Ultrasound
Ultrasound refers to any sound wave or vibration, the frequency of more than human ears can hear the maximum threshold of 20kHz (kHz). Ultrasound due to its high frequency characteristics are widely used in many fields, such as metal testing, workpiece cleaning and so on. Some animals, such as dogs, dolphins, and bats, are all beyond the human ears, and therefore can hear the ultrasound. Some people use this feature to produce can produce ultrasound to call the dog dog flute. The so-called ultrasound, only through the elastic and inertial media, such as air, when the air itself once the expansion or compression, through the movement of its molecules and fluctuations in the transmission. As a result, sonic waves can not be propagated in a vacuum. Human hearing can detect fluctuations, called the sound. At this time sound waves, that is called audible wave. ...