Ultrasound has many applications in medicine, military, industry and agriculture. Ultrasound is named because its lower frequency limit is greater than the upper heari
Ultrasound has many applications in medicine, military, industry and agriculture. Ultrasound is named because its lower frequency limit is greater than the upper hearing limit of human beings. So how much do you know about ultrasound? The following is what I have compiled about ultrasound, I hope you like it!
What is ultrasound?
Ultrasonic wave is a sound wave with a frequency higher than 20000 Hz. It has good directivity, strong penetration ability, easy to obtain concentrated acoustic energy and long propagation distance in water. It can be used for ranging, measuring speed, cleaning, welding, crushing, disinfection and so on. It has many applications in medicine, military, industry and agriculture. Ultrasound is named because its lower frequency limit is greater than the upper hearing limit of human beings.
Scientists call the number of vibrations per second the frequency of sound, and the unit is hertz * * * hertz * *. The frequency of sound waves that our ears can hear is 20Hz-20000Hz. So we call the sound wave with frequency higher than 20000Hz "ultrasonic wave". The ultrasonic frequency usually used for medical diagnosis is 1 MHz -30 MHz.
Theoretical research shows that the vibration energy of an object is proportional to the vibration frequency at the same amplitude. When the ultrasonic wave propagates in the medium, the vibration frequency of the medium particles is very high, so the energy is very large. In the dry winter in northern China, if ultrasonic waves are put into a water tank, the violent vibration will break the water in the water tank into many small drops, and then these small drops will be blown into the room by a small fan, which can increase the indoor air humidity. This is the principle of ultrasonic humidifier. Such as pharyngolaryngitis, tracheitis and other diseases, it is difficult to use blood flow to make drugs reach the affected area. Using the principle of humidifier, the curative effect can be improved by atomizing the liquid medicine and inhaling it by the patient. The huge energy of ultrasound can also make the stones in the human body violently and forcibly vibrate and break, thus alleviating the pain and achieving the purpose of healing. Ultrasonic wave is widely used in medicine, which can sterilize articles.
The role of ultrasound
Ultrasonic effect: When ultrasonic waves propagate in a medium, the medium undergoes physical and chemical changes due to the interaction between ultrasonic waves and the medium, resulting in 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, the tiny particles suspended in the fluid condense at the nodes due to the mechanical force, and form periodic accumulation in space. When ultrasonic waves propagate in piezoelectric materials and magnetostrictive materials, induced polarization and induced magnetization caused by the mechanical action of ultrasonic waves are manifested in both dielectric physics and magnetostrictive materials.
② Cavitation. When ultrasonic wave acts on liquid, it will produce a large number of small bubbles. One reason is that there is regional tensile stress in the liquid, resulting in negative pressure. The decrease of pressure makes the gas originally dissolved in the liquid supersaturated 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; The 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.
Application of ultrasonic wave
Ultrasonic effect is widely used in practice, mainly in the following aspects:
ultrasonic test
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. Ultrasonic waves emitted from the transducer are focused on an opaque sample through an acoustic lens. The ultrasonic wave emitted by the sample carries the information of the irradiated part, such as the ability to reflect, absorb and scatter sound waves, and is concentrated on the piezoelectric receiver through the acoustic lens. The obtained electrical 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. Real-time observation is usually carried out through cameras and televisions.
ultrasonication
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.
Ultrasonic washing
The ultrasonic application principle of cleaning is to convert the high-frequency oscillation signal sent by the ultrasonic generator into high-frequency mechanical oscillation through the transducer and propagate it into the medium. The ultrasonic wave in the cleaning solution alternately radiates forward in the cleaning solution, which makes the liquid flow and produces tens of thousands of tiny bubbles. The tiny bubbles * * * cavitation nuclei * * existing in liquid vibrate under the action of sound field. When the sound pressure reaches a certain value, the bubbles grow rapidly and then suddenly close. When the bubble closes, it produces shock wave, which produces thousands of atmospheres around it, destroying insoluble dirt and dispersing it in the cleaning solution. When the granules are wrapped by oil stains and attached to the surface of the cleaning part, the oil is emulsified and the solid particles are separated, thus achieving the purpose of cleaning the surface of the cleaning part.
