Sound refers to pressure waves that can propagate in gases, liquids and solids, but not in a vacuum. The cause is always a sound source that causes a propagating mechanical deformation of the transmission medium.
The sound effects in the propagation medium depend essentially on the wave form, the intensity of the source and the type of medium. In liquids and gases, for example, only longitudinal waves propagate; this means that the sound waves cause a periodic pressure and tension phase in the direction of oscillation.
In acoustics, the following frequency ranges are distinguished.
0 Hz < f < 20 Hz
16 Hz < f < 20 kHz
16 kHz < f < 1 GHz
f > 500 MHz
1 Hz = 1 oscillation per second = 1 hertz
Ultrasound is the term used to describe sound waves above the audibility threshold of humans in a range from about 16 kHz to 1 GHz. Ultrasound can also be generated with considerably more energy, i.e. "louder" than auditory sound.
Ultrasound applications are roughly divided into small-signal and power-sound applications
Small signal applications: Intensity 100 kHz
Power sound applications: Intensity > 1 W/cm² and frequency < 100 kHz
There are also applications that do not fit into this scheme:
In medical therapy, low frequencies at low power are required, in the wafer industry, high power at high frequencies.
Of the above-mentioned application areas, BANDELIN electronic specialises in
Cleaning - Homogenisation - Medical therapy
The following books provide an overall presentation of ultrasound. In addition, there are numerous publications on individual ultrasound applications.
Bergmann, Ludwig: Ultrasound and its applications in science and technology; Stuttgart 1954
Kuttruff, Heinrich: Physics and Technology of Ultrasound; Stuttgart 1988
Lehfeldt, Wilhelm: Ultrasound in brief; Würzburg 1973
Millner, Rudolf: Wissensspeicher Ultraschalltechnik; Leipzig 1987
Sorge, Georg and Hauptmann, Peter: Ultrasound in Science and Technology; Frankfurt a. M. 1985