k-Wave

1. aall
   

   Member
   Joined: Apr '14
   Posts: 3

   Hi,

   My simulation is based on the example_us_bmode_phased_array.
   The scattering region is located at 160mm from the transducer.
   The spectrum of the transmitted signal is shifted by 3MHz, far more than the expected (according to literature - hundreds Hz).

   The transmitted signal properties:
   ----------------------------------
   source_strength = 1e6; % [Pa]
   tone_burst_freq = 4e6/sc; % [Hz]
   tone_burst_cycles = 3;

   Medium properties:
   ------------------
   medium.alpha_coeff = 0.75; % [dB/(MHz^y cm)]
   medium.alpha_power = 1.05;
   % mediun.alpha_mode = 'no_dispersion';
   % medium.BonA = 6;

   Any suggestions?

   Thanks!

   Posted 10 years ago #

2. Bradley Treeby
   

   Developer
   Joined: Mar '10
   Posts: 1,643

   Hi aall,

   I'm not sure I completely understand your question. Do you mean that you transmit an ultrasound signal centred around 4 MHz, and then receive one centred around 1 MHz? What is the maximum supported frequency for your simulation? This is printed to the command line, or you can work it out by:

   f_max = min(medium.sound_speed(:))/(2*kgrid.dx)

   Do you get the same result if you make the simulation lossless by not specifying the absorption parameters?

   Brad.

   Posted 10 years ago #

3. aall
   

   Member
   Joined: Apr '14
   Posts: 3

   Hi Brad,
   Thank you very much for your responding.
   What you wrote is what i got in the simulation result.
   I took in account the maximum frequency (which is around 9 MHz).
   I will run the simulation you recommended, but the thing is that we want to see the frequency shift, which supposed to be around 400 KHz.
   I think they may be differences between the attenuation model I know and the one in k-wave.
   i would like to know how it was implemented in k-wave? i.e. the attenuation as a function of: frequency, distance, alpha_power and alpha_coefficient.

   Thanks,
   Almog.

   Posted 10 years ago #

4. Bradley Treeby
   

   Developer
   Joined: Mar '10
   Posts: 1,643

   Hi Almog,

   The absorption model is described here and here.

   I agree the result seems peculiar. How do you measure the frequency shift?

   Brad.

   Posted 10 years ago #

5. aall
   

   Member
   Joined: Apr '14
   Posts: 3

   Hi Brad,
   Sorry for the delay (we had a holiday), and thanks again for your reply.
   In order to measure the frequency shift, i simply do FFT on the sensor_data of one element, or FFT on the scan_line. Then I can see clearly the Gaussian is around 1MHz.
   I'll go over the articles you sent me.

   Almog.

   Posted 10 years ago #

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