What is ultrasound?

UltraschallUltrasound refers to a frequency spectrum of sound beyond the audible range for humans, starting from about 16 kHz (kilohertz) to 1.6 GHz (gigahertz). Ultrasound waves always require a medium through which to propagate. This could be air, water or any other solid or liquid. Basically, ultrasound propagates as a so-called longitudinal wave.

Air-borne noise can only transition into a solid body if the sound wave is emitted within immediate proximity, and if there is a coupling medium of a specific density and appropriate acoustic properties in between. Depending on the properties of an obstacle, ultrasound will either be reflected from it, absorbed by it or simply transmitted through it. As with all wave types, diffraction, refraction and interference can all occur with ultrasound. Basically, ultrasound transmits very readily through a closed, humid environment. The penetration depth of ultrasound depends primarily on the frequency used and the amplitude (or strength) of the signal. The rule with ultrasound is: the lower the frequency, the deeper the sound wave penetrates into the tissue. This is rather ironic, in an age where the market typically wants everything to go "faster, higher and further". For medical and cosmetic treatment, there are two different ways to employ ultrasound:

  1. Continuous ultrasound: In this case, the sound is produced continuously and output at a specific frequency and amplitude (strength) of the signal.
  2. Impulse ultrasound: This is where a specific frequency and amplitude is output in discrete pulses.

An advantage of continuous ultrasound over impulse ultrasound is that it always involves a heating reaction. Care must be taken when working with veryhigh amplitudes, however – if the ultrasound remains too long on one point oftissue, then it can lead to a so-called "hotspot" (strong warming to the point of excessive heat).