Despite the fact that the study of ultrasonic waves began more than a hundred years ago, only the last half century they have become widely used in various fields of human activity. This is due to the active development of both quantum and nonlinear sections of acoustics, as well as quantum electronics and solid state physics. Today, ultrasound is not just a designation of the high-frequency region of acoustic waves, but a whole scientific direction in modern physics and biology, which is associated with industrial, information and measurement technologies, as well as diagnostic, surgical and therapeutic methods of modern medicine.
What is this?
All sound waves can be divided into those that are audible to humans - these are frequencies from 16 to 18 thousand Hz, and those that are outside the range of human perception - infrared and ultrasound. Infrasound refers to waves similar to sound, but with frequencies lower than those perceived by the human ear. The upper limit of the infrasonic region is 16 Hz, and the lower limit is 0.001 Hz.
Ultrasound- these are also sound waves, but only their frequency is higher than the human hearing aid can perceive. As a rule, they mean frequencies from 20 to 106 kHz. Their upper limit depends on the medium in which these waves propagate. So, in a gaseous medium, the limit is 106 kHz, and in solids and liquids it reaches 1010 kHz. There are ultrasonic components in the noise of rain, wind or waterfalls, lightning discharges and the rustling of pebbles rolled by the sea wave. It is thanks to the ability to perceive and analyze ultrasonic waves that whales and dolphins, bats and nocturnal insects orient themselves in space.
A bit of history
The first studies of ultrasound (US) were carried out at the beginning of the 19th century by the French scientist F. Savart, who sought to find out the upper frequency limit of audibility of the human hearing aid. In the future, such well-known scientists as the German V. Vin, the Englishman F. G alton, the Russian P. Lebedev and a group of students were engaged in the study of ultrasonic waves.
In 1916, the French physicist P. Langevin, in collaboration with the Russian émigré scientist Konstantin Shilovsky, was able to use quartz to receive and emit ultrasound for marine measurements and detect underwater objects, which allowed researchers to create the first sonar, consisting of transmitter and receiver of ultrasound.
In 1925, the American W. Pierce created a device, today called the Pierce interferometer, which measures velocities and absorption with great accuracyultrasound in liquid and gas media. In 1928, the Soviet scientist S. Sokolov was the first to use ultrasonic waves to detect various defects in solids, including metallic ones.
In the post-war 50-60s, based on the theoretical developments of a team of Soviet scientists headed by L. D. Rozenberg, ultrasound began to be widely used in various industrial and technological fields. At the same time, thanks to the work of British and American scientists, as well as the research of Soviet researchers such as R. V. Khokhlova, V. A. Krasilnikov and many others, such a scientific discipline as nonlinear acoustics is rapidly developing.
Around the same time, the first American attempts to use ultrasound in medicine were made.
Soviet scientist Sokolov at the end of the forties of the last century developed a theoretical description of an instrument designed to visualize opaque objects - an "ultrasonic" microscope. Based on these works, in the mid-70s, experts from Stanford University created a prototype of a scanning acoustic microscope.
Features
Having a common nature, the waves of the audible range, as well as ultrasonic waves, obey physical laws. But ultrasound has a number of features that allow it to be widely used in various fields of science, medicine and technology:
1. Small wavelength. For the lowest ultrasonic range, it does not exceed a few centimeters, causing the ray nature of the signal propagation. At the same time, the wavefocused and propagated by linear beams.
2. Insignificant oscillation period, due to which ultrasound can be emitted in pulses.
3. In various environments, ultrasonic vibrations with a wavelength not exceeding 10 mm have properties similar to light rays, which makes it possible to focus vibrations, form directed radiation, that is, not only send energy in the right direction, but also concentrate it in the required volume.
4. With a small amplitude, it is possible to obtain high values of vibration energy, which makes it possible to create high-energy ultrasonic fields and beams without the use of large equipment.
5. Under the influence of ultrasound on the environment, there are many specific physical, biological, chemical and medical effects, such as:
- dispersion;
- cavitation;
- degassing;
- local heating;
- disinfection and more. others
Views
All ultrasonic frequencies are divided into three types:
- ULF - low, with a range of 20 to 100 kHz;
- MF - mid-range - from 0.1 to 10 MHz;
- UZVCh - high-frequency - from 10 to 1000 MHz.
Today, the practical use of ultrasound is primarily the use of low-intensity waves for measuring, controlling and studying the internal structure of various materials and products. High-frequency are used to actively influence various substances, which allows you to change their propertiesand structure. Diagnosis and treatment of many diseases with ultrasound (using different frequencies) is a separate and actively developing area of modern medicine.
Where does it apply?
