supersonic
We know that when an object vibrates, it will make a sound. Scientists call the number of vibrations per second the frequency of sound, in hertz. The frequency of sound waves that our ears can hear is 20 ~ 20000 Hz. Therefore, when the vibration of an object exceeds a certain frequency, that is, it is higher than the upper limit of human hearing threshold, people can't hear it. This sound wave is called "ultrasonic wave". The ultrasonic frequency usually used for medical diagnosis is 1 ~ 5 MHz. Ultrasonic wave has the characteristics of good directivity, strong penetration, easy to obtain concentrated acoustic energy and long propagation distance in water. It can be used for ranging, measuring speed, cleaning, welding, breaking stones, etc.
Although humans can't hear ultrasound, many animals have this ability. They can use ultrasound to "navigate", chase food or avoid dangerous things. You may have seen many bats flying back and forth in the yard on summer nights. Why don't they get lost when they fly without light? The reason is that bats can emit ultrasonic waves of 20 ~ 65438+ megahertz, just like a mobile "radar station". Bats use this kind of "radar" to judge whether there are insects or obstacles flying ahead.
We humans didn't learn to use ultrasound until World War I, that is, we used the principle of "sonar" to detect underwater targets and their status, such as the position of submarines. At this time, people emit a series of ultrasonic waves with different frequencies into the water, and then record and process the reflected echoes. From the characteristics of echo, we can estimate the distance, shape and dynamic change of the detected object. The earliest application of ultrasound in medicine was in 1942. Austrian doctor Dusik used ultrasound technology to scan brain structure for the first time. Later, in the 1960s, doctors began to apply ultrasound to the detection of abdominal organs. Nowadays, ultrasonic scanning technology has become an indispensable tool for modern medical diagnosis.
The working principle of medical ultrasonic examination is similar to sonar, that is, when ultrasonic waves are emitted into the human body, they will be reflected and refracted when they meet the interface in the body, and may be absorbed and attenuated in the human tissue. Due to the different shapes and structures of various tissues in the human body, the degree of reflection, refraction and absorption of ultrasonic waves is also different. Doctors distinguish it by the characteristics of the wave pattern, curve or image reflected by the instrument. In addition, combined with anatomical knowledge, normal and pathological changes, we can diagnose whether the examined organ is sick or not.
At present, the ultrasonic diagnosis methods used by doctors have different forms, which can be divided into four categories: A, B, M and D.
Type A: It is a method of displaying tissue characteristics with waveforms, which is mainly used to measure the diameter of organs to determine their size. It can be used to identify some physical characteristics of diseased tissue, such as substance, whether there is liquid or gas, etc.
B-type: display the specific situation of the probed tissue in the form of plane graphics. During inspection, the reflected signal of human interface is first converted into light spots with different intensities, which can be displayed on the fluorescent screen. This method is intuitive and repeatable, and can be used for before and after comparison, so it is widely used in the diagnosis of gynecological, urinary, digestive and cardiovascular diseases.
M-type: it is a method used to observe the time change of active interface. It is most suitable for checking the heart activity. The dynamic change of its curve is called echocardiography, which can be used to observe the position, activity and structure of each layer of the heart, and is mostly used to assist in the diagnosis of heart and great vascular diseases.
D-mode: It is a special ultrasonic diagnostic method for detecting blood flow and organ activity, also known as Doppler ultrasonic diagnosis. Can determine whether the blood vessels are unobstructed, whether the lumen is narrow, occluded and the lesion site. The new generation of D-mode ultrasound can also quantitatively measure the blood flow in the lumen. In recent years, scientists have developed a color-coded Doppler system, which can display the direction of blood flow with different colors under the instruction of anatomical markers of echocardiography, and the depth of color represents the speed of blood flow. At present, ultrasound techniques such as stereo ultrasound imaging, ultrasound CT and ultrasound endoscope are constantly emerging, which can be combined with other inspection instruments to greatly improve the diagnostic accuracy of diseases. Ultrasonic technology plays a great role in the medical field. With the progress of science, it will be more perfect and will benefit mankind better.
Sound waves with frequencies higher than 20000 Hz. A branch of acoustics that studies the generation, propagation and reception of ultrasonic waves, as well as various ultrasonic effects and applications, is called ultrasound. produce
Ultrasonic devices include mechanical ultrasonic generators (such as air whistle, whistle and liquid whistle). ), an electro-ultrasonic generator based on the principle of electromagnetic induction and electromagnetic action,
And an electroacoustic transducer made of electrostrictive effect of piezoelectric crystal and magnetostrictive effect of ferromagnetic material.
