Mechanical waves with a frequency of oscillation, more 20 000 Hz, not perceived as sound man. From the call ultrasonic waves, or ultrasound. Ultrasound is highly absorbed by the gases and many times weaker solids and liquids. Therefore, ultrasound waves can propagate considerable distances only in solids and liquids.

As energy, that shift wave, proportional to the density of Wednesday and the square of the frequency, the ultrasound can transfer energy, a much greater, than sound waves. Another important feature of ultrasound is, that it is a relatively simple directional radiation. All this makes extensive use of ultrasound in technology.

Described property used in the ultrasonic Fishfinder-device to determine the depth of the sea (rice. 25,11). Ship supply source and receiver of ultrasound of a certain frequency. The source sends a short ultrasonic pulses, and the receiver picks up the reflected pulses. Knowing the time between sending and receiving impulses and propagation speed of ultrasound in water, using the formula l = vt/2 determine the depth of the sea. Similarly applies ultrasonic Locator, which is used to determine the distance to the obstacle in the way of a ship in the horizontal direction. In the absence of such obstacles, ultrasonic pulses are not returned to the ship.

Interesting, that some animals, for example, bats, have the authorities, acting on the principle of ultrasonic Locator, that allows them to navigate in the dark. Perfect ultrasonic Locator are dolphins.

When passing through the liquid particles liquid ultrasonic acquire great acceleration and greatly affect various body, placed in liquid. It is used to accelerate a wide variety of technological processes (for example, preparation of solutions, cleaning of parts, tanning of hides, etc. D.).

Under intensive ultrasonic vibrations in the fluid particles are becoming such a big acceleration, that fluid formed on short time breaks (void), that severely slam, creating many small bumps, t. e. cavitation occurs. In such circumstances, the fluid has a strong sword action, that it is used for preparation of suspensions, consisting of sputtered particles of a solid body in a liquid, and emulsions — mists of small droplets of one liquid in another.

Ultrasound is used to detect defects in metal parts. In the modern use of ultrasound technology so extensively, that it is difficult even to list all the areas of its use.

Note, that mechanical waves with a frequency of fluctuations less 16 Hz is called infrasound wave MI or infrazvukom. They also do not cause sound sensations. Infrasound waves arise at sea during storms and earthquakes. The speed of propagation of infrasound in water much more, than the speed of movement of a hurricane or gigantic tsunami waves, formed during the earthquake. This enables some sea animals, having the ability to perceive infrasound waves, receive in this way signals about approaching danger.