ultrasonic humidifier
Theoretical research shows that the vibration energy of an object is proportional to the vibration frequency at the same amplitude. When the ultrasonic wave propagates in the medium, the vibration frequency of the medium particles is very high, so the energy is very large. In the dry winter in northern China, if ultrasonic waves are put into a water tank, the violent vibration will break the water in the water tank into many small drops, and then these small drops will be blown into the room by a small fan, which can increase the indoor air humidity. This is the principle of ultrasonic humidifier. Such as pharyngolaryngitis, tracheitis and other diseases, it is difficult to use blood flow to make drugs reach the affected area. Using the principle of humidifier, the curative effect can be improved by atomizing the liquid medicine and inhaling it by the patient. The huge energy of ultrasound can also make the stones in the human body violently and forcibly vibrate and break, thus alleviating the pain and achieving the purpose of healing. Ultrasonic wave is widely used in medicine, which can sterilize articles.
fundamental 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 dimensions, which is manifested as the absorption of sound waves on the macro level. 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 solid and the study of sound phenomena in quantum liquid-liquid helium constitute a new field of modern acoustics.
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. The devices for generating ultrasonic waves include mechanical ultrasonic generators, such as air whistles, whistles and liquid whistles, electro-ultrasonic generators based on electromagnetic induction and electromagnetic action, and electro-acoustic transducers based on electrostrictive effect of piezoelectric crystals and magnetostrictive effect of ferromagnetic substances.
Ultrasonic mites removal
The researchers found that the auditory nervous system of mites is very fragile and very sensitive to ultrasonic waves with specific frequencies. This physiological characteristic of mites has been studied by technology companies. A href ='' target =' _ blank'> Stupid cough? 3. junshun? ǔ? It's just that a buddhist nun from Luanhe River stole someone and took them to Astrin? ⒌? Benzyou, manganese Jue, mixed Germany, Shinichi? Hey? Fresh milk? Hey? Low frequency? Shen Shen? Is the cave low and clear? Talk about it? Scale? Emblem What's the mystery? Miao who plays manganese, especially Wei Wei? б┘б? sorry What is this? Even praise the picture and suppress the harmonic comb. What's the matter with you? /p & gt；
Ultrasonic degreasing
The oil removal process is called ultrasonic oil removal, which is to put the parts with oil pollution into the oil removal liquid and remove oil under the action of ultrasonic field with a certain frequency. The introduction of ultrasonic can strengthen the degreasing process, shorten the degreasing time, improve the degreasing quality and reduce the consumption of chemicals. Especially for parts with complex shapes, small precision parts, parts with difficult dirt removal on the surface and parts made of insulating materials, it has obvious degreasing effect, which can save time-consuming manual labor and prevent parts from being damaged.
The effect of ultrasonic degreasing is related to the shape, size, surface oil stain properties, solution composition, location and so on. Therefore, the best ultrasonic degreasing process should be determined through experiments. The frequency of ultrasonic oil removal is generally around 30kHz. When the parts are small, adopt higher frequency; When the part is large, use a lower frequency. Ultrasonic waves travel in a straight line, so it is difficult to reach the covered part. Therefore, the parts should be rotated or rotated in the oil removal tank, so that all the parts on the surface are irradiated by ultrasonic waves to get better oil removal effect. In addition, the concentration and temperature of ultrasonic degreasing solution are lower than those of corresponding chemical degreasing and electrochemical degreasing, which does not affect the propagation of ultrasonic waves and reduces the corrosion of metal materials.
Chemical principle of ultrasonic cavitation refining
Strong ultrasonic waves generated inside the liquid trigger high-energy dense cavitation groups. When a cavitation bubble explodes, a pressure as high as 1000 atmospheric pressure and a high temperature of thousands of degrees are instantaneously generated in a tiny space.
At high pressure and high temperature, the C-C bond in heavy oil molecules is broken, and the hydrocarbons of macromolecules are decomposed into hydrocarbons of micromolecules. Under the action of ultrasonic wave and cavitation, the C-S bond of sulfur-containing organic compounds in raw materials is broken and converted into intermediate olefins, normal alkanes, aromatic hydrocarbons and hydrogen sulfide. The produced olefins are converted into normal alkanes and aromatics during ultrasonic pyrolysis.
Convert heavy oil with high sulfur content into gasoline and diesel oil with low sulfur content. A small amount of unconverted or low-converted residues are used to prepare high-quality asphalt. What is ultrasound? "People also saw: