http://www.k-wave.org/forum/topic/questions-about-the-code-for-defining-the-attenuation-and-the-simulation-error Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 06:46:24 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/questions-about-the-code-for-defining-the-attenuation-and-the-simulation-error#post-7819 Sat, 12 Sep 2020 13:33:42 +0000 saya mizutani 7819@http://www.k-wave.org/forum/ <p>Thank you very much, Brad.</p> <p>Saya </p> http://www.k-wave.org/forum/topic/questions-about-the-code-for-defining-the-attenuation-and-the-simulation-error#post-7817 Fri, 11 Sep 2020 18:06:35 +0000 Bradley Treeby 7817@http://www.k-wave.org/forum/ <p>You can set medium.alpha_coeff as a matrix in the same way as medium.sound_speed etc. Note that medium.alpha_power must be a scalar. </p> http://www.k-wave.org/forum/topic/questions-about-the-code-for-defining-the-attenuation-and-the-simulation-error#post-7816 Fri, 11 Sep 2020 16:10:16 +0000 saya mizutani 7816@http://www.k-wave.org/forum/ <p>Hi Brad,</p> <p>Thank you for your reply.I'm sorry for missing the description what BWI is.<br /> I just tried to run the simulation after fixing the time step and it worked!<br /> I really appreciate your helpful advice.</p> <p>I actually have one more question.<br /> I would like to set the different attenuation coefficients for each region. Is there any instruction for that? (Could I do that?)</p> <p>Saya </p> http://www.k-wave.org/forum/topic/questions-about-the-code-for-defining-the-attenuation-and-the-simulation-error#post-7802 Fri, 11 Sep 2020 09:52:04 +0000 Bradley Treeby 7802@http://www.k-wave.org/forum/ <p>Hi Saya,</p> <p>I can't run your code (it's missing what BWI is), but I'm guessing it's because the simulation becomes unstable. Try reducing the CFL / size of the time step. You can check for the maximum stable time step using <code>checkStability</code>.</p> <p>Brad </p> http://www.k-wave.org/forum/topic/questions-about-the-code-for-defining-the-attenuation-and-the-simulation-error#post-7778 Sat, 29 Aug 2020 06:10:51 +0000 saya mizutani 7778@http://www.k-wave.org/forum/ <p>Hi, Thank you for letting me use the amazing toolbox.<br /> I have a question.</p> <p>Is it right that all I have to do for defining the attenuation parameters in the simulation is adding the following two codes after defining the sound speeds?</p> <p>medium.alpha_coeff = 2; % [dB/(MHz^y cm)]<br /> medium.alpha_power = 1.05; </p> <p>Without the attenuation definition, the simulation works. However, once I defined the attenuation parameters, it doesn't work because of these errors.<br /> ----------------------------------------------------------------------------------<br /> error : waitbar (line 100)<br /> The second argument must be a message string or a handle to an existing waitbar.</p> <p>error : kspaceFirstOrder2D (line 964)<br /> waitbar(t_index / kgrid.Nt, pbar);<br /> ----------------------------------------------------------------------------------<br /> How can I solve it?<br /> Let me put my simulation code below.<br /> Thank you in advance.</p> <p>%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%My code%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%<br /> % % Define sound speed at every grid points<br /> sound_speed = 340; %[m/s] : base<br /> medium.sound_speed = sound_speed * ones(Nx,Ny); % 340 [m/s]<br /> medium.sound_speed = medium.sound_speed + BWI * 1200; % 1540[m/s]<br /> medium.sound_speed = medium.sound_speed + BWI1 * 102; % 1567[m/s]<br /> medium.sound_speed = medium.sound_speed + BWI2 * 147; % 1612[m/s]<br /> medium.sound_speed = medium.sound_speed + BWI3 * 147; % 1612[m/s]<br /> medium.sound_speed = medium.sound_speed + BWI4 * 125; % 1590[m/s]<br /> medium.sound_speed = medium.sound_speed + BWI5 * 35; % 1500[m/s]<br /> medium.sound_speed = medium.sound_speed + BWI6 * 119; % 1584[m/s]<br /> medium.sound_speed = medium.sound_speed + BWI7 * 119; % 1584[m/s]<br /> medium.sound_speed = medium.sound_speed + BWI8 * 35; % 1575[m/s]<br /> medium.sound_speed = medium.sound_speed - BWI9 * 110; % 1465[m/s]<br /> medium.sound_speed = medium.sound_speed + BWI10 * 2060; % 3635[m/s]</p> <p>% medium.sound_speed = 1540 * ones(Nx,Ny);</p> <p>% create a duplicate of the propagation medium structure and append the<br /> % absorption properties<br /> medium.sound_speed_ref = 1540; %[m/s]<br /> medium.alpha_coeff = 2; % [dB/(MHz^y cm)]<br /> medium.alpha_power = 1.05; </p> <p>% make time array<br /> % t_end should be longer than Nx*dx/slowest_sound_speed<br /> t_end = 4e-4; % [s]<br /> cfl = 1540*10^(-7)/dx; % the basical sound speed is 1540 [m/s]<br /> kgrid.makeTime(1540,cfl,t_end);</p> <p>% Define 1050[kg/m^3] as density at every grid points<br /> medium.density = 1050 * ones(Nx, Ny); % [kg/m^3]</p> <p>% % send the pulse<br /> smask = zeros(Nx,Ny);<br /> % cordination of the source<br /> source_x = 0.0003; %[m]<br /> source_y = -0.0096; %[m]<br /> % % in case the number of grid points is odd<br /> source_grid_x = round(Nx/2 + source_cordination_x/dx);<br /> source_grid_y = round(Ny/2 + source_cordination_y/dy);</p> <p>source_cordination_x = kgrid.x(source_grid_x,source_grid_y);<br /> source_cordination_y = kgrid.y(source_grid_x,source_grid_y);<br /> smask(source_grid_x,source_grid_y) = 1;<br /> source.p_mask = smask;</p> <p>source_strength = 10; % [Pa]<br /> tone_burst_freq = 1e6; % [Hz]<br /> tone_burst_cycles = 5;<br /> sampling_freq = 1/kgrid.dt;<br /> toneBurst(sampling_freq, tone_burst_freq, tone_burst_cycles, 'Plot', true);<br /> % create the input signal using toneBurst<br /> source.p = source_strength .* toneBurst(sampling_freq, tone_burst_freq, tone_burst_cycles);<br /> source_capsule = source.p; </p> <p>[max_source,index_source] = max(source.p);</p> <p>%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%<br /> %Define the sensor<br /> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%<br /> Edge = imread('Edge.jpg');<br /> sp = Edge;<br /> [row,col,v] = find(sp);<br /> tx = kgrid.x(row,col);<br /> ty = kgrid.y(row,col);<br /> transx = tx(:,1);<br /> transy = ty(1,:);<br /> number_of_elements = size(v,1);<br /> % define a centered circular sensor<br /> sensor.mask = sp;</p> <p>% run the simulation with optional inputs for plotting the simulation<br /> % layout in addition to removing the PML from the display<br /> sensor_data = kspaceFirstOrder2D(kgrid, medium, source, sensor, ...<br /> 'PlotLayout', true, 'PlotPML', false, 'RecordMovie',true,'PlotSim',true,'DataCast','gpuArray-single');<br /> sensor_data = gather(sensor_data);</p> <p>Saya Mizutani </p>