What is the term for the areas where an acoustic wave is less dense?

The term for the areas where an acoustic wave is less dense is "rarefactions." In the context of wave propagation, particularly with sound waves, rarefactions occur when the pressure in a medium decreases, leading to a lower density in that area compared to the surrounding regions. This phenomenon happens as the wave oscillates, creating alternating regions of compression (higher density) and rarefaction (lower density).

Understanding how rarefactions work is essential in sonography as these variations in density affect how sound waves travel through different tissues. Areas of rarefaction contribute to the overall acoustic wave pattern, influencing aspects like wave speed and interaction with different tissues, which is critical for accurate imaging.

Compressions refer to areas of higher density where air pressure is increased, reflections involve the bouncing back of sound waves, and densities is a general term that does not specifically describe the wave's behavior in terms of compression and rarefaction.