Despite the fact that the study of ultrasonic waves began more than a hundred years ago, only the last half century they began to be widely used in various fields of human activity. This is due to the active development of both the quantum and nonlinear sections of acoustics, and 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 measuring technologies, as well as diagnostic, surgical and therapeutic methods of modern medicine.
What is it?
All sound waves can be divided into audible by humans - these are frequencies from 16 to 18 thousand Hz, and those that are outside the range of human perception - infra- and ultrasound. Infrasound refers to waves similar to sound, but with frequencies lower than those perceived by the human ear. The upper boundary of the infrasound region is considered to be 16 Hz, and the lower - 0.001 Hz.
Ultrasound is also sound waves, but only their frequency is higher than the hearing aid of a person can perceive. As a rule, they mean frequencies from 20 to 106 kHz. Their upper boundary 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 the level of 1010 kHz. There are ultrasonic components in the noise of rain, wind or a waterfall, lightning discharges and the rustling of a pebble being rolled by a sea wave. Due to the ability to perceive and analyze ultrasonic waves, whales and dolphins, bats and nocturnal insects are oriented in space.
A bit of history
The first ultrasound studies (US) were carried out at the beginning of the XIX century by the French scientist F. Savart (F. Savart), who sought to find out the upper frequency limit of audibility of the human auditory apparatus. Further, the study of ultrasonic waves was carried out by such famous scientists as the German V. Vin, the Englishman F. Galton, the Russian P. Lebedev with a group of students.
In 1916, a physicist from France P. Langevin, in collaboration with the Russian emigrant scientist Konstantin Shilovsky, was able to use quartz to receive and emit ultrasound for marine measurements and the detection of underwater objects, which allowed researchers to create the first sonar consisting of an emitter and an ultrasound receiver.
In 1925, the American W. Pierce created a device, called the Pierce interferometer today, which measures with great accuracy the speed and absorption of ultrasound 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 metal,.
In the post-war 50-60s, on the basis of theoretical developments by a team of Soviet scientists led by L. D. Rosenberg, widespread use of ultrasound in various industrial and technological fields begins. At the same time, thanks to the work of English and American scientists, as well as the research of Soviet researchers such as R.V. Khokhlova, V.A. Krasilnikov and many others, such a scientific discipline as non-linear acoustics is rapidly developing.
Around the same time, the first attempts by Americans to use ultrasound in medicine were made.
Back in the late forties of the last century, the Soviet scientist Sokolov developed a theoretical description of a device designed to visualize opaque objects - an “ultrasound” microscope. Based on these works, in the mid-70s, specialists from Stanford University created a prototype scanning acoustic microscope.
Features
Having a common nature, the waves of the audible range, as well as ultrasonic, 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 radiation character of the signal propagation. In this case, the wave is focused and propagated by linear beams.
2. An insignificant period of oscillations, so that ultrasound can be emitted pulsed.
3. In various media, ultrasonic vibrations with a wavelength not exceeding 10 mm have properties similar to light rays, which allows you to focus the vibrations, generate 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 vibrational energy, which makes it possible to create high-energy ultrasonic fields and beams without the use of large-sized equipment.
5. Under the influence of ultrasound on the medium, many specific physical, biological, chemical and medical effects arise, such as:
- dispersion;
- cavitation;
- degassing;
- local heating;
- disinfection and many others other
Kinds
All ultrasonic frequencies are divided into three types:
- ULF - low, with a range from 20 to 100 kHz;
- USCH - mid-frequency - from 0.1 to 10 MHz;
- UHF - high frequency - from 10 to 1000 MHz.
Today, the practical use of ultrasound is primarily the use of low-intensity waves for measuring, monitoring and studying the internal structure of various materials and products. High-frequency ones are used to actively influence various substances, which allows changing their properties and structure. Diagnosis and ultrasound treatment of many diseases (using various frequencies) is a separate and actively developing area of modern medicine.
Where is it used?
