http://www.k-wave.org/forum/topic/reflected-wave-that-in-the-received-signal-does-not-make-sense Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 03:13:24 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/reflected-wave-that-in-the-received-signal-does-not-make-sense#post-5679 Wed, 14 Sep 2016 08:55:25 +0000 Bradley Treeby 5679@http://www.k-wave.org/forum/ <p>Hi ssg47,</p> <p>With this configuration, there is no way to remove the edge wave, as it's part of the physics! However, you could appodize the source pressure to reduce the effects, i.e., by assigning the variation of the source magnitude over the line as a Gaussian. Alternatively, you could use a velocity source instead of a pressure source which will be more directional (a velocity source is used in the transducer model).</p> <p>Brad. </p> http://www.k-wave.org/forum/topic/reflected-wave-that-in-the-received-signal-does-not-make-sense#post-5672 Sat, 10 Sep 2016 15:18:52 +0000 ssg47 5672@http://www.k-wave.org/forum/ <p>Also I wanted to add that, when I add a layer that is of different acoustic impedance infront of the target, I see reflections but I can't be sure if its from the main excitation signal or the edge wave. This is why it is important for me to get rid of edge wave. </p> http://www.k-wave.org/forum/topic/reflected-wave-that-in-the-received-signal-does-not-make-sense#post-5671 Sat, 10 Sep 2016 12:38:12 +0000 ssg47 5671@http://www.k-wave.org/forum/ <p>Is there any way to get rid of it or would I have to use a transducer model? I see that you don't get edge wave when I run one of the ultrasound examples with a transducer. </p> <p>Thanks! </p> http://www.k-wave.org/forum/topic/reflected-wave-that-in-the-received-signal-does-not-make-sense#post-5668 Fri, 09 Sep 2016 21:32:39 +0000 Bradley Treeby 5668@http://www.k-wave.org/forum/ <p>Hi ssg47,</p> <p>This is not a reflection, but the edge wave from the transducer. If you turn on plotting and set <code>&#39;PlotScale&#39;, [-1 1]*source_strength</code>, you should see what I mean.</p> <p>Hope that helps,</p> <p>Brad. </p> http://www.k-wave.org/forum/topic/reflected-wave-that-in-the-received-signal-does-not-make-sense#post-5660 Thu, 08 Sep 2016 23:15:00 +0000 ssg47 5660@http://www.k-wave.org/forum/ <p>Hi Dr. Treeby,<br /> I am doing plane wave simulation and have a homogenous medium with two point scatterers with different acoustic impedance. The received waveform has the original excitation signal and a small reflection followed by the signal from the scatterers. I am not sure where the reflection is from. I have the PML layer set outside with PML_alpha with the default value of 2. I have tried setting PML alpha value [0 2] and it didn't work. I posted the code below and here is the received signal at the sensor:<br /> <a href="http://tinypic.com/r/ix409h/9" rel="nofollow">http://tinypic.com/r/ix409h/9</a></p> <p>% create the computational grid<br /> clear all;<br /> pml_x_size = 20;<br /> pml_y_size = 20;<br /> Nx = 256 - 2*pml_x_size;<br /> Ny = 96 - 2*pml_y_size;<br /> dx = 0.2e-3;<br /> dy = 0.2e-3;<br /> kgrid = makeGrid(Nx, dx, Ny, dy);<br /> gridx_pts =11;<br /> c0 = 1540; % [m/s]<br /> rho0 = 1000; % [kg/m^3]<br /> medium.sound_speed_ref = c0;<br /> medium.alpha_power = 1.2;<br /> medium.alpha_coeff = 0.75;<br /> %medium.alpha_mode = 'no_absorption';</p> <p>t_end = (Nx*dx)*2.4/c0; % [s]<br /> kgrid.t_array = 0:15e-9:t_end;<br /> source_strength = 1e6; % [Pa]<br /> tone_burst_freq = 1.875e6; % [Hz]<br /> tone_burst_cycles = 5;<br /> input_signal = source_strength*toneBurst(1/kgrid.dt, tone_burst_freq, tone_burst_cycles);</p> <p>source.p_mask = zeros(Nx,Ny);<br /> num_elements = 48; % [grid points]<br /> x_offset = 1 ; % [grid points]<br /> start_index = Ny/2 - round(num_elements/2) + 1;<br /> source.p_mask(x_offset, start_index:start_index + num_elements - 1) = 1;<br /> source.p = input_signal;<br /> sensor.mask = zeros(Nx,Ny);<br /> sensor.mask(x_offset, start_index:start_index + num_elements - 1) = 1;</p> <p>sound_speed_map = c0*ones(Nx, Ny);<br /> density_map = rho0*ones(Nx, Ny);<br /> cwire = 3000;<br /> scattering_rho0 = cwire/1.5;<br /> xc = Nx - 5;<br /> yc = (floor(Ny/2));</p> <p>scattering_region5 = makeDisc(Nx, Ny, xc-14, yc,1); %<br /> scattering_region6 = makeDisc(Nx, Ny, xc-8, yc+4,1);<br /> sound_speed_map(scattering_region5 == 1) = cwire;<br /> density_map(scattering_region5 == 1) = scattering_rho0;<br /> sound_speed_map(scattering_region6 == 1) = cwire;<br /> density_map(scattering_region6 == 1) = scattering_rho0;</p> <p>Ls = round(kgrid.Nt/2); % sample size<br /> input_args = {'PMLInside', false, 'PMLSize', [pml_x_size, pml_y_size],'PlotSim',false,'PlotScale',[-10 10]};<br /> medium.sound_speed = sound_speed_map;<br /> medium.density = density_map;<br /> sensor_data = kspaceFirstOrder2D(kgrid, medium, source, sensor,input_args{:}); % collect data for image<br /> sd = sensor_data(2,:);<br /> plot(sd) </p>