Sound waves are one of the categories of sound, belonging to mechanical waves. Sound waves refer to longitudinal waves that can be felt by the human ear, with a frequency range of 16Hz-20KHz. When the frequency of sound waves is below 16Hz, it is called infrasound waves, and above 20KHz, it is called ultrasonic sound waves. Ultrasound is widely used in fields such as diagnosis, therapy, engineering, and biology. The Saifurui home ultrasound therapy machine belongs to the application category of ultrasound therapy. （1） Engineering applications: underwater positioning and communication, underground resource exploration, etc. (2) Biological applications: cutting macromolecules, biotechnology, and seed processing, etc. (3) Diagnostic applications: A-type, B-type, M-type, D-type, dual function, and color ultrasound, etc. (4) Therapeutic applications: the use of ultrasound in physical therapy, cancer treatment, surgery, extracorporeal lithotripsy, dentistry, and other fields Removing scale from glass and ceramic products is a troublesome task. If these items are placed in cleaning solution and ultrasonic waves are introduced, the severe vibration of the cleaning solution can quickly clean the dirt on the items Although humans cannot hear ultrasound, many animals have the ability to do so. They can use ultrasound to 'navigate', chase food, or avoid dangerous objects. You may have seen many bats flying back and forth in the courtyard on summer nights. Why do they fly without light and not lose their direction? The reason is that bats can emit ultrasound waves ranging from 20000 to 100000 hertz, which is like an active "radar station". Bats use this' sonar 'to determine whether insects or obstacles are ahead of them during flight. And the quality of radar can range from tens, hundreds, to thousands of kilograms, depending on some important performance metrics The anti-interference ability of bats is far superior to modern radio locators In depth research on the functions and structures of various organs in animals, using the knowledge gained to improve existing equipment, is a new discipline developed in recent decades called bionics We humans did not learn to use ultrasound until World War II, which is the principle of using sonar to detect underwater targets and their status, such as the position of submarines. At this time, people emit a series of ultrasound waves of different frequencies into the water, and then record and process the reflected echoes. From the characteristics of the echoes, we can estimate the distance, shape, and dynamic changes of the detected object. The earliest use of ultrasound in medicine was in 1942, when Austrian doctor Dusik used ultrasound technology to scan brain structures; In the 1960s, doctors began to apply ultrasound to the detection of abdominal organs. Nowadays, ultrasound scanning technology has become a tool for modern medical diagnosis. The difference between sonar and radar is that sonar uses ultrasonic radar to perform medical ultrasound examinations through radio waves. The working principle of sonar is similar to that of sonar, which is to emit ultrasonic waves into the human body. When it encounters an interface in the body, it will reflect and refract, and may be absorbed and attenuated in human tissues. Because the morphology and structure of various tissues in the human body are different, the degree of reflection, refraction, and absorption of ultrasound waves also varies. Doctors distinguish them by the characteristics of the wave patterns, curves, or images reflected by the instruments. During the examination, the first step is to convert the reflected signal of the human interface into light points of different strengths and weaknesses, which can be displayed through a fluorescent screen. This method is intuitive, highly reproducible, and can be compared before and after. Therefore, it is widely used for the diagnosis of gynecological, urinary, digestive, and cardiovascular diseases. M-type: It is a method used to observe the temporal changes in the activity interface. Zui is suitable for checking the activity of the heart, and the dynamic changes in its curve are called echocardiography. It can be used to observe the position, activity status, and structural condition of various layers of the heart, and is often used to assist in the diagnosis of heart and large vessel diseases. D-type: It is a type of ultrasound diagnostic method specifically used to detect blood flow and organ activity, also known as Doppler ultrasound diagnostic method. Can determine whether the blood vessels are unobstructed, whether the lumen is narrowed or occluded, and the location of the lesion. The new generation of D-type ultrasound can also quantitatively measure the blood flow inside