Ultrasound, ultrasonic vibrations, mechanical fluctuations in gases, liquids and solid bodies, the frequency of which exceeds 15 000 Hz (Hertz).
The human ear does not perceive the ultrasound, but some animals, such as bats, can perceive and emit ultrasound. Partially perceive ultrasound rodents, cats, dogs, whales, dolphins. Ultrasonic oscillations arise in the work of engines, machines and rocket engines.
In practice to obtain ultrasound is usually used Electromechanical ultrasonic generators, which are based on the ability of some materials to change their sizes under the action of magnetic-magnetic striktsionnyj generators) or electric field (piezoelectric generators), making sounds of appropriate height (frequency). For example, plate cut from crystal quartz and placed in an alternating electric field, undergoes periodic compression and expansion, with a frequency equal to the frequency of oscillations of the electric field. If the latter varies with ultrasonic frequency, quartz plate will emit ultrasound.
Ultrasound is used in practice for echolocation, for the detection and treatment of tumors and certain defects in the tissues of the body; in surgery and traumatology for dissection of soft and bone tissues in different operational benefits for welding broken bones, for the destruction of cells and other Cm. also, Ultrasonic therapy.
Ultrasound - occupational hazards. Ultrasound (usually in combination with noise) with prolonged exposure and significant intensity impact (120 dB or more) - over the air or by direct contact with ultrasonic generators or objects on which it acts (tool, a solution, etc.,), can cause headaches, fatigue, sleep disturbances, irritability, increased sensitivity to sounds, the feeling of stuffiness in the ears. By the end of the working day may be fluctuations in body temperature and decrease heart rate. In the case of chronic exposure can be formed asthenic syndrome, occurs weight loss and other changes in the body.
Preventive measures are the same as for noise control (see): the use of sound-absorbing and reflecting screens and devices. Contact exposure to ultrasound should be completely eliminated by proper organization of labour. In the short-term forced contact with ultrasound need to apply means of individual protection (rubber and cotton gloves, remote equipment and so on).
The state of health of persons working in the zone of influence of ultrasound, systematic medical check - preliminary and periodic medical examinations at least once a year.