Ultrasonic effect When ultrasonic waves propagate in the medium, the interaction between ultrasonic waves and the medium causes physical and chemical changes in the medium, which leads to.
A series of mechanical, thermal, electromagnetic and chemical ultrasonic effects, including the following four effects:
① Mechanical effect. The mechanical action of ultrasonic wave can promote the emulsification of liquid, the liquefaction of gel and the dispersion of solid. When standing waves are formed in the ultrasonic fluid medium, tiny particles suspended in the fluid condense at the nodes due to the mechanical force, forming periodic accumulation in space. When ultrasonic waves propagate in piezoelectric materials and magnetostrictive materials, induced polarization and induced magnetization occur due to the mechanical action of ultrasonic waves (see dielectric physics and magnetostrictive).
② Cavitation. When ultrasonic wave acts on liquid, it will produce a large number of small bubbles. One reason is that the local tensile stress in the liquid forms negative pressure, and the decrease of pressure makes the gas originally dissolved in the liquid supersaturate and escape from the liquid into small bubbles. Another reason is that the strong tensile stress "tears" the liquid into a cavity, which is called cavitation. The cavity is filled with liquid vapor or another gas dissolved in the liquid, even vacuum. Small bubbles formed by cavitation will suddenly move, grow up or burst with the vibration of the surrounding medium. When it bursts, the surrounding liquid suddenly rushes into bubbles, producing high temperature, high pressure and shock wave. Internal friction related to cavitation can form charge, and discharge in bubbles can produce luminescence. Ultrasonic treatment technology in liquid is mostly related to cavitation.
③ Thermal effect. Because of the high frequency and high energy of ultrasonic wave, it can produce significant thermal effect when it is absorbed by medium.
④ Chemical action. The action of ultrasound can promote or accelerate some chemical reactions. For example, pure distilled water generates hydrogen peroxide after ultrasonic treatment; Nitrite is produced by ultrasonic treatment of water dissolved with nitrogen; Dye aqueous solution will change color or fade after ultrasonic treatment. These phenomena are always accompanied by cavitation. Ultrasound can also accelerate the hydrolysis, decomposition and polymerization of many chemicals. Ultrasound also has obvious influence on photochemical and electrochemical processes. After ultrasonic treatment, the characteristic absorption bands of various amino acids and other organic aqueous solutions disappeared, showing uniform general absorption, indicating that cavitation changed the molecular structure.
Ultrasonic application ultrasonic effect has been widely used in practice, mainly in the following aspects:
① Ultrasonic examination. Ultrasonic wave has shorter wavelength than ordinary sound wave, better directivity and can penetrate opaque substances. This characteristic has been widely used in ultrasonic flaw detection, thickness measurement, distance measurement, remote control and ultrasonic imaging technology. Ultrasonic imaging is a technology that uses ultrasonic waves to present the internal image of opaque objects. The ultrasonic wave emitted by the transducer is focused on the opaque sample through the acoustic lens, and the ultrasonic wave emitted by the sample carries the information of the irradiated part (such as the ability of reflecting, absorbing and scattering sound waves), and is concentrated on the piezoelectric receiver through the acoustic lens, and the obtained electric signal is input into the amplifier, and the image of the opaque sample can be displayed on the fluorescent screen by using the scanning system. The device above is called an ultrasonic microscope. Ultrasonic imaging technology has been widely used in medical examination. It is used to test large-scale integrated circuits in the manufacture of microelectronic devices, and to display the regions and grain boundaries of different components in alloys in materials science. Acoustic holography is an acoustic imaging technology that records and reproduces the stereoscopic image of opaque objects by using the interference principle of ultrasonic waves. Its principle is basically the same as that of light wave holography, but the recording means are different (see holography). The two transducers placed in the liquid are excited by the same ultrasonic signal source, and they respectively emit two coherent ultrasonic waves: one beam becomes an object wave after passing through the studied object, and the other beam is used as a reference wave. Acoustic hologram is formed by the coherent superposition of object wave and reference wave on liquid surface. The acoustic hologram is irradiated with a laser beam, and the reconstructed image of the object is obtained by using the diffraction effect produced when the laser is reflected on the acoustic hologram. Usually, real-time observation is carried out through a camera and a TV set.
② Ultrasound therapy. Ultrasonic welding, drilling, solid crushing, emulsification, degassing, dust removal, cleaning, sterilization, promoting chemical reaction and biological research can be carried out by using the mechanical action, cavitation, thermal effect and chemical effect of ultrasound, which has been widely used in various departments such as industry, mining, agriculture and medical treatment.
