k-Wave User Forum » Topic: Problem met with when simulating small scatters

k-Wave User Forum » Topic: Problem met with when simulating small scatters http://www.k-wave.org/forum/topic/problem-met-with-when-simulating-small-scatters Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 09:00:13 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://www.k-wave.org/forum/search.php cryospherewang@163.com on "Problem met with when simulating small scatters" http://www.k-wave.org/forum/topic/problem-met-with-when-simulating-small-scatters#post-7683 Thu, 02 Jul 2020 21:12:51 +0000 cryospherewang@163.com 7683@http://www.k-wave.org/forum/ Hi Brad, Thanks for your response. Yes, the source signal comes from the transducer. Please see the image of the scatter <a href="https://i.imgur.com/4bxiUHx.jpg" rel="nofollow">https://i.imgur.com/4bxiUHx.jpg</a>. the image of the sensor data (Time series * Element) after the same windowing operation as your examples <a href="https://i.imgur.com/CqnxG1a.jpg" rel="nofollow">https://i.imgur.com/CqnxG1a.jpg</a> and the plot of a single element sensor data (Magnitude * Time series) <a href="https://i.imgur.com/wNH7Lty.jpg" rel="nofollow">https://i.imgur.com/wNH7Lty.jpg</a> It can be seen that the response I got has some unreasonable components, could you please tell me whether there are some errors in my simulation that result in such weird echoes? Thank you very much. Best, Bingxue Bradley Treeby on "Problem met with when simulating small scatters" http://www.k-wave.org/forum/topic/problem-met-with-when-simulating-small-scatters#post-7551 Sat, 06 Jun 2020 13:25:39 +0000 Bradley Treeby 7551@http://www.k-wave.org/forum/ Hi Bing, Could you post a picture? Is it the source signal from the transducer, i.e., the waves travelling directly from the source to the sensor across the face of the transducer? Brad. cryospherewang@163.com on "Problem met with when simulating small scatters" http://www.k-wave.org/forum/topic/problem-met-with-when-simulating-small-scatters#post-7490 Sat, 09 May 2020 17:34:10 +0000 cryospherewang@163.com 7490@http://www.k-wave.org/forum/ Hi Brad, Thanks for your reply! The signals do not make sense before windowing. I tried version 1.3 and ran the same script, unfortunately, the unreasonable strong signals that can mask the weak echoes from a single, small scatter still exist. I am not sure is that because the frequency response of a small scatter is infinite and this will introduce some problems. Regards, Bing Bradley Treeby on "Problem met with when simulating small scatters" http://www.k-wave.org/forum/topic/problem-met-with-when-simulating-small-scatters#post-7463 Fri, 01 May 2020 09:19:14 +0000 Bradley Treeby 7463@http://www.k-wave.org/forum/ Hi Bing, I haven't run your code. Do you signals make sense before the windowing operation? Note, if you're using k-Wave V1.3, combine_sensor_data is automatically called inside kspaceFirstOrder3DC/G. Brad. cryospherewang@163.com on "Problem met with when simulating small scatters" http://www.k-wave.org/forum/topic/problem-met-with-when-simulating-small-scatters#post-7386 Sun, 12 Apr 2020 13:52:33 +0000 cryospherewang@163.com 7386@http://www.k-wave.org/forum/ I just tried to play with k-Wave using different parameters and see what happened. Then when I was simulating a linear medium with a small scatter, which has a radius of 1 (i know this small radius does not make much sense and is not practical), I got some strange sensor data. Following is my code: '%% define medium, scatter and grid points clc; clearvars; % set the size of the perfectly matched layer (PML) pml_x_size = 10; % [grid points] pml_y_size = 10; % [grid points] pml_z_size = 10; % [grid points] % set total number of grid points not including the PML Nx = 190 - 2*pml_x_size; % [grid points] Ny = 100 - 2*pml_y_size; % [grid points] Nz = 600 - 2*pml_z_size; % [grid points] % define the properties of the propagation medium c0=1500; rho0=1040; tone_burst_freq = 3e6; tone_burst_cycles = 4; source_strength = 1e6; % [Pa] % at least 3 points per wavelength is recommended dx = c0/tone_burst_freq/4; % grid point spacing in the x direction [m] dy = dx; dz = dx; kgrid = kWaveGrid(Nz,dz,Nx, dx, Ny, dy); kgrid.makeTime(c0, 0.3, (Nz * dz) * 2 / c0); input_signal = toneBurst(1/kgrid.dt, tone_burst_freq, tone_burst_cycles); input_signal = (source_strength ./ (c0 * rho0)) .* input_signal; %% Create The Transducer % physical properties of the transducer transducer.number_elements = 80; % total number of transducer elements transducer.element_width = round(0.23e-3/dx); % width of each element [grid points] transducer.element_length = round(6.5e-3/dx); % length of each element [grid points] transducer.element_spacing = round(0.04e-3/dx); % spacing (kerf width) between the elements [grid points] transducer.radius = inf; % radius of curvature of the transducer [m] % calculate the width of the transducer in grid points transducer_width = transducer.number_elements * transducer.element_width ... + (transducer.number_elements - 1) * transducer.element_spacing; % use this to position the transducer in the middle of the computational grid transducer.position = round([1, Nx/2-transducer_width/2, Ny/2-transducer.element_length/2]); %transducer_central.position = [z x y]; % properties used to derive the beamforming delays transducer.sound_speed = c0; % sound speed [m/s] transducer.focus_distance = inf; % focus distance [m] transducer.elevation_focus_distance = 77e-3; % focus distance in the elevation plane [m] transducer.steering_angle = 0; % steering angle [degrees] % apodization transducer.transmit_apodization = 'Hanning'; transducer.receive_apodization = 'Hanning'; % define the transducer elements that are currently active number_active_elements = transducer.number_elements; transducer.active_elements = ones(transducer.number_elements, 1); % append input signal used to drive the transducer transducer.input_signal = input_signal; % create the transducer using the defined settings transducer = kWaveTransducer(kgrid, transducