Ultrasound is probably best known from medical diagnostics where it is used to take pictures of unborn babies. In industry, ultrasound is used in a wide range of processes, such as cleaning, welding of plastics and metals, cutting, forming, testing of materials, separating, mixing, de-gassing, atomising, localising, measuring and many others.
Ultrasound refers to sound in the range that is not audible for humans. Sound is a propagation of minute fluctuations in pressure and density in an elastic medium (gases, liquids, solids). The number of vibrations within one second is called frequency and is measured in Hertz (Hz). The frequency range that is audible for humans is between 16 Hz and 20,000 Hz. The range above 20,000 Hz is referred to as ultrasound.