the lumen. In recent years, scientists have developed color coded Doppler systems, which can display the direction of blood flow in different colors under the indication of anatomical landmarks in echocardiography. The depth of color represents the flow velocity of blood flow. Nowadays, ultrasound technologies such as stereoscopic ultrasound imaging, ultrasound CT, and ultrasound endoscopy continue to emerge, and can also be combined with other examination instruments to greatly improve the accuracy of disease diagnosis. Ultrasonic technology is playing a huge role in the medical field, and with the advancement of science, it will become more perfect and better benefit humanity. The acoustic branch that studies the generation, propagation, reception, various ultrasonic effects, and applications of ultrasound is called ultrasound. The devices that generate ultrasonic waves include mechanical ultrasonic generators (such as air whistles, steam whistles, and liquid whistles), electric ultrasonic generators made using electromagnetic induction and electromagnetic action principles, and those that utilizePiezoelectric crystalThe electrostrictive effect and ferromagnetic materialsMagnetostriction effectProduced electroacoustic transducers, etc. When ultrasound propagates in a medium, the interaction between ultrasound and the medium causes physical and chemical changes in the medium, resulting in a series of mechanical, thermal, electromagnetic, and chemical ultrasound effects, including the following four effects: ① mechanical effects. The mechanical action of ultrasound can promote the emulsification of liquid, the liquefaction of gel and the dispersion of solid. When standing waves are formed in ultrasonic fluid media, tiny particles suspended in the fluid condense at the nodes due to mechanical forces, forming periodic accumulations in space. Ultrasonic waves are presentpiezoelectric materialInduced by the mechanical action of ultrasonic waves during propagation in magnetostrictive materialselectrode polarizationAnd induced magnetization (seeDielectric PhysicsAnd magnetostriction). ②空化作用Ultrasonic waves can generate a large number of small bubbles when applied to liquids. One reason is that local tensile stress occurs inside the liquid, forming negative pressure. The decrease in pressure causes the gas originally dissolved in the liquid to become supersaturated and escape from the liquid, becoming small bubbles. Another reason is that strong tensile stress tears apart the liquid into a cavity, known as cavitation. The cavity contains liquid vapor or another gas dissolved in the liquid, and may even be a vacuum. Small bubbles formed by cavitation will continuously move, grow, or suddenly burst with the vibration of the surrounding medium. When it bursts, the surrounding liquid suddenly rushes into the bubble, producing high temperature, high pressure, and a shock wave. The internal friction associated with cavitation can form charges and generate luminescence within the bubble due to discharge. The technology of ultrasonic treatment in liquids is mostly related to cavitation. ③ Thermal effect. Due to the high frequency and energy of ultrasound, it can produce significant thermal effects when absorbed by the medium. ④ Chemical effects. The action of ultrasound can promote or accelerate certain chemical reactions. For example, pure distilled water produces hydrogen peroxide after ultrasonic treatment; Nitrous acid is produced after ultrasonic treatment of water containing nitrogen gas; The aqueous solution of dye will change color or fade after ultrasonic treatment. The occurrence of these phenomena is always accompanied by cavitation. Ultrasonic waves can also accelerate the hydrolysis, decomposition, and polymerization processes of many chemical substances. Ultrasonic waves also have a significant impact on photochemical and electrochemical processes. After ultrasonic treatment, the characteristic absorption spectral bands of various amino acids and other organic substances in aqueous solutions disappear and show uniform general absorption, indicating that cavitation has altered the molecular structure. The ultrasound effect has been widely used in practice, mainly in the following aspects: ① Ultrasonic testing. Ultrasonic waves have shorter wavelengths than regular sound waves, better directionality, and can pass through opaque materials. This characteristic has been widely used in ultrasonic flaw detection, thickness measurement, distance measurement, remote control, and ultrasonic imaging technology. Ultrasonic imaging is a technique that uses ultrasound to present the internal image of opaque objects. The ultrasonic waves emitted from the transducer are focused on an opaque sample through an acoustic lens. The