Signal coupling in ultrasound is a term used to describe the state of sound propagation between the transducer and tissue. Signal coupling is degraded by air bubbles and materials that do not conduct sound.

Ultrasound waves propagate poorly through a gaseous medium that result usually in inadequate imaging.
The effect of propagation through dense zones is that nearly all of the ultrasound waves are reflected. Structures below dense zones, for example bone, calcium, metal are also poorly imaged.

See also Signal Coupling.