different frequency and intensity (forces) arising from the oscillatory movement of particles in elastic media (solid, liquid, gaseous).

The process of distribution of the oscillatory movement in the medium is called sound wave, and the area of \u200b\u200bthe medium in which sound waves are distributed - sound field.

Distinguish Impact, mechanical, aerohydrodynamic noise. Shock noise occurs when stamping, riveting, forging, etc.

Mechanical noise There occurs with the friction and bias of the nodes and parts of machines and mechanisms (crushers, mills, electric motors, compressors, pumps, centrifuges, etc.).

Aerodynamic noise It occurs in the devices and pipelines at high speeds of air, gas or liquid and with sharp changes in the direction of their movement and pressure.

The main physical characteristics of the sound:

- Frequency F (Hz),

- sound pressure P (PA),

- intensity or sound strength i (W / m 2),

- sound power W (W).

The speed of propagation of sound waves in the atmosphere at 20 ° C is 344 m / s.

Human hearing organs perceive sound oscillations in the frequency range from 16 to 20,000 Hz. Oscillations with a frequency below 16 Hz ( infrasound) and with a frequency above 20,000 ( ultrasound) Not perceived by hearing organs.

When the sound of sound oscillations in the air periodically appear areas of permanent and increased pressure. Pressure difference in indignant and unperturbed media is called sound pressure P, which is measured in Pascal (PA).

The propagation of the sound wave is accompanied by energy transfer. The amount of energy carried by the sound wave per unit of time through the surface unit oriented perpendicular to the direction of the wave propagation is called sound intensity or power I is measured in W / m 2.

The intensity of sound is associated with sound pressure as the following ratio:

where R 0 is the density of the medium in which the sound wave is propagated, kg / m 3; C is the speed of sound distribution in this environment, m / s; V is the mean square value of the vibrational velocity of particles in the sound wave, m / s.

The work is called specific acoustic resistancewhich characterizes the degree of reflection of sound waves when moving from one medium to another, as well as the soundproofing properties of materials.

The minimum intensity of the sound that is perceived by the ear called the threshold of hearingness. As a standard comparison frequency, a frequency of 1000 Hz is adopted. With this frequency, the threshold of hearing I 0 \u003d 10 -12 W / m 2, and the corresponding sound pressure p 0 \u003d 2 × 10 -5 pa. The maximum intensity of the sound at which the hearing body begins to experience painful feeling, is called threshold of painequal to 10 2 W / m 2, and the corresponding sound pressure p \u003d 2 × 10 2 pa.

Since changes in the intensity of sound and sound pressure of hearing people are huge and constitute 10 14 and 10 and 10 times, respectively, to use the absolute values \u200b\u200bof the intensity of sound or sound pressure are extremely uncomfortable.

For the hygienic assessment of noise, it is customary to measure its intensity and sound pressure not with absolute physical quantities, but logarithms of these values \u200b\u200bto a conditional zero level corresponding to the threshold of the standard tone of a frequency of 1000 Hz. These logarithms of relationships call intensity and sound pressure levels, pronounced in belakh (B). Since the human hearing body is able to distinguish the change in the level of sound intensity by 0.1 Bela, then for practical use it is more convenient than one 10 times less - decibel (dB).

The level of intensity of the sound L in decibels is determined by the formula

Since the intensity of sound is proportional to the square of the sound pressure, then this formula can also be written as

The use of a logarithmic scale for measuring the noise level allows you to lay a large range of values \u200b\u200bI and P in a relatively small range of logarithmic values \u200b\u200bfrom 0 to 140 dB.

The threshold value of the sound pressure P 0 corresponds to the threshold of hearingness L \u003d 0 dB, the threshold of the painful sensation of 120-130 dB. Noise, even when it is small (50-60 dB) creates a significant burden on nervous systemBy providing psychological impact. Under the action of noise, more than 140-145 dB is possible a breakpatch breakpoint.

The total sound pressure L, created by several sound sources with the same sound pressure level L i, are calculated by the formula

where n is the number of noise sources with the same sound pressure level.

For example, if the noise creates two identical noise sources, then their total noise is 3 dB more than each of them separately.

Summary sound pressure of several different sound sources, determined by the formula

where L 1, L 2, ..., L n is the levels of sound pressure, created by each of the sound sources in the studied point of the space.

In terms of the intensity of the sound, it is still impossible to judge the physiological sensation of this sound, since our hearing body is not very sensitive to the sounds of different frequencies; Sounds are equal in force, but of different frequencies, it seems unequal loud. For example, the sound of a frequency of 100 Hz and a force of 50 dB is perceived as an equal sound with a frequency of 1000 Hz and a force of 20 dB. Therefore, to compare the sounds of different frequencies, along with the concept of the level of sound intensity, the concept has been introduced volume level With a conditional unit - background. One background - Sound volume at a frequency of 1000 Hz and level of intensity in 1 dB. At the frequency of 1000 Hz, the volume levels are taken with equal sound pressure levels.

In fig. 1 shows the curves of equal volume of sounds obtained according to the results of the study of the properties of the hearing body to estimate the sounds of different frequencies on a subjective sensation of volume. From the graph, it can be seen that our ear has the greatest sensitivity of 800-4000 Hz, and the smallest - at 20-100 Hz.

Typically, noise and vibration parameters are estimated in octave bands. Over the width of the strip accepted octave. The frequency interval in which the highest frequency F 2 is twice as much lower F 1. As a frequency characterizing the band as a whole, the medium meterometric frequency is taken. Medium meterometric frequencies of octave stripes Standardized GOST 12.1.003-83 "Noise. General Security Requirements" and make up 63, 125, 250, 500, 1000, 2000, 4000 and 8000 Hz with the corresponding boundary frequencies of 45-90, 90-180, 180-355, 355-710, 710-1400, 1400-2800, 2800-5600 , 5600-11200.

