k-Wave

1. wenxiu
   

   Member
   Joined: Jul '18
   Posts: 6

   Hello,

   I'm trying to simulate a simple example of acoustic propagation in water in 2D, which is received by a focused transducer. And I have several problems need your help.

   1) The central frequency of transducer is about 50 MHz, so what the resolution to divide the mesh? I set the resolution to 1 micrometer, and the result told the maximum supported frequency is 750 MHz. But the radius of 'source.p0' is 2 micrometer. Is it OK? If the resolution be finer, it will cost too much time.

   2) In the experiment, I use an acoustic lens in front of transducer. So that the sensor is focused, but I'm not familiar with how to set it.
   I use a flat transducer to replace it in the simulation, and there is also a small question.The parameter I set:
   sensor_radius = 3e-3;
   num_sensor_points = 2*sensor_radius/n;
   sensor.mask = 0*ones(Nx,Ny);
   sensor.mask(200,Ny/2-3000:Ny/2+3000)=1;
   I'm confused about the sensor_radius and sensor.mask, are they the same? I think the diameter of sensor is set in the sensor.mask. It seems that sensor_radius and num_sensor_points won't appear again later. And when the sensor_radius and sensor.mask mismatch, there is nothing happened.

   3)After simulation, I use the average value of every sensor point of the same time, I use it as the simulation output data of the transducer, is it OK?

   Thanks you!

   Posted 6 years ago #

2. Bradley Treeby
   

   Developer
   Joined: Mar '10
   Posts: 1,643

   Hi wenxiu,

   (1) In practice, I would suggest using a least 3 points per wavelength at the highest frequency of transducer. Any less, and the effectiveness of the PML starts to decrease (see here for an example).

   (2) Details of how to set the sensor mask are given in the k-Wave manual and the examples. In short, in this example you are using a binary sensor mask. Wherever you have set a 1 in your matrix, the pressure will be recorded. You can take a look at the sensor mask using imagesc(sensor.mask);

   (3) This seems sensible, yes.

   Brad.

   Posted 6 years ago #

3. wenxiu
   

   Member
   Joined: Jul '18
   Posts: 6

   Hi Bradley,

   Thanks for your reply. Your guidance helps a lot.

   Posted 5 years ago #

4. khoslaygr26
   

   Member
   Joined: Nov '18
   Posts: 2

   Hi

   I have a doubt regarding the parameter medium.alpha_coeff. The unit mentioned is dBcm-1Mhz-y, can anybody tell me if i have a 40Khz source sensor, will the attenuation coefficient still be the same, because most materials refer to the attenuation coefficient around 1 for 1MHZ, will it be the same even for a lower frequency?

   Thank you.

   Posted 5 years ago #

5. wenxiu
   

   Member
   Joined: Jul '18
   Posts: 6

   Hi khoslaygr26,

   I recommend you to read the reference in the k-wave's user manual:
   J. C. Bamber, \Attenuation and Absorption," in Physical Principles of Medical Ultrasound
   (C. R. Hill, J. C. Bamber, and G. R. ter Haar, eds.), pp. 93{166, Chichester: John Wiley,
   2004

   I met the similar question with yours several days before.And I choose water as the medium.
   The attenuation coefficient is determined by frequency, and the relationship is very complex. But the attenuation coefficient could be thought as linear to the square of frequency with a certain range. So the medium.alpha_power can be set as 2.
   As for your question. I suggest you to find the references about the material you chosen. Choosing the approximated values of medium.alpha_power and medium.alpha_coeff.

   Wenxiu

   Posted 5 years ago #

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