http://www.k-wave.org/forum/topic/can-help-identify-the-signal-stream-tailed-for-an-heterogeneous-propagating-medi Support for the k-Wave MATLAB toolbox en-US Tue, 12 May 2026 23:40:24 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/can-help-identify-the-signal-stream-tailed-for-an-heterogeneous-propagating-medi#post-384 Mon, 12 Mar 2012 15:53:41 +0000 bencox 384@http://www.k-wave.org/forum/ <p>Hi Eldhose,</p> <p>This looks correct. The 'tails' are just the reflections from where the impedance changes due to the change in sound speed.</p> <p>(There will be a slight tail even in the homogeneous case due to the fact that the example is in 2D and acoustic waves in 2D have tails - they never quite return to zero.)</p> <p>Ben </p> http://www.k-wave.org/forum/topic/can-help-identify-the-signal-stream-tailed-for-an-heterogeneous-propagating-medi#post-383 Sun, 11 Mar 2012 15:03:05 +0000 eldhochhan 383@http://www.k-wave.org/forum/ <p>Hi Brad,</p> <p>Thanks for the options given out to try. </p> <p>I have tried setting the PML layer outside the domain as you have advised together with a smaller input frequency of 7MHz since the filter cut off frequency is 7.4MHz. But its still looks the same. </p> <p>May be you can help me explain why these tailoring signals occur in the results of the example "Heterogeneous Propagation Medium Example" of Initial Value Problems inside the toolbox.</p> <p>I have pasted a link of the result after running the example exactly as it is in the toolbox.</p> <p><a href="http://tinypic.com/r/122c00m/5" rel="nofollow">http://tinypic.com/r/122c00m/5</a></p> <p>Thanks,<br /> Eldhose </p> http://www.k-wave.org/forum/topic/can-help-identify-the-signal-stream-tailed-for-an-heterogeneous-propagating-medi#post-375 Thu, 08 Mar 2012 23:11:25 +0000 Bradley Treeby 375@http://www.k-wave.org/forum/ <p>Hi Eldhose,</p> <p>A few points:</p> <p>1. Your 10 MHz input signal is almost completely removed by the call to <code>filterTimeSeries</code>. If you look at the command line outputs you can see the maximum frequency supported by the grid is 11.1 MHz while the filter cutoff frequency is 7.4 MHz.</p> <p>2. For this type of simulation, you would most likely want to use the default PML settings unless you are trying to simulate a plane wave (see Ben's comments above).</p> <p>3. Part of your detector is within the PML. Either use a smaller detector, or set <code>&#39;PMLInside&#39;</code> to <code>false</code>.</p> <p>4. It seems most of the lower section of your computational domain is not used (homogeneous sound speed and no source or detector points). You could speed up your simulations by using a smaller domain. </p> <p>I hope that helps,</p> <p>Brad. </p> http://www.k-wave.org/forum/topic/can-help-identify-the-signal-stream-tailed-for-an-heterogeneous-propagating-medi#post-370 Thu, 08 Mar 2012 11:18:43 +0000 eldhochhan 370@http://www.k-wave.org/forum/ <p>Hi Ben</p> <p>The source code of the program is given below:</p> <p>clear all;<br /> close all;<br /> clc;</p> <p>% =========================================================================<br /> % SIMULATION<br /> % =========================================================================</p> <p>% create the computational grid<br /> Nx = 600; % number of grid points in the x (row) direction<br /> Ny = 600; % number of grid points in the y (column) direction<br /> dx = 6.52e-5; % grid point spacing in the x direction [m]<br /> dy = 6.52e-5; % grid point spacing in the y direction [m]<br /> kgrid = makeGrid(Nx, dx, Ny, dy);</p> <p>% define the properties of the propagation medium (Mucosa and Submucosa)<br /> medium.sound_speed = 1500*ones(Nx, Ny); % [m/s]<br /> medium.sound_speed(300:315,:) = 1500; % [m/s]<br /> medium.density = 1000*ones(Nx, Ny); % [kg/m^3]<br /> medium.density(300:315,:) = 1200; % [kg/m^3]<br /> %medium.alpha_power = 1.5;<br /> %medium.alpha_coeff = 1.8; % [dB/(MHz^y cm)]</p> <p>% define the properties of the propagation medium (Muscle)<br /> medium.sound_speed(316:329,:) = 1580; % [m/s]<br /> medium.density(316:329,:) = 1000; % [kg/m^3]</p> <p>% define the properties of the propagation medium (Fat)<br /> medium.sound_speed(330:335,:) = 1450; % [m/s]<br /> medium.density(330:335,:) = 910; % [kg/m^3]</p> <p>% define the properties of the propagation medium (Water)<br /> medium.sound_speed(336:end,:) = 1482; % [m/s]<br /> medium.density(336:end,:) = 1000; % [kg/m^3] </p> <p>% create the time array<br /> [kgrid.t_array, dt] = makeTime(kgrid, medium.sound_speed);<br /> Nt = length(kgrid.t_array);</p> <p>% define a single source element<br /> source.p_mask = zeros(Nx, Ny);<br /> source.p_mask( Nx/2, Ny/2) = 1;</p> <p>% define a time varying sinusoidal source<br /> source_freq = 10e6; % [Hz]<br /> source_mag = 15; % [au]<br /> source.p = source_mag*sin(2*pi*source_freq*kgrid.t_array);</p> <p>% smooth the source<br /> source.p = filterTimeSeries(kgrid, medium, source.p);</p> <p>% define a centered circular sensor<br /> sensor_x_pos = Nx/2; % [grid points]<br /> sensor_y_pos = Ny/2; % [grid points]<br /> sensor_radius = 290; % [m]<br /> sensor_arc_angle = pi;<br /> sensor.mask = makeCircle(Nx, Ny, sensor_x_pos, sensor_y_pos, sensor_radius, sensor_arc_angle);</p> <p>% run the simulation<br /> sensor_data = kspaceFirstOrder2D(kgrid, medium, source, sensor, 'PlotLayout', true, 'PMLAlpha', [0 2]);</p> <p>% =========================================================================<br /> % VISUALISATION<br /> % =========================================================================</p> <p>% plot the simulated sensor data<br /> figure;<br /> imagesc(sensor_data, [-1, 1]);<br /> colormap(getColorMap);<br /> ylabel('Sensor Position');<br /> xlabel('Time Step');<br /> colorbar;</p> <p>Thanks,<br /> Eldhose </p> http://www.k-wave.org/forum/topic/can-help-identify-the-signal-stream-tailed-for-an-heterogeneous-propagating-medi#post-369 Thu, 08 Mar 2012 11:08:24 +0000 bencox 369@http://www.k-wave.org/forum/ <p>Hi Eldhose,</p> <p>Mmm. I'm afraid I can't tell what's going on without more details of the simulation you're running. Can you post your code and I'll run it and see if I spot anything obvious.</p> <p>Thanks,</p> <p>Ben </p> http://www.k-wave.org/forum/topic/can-help-identify-the-signal-stream-tailed-for-an-heterogeneous-propagating-medi#post-366 Thu, 08 Mar 2012 04:14:24 +0000 eldhochhan 366@http://www.k-wave.org/forum/ <p>Hi Ben,</p> <p>I have tried to set the input parameter PMLAlpha [0,2] as per your previous comment. Now i am seeing a totally different effect as you have suspected.</p> <p><a href="http://tinypic.com/r/210ivj4/5" rel="nofollow">http://tinypic.com/r/210ivj4/5</a></p> <p>Thanks,<br /> Eldhose </p> http://www.k-wave.org/forum/topic/can-help-identify-the-signal-stream-tailed-for-an-heterogeneous-propagating-medi#post-365 Wed, 07 Mar 2012 20:29:25 +0000 bencox 365@http://www.k-wave.org/forum/ <p>Hi Eldhose</p> <p>Try this line instead. </p> <p>sensor_data = kspaceFirstOrder2D(kgrid, medium, source, sensor, 'PlotLayout', true, 'PMLAlpha', [0 2]);</p> <p>I think you were just asking the program not to plot the absorbing boundary layer region, but you weren't actually turning it off. If you want to use a plane wave exactly aligned to the grid then by turning off the PML where it reaches the edges you can simulate a true (infinite) plane wave, as the spectral gradient calculations in the code will implicitly make the function periodic.</p> <p>Does this solve the problem, or was it another effect you were seeing?</p> <p>Ben </p> http://www.k-wave.org/forum/topic/can-help-identify-the-signal-stream-tailed-for-an-heterogeneous-propagating-medi#post-364 Wed, 07 Mar 2012 13:49:57 +0000 eldhochhan 364@http://www.k-wave.org/forum/ <p>Hi Ben,</p> <p>sensor_data = kspaceFirstOrder2D(kgrid, medium, source, sensor, 'PlotLayout', true, 'PlotPML', false);</p> <p>This is how i have defined the sensor_data in the program. And i believe that the PML layer is turned off.</p> <p>Thanks,<br /> Eldhose </p> http://www.k-wave.org/forum/topic/can-help-identify-the-signal-stream-tailed-for-an-heterogeneous-propagating-medi#post-362 Wed, 07 Mar 2012 11:08:22 +0000 bencox 362@http://www.k-wave.org/forum/ <p>Hi Eldhose,</p> <p>Is it a PML issue? Try turning off the PML on the two sides to see if it goes away.</p> <p>Ben </p> http://www.k-wave.org/forum/topic/can-help-identify-the-signal-stream-tailed-for-an-heterogeneous-propagating-medi#post-359 Wed, 07 Mar 2012 09:05:00 +0000 eldhochhan 359@http://www.k-wave.org/forum/ <p>Hi Ben and Bradely,</p> <p>I was trying to stimulate the example Heterogeneous Propagation medium with a few layers of different sound speed and density. And there is actually an extra stream of signal that follows the actual signal. I dont really get the reason for this. Could you please help me explain??</p> <p>The pic of the result is uploaded in this link:<br /> <a href="http://tinypic.com/r/o86r5s/5" rel="nofollow">http://tinypic.com/r/o86r5s/5</a></p> <p>Thanks,<br /> Eldhose </p>