In recent decades, not only scientific theorists are interested in ultrasound, but also practitioners who are increasingly introducing it into various types of human activity. Today ultrasonic units are used for:
| Obtaining information about substances and materials | Events | Frequency in kHz | ||
| from | to | |||
| Research on the composition and properties of substances | solid bodies | 10 | 106 | |
| liquids | 103 | 105 | ||
| gases | 10 | 103 | ||
| Control sizes and levels | 10 | 103 | ||
| Sonar | 1 | 100 | ||
| Defectoscopy | 100 | 105 | ||
| Medical diagnostics | 103 | 105 | ||
|
Impacts on substances |
Soldering and plating | 10 | 100 | |
| Welding | 10 | 100 | ||
| Plastic deformation | 10 | 100 | ||
| Machining | 10 | 100 | ||
| Emulsification | 10 | 104 | ||
| Crystallization | 10 | 100 | ||
| Spray | 10-100 | 103-104 | ||
| Aerosol coagulation | 1 | 100 | ||
| Dispersion | 10 | 100 | ||
| Cleaning | 10 | 100 | ||
| Chemical processes | 10 | 100 | ||
| Influence on combustion | 1 | 100 | ||
| Surgery | 10 to 100 | 103 to 104 | ||
| Therapy | 103 | 104 | ||
| Signal processing and management | Acoustoelectronic transducers | 103 | 107 | |
| Filters | 10 | 105 | ||
| Delay lines | 103 | 107 | ||
| Acousto-optic devices | 100 | 105 | ||
In today's world, ultrasound is an important technological tool in industries such as:
- metallurgical;
- chemical;
- agricultural;
- textile;
- food;
- pharmacological;
- machine and instrument-making;
- petrochemical, refining and others.
In addition, ultrasound is increasingly being used in medicine. That's what we'll talk about in the next section.
Medical use
In modern practical medicine, there are three main areas of use of ultrasound of various frequencies:
1. Diagnostic.
2. Therapeutic.
3. Surgical.
Let's take a closer look at each of these three areas.
Diagnosis
One of the most modern and informative methods of medical diagnostics is ultrasound. Its undoubted advantages are: minimal impact on human tissues and high information content.
As already mentioned, ultrasound is sound waves,propagating in a homogeneous medium in a straight line and at a constant speed. If there are areas with different acoustic densities on their way, then part of the oscillations is reflected, and the other part is refracted, while continuing its rectilinear movement. Thus, the greater the difference in the density of the boundary media, the more ultrasonic vibrations are reflected. Modern methods of ultrasound examination can be divided into locational and translucent.
Ultrasonic location
In the process of such a study, pulses reflected from the boundaries of media with different acoustic densities are recorded. With the help of a movable sensor, you can set the size, location and shape of the object under study.
Translucent
This method is based on the fact that different tissues of the human body absorb ultrasound differently. During the study of any internal organ, a wave with a certain intensity is directed into it, after which the transmitted signal is recorded from the reverse side with a special sensor. The picture of the scanned object is reproduced based on the change in signal intensity at the "input" and "output". The received information is processed and converted by a computer in the form of an echogram (curve) or a sonogram - a two-dimensional image.
Doppler method
This is the most actively developing diagnostic method, which uses both pulsed and continuous ultrasound. Dopplerography is widely used in obstetrics, cardiology and oncology, as it allowstrack even the smallest changes in capillaries and small blood vessels.
Fields of application of diagnostics
Today, ultrasound imaging and measurement methods are most widely used in medical fields such as:
- obstetrics;
- ophthalmology;
- cardiology;
- neurology of newborns and infants;
- examination of internal organs:
- kidney ultrasound;
- liver;
- gallbladder and ducts;
- female reproductive system;
diagnosis of external and superficial organs (thyroid and mammary glands)
Use in therapy
The main therapeutic effect of ultrasound is due to its ability to penetrate human tissues, warm up and warm them up, and perform micromassage of individual areas. Ultrasound can be used for both direct and indirect effects on the focus of pain. In addition, under certain conditions, these waves have a bactericidal, anti-inflammatory, analgesic and antispasmodic effect. Ultrasound used for therapeutic purposes is conditionally divided into high and low intensity vibrations.
It is the low-intensity waves that are most widely used to stimulate physiological responses or slight, non-damaging heating. Ultrasound treatment has shown positive results in diseases such as:
- arthritis;
- arthritis;
- myalgia;
- spondylitis;
- neuralgia;
- varicose and trophic ulcers;
- Ankylosing spondylitis;
- obliterating endarteritis.
Studies are underway that use ultrasound to treat Meniere's disease, emphysema, duodenal and gastric ulcers, asthma, otosclerosis.
Ultrasonic Surgery
Modern surgery using ultrasound waves is divided into two areas:
- selectively destroying tissue areas with special controlled high-intensity ultrasonic waves with frequencies from 106 to 107 Hz;
- using a surgical instrument with superimposed ultrasonic vibrations from 20 to 75 kHz.
An example of selective ultrasound surgery is the crushing of stones by ultrasound in the kidneys. In the process of such a non-invasive operation, an ultrasonic wave acts on the stone through the skin, that is, outside the human body.
Unfortunately, this surgical method has a number of limitations. Do not use ultrasonic crushing in the following cases:
- pregnant women at any time;
- if the diameter of the stones is more than two centimeters;
- for any infectious diseases;
- in the presence of diseases that disrupt normal blood clotting;
- in case of severe bone lesions.
Despite the fact that the removal of kidney stones by ultrasound is performed without operatingincisions, it is quite painful and is performed under general or local anesthesia.
Surgical ultrasonic instruments are used not only for less painful dissection of bone and soft tissues, but also to reduce blood loss.
Let's turn our attention towards dentistry. Ultrasound removes dental stones less painfully, and all other doctor's manipulations are much easier to bear. In addition, in trauma and orthopedic practice, ultrasound is used to restore the integrity of broken bones. During such operations, the space between the bone fragments is filled with a special compound consisting of bone chips and a special liquid plastic, and then it is exposed to ultrasound, due to which all components are firmly connected. Those who have undergone surgical interventions during which ultrasound was used leave different reviews - both positive and negative. However, it should be noted that there are still more satisfied patients!