③ Basic research. After the ultrasonic wave acts on the medium, the acoustic relaxation process occurs in the medium. The acoustic relaxation process is accompanied by the transport process of energy between molecular degrees, which is macroscopically manifested as the absorption of sound waves (see sound waves). The characteristics and structure of matter can be explored through the law that matter absorbs ultrasonic waves, which constitutes the branch of acoustics of molecular acoustics. The wavelength of ordinary sound wave is larger than the atomic spacing in solid, and under this condition, solid can be regarded as a continuous medium. However, for ultrasonic waves with a frequency above 10 12 Hz, its wavelength can be comparable to the atomic spacing in solids, so solids must be regarded as a lattice structure with spatial periodicity. The energy of lattice vibration is quantized and called phonon (see solid state physics). The effect of ultrasound on solids can be attributed to the interaction between ultrasound and thermal phonons, electrons, photons and various quasi-particles. The generation, detection and propagation of ultrasonic waves in solids and the study of sound phenomena in quantum liquid-liquid helium constitute a new field of modern acoustics-
Sound wave belongs to one of the categories of sound and belongs to mechanical wave. Sound wave refers to a kind of longitudinal wave that can be felt by human ears, and its frequency range is 16Hz-20KHz. When the frequency of sound wave is lower than 16Hz, it is called infrasound wave, and when it is higher than 20KHz, it is called ultrasonic wave.
Ultrasonic wave has the following characteristics:
1) Ultrasonic wave can propagate effectively in gas, liquid, solid, solid melt and other media.
2) Ultrasonic waves can transmit strong energy.
3) Ultrasonic waves will produce reflection, interference, superposition and * * * vibration.
4) When ultrasonic wave propagates in liquid medium, it can produce strong impact and cavitation on the interface.
Ultrasound is a member of the sound wave family.
Sound wave is the propagation form of mechanical vibration state (or energy) of an object. The so-called vibration refers to the back and forth movement of the particles of a substance near its equilibrium position. For example, after the drum head is hit, it vibrates up and down, and this vibration state propagates in all directions through the air medium, which is the sound wave.
Ultrasonic wave refers to the sound wave with vibration frequency above 20KHz, which people can't hear or feel in the natural environment.
The concept of ultrasonic therapy:
Ultrasound therapeutics is an important part of ultrasound medicine. Ultrasonic energy is applied to the diseased part of human body during ultrasonic treatment, so as to achieve the purpose of treating diseases and promoting physical rehabilitation.
In the world, ultrasound is widely used in diagnostics, therapeutics, engineering, biology and other fields. Saifurui's home ultrasonic therapy machine belongs to the application category of ultrasonic therapy.
(1) engineering applications: underwater positioning and communication, underground resource exploration, etc.
(2) Biological applications: shearing macromolecules, bioengineering and seed treatment.
(3) Diagnostic applications: type A, type B, type M, type D, dual-function and color ultrasound.
(4) Therapeutic application: physiotherapy, cancer treatment, surgery, extracorporeal lithotripsy, dentistry, etc.
Characteristics of ultrasonic wave:
1. When ultrasonic wave propagates, it has strong directivity and easy energy concentration.
2. Ultrasonic waves can propagate in different media and far enough.
3. The interaction between ultrasonic wave and sound transmission medium is moderate, and it is easy to carry the information of sound transmission medium state (diagnosis or function of sound transmission medium). (treatment)
Ultrasonic wave is a waveform, which can be used as a carrier or medium for detecting and loading information (such as B-ultrasound for diagnosis); At the same time, ultrasound is a form of energy. When its intensity exceeds a certain value, it can affect, change or even destroy the state, nature and structure of the medium that propagates ultrasonic waves (used for treatment).
The development history of ultrasound;
First, internationally:
/kloc-from the end of 0/9 to the beginning of the 20th century, after the piezoelectric effect and anti-piezoelectric effect in physics were discovered, people solved the method of using electronic technology to generate ultrasonic waves, which quickly opened a historical chapter in the development and popularization of ultrasonic technology.
1922, the first invention patent of ultrasonic therapy appeared in Germany.
1939 published a literature report on the clinical effect of ultrasonic therapy.
In the late 1940s, ultrasonic therapy rose in Europe and America. It was not until the first international conference on medical ultrasound held in 1949 that papers on ultrasound therapy were exchanged, which laid the foundation for the development of ultrasound therapy. 1956 many papers were published in the second international congress of ultrasound medicine, and ultrasound therapy has entered a practical and mature stage.
