Sound waves belong to one of the categories of sound, belonging to mechanical waves. Sound waves refer to longitudinal waves that can be felt by human ears, and their frequency ranges from 16 Hz to 2 Hz. When the frequency of sound wave is lower than 16Hz, it is called infrasound wave, and higher than 2KHz, it is called ultrasonic sound wave.
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) applications in engineering: underwater positioning and communication, underground resource exploration, etc.
(2) applications in biology: shearing macromolecules, bioengineering and seed treatment, etc.
(3) applications in diagnostics: A-type, B-type, M-type, D-type, duplex function and color Doppler ultrasound, etc.
(4) applications in therapeutics.
The role of ultrasonic waves in dentistry
The descaling of glass parts, glass and ceramic products is a troublesome thing. If these items are put into a cleaning solution and then ultrasonic waves are applied, the violent vibration of the cleaning solution will impact the dirt on the items and they can be cleaned quickly.
Although humans can't hear ultrasonic waves, 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 courtyard on summer nights. Why do they fly without light and not get lost? The reason is that bats can emit ultrasonic waves of 2 ~ 1, Hz, which is like a mobile "radar station". It is this kind of "sonar" that bats use to judge whether insects or obstacles are flying in front. The quality of radar is tens, hundreds and thousands of kilograms, but in some important performances, such as accuracy and anti-jamming ability, bats are far superior to modern radio locators. It is a new discipline developed in recent decades to study the functions and structures of various organs in animals and use the acquired knowledge to improve existing equipment.
We humans didn't learn to use ultrasound until World War I, that is, to use sonar. At this time, people send a series of ultrasonic waves with different frequencies into the water, and then record and process the reflected echo. From the characteristics of the echo, we can estimate the distance, shape and dynamic change of the detected object. The earliest use of ultrasound in medicine was in 1942, when Austrian doctor Dusik first scanned the brain structure with ultrasound technology. Later, in the 196s, 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 difference between sonar and radar
sonar passes through ultrasonic waves
radar passes through radio waves
The working principle of medical ultrasonic examination is similar to sonar, that is, when ultrasonic waves are emitted into human body, they will be reflected and refracted when they meet the interface in the body, and may be absorbed and attenuated in human tissues. Because the shapes and structures of various tissues in the human body are different, the degree of reflection and refraction and absorption of ultrasonic waves are also different. Doctors distinguish them by the characteristics of wave patterns, curves or images reflected by instruments. In addition, combined with anatomical knowledge, normal and pathological changes, we can diagnose whether the examined organs are 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..
A-type: It is a method to display the characteristics of tissues 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 parenchyma, whether liquid or gas exists, etc.
type b: the specific situation of the probed tissue is displayed in the form of plane graphics. During the examination, the reflected signal of the human interface is first converted into light spots with different strengths, which can be displayed through the fluorescent screen. This method is intuitive and repeatable, and can be used for comparison before and after, so it is widely used in the diagnosis of gynecological, urinary, digestive and cardiovascular diseases.
M-mode: it is a method used to observe the time change of the active interface. It is most suitable for checking the activity of the heart. The dynamic change of its curve is called echocardiography, which can be used to observe the position, activity state and structural condition of each layer of the heart, and is mostly used to assist the diagnosis of heart and great vascular diseases.
D-mode: It is an ultrasonic diagnostic method specially used to detect blood flow and organ activity, also known as Doppler ultrasonic diagnostic method. 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 in different colors under the instruction of anatomical marks of echocardiography, and the depth of color represents the velocity of blood flow. At present, ultrasound techniques such as stereoscopic ultrasound imaging, ultrasound CT and ultrasound endoscope are constantly emerging, and they can also be combined with other inspection instruments to greatly improve the diagnostic accuracy of diseases. Ultrasonic technology is playing a huge role in the medical field. With the progress of science, it will be more perfect and will benefit mankind better.
The branch of acoustics that studies the generation, propagation and reception of ultrasonic waves, as well as various ultrasonic effects and applications, is called ultrasound. There are mechanical ultrasonic generators (such as air whistle, whistle and liquid whistle), electric ultrasonic generators based on the principle of electromagnetic induction and action, < P > and electroacoustic transducers based on electrostrictive effect of piezoelectric crystals and magnetostrictive effect of ferromagnetic substances.
ultrasonic effect when ultrasonic waves propagate in a medium, the medium changes physically and chemically due to the interaction between ultrasonic waves and the medium, thus producing 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 ultrasonic fluid medium, tiny particles suspended in the fluid are condensed at the nodes due to mechanical force, forming periodic accumulation in space. When ultrasonic waves propagate in piezoelectric materials and magnetostrictive materials, induced polarization and induced magnetization are caused by the mechanical action of ultrasonic waves (see dielectric physics and magnetostrictive).
