http://www.k-wave.org/forum/topic/sudden-loss-of-signal-after-some-depth Support for the k-Wave MATLAB toolbox en-US Tue, 12 May 2026 22:02:58 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/sudden-loss-of-signal-after-some-depth#post-8989 Wed, 13 Dec 2023 22:57:04 +0000 binpersonal 8989@http://www.k-wave.org/forum/ <p>Dr.Treeby, also, the <code>no_dispersion</code> flag doesn't seem to help the sudden loss of signal, with the <code>medium.alpha_power = 1.0001</code> and <code>no_dispersion</code> flag, there is still loss of signal after some depth, but with <code>medium.alpha_power = 1.1</code>, there is no loss.</p> <p>I somehow can not set <code>medium.alpha_power = 1</code> with <code>no_dispersion</code> flag or without. It produces errors. </p> http://www.k-wave.org/forum/topic/sudden-loss-of-signal-after-some-depth#post-8988 Wed, 13 Dec 2023 22:02:39 +0000 binpersonal 8988@http://www.k-wave.org/forum/ <p>Thanks! Is there a way to simulate <code>medium.alpha_power = 1</code> ? Even I set the <code>no_dispersion</code> flag, I still can not set <code>medium.alpha_power = 1</code>, K-Wave generates errors. </p> http://www.k-wave.org/forum/topic/sudden-loss-of-signal-after-some-depth#post-8983 Tue, 12 Dec 2023 10:42:21 +0000 Bradley Treeby 8983@http://www.k-wave.org/forum/ <p>If you want the waves to travel at <code>medium.sound_speed</code>, I'd suggest setting the <code>no_dispersion</code> flag. Otherwise, keep increasing <code>t_end</code>, or do a calculation for what the dispersive sound speed is based on power law, e.g., using <code>powerLawKramersKronig</code>. </p> http://www.k-wave.org/forum/topic/sudden-loss-of-signal-after-some-depth#post-8982 Fri, 08 Dec 2023 01:04:40 +0000 binpersonal 8982@http://www.k-wave.org/forum/ <p>Thanks! What is the suitable simulation time (<code>t_end</code>) for <code>medium.alpha_power = 1.001</code>? </p> <p>I found the problem is due to <code>medium.alpha_power</code>, if I change <code>medium.alpha_power = 1.1</code>, there is no sudden loss of signal. </p> http://www.k-wave.org/forum/topic/sudden-loss-of-signal-after-some-depth#post-8954 Fri, 24 Nov 2023 17:28:36 +0000 Bradley Treeby 8954@http://www.k-wave.org/forum/ <p>I haven't run your simulation, but I suspect it's because you also need to change the simulation time (<code>t_end</code>) to be long enough for the waves to reach the bottom of the image and back. You likely see a change as you change the attenuation value, as this also changes the sound speed due to dispersion. This is especially true close to y = 1. If you don't want this behaviour, you can set <code>medium.alpha_mode = &#39;no_dispersion&#39;</code>. </p> http://www.k-wave.org/forum/topic/sudden-loss-of-signal-after-some-depth#post-8943 Tue, 07 Nov 2023 18:12:28 +0000 binpersonal 8943@http://www.k-wave.org/forum/ <p>It seems the sudden loss/decrease of signal is related to medium.alpha_coeff, if I use 0.3 for attenuation, the depth of sudden loss of signal increases (around 11000 sample points at 200 MHz sampling rate).</p> <p>I don't understand why there is a sudden decrease (completely black in B mode, but not zero), not gradually decrease in amplitude due to attenuation? </p> http://www.k-wave.org/forum/topic/sudden-loss-of-signal-after-some-depth#post-8942 Tue, 07 Nov 2023 06:30:37 +0000 binpersonal 8942@http://www.k-wave.org/forum/ <p>Dear Sir or Madam,</p> <p>I observed sudden loss of signal after a certain depth after I changed the B-mode linear array example. I can see the variations in speed map and density map up to 60 mm after plot, however, the beamformed scanline data suddenly drops after around 38.5 mm (around 10000 sample points at 200 MHz sampling rate), and the B-mode image becomes suddenly black after around 38.5 mm, and I didn't observe the gradually changes due to attenuation either.</p> <p>I think I used enough t_end, below are the changes I made: </p> <pre><code>% set the size of the perfectly matched layer (PML) pml_x_size = 10; % [grid points] pml_y_size = 5; % [grid points] pml_z_size = 5; % [grid points] % set total number of grid points not including the PML Nx = 128*10 - 2 * pml_x_size; % [grid points] Ny = 128*3 - 2 * pml_y_size; % [grid points] Nz = 128 - 2 * pml_z_size; % [grid points] % set desired grid size in the x-direction not including the PML x = 60e-3; % [m] % calculate the spacing between the grid points dx = x / Nx; % [m] dy = dx; % [m] dz = dx; % [m] fs = 200 e6; t_end = (Nx * dx) * 2.1 / c0); kgrid.t_array = 0:1/fs:t_end; tone_burst_freq = 3e6; tone_burst_cycles = 2; medium.alpha_coeff = 0.5; medium.alpha_power = 1.001; transducer.number_elements = 64; % total number of transducer elements transducer.element_width = 4; % width of each element [grid points] transducer.element_length = 72; % length of each element [grid points] transducer.element_spacing = 1; % spacing (kerf width) between the elements [grid points] transducer.focus_distance = 30e-3; % focus distance [m] transducer.elevation_focus_distance = 29e-3; % focus distance in the elevation plane [m] number_scan_lines = 64; number_active_elements = 64;</code></pre> <p>I also removed the all the highly scattering regions from the example.Others lines are copied from the example.</p> <p>Is there any settings I did wrong? Anyone run into similar problems? </p>