The concept of sound

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.

Infrasound

0 Hz < f < 20 Hz
Audible sound

16 Hz < f < 20 kHz
Ultrasound

16 kHz < f < 1 GHz
Hypersonic

f > 500 MHz
1 Hz = 1 oscillation per second = 1 hertz

Ultrasound is the term used to describe sound waves above the threshold of human hearing in a range from around 16 kHz to 1 GHz. Ultrasound can also be generated with considerably more energy, i.e. "louder" than audible 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

References

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