Attenuation of sound in ultrasonic testing.

When sound travels through a medium, it's extreme less with distance. In visual material,  sound pressure (signal amplitude) is only reduced by the spreading of the wave. Natural materials,however, all produce an effect which further weakens the sound. This further weakening results from scattering and absorption. Scattering is the reflection of the sound in directions other than its original direction of propagation. Absorption is the conversion of the sound energy to other forms of energy. The combined effect of scattering and absorption is called attenuation. Ultrasonic attenuation is the decay rate of the wave as it propagates through material. Attenuation of sound with in material itself  is often not essential interest. However, natural properties and loading condition can be related to attenuation. Attenuation often serves as a measurement tool that leads to the formation of theories to explain physical or chemical phenomenon that decreases the ultrasonics intensity.