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Introdução básica:

O ultrassom é uma onda sonora com frequência superior a 20.000 Hz, que é dividida em ultrassom de potência e ultrassom de detecção em aplicações práticas. Tem boa direcionalidade, forte capacidade de penetração e é fácil de obter energia sonora concentrada. Ele pode se propagar por longas distâncias em sólidos e líquidos de alta densidade e pode ser usado para alcance, testes industriais, ultrassom médico, limpeza, soldagem, perfuração, cascalho, esterilização e desinfecção, etc.

Os cientistas referem-se ao número de vibrações por segundo como a frequência do som, que é medida em hertz (Hz). A frequência das ondas sonoras que podem ser ouvidas por nossos ouvidos humanos está entre 20 Hz e 20.000 Hz. Quando a frequência de vibração das ondas sonoras é menor que 20 Hz ou maior que 20.000 Hz, não podemos ouvi-las. Portanto, nos referimos às ondas sonoras com frequências acima de 20.000 hertz como 'ondas ultrassônicas'. A frequência ultrassônica comumente usada para diagnóstico médico varia de 1 MHz a 10 MHz.

Pesquisas teóricas mostram que nas mesmas condições de amplitude, a energia da vibração de um objeto é diretamente proporcional à frequência de vibração. Quando as ondas ultrassônicas se propagam em um meio, a frequência de vibração das partículas no meio é muito alta, resultando em uma grande quantidade de energia. No inverno seco do norte da China, se ondas ultrassônicas forem introduzidas em um tanque de água, a vibração intensa fará com que a água do tanque se quebre em muitas pequenas gotas. Em seguida, um pequeno ventilador pode ser usado para soprar as gotas na sala, o que pode aumentar a umidade do ar interno. Este é o princípio dos umidificadores ultrassônicos. For diseases such as pharyngitis and tracheitis, it is difficult to use blood flow to reach the affected area with medication. Using the principle of a humidifier to atomize the medication and allow the patient to inhale can improve the therapeutic effect. The enormous energy of ultrasound can also cause stones in the human body to undergo intense forced vibrations and shatter, thereby alleviating pain and achieving the goal of healing. Ultrasound is widely used in medicine, such as color ultrasound, B-ultrasound, and lithotripsy (such as gallstones, kidney stones, eye bags, etc.), which can also damage bacterial structures and disinfect items.

Generation method:

Sound waves are the form of propagation of mechanical vibration states (or energy) of objects. The so-called vibration refers to the round-trip motion of particles of a substance near their 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 called sound wave. Ultrasound refers to a sound wave with a vibration frequency greater than 20000 Hz, and its frequency per second is very high, exceeding the general upper limit of human hearing (20000 Hz). People refer to this kind of invisible sound wave as ultrasound. Ultrasound and audible sound are essentially the same, and their common feature is a mechanical vibration mode that typically propagates in an elastic medium as a longitudinal wave, which is a form of energy propagation. The difference is that ultrasound has a high frequency, short wavelength, and good beam and directionality when  propagating along a straight line within a certain distance. Currently, the frequency range used for abdominal ultrasound imaging is between 2-5 MHz, Commonly used is 3~3.5 megahertz (1 vibration per second is 1Hz, 1 megahertz=10 ^ 6Hz, that is, 1 million vibrations per second, and the frequency of audible waves is between 16-20000 Hz).

The propagation laws of ultrasound in media, such as reflection, refraction, diffraction, and scattering, are not fundamentally different from those of audible sound waves. But the wavelength of ultrasound is very short, only a few centimeters, or even a few thousandths of a millimeter. Compared with audible sound waves, ultrasound has many strange characteristics: propagation characteristics - the wavelength of ultrasound is very short, and the size of typical obstacles is many times larger than that of ultrasound waves. Therefore, the diffraction ability of ultrasound is poor, and it can propagate in a straight direction in a uniform medium. The shorter the wavelength of ultrasound, the more significant this characteristic is. Power characteristics - When sound propagates in the air, it drives the particles in the air to vibrate back and forth, doing work on the particles. Sound power is a physical quantity that represents the speed at which sound waves do work. At the same intensity, the higher the frequency of a sound wave, the greater its power.

Due to the high frequency of ultrasound, its power is very high compared to ordinary sound waves. Cavitation - When ultrasonic waves propagate in a liquid, small cavities are created inside the liquid due to the intense vibration of liquid particles. These small cavities rapidly expand and close, causing violent collisions between liquid particles, resulting in pressures of thousands to tens of thousands of atmospheres. The intense interaction between particles can cause a sudden increase in the temperature of the liquid, providing a good stirring effect, thereby emulsifying two immiscible liquids (such as water and oil), accelerating the dissolution of solutes, and accelerating chemical reactions. The various effects caused by the action of ultrasound in liquids are called the cavitation effect of ultrasound.

Frequency above 2 × A sound wave of 10 kHz. The branch of acoustics that studies the generation, propagation, reception, and various ultrasonic effects and applications of ultrasound is called ultrasonics. The devices that generate ultrasonic waves include mechanical ultrasonic generators (such as gas whistles, sirens, and liquid whistles), electric ultrasonic generators made using the principles of electromagnetic induction and action, and electro-acoustic transducers made using the electrostrictive effect of piezoelectric crystals and the magnetostrictive effect of ferromagnetic materials.