# Acoustic Contrast Factor

1. Aug 11, 2010

### SFB

Hi

I have some confusion in understanding the acoustic contrast actor . You can check wiki if you are not familiar with the term.

http://en.wikipedia.org/wiki/Acoustic_contrast_factor

If there is a foreign particle in the path of a sound wave (to be specific Standing wave for my case), the sign of acoustic contrast factor determines whether the acoustic radiation force will push the particle toward pressure nodes or antinodes.

As the radiation force is a function of acoustic contrast factor , mathematically sign of the contrast factor determines the force direction.

But I am interested know the physics behind it. How the compressibilty of the particle and medium of propagation determines the direction. What actually happens when sound waves confront a compressible bubble or an incompressible rigid particle ?

I tried to trace some resources , but they are full of mathematics as well.

I would appreciate if you can kindly share your opinion in this regard.

Thanks

, it is quite obvious mathematically that a

2. Jun 22, 2016

### hamilton17

Hi,

I would look up Iso acoustic focussing of particles, this would make this concept easier.
Basically the movement of a particle in a microchannel will either be positive (inwards to the centre) or negative (outwards to the sides).
This depends on both the compressibility and density of the particles, when acoustically activated a radiation force F(rad) is generated.
The particle will move to a point where acoustic impedance matches that of the medium.

Hope this helps