k-Wave

1. Civilian
   

   Member
   Joined: Jan '13
   Posts: 4

   Hi k-Wave,

   I am trying to simulate ultrasound through a medium with a relatively high absorption coefficient (20 dB/cm at 1 MHz). The way I understand, please correct me if I am mistaken, the simulation parameters should be set is that alpha_coeff*freq^alpha_power should be equal to 20. So if the frequency I am using is 0.2 MHz and assume alpha_power is 1.5, then alpha_coeff should be 223.6.

   The problem is that when I provide these values the whole simulation will blow up! Am I doing anything wrong at all?

   Your help will be highly appreciated.

   Posted 12 years ago #

2. Bradley Treeby
   

   Developer
   Joined: Mar '10
   Posts: 1,643

   Hi Civilian,

   The absorption coefficient pre-factor (alpha_coeff) is defined in units of dB/(MHz^y cm), where alpha = alpha_coeff * f ^ alpha_power. In your case, alpha = 20, so if you assume your absorption varies with y = 1.5, you would then set alpha_coeff = 20 / 1^1.5 = 20.

   With very high values of absorption, the stability criterion of the model used in k-Wave becomes more stringent. If you are still seeing instabilities with alpha_coeff = 20, try decreasing the size of the time step (you can do this by reducing the CFL number in makeTime).

   Brad.

   Posted 12 years ago #

3. Civilian
   

   Member
   Joined: Jan '13
   Posts: 4

   Thanks Brad!
   My simulation works fine with these values. I understand now that the frequency in the absorption model is meant to be the frequency at which the absorption coefficient is measured not the ultrasonic frequency I am using. Thank you for the clarification.

   Posted 12 years ago #

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