Attenuation is the decrease in the intensity of a wave propagating through a medium.

Resonance is impacted by the fact that real waves undergo attenuation (damping). One cause of attenuation is reflection. Attenuation of sound waves due to reflection makes it difficult to create ultrasonic images of a bone’s interior. Because bone is much denser than the surrounding tissue, almost all of the ultrasound waves are reflected at its boundary. As a result, very few sound waves continue into and reflect off the interior of the bone. Another possible cause of attenuation is spreading: recall that as a sound wave spreads over a larger and larger area, its intensity is reduced. Yet another case of attenuation is absorption.

When a wave attenuates, its intensity decreases. Remember, intensity depends on the square of both frequency and amplitude as well as the density of the medium and wave velocity. Frequency is a constant determined by the wave source, so it is the amplitude and velocity that decrease as intensity decreases. The loss of energy of the wave is most evident in its loss of amplitude.

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Key Points

• Attenuation is the decrease in the intensity of a wave propagating through a medium.

• Causes of attenuation include reflection and absorption.

• When a wave attenuates, its intensity decreases. The loss of energy of the wave is most evident in its loss of amplitude.

Key Terms

Attenuation (damping): The reduction of the force, effect, or value of something.

Amplitude: Distance between the rest position and the crest of the wave. Proportional to intensity.

Reflection: The repetition of a sound resulting from reflection of the sound waves.

Absorption: The loss of sound energy when sound waves comes into contact with an absorbent material such as ceilings, walls, floors and other objects, as a result of which, the sound is not reflected back into the space.