Sounds with a high frequency, over 20000 Hz is ultrasound. They are very weakly scattered, go like a "ray" and therefore very convenient for location. For this reason, not only bats, but also modern instruments - sonars, use ultrasound for echolocation, especially in water. At night butterflies from the family of bears, an ultrasonic noise generator has developed, "knocking off" the bats that are chasing these insects. Echolocation is used for navigation and birds are fat kozodos, or guaharo. They inhabit the mountains caves of Latin America - from Panama to the north to the west to Peru in the south and Suriname to the east. Living in pitch darkness, fat kozodos, nevertheless, have adapted to masterfully fly through the caves. They produce soft snapping sounds, perceived by the human ear (their frequency is about 7000 Hertz). Each click lasts one to two milliseconds. The sound of the click is reflected from the walls of the dungeon, various protrusions and obstacles and is perceived by the sensitive hearing of the bird.

Ultrasound is now widely used in engineering and life

Ultrasound is now widely used in engineering and life. Who does not know ultrasonic washing machines - "tablets" or "balls" - they gently wash fabrics, spending very little energy. The ability of ultrasound to rupture cells has found application in biological research, for example, if necessary, separate the cell from enzymes. Ultrasound is also used to destroy intracellular structures such as mitochondria and chloroplasts in order to study the relationship between their structure and functions.

In medicine ultrasound successfully "shines through" and the human body, and this "X-ray" is not dangerous, as, for example, X-ray. It is interesting that ultrasound can "enlighten" and huge metal layers - in 1 m and more, which is completely inaccessible to X-rays. Ultrasound is freely distributed in metal and, being reflected by inhomogeneities (voids , shells, cracks), shows it. On this principle, devices - defectoscopes are arranged, where ultrasonic signals from the radiator and, passing through the metal, are captured by the probe and transmitted to the receiver. Recently, the direction of ultrasonic microscopy has been developed, which makes it possible to investigate the subsurface layer of a material with a good resolving power.

Ultrasound has a harmful effect on bacteria and even cold-blooded animals - small fishes and frogs die with ultrasound irradiation for 1 to 2 minutes. But for a person he is not dangerous, otherwise "pregnant women" would not "shine through" to him. Now ultrasound is divided into three ranges: low frequencies - up to 105 Hz; average - up to 105 - 107 Hz and high - up to 109 Hz. Elastic waves with frequencies 109 - 1013 Hz are called hypersound. And more often - simply does not happen, because these waves along the length correspond already to the interatomic distance in solids.

The speed of sound propagation in a medium is judged on its physical characteristics. Measurements of velocity at ultrasonic frequencies allow, with very small errors, to determine, for example, the adiabatic characteristics of fast processes, the specific heat of gases, the elastic constants of solids.

Ultrasound emitters can be divided into two large groups. The first includes radiators-generators; fluctuations in them are excited because of the presence of obstacles in the way of a constant flow-a jet of gas or liquid. The second group of radiators is electroacoustic transducers; they convert the already given oscillations of the electric voltage or current into a mechanical oscillation of the solid body, which emits acoustic waves into the environment.