Ultrasonic Attenuation Factors

1. Diffusion attenuation
Acoustic wave propagation in the medium, with the diffusion of the beam, so that the wave front is constantly expanding, and its propagation energy with the increase in distance and the phenomenon called diffusion attenuation. Diffusion attenuation depends on the shape of the wavefront, it has nothing to do with the nature of the medium itself. Plane wave wavefront surface for the plane, so there is no diffusion of the beam, there is no diffusion attenuation. Column wave, spherical wave beam diffusion around the existence of diffusion attenuation, diffusion attenuation and sound pressure and propagation distance.
2. Scattering attenuation
Acoustic wave propagation in the medium, encountering different acoustic impedance of the interface to produce scattered reflections caused by the attenuation is called scattering attenuation. Scattering attenuation and material grain size is closely related to the cast steel or austenitic stainless steel on the ultrasonic detection, material grain coarse, directly affecting the sound transmittance of the sound wave, greatly improving the scattering attenuation, scattered waves along different paths will be propagated to the probe, will show the echo on the oscilloscope, reducing the signal-to-noise ratio, causing great difficulties in the assessment of defects. 
3. Absorption attenuation
Ultrasonic propagation in the medium, due to internal friction and heat conduction in the medium between the plasmas caused by acoustic attenuation, so the detection process when the temperature of the workpiece changes, the propagation of acoustic energy more or less will be consumed. In addition to the above attenuation, there are also misalignment attenuation, attenuation caused by magnetic domain walls and attenuation caused by residual stress.
4. Attenuation coefficient
The so-called attenuation coefficient α, do not take into account the material temperature changes and the influence of diffusion attenuation of the wave source, only consider the medium of the scattering and absorption attenuation, metal materials and other solid media, the medium attenuation coefficient α is equal to the scattering attenuation coefficient αs and the absorption of the attenuation coefficient αa and the sum of the attenuation coefficient through the attenuation coefficient formula it is not difficult to find that, acoustic attenuation is not only associated with the medium itself is inherently related to the state, but also associated with the choice of the acoustic wave frequency.