Ultrasonic wave is a kind of mechanical wave with extremely short wavelength, which is generally shorter than 2cm (cm) in air. It must rely on the media to spread and cannot exist in a vacuum (such as space).

It travels farther in water than in air, but it is easy to be lost and scattered in air because of its short wavelength, which is not as far as audible sound and infrasound. However, because of its short wavelength, it is easier to obtain anisotropic acoustic energy, which can be used for cleaning, crushing, disinfection and so on. It has many applications in medicine and industry.

Several main parameters of ultrasonic wave:

Wavelength: λ≤2cm in air at 20℃ (in practical application, mechanical waves with λ≤3.4cm, that is, f≥ 10KHz, are usually called ultrasonic waves because of their similar functions).

Wave velocity: in air at 20℃, v=343m/s, which is faster in liquid and fastest in solid.

Power density:

Defined as p= emission power (W)/ emission area (cm? ), usually p≥0.3W/cm? . Ultrasonic waves propagating in liquid can clean dirt on the surface of objects,

Its principle can be explained by "cavitation" phenomenon: when the pressure caused by ultrasonic mechanical waves in liquid reaches one atmosphere, its power density is 0.35W/cm? At this time, the peak of ultrasonic wave can reach vacuum or negative pressure, but there is actually no negative pressure, so great pressure is generated in the liquid, which makes the liquid molecules crack into cavities-cavitation nuclei.

This cavity is very close to vacuum, and it will rupture when the ultrasonic reverse reaches the maximum, and the strong impact force generated by the rupture will knock down the dirt on the surface of the object. This shock wave phenomenon caused by the rupture of countless tiny cavitation bubbles is called "cavitation" phenomenon. Too small sound intensity cannot produce cavitation effect.

phylogeny

International aspect

Compared with optical methods such as infrared ray and ultraviolet ray, ultrasonic wave started late, with a history of less than 100 years. /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 first put forward the definition of ultrasound, and ultrasound became a brand-new concept. 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.

Domestic aspect

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 wavelength of 430μm was first used in Beijing to treat various diseases, and it was gradually popularized in 1950s, and it was made in China.

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, focused ultrasound surgery (HIFU) is regarded as the latest technology for treating tumors in 2 1 century.