Second, the domestic side:
In China, the field of ultrasound therapy started late, and only a few hospitals carried out ultrasound therapy in the early 1950s. From 65438 to 0950, the ultrasonic therapeutic machine with the frequency of 800KHz was first used in Beijing to treat various diseases, and it was gradually popularized in the 1950s, with domestic instruments. The published literature report began at 1957. In the 1970s, various types of ultrasonic therapeutic instruments appeared in China, and ultrasonic therapy was popularized in major hospitals all over the country.
Over the past 40 years, major hospitals in China have accumulated a considerable amount of information and rich clinical experience. Especially in the early 1980s, ultrasonic extracorporeal mechanical wave lithotripsy (ESWL) and ultrasonic surgery appeared, which was a major breakthrough in the treatment history of lithiasis. Now it has been popularized and applied internationally. High intensity focused ultrasound noninvasive surgery makes ultrasound therapy occupy an important position in contemporary medical technology. In 2 1 century (HIFU), focused ultrasound surgery is regarded as the latest technology for treating tumors in 2 1 century.
Mechanism of ultrasonic treatment;
1. Mechanical effect: the effect produced when ultrasonic waves advance in a medium. (The propagation of ultrasonic wave in medium is a mechanical effect produced by reflection) It can cause some reactions in the body. Ultrasonic vibration can cause the movement of substances in tissues and cells. Due to the fine massage of ultrasonic waves, the cytoplasm flows, and the cells vibrate, rotate and rub, thus producing the effect of cell massage, also known as "internal massage". This is the unique feature of ultrasonic therapy, which can change the permeability of cell membrane, stimulate the diffusion process of cell semipermeable membrane, promote metabolism, accelerate blood and lymphatic circulation, improve cell ischemia and hypoxia, improve tissue nutrition, change protein synthesis rate and improve regeneration function. Changing the internal structure of cells leads to changes in the function of cells and softens the extension of hard connective tissue.
The mechanical action of ultrasound can soften tissues, enhance infiltration, improve metabolism, promote blood circulation and stimulate nervous system and cell function, so it has unique therapeutic significance.
2. Warm effect: human tissues have a relatively large absorption capacity of ultrasonic energy, so when ultrasonic waves propagate in human tissues, their energy is continuously absorbed by the tissues and becomes heat, resulting in the temperature rise of the tissues themselves.
The process of heat production is not only an energy conversion process in which mechanical energy is converted into heat energy in a medium. Namely endogenous heat. Ultrasonic hyperthermia can increase blood circulation, accelerate metabolism, improve local tissue nutrition and enhance enzyme activity. Generally speaking, the thermal effect of ultrasound is significant in bones and connective tissues, while fat and blood are the least.
3. Physical and chemical effects: Both mechanical effects and thermal effects of ultrasound will cause some physical and chemical changes. Practice has proved that some physical and chemical effects are often the secondary effects of the above effects. TS-C therapeutic instrument has the following five functions through physical and chemical actions:
A dispersion: ultrasound can improve the permeability of biofilm, and the permeability of cell membrane to potassium and calcium ions changes strongly after ultrasound. Thereby enhancing the diffusion process of biofilm, promoting material exchange, accelerating metabolism and improving tissue nutrition.
B. Thixotropic effect: under the action of ultrasonic wave, gel can be transformed into sol state. Softening effect on muscles and tendons, and some pathological changes related to tissue water shortage. Such as rheumatoid arthritis and degenerative diseases of joints, tendons and ligaments.
C. Cavitation: Cavitation forms, or keeps steady unidirectional vibration, or expands and collapses, changes cell function, and increases intracellular calcium level. Fibroblasts were activated, protein synthesis increased, vascular permeability increased, angiogenesis accelerated, and collagen tension increased.
D. Polymerization and depolymerization: Polymerization of water molecules is the process of synthesizing multiple identical or similar molecules into a larger molecule. The depolymerization of macromolecules is a process in which macromolecules become small molecules. It can increase the activity of hydrolase and collagenase in joints.
E. Anti-inflammatory repair of cells and molecules: Under the action of ultrasound, the PH value of tissues can develop to alkalinity. Relieve local acidosis related to inflammation. Ultrasound can affect blood flow, produce inflammation, inhibit and play an anti-inflammatory role. Make white blood cells move and promote angiogenesis. Collagen synthesis and maturation. Promote or inhibit the repair and healing process of injury. So as to achieve the process of cleaning, activating and repairing damaged cells and tissues.
Quantum acoustics.
Ultrasonic waves can also be used for radar detection. When cleaning delicate articles such as clocks and watches, you can use ultrasonic waves to crush gallstones in patients, or you can use ultrasonic waves to measure distance.
Ultrasonic testing is also used to test the solder joint strength of resistance welding.