In recent decades, not only scientific theorists have been interested in ultrasound, but also practitioners, who are increasingly actively introducing it into various types of human activity. Today, ultrasound systems are used for:
Obtaining information about substances and materials | Events | Frequency in kHz |
from | before |
Study of the composition and properties of substances | solids | 10 | 10 6 |
liquids | 10 3 | 10 5 |
gases | 10 | 10 3 |
Size and Level Control | 10 | 10 3 |
Sonar | 1 | 100 |
Flaw detection | 100 | 10 5 |
Medical diagnostics | 10 3 | 10 5 |
Impacts on substances | Soldering and metallization | 10 | 100 |
Welding | 10 | 100 |
Plastic deformation | 10 | 100 |
Mechanical restoration | 10 | 100 |
Emulsification | 10 | 10 4 |
Crystallization | 10 | 100 |
Spraying | 10-100 | 10 3 -10 4 |
Aerosol coagulation | 1 | 100 |
Dispersion | 10 | 100 |
Cleaning | 10 | 100 |
Chemical processes | 10 | 100 |
Effects on combustion | 1 | 100 |
Surgery | 10 to 100 | 10 3 to 10 4 |
Therapy | 10 3 | 10 4 |
Signal Processing and Management | Acoustoelectronic Converters | 10 3 | 10 7 |
Filters | 10 | 10 5 |
Delay lines | 10 3 | 10 7 |
Acousto-optical devices | 100 | 10 5 |
In the modern world, ultrasound is an important technological tool in such industrial sectors as:
- metallurgical;
- chemical;
- agricultural;
- textile;
- food;
- pharmacological;
- machine and instrument making;
- petrochemical, processing and others.
In addition, ultrasound is increasingly used in medicine. This is what we will talk about in the next section.
Use in medicine
In modern practical medicine, there are three main directions of using ultrasound of various frequencies:
1. Diagnostic.
2. Therapeutic.
3. Surgical.
Let us consider in more detail each of these three areas.
Diagnostics
One of the most modern and informative methods of medical diagnosis 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 rectilinearly and at a constant speed. If areas with different acoustic densities are in their path, then part of the oscillations is reflected, and the other part is refracted, while continuing its straightforward motion. Thus, the greater the difference in the density of the boundary media, the more ultrasonic vibrations are reflected. Modern methods of ultrasound can be divided into location and translucent.
Ultrasonic Location
In the process of such a study, pulses reflected from the boundaries of media with different acoustic densities are recorded. Using the movable sensor, you can set the size, location and shape of the object under study.
Transillumination
This method is based on the fact that various tissues of the human body absorb ultrasound in different ways. During the study of an internal organ, a wave with a certain intensity is sent to it, after which a transmitted signal from the reverse side is recorded with a special sensor. The picture of the scanned object is reproduced on the basis of a change in the 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 in which both pulsed and continuous ultrasound are used. Dopplerography is widely used in obstetrics, cardiology and oncology, as it allows you to track even the most minor changes in the capillaries and small blood vessels.
Diagnostic Applications
Today, ultrasonic imaging and measurement methods are most widely used in such fields of medicine as:
- obstetrics;
- ophthalmology;
- cardiology;
- neurology of newborns and infants;
- examination of internal organs:
- ultrasound of the kidneys;
- liver;
- gall bladder and ducts;
- female reproductive system;
- diagnosis of external and surface organs (thyroid and mammary glands).
Use in therapy
The main therapeutic effect of ultrasound is due to its ability to penetrate into human tissues, heat and warm them, and micromassage individual sections. Ultrasound can be used both for 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. Used for therapeutic purposes, ultrasound is conventionally divided into high and low intensity vibrations.
It is waves of low intensity that are most widely used to stimulate physiological reactions or insignificant, non-damaging heating. Ultrasound treatment has yielded positive results in diseases such as:
- arthrosis;
- arthritis;
- myalgia;
- spondylitis;
- neuralgia;
- varicose and trophic ulcers;
- Ankylosing spondylitis;
- obliterating endarteritis.
Studies are being conducted during which ultrasound is used to treat Meniere's disease, emphysema, duodenal ulcers and stomach, bronchial asthma, otosclerosis.
Ultrasound surgery
Modern surgery using ultrasonic waves is divided into two areas:
- selectively destroying tissue sections with special controlled ultrasonic waves of high intensity with frequencies from 10 6 to 10 7 Hz;
- using a surgical instrument with superposition of ultrasonic vibrations from 20 to 75 kHz.
An example of selective ultrasound surgery can be the crushing of stones with ultrasound in the kidneys. In the process of such non-invasive surgery, an ultrasonic wave acts on the stone through the skin, that is, outside the human body.
Unfortunately, such a surgical method has several limitations. You can 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 violate the normal coagulation of blood;
- in case of severe bone damage.
Despite the fact that ultrasound removal of kidney stones is performed without surgical incisions, it is quite painful and is performed under general or local anesthesia.
Surgical ultrasound instruments are used not only for less painful dissection of bone and soft tissues, but also to reduce blood loss.
Let us turn our attention to dentistry. Ultrasound removes dental stones less painfully, and all other doctor's manipulations are much easier to carry. In addition, in traumatological 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 composition consisting of bone chips and a special liquid plastic, and then they are subjected to ultrasound, due to which all components are firmly connected. Those who underwent 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!