Despite the fact that the research of ultrasoundwaves began more than a hundred years ago, only the last half century they have become widely used in various areas 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 an entire scientific direction in modern physics and biology, with which industrial, information and measurement technologies are connected, as well as diagnostic, surgical and therapeutic methods of modern medicine.
All sound waves can be divided into audibleman is 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 below the perceived human ear. The upper limit of the infrasound area is 16 Hz, and the lower limit is 0.001 Hz.
Ultrasound is also sound waves, but onlytheir frequency is higher than what a human hearing aid can absorb. As a rule, they are understood as frequencies from 20 to 106 kHz. Their upper boundary depends on the medium in which these waves propagate. So, in the gas environment the limit is 106 kHz, and in solids and liquids it reaches 1010 kHz. In the noise of rain, wind or waterfall, lightning discharges and the rustling of a shingle of sea pebbles, there are ultrasonic components. It is thanks to the ability to perceive and analyze waves of the ultrasonic range of whales and dolphins, bats and night insects orient themselves in space.
The first ultrasound (US) studies wereThey were conducted at the beginning of the 19th century by the French scientist F. Savart, who sought to determine the upper frequency limit of the audibility of the human hearing aid. In the future, such famous scientists as German W. Wine, Englishman F. Galton, Russian P. Lebedev and a group of students were engaged in studying ultrasonic waves.
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 to detect underwater objects, which allowed the researchers to create the first sonar, consisting of a radiator and ultrasound receiver.
In the postwar 50-60-ies, based ontheoretical developments of the collective of Soviet scientists led by L. D. Rosenberg, the wide application of ultrasound in various industrial and technological fields begins. At the same time, due to the work of British and American scientists, as well as the research of Soviet researchers such as RV Khokhlov, VA Krasilnikov and many others, such a scientific discipline as nonlinear acoustics is developing rapidly.
Approximately at the same time, the first attempts of Americans to use ultrasound in medicine are undertaken.
Soviet scientist Sokolov back in the late fortiesyears of the last century developed a theoretical description of the device intended for visualization of opaque objects - the "ultrasonic" microscope. Based on these studies, in the mid-1970s specialists from Stanford University created a prototype of a scanning acoustic microscope.
Having a common nature, waves of audible range,as well as ultrasonic, are subject to 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. Low wavelength. For the lowest ultrasonic range, it does not exceed a few centimeters, causing the beam propagation of the signal. In this case, the wave is focused and propagated by linear beams.
2. An insignificant period of oscillation, due to which 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 focusing the oscillations, forming directional radiation, that is, not only sending energy in the right direction, but also concentrating it in the required volume.
4. With a small amplitude, it is possible to obtain high values of the vibration energy, which makes it possible to create high-energy ultrasonic fields and beams without using large-sized equipment.
All ultrasonic frequencies are divided into three types:
Today, the practical use of ultrasound -this is primarily the use of low-intensity waves for measurement, control and research of 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 treatment of many diseases by ultrasound (using various frequencies) is a separate and actively developing direction of modern medicine.
In recent decades, ultrasound has been interested innot only scientific theorists, but also practitioners, which are increasingly introducing it into various types of human activity. Today ultrasonic devices are used for:
Getting information about substances and materials
Frequency in kHz
Investigation of the composition and properties of substances
Controlling sizes and levels
Soldering and plating
Coagulation of aerosols
Effects on combustion
10 to 100
103 to 104
Signal Processing and Management
Lines of delay
In the modern world, ultrasound is an important technological tool in such industrial sectors as:
In addition, ultrasound is increasingly used in medicine. We'll talk about this in the next section.
In modern practical medicine there are three main directions of using ultrasound of different frequencies:
Let us consider in more detail each of these three directions.
One of the most modern and informativemethods of medical diagnosis is ultrasonic. Its undoubted advantages are: minimal impact on human tissues and high informativeness.
As already mentioned, ultrasound is soundwaves propagating in a homogeneous medium rectilinearly and at a constant velocity. If on their way there are regions with different acoustic densities, some of the vibrations are reflected, and the other part is refracted, while continuing its rectilinear 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 locational and translucent.
In the process of such a study,reflected from the boundaries of media with different acoustic densities impulses. With the help of a movable sensor, you can set the size, location and shape of the object under study.
This method is based on the fact that different tissuesthe human body absorbs ultrasound differently. During the investigation of an internal organ, a wave with a certain intensity is sent to it, after which a special sensor registers the transmitted signal from the back side. The picture of the scanned object is reproduced on the basis of a change in signal intensity at the "input" and "output". The received information is processed and transformed by a computer in the form of an echogram (curve) or a sonogram - a two-dimensional image.
This is the most actively developing methodDiagnostics in which both pulsed and continuous ultrasound are used. Dopplerography is widely used in obstetrics, cardiology and oncology, since it allows you to track even the smallest changes in capillaries and small blood vessels.
Today ultrasonic methods of visualization and measurements are most widely used in such fields of medicine as:
- ultrasound of the kidneys;
- the gallbladder and ducts;
- Female reproductive system;
The main therapeutic effect of ultrasoundis caused by its ability to penetrate into human tissues, to warm up and warm them, to carry out micromassage of separate sites. US can be used both for direct and indirect effects on the focus of pain. In addition, under certain conditions these waves have bactericidal, anti-inflammatory, analgesic and spasmolytic effects. The ultrasound used for therapeutic purposes is conditionally divided into high and low intensity oscillations.
Studies are being conducted, during which ultrasound is used to treat Meniere's disease, emphysema, duodenal ulcers and stomach, bronchial asthma, otosclerosis.
Modern surgery using ultrasonic waves is divided into two directions:
- selectively destroying tissue sites by special controlled ultrasonic waves of high intensity with frequencies from 106 to 107 Hz;
- using a surgical instrument with the imposition of ultrasonic vibrations from 20 to 75 kHz.
An example of elective ultrasound surgery may beserve to crush stones ultrasound in the kidneys. In the process of such a non-invasive operation, the ultrasonic wave acts on the stone through the skin, that is, outside the human body.
- 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 the normal coagulability of the blood;
- in case of severe lesions of bone tissue.
Despite the fact that ultrasound removal of kidney stones is carried out without surgical incisions, it is quite painful and is performed under general or local anesthesia.
Surgical ultrasound instruments are used not only for less painful dissections of bone and soft tissues, but also to reduce blood loss.