By definition, sound is “a mechanical wave motionof a material environment (or molecule)” that, acting on the human ear, produces auditory sensations. Familiar examples include wavy paper and rulers. [Sound is composed of periodic soundand its opposite, noise . Furthermore, sound consists of pure soundwith a single frequency and complex sound with several different frequencies. Sound waves propagate toward the source at a speed that depends on environmental conditions, e.g., pressure, temperature, humidity, etc., and decay gradually.
Mechanical waves with a frequency below 16 Hz are called low frequency sound . Conversely, if the frequency is greater than 16,000 Hz, they are called ultrasonic . 37]
Very Low Frequency
Although humans do not hear infrasound, it can still cause health problems such as dizziness and heart attacks. Some animals, such as elephants, rhinos, hippopotamuses, and whales, use infrasound to communicate. In addition to some animals, sources of infrasound include wind turbines and volcanic activity.
Ultrasound
Mechanical ultrasound is generated by the repeated deformation (contraction and re-expansion) of suitable materials and the application of electrical voltage to them. Like infrasound, ultrasound is beyond the range of human hearing. Again, some animals, such as dolphins, dogs, and bats, can perceive ultrasound and communicate through it.
It also plays an important role in so-called “echolocation. This is a method of transmission and recapture of reflected sound used by cetaceans and other mammals to measure distance and to confirm direction in space. Humans can utilize this method through a device called sonar
, which can be used for echolocation. In addition to echolocation, ultrasound can be used for ultrasonic examination of internal organs and body structures inmedicine, fine to ultrafine cleaningof various materials, detection of their thickness or internal defects,disinfection of solutions, or humidificationof air.or humidifying the air
.