http://www.k-wave.org/forum/topic/reflected-echoes-not-absorbed-by-the-pml Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 01:50:28 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/reflected-echoes-not-absorbed-by-the-pml#post-5516 Thu, 26 May 2016 18:43:30 +0000 ssg47 5516@http://www.k-wave.org/forum/ <p>That worked! Thank you so much! </p> http://www.k-wave.org/forum/topic/reflected-echoes-not-absorbed-by-the-pml#post-5515 Thu, 26 May 2016 16:24:48 +0000 Bradley Treeby 5515@http://www.k-wave.org/forum/ <p>Hi Susan,</p> <p>Is this a plot scale issue? The PML with the default parameters will reduce the amplitude of the incoming waves by 3 to 4 orders of magnitude. However, with <code>&#39;PlotScale&#39;, &#39;auto&#39;</code>, as soon as the wave has left the domain, you will see the remaining waves, even though they are very small. What about if you try to set a fixed plot scale?</p> <p>Brad. </p> http://www.k-wave.org/forum/topic/reflected-echoes-not-absorbed-by-the-pml#post-5513 Tue, 24 May 2016 19:11:49 +0000 ssg47 5513@http://www.k-wave.org/forum/ <p>Hi Dr.Treeby,<br /> I have running a simple code shown below. I have set ample simulation time, and made sure the all the other parameters are met for stable simulations. But there seems to be an issue towards the end of my simulation. The reflected waves are not absorbed by the PML layer close to the sensor mask. I have tried increasing the PMLAlpha value but didn't see any difference. I'm afraid it might be affecting the results I am supposed to be getting. Any help would be appreciated!<br /> Thanks, Susan<br /> <pre><code>% create the computational grid clear all; pml_x_size = 20; pml_y_size = 20; Nx = 256 - 2*pml_x_size; Ny = 96 - 2*pml_y_size; dx = 0.2e-3; % grid point spacing in the x direction [m] dy = 0.2e-3; % grid point spacing in the y direction [m] kgrid = makeGrid(Nx, dx, Ny, dy); gridx_pts =11; c0 = 1540; % [m/s] rho0 = 1000; % [kg/m^3] medium.sound_speed_ref = c0; medium.alpha_coeff = 0.75; % [dB/(MHz^y cm)] medium.alpha_power = 1.5; %medium.alpha_mode = &#39;no_absorption&#39;; t_end = (Nx*dx)*2.4/c0; % [s] kgrid.t_array = 0:15e-9:t_end; source_strength = 1e6; % [Pa] tone_burst_freq = 1.875e6; % [Hz] tone_burst_cycles = 5; input_signal = source_strength*toneBurst(1/kgrid.dt, tone_burst_freq, tone_burst_cycles); source.p_mask = zeros(Nx,Ny); num_elements = 32; % [grid points] x_offset = 1 ; % [grid points] start_index = Ny/2 - round(num_elements/2) + 1; source.p_mask(x_offset, start_index:start_index + num_elements - 1) = 1; source.p = input_signal; sensor.mask = zeros(Nx,Ny); sensor.mask(x_offset, start_index) = 1; sensor.mask(x_offset,18) = 1; %% Ny_tot = Ny+(41); Nx_tot = Nx; sound_speed_map = c0*ones(Nx_tot, Ny_tot); density_map = rho0*ones(Nx_tot, Ny_tot); cwire = 3000; scattering_rho0 = cwire/1.5; % define the fishing wire point radius = 0.4e-3; % [m] xc = Nx_tot - 5; yc = floor(Ny_tot/2); %scattering_region = makeCircle(Nx_tot, Ny_tot, xc, yc,radius,&#39;true&#39;); scattering_region = makeDisc(Nx_tot, Ny_tot, xc, yc,1,&#39;true&#39;); % results %are not clean if you use makeDisc % assign scatterer the properties sound_speed_map(scattering_region == 1) = cwire; density_map(scattering_region == 1) = scattering_rho0; %% input_args = {&#39;PMLInside&#39;, false, &#39;PMLSize&#39;, [pml_x_size, pml_y_size],&#39;PlotSim&#39;,false,&#39;PlotScale&#39;,&#39;auto&#39;}; psny = 1; medium.sound_speed = sound_speed_map(:,psny:psny+Ny-1); medium.density = density_map(:,psny:psny+Ny-1); sensor_data = kspaceFirstOrder2D(kgrid, medium, source, sensor,input_args{:});</code></pre>