The dependence of the values \u200b\u200bcharacterizing the noise from its frequency is called frequency spectrum noise. For the convenience of physiological assessment of the effects of noise per person distinguish low-frequency (up to 300 Hz), mid-frequency (300-800 Hz) and high frequency (above 800 Hz) noise.

GOST 12.1.003-83 and CH 9-86 RB 98 "noise at workplaces. Maximum permissible levels" Classifies the noise by the nature of the spectrum and the time of action.

By the nature of the spectrum:

– broadbandif it has a continuous spectrum of more than one octave width,

– tonalIf there are pronounced discrete tones in the spectrum. In this case, the tonal nature of noise for practical purposes is mounted in the normal frequency band (for a third-string band to exceed the sound pressure level in one strip above the adjacent no less than 10 dB.

By temporary characteristics:

– constant, the sound level of which is changed over the 8-hour working day in time not more than 5 dB,

– unstable, The sound level of which for an 8-hour working day varies in time by more than 5 dB.

Non-permanent noises are divided into:

spinning in time, the sound level of which is continuously changing over time;

intermittent, the sound level of which stepwise changes (5 dB and more);

pulseconsisting of one or more audible signals, each duration of less than 1 s.

Tonal, high-frequency and non-permanent noises are the greatest danger.

Ultrasound for distribution method is divided into:

– contractable by air (air ultrasound);

– distributed by contact path When contact with solid and liquid media (contact ultrasound).

Ultrasonic frequency range is divided into:

– low-frequency oscillations (1.12 × 10 4 - 1 × 10 5 Hz);

– high frequency (1 × 10 5 - 1 × 10 9 Hz).

Sources of ultrasound is the production equipment in which ultrasound fluctuations are generated to perform the technological process, technical control and measurement, as well as equipment, during the operation of which ultrasound occurs as an accompanying factor.

The characteristic of air ultrasound in the workplace in accordance with GOST 12.1.001 "Ultrasound. General security requirements" and CH 9-87 RB 98 "Ultrasound transmitted by air. Maximum permissible levels in workplaces" are the levels of sound pressure in third-party stripes with medium-meter frequencies 12.5; 16.0; 20.0; 25.0; 31.5; 40.0; 50.00; 63.0; 80.0; 100.0 kHz.

Contact Ultrasound Characteristic In accordance with GOST 12.1.001 and CH 9-88 RB 98 "Ultrasound transmitted by contact path. Maximum permissible levels on workplaces" are peak values \u200b\u200bof vibration and vibration levels in octave bands with medium meterometric frequencies 8; sixteen; 31.5; 63; 125; 250; 500; 1000; 2000; 4000; 8000; 16000; 31500 kHz.

Vibration - These are the oscillations of solid bodies - parts of the apparatuses, machinery, equipment, structures, perceived by the human body as concussion. Often vibrations are accompanied by audible noise.

According to the method of transferring a person, vibration is divided into local and common.

Total vibration Transmitted through the supporting surfaces on the body of the standing or sitting person. The most dangerous frequency of general vibration lies in the range of 6-9 Hz, since it coincides with its own frequency of oscillations of the internal organs of a person, as a result of which resonance may occur.

Local (local) vibration Transmitted through man's hands. The vibration acting on the legs of a seated person and on the forearm in contact with the vibrating surfaces of desktops can be attached to the local vibration.

Sources of local vibration transmitted on working, can be: manual machines with a motor or a manual mechanized tool; controls of machinery and equipment; Hand tools and processed parts.

General vibration, depending on the source of its occurrence, is divided into:

general vibration 1 category – transportationaffecting a person in the workplace in self-propelled and trailed machines, vehicles when driving around the terrain, roads and agriculturals;

general Vibration 2 categories - Transport and Technologicalaffecting a person in workplaces in machines moving on specially prepared surfaces of industrial premises, industrial sites, mining workings;

3a - on the permanent workplaces of industrial premises of enterprises;

3B - in workplaces in warehouses, in the canteens, household, duty and other auxiliary industrial premises, where there are no cars generating vibration;

3B - in workplaces in administrative and official premises of plant management, design bureaus, laboratories, training points, computing centers, health care, office premises and other premises of mental work workers.

By temporary characteristics, vibration is divided into:

– permanentfor which the spectral or frequency corrected normized parameter during observation (at least 10 minutes or the process of the technological cycle) is changed by no more than 2 times (6 dB) when measuring with a time constant 1 s;

– non-permanent Vibration for which the spectral or frequency corrected parameter during observation (at least 10 minutes or the process of the technological cycle) varies more than 2 times (6 dB) when measuring with a time constant 1 s.

The main parameters characterizing vibration:

- Frequency F (Hz);

- the amplitude of the displacement A (M) (the magnitude of the greatest deviation of the oscillating point on the equilibrium position);

- oscillatory speed V (m / s); oscillatory acceleration A (m / s 2).

As for noise, the entire spectrum of the frequency of vibrations perceived by a person is divided into octave stripes with medium meterometric frequencies 1, 2, 4, 8, 16, 32, 63, 125, 250, 500, 1000, 2000 Hz.

Since the range of changes in vibration parameters from threshold values, under which it is not dangerous, to real - large, it is more convenient to measure the invalid values \u200b\u200bof these parameters, and the logarithm of the actual values \u200b\u200bto the thresholds. Such a magnitude is called the logarithmic level of the parameter, and the unit of its measurement is decibel (dB).

So the logarithmic level of vibrationability L V (dB) is determined by the formula

where V is the actual mean square value of vibration, m / s: - threshold (reference) vibration, m / s.