ultrasonic waves emitted from the sample carry information about the illuminated area (such as the ability to reflect, absorb, and scatter sound waves), and are converged on a piezoelectric receiver through the acoustic lens. The resulting electrical signal is input into an amplifier, and the image of the opaque sample can be displayed on a fluorescent screen using a scanning system. The above device is called an ultrasonic microscope. Ultrasound imaging technology has been widely applied in medical examinations, used in microelectronic device manufacturing to inspect large-scale integrated circuits, and in materials science to display regions and grain boundaries of different components in alloys. Holography is an acoustic imaging technique that uses the interference principle of ultrasound to record and reproduce three-dimensional images of opaque objects. Its principle is similar to that of light wavesholographyBasically the same, only with different recording methods (see holography). Using the same ultrasound signal source to excite two transducers placed in a liquid, they emit two coherent ultrasound waves: one beam becomes the object wave after passing through the object being studied, and the other beam serves as the reference wave. The sound hologram is formed by the coherent superposition of object waves and reference waves on the liquid surface. The sound hologram is irradiated with a laser beam, and the reconstructed image of the object is obtained by the diffraction effect generated by the reflection of the laser on the sound hologram. It is usually observed in real time by cameras and televisions. ② Ultrasonic treatment. The mechanical, cavitation, thermal, and chemical effects of ultrasound can be utilized for ultrasonic welding, drilling, solid crushing, emulsification, degassing, dust removal, descaling, cleaning, sterilization, promoting chemical reactions, and conducting biological research. It has been widely used in various sectors such as industry, mining, agriculture, and medicine. ③ Basic research. After ultrasound is applied to a medium, it produces a process of acoustic relaxation in the medium, which is accompanied by the transport of energy between the individual electrical degrees of molecules and exhibits absorption of sound waves at the macroscopic level (see sound waves). The absorption law of ultrasound by substances can explore the characteristics and structure of substances, and this research constitutes the acoustic branch of molecular acoustics. The wavelength of ordinary sound waves is greater than the atomic spacing in solids, and under these conditions, solids can be treated as continuous media. But for ultrasonic waves with frequencies above 1012 Hz, the wavelength can be compared to the atomic spacing in solids, and solids must be treated as lattice structures with spatial periodicity. The energy of lattice vibrations is quantized and called phonons (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 study of the generation, detection, and propagation laws of ultrasound in solids, as well as the study of acoustic phenomena in quantum liquids such as liquid helium, constitute a new field of modern acoustics. Sound waves belong to the category of sound and are mechanical waves. Sound waves refer to longitudinal waves that can be felt by the human ear, with a frequency range of 16Hz-20KHz. When the frequency of sound waves is below 16Hz, it is called infrasound waves, and above 20KHz, it is called ultrasonic sound waves. Ultrasonic waves have the following characteristics: 1) Ultrasonic waves can effectively propagate in media such as gases, liquids, solids, and solid melts. 2) Ultrasonic waves can transmit strong energy. 3) Ultrasonic waves can cause reflection, interference, superposition, and resonance phenomena. 4) When ultrasound propagates in liquid media, it can generate strong impacts and cavitation phenomena at the interface. Ultrasonic waves are a member of the sonic family. Sound waves are the propagation form of the mechanical vibration state (or energy) of an object. The so-called vibration refers to the back and forth motion of a material particle near its equilibrium position. For example, after being struck, the drum surface vibrates up and down, and this vibration state propagates in all directions through the air medium, which is sound waves. Ultrasonic waves refer to sound waves with a vibration frequency greater than 20KHz that humans cannot hear or feel in natural environments. The concept of ultrasound therapy: Ultrasound therapy is an important component of ultrasound medicine. During ultrasound therapy, ultrasound energy is applied to the affected area of the human body to achieve the goal of treating diseases and promoting physical recovery