② cavitation. When ultrasonic wave acts on liquid, a large number of small bubbles can be produced. 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 and become 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 liquid, and may even be vacuum. Small bubbles formed by cavitation will move, grow or burst suddenly with the vibration of the surrounding medium. When it bursts, the surrounding liquid suddenly rushes into bubbles, resulting in high temperature, high pressure and shock wave. Internal friction associated with cavitation can form electric charge, and the phenomenon of light emission can be generated by discharge in bubbles. The technology of ultrasonic treatment 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 effect. The action of ultrasound can promote or accelerate some chemical reactions. For example, pure distilled water generates hydrogen peroxide after ultrasonic treatment; Nitrous acid is produced by ultrasonic treatment of water dissolved with nitrogen; The aqueous solution of dye 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 aqueous solutions of various amino acids and other organic substances disappear and show uniform general absorption, which indicates that cavitation has changed the molecular structure.
Ultrasound has been widely used in practice, mainly in the following aspects:
① Ultrasonic inspection. The wavelength of ultrasonic wave is shorter than that of ordinary sound wave, which has good directivity and can penetrate opaque substances. This characteristic has been widely used in ultrasonic flaw detection, thickness measurement, ranging, 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 from the transducer is focused on the opaque sample through the acoustic lens, and the ultrasonic wave emitted from the sample carries the information of the illuminated part (such as the ability to reflect, absorb and scatter sound waves), which is concentrated on the piezoelectric receiver through the acoustic lens, and 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 above device is called an ultrasonic microscope. Ultrasonic imaging technology has been widely used in medical inspection. It is used to inspect large-scale integrated circuits in microelectronic device manufacturing, and to display the regions and grain boundaries of different components in alloys in material science. Acoustic holography is an acoustic imaging technology that records and reproduces the stereoscopic images 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). Two transducers placed in liquid are excited by the same ultrasonic signal source, and they emit two coherent ultrasonic waves respectively: one beam becomes an object wave after passing through the studied object, and the other beam is used as a reference wave. The acoustic hologram is formed by the coherent superposition of the object wave and the reference wave on the liquid surface. The acoustic hologram is irradiated by a laser beam, and the reconstructed image of the object is obtained by using the diffraction effect generated when the laser is reflected on the acoustic hologram. Usually, the real-time observation is made by a camera and a TV set.
② ultrasonic treatment. Ultrasonic welding, drilling, solid crushing, emulsification, degassing, dust removal, cleaning, sterilization, chemical reaction promotion and biological research can be carried out by using the mechanical action, cavitation, thermal effect and chemical effect of ultrasound, and it 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, an acoustic relaxation process occurs in the medium. The acoustic relaxation process is accompanied by the transport process of energy between the respective degrees of molecules, and it shows the absorption of sound waves on a macro level (see sound waves). The characteristics and structure of matter can be explored through the law of absorption of ultrasound by matter, and this research constitutes the branch of acoustics of molecular acoustics. The wave length 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 the ultra-ultrasonic wave with frequency above 112 Hz, the wavelength can be comparable to the atomic spacing in the solid, so the solid 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 ultra-sonic on solids can be attributed to the interaction between ultra-sonic and thermal phonons, electrons, photons and various quasi-particles. The research on the generation, detection and propagation of ultra-sound in solid and the sound phenomenon 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 longitudinal wave that can be felt by human ears, and its frequency range is 16 Hz-2 Hz. When the frequency of sound wave is lower than 16Hz, it is called infrasound wave, and higher than 2KHz, it is called ultrasonic sound wave.
Ultrasonic wave has the following characteristics:
1) Ultrasonic wave can spread effectively in gas, liquid, solid, solid melt and other media.
2) Ultrasonic wave can transmit strong energy.
3) Ultrasonic waves will cause 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 the mechanical vibration state (or energy) of an object. The so-called vibration refers to the reciprocating motion of the particle of a substance near its equilibrium position. For example, after the drum surface is struck, it vibrates up and down, and this vibration state propagates in all directions through the air medium, which is sound wave.
Ultrasonic wave refers to the sound wave whose vibration frequency is more than 2KHz, which people can't hear and feel in the natural environment.
the concept of ultrasound therapy:
ultrasound therapeutics is an important part of ultrasound medicine. In ultrasonic treatment, ultrasonic energy is applied to the diseased parts of human body to achieve the purpose of treating diseases and promoting the recovery of the body.