SaM - Scattering and Diffuse Reflection of an Ultrasonic Wave

Remeber:

We have talked about reflection of an ultrasonic wave, and we have supposed an ==infinite smooth plane on which the wave reflects==. In real world however we don’t have this kind of infinite plane surface which separates it two media. So the obstacle will have a surface surrounding it which has a certain geometry:

Two things can happen:

1. If $D\ll {\lambda }_w$ (so if the diameter of the obstacle is much smaller than the wavelength)
   We are talking about scattering, and we consider the wave to spread in all directions:
   
   The resulting echos from a scattering will be very weak comperated to a normal reflection.
2. If $D\gg {\lambda }_w$, but the incident plane is not smooth, and we can say that its surface roughness $h$ is much smaller than the wavelength ${\lambda }_w$
   We are talking about diffuse reflection, the wave will mostly bounce back, but it will also spread in many directions, because each of these surface imperfections give rise to scattering:
   
   The resulting echos from this diffuse reflection will be weak comperated to a normal reflection.

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Memory Card

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In real world obviously we don’t have this kind of infinite plane surface which separates it two media.

So the obstacle will have a surface surrounding it which has a certain geometry:

• So if the dimension (the size) of the obstacle, let’s call the mean size $D$ is much larger than the wavelength $\lambda$, then we can speak about reflection in any case.

On the other hand if we have a small obstacle which is an obstacle with a dimension, with a size, comparable, similar to the wavelength, or the smaller than the wavelength, we don’t have a reflected wave but we have a wave with an approximately spherical wave front. And in this case we talk about scattering:

However thare could also happend (most cases) that our large surface is not smooth, in this case we talk about diffues reflection:

• $h$ : is a roughness measurement.
• We will have a reflection, which is called the “diffuse reflection” because each of these surface imperfections give rise to scattering.

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Different type of Interaction between Waves and Media

• Obviously the amplitude of the vehicles are stronger depending on the transmission coefficient and reflection coefficient.
• Scattering is more difficult to work with since the wave is riflected in almost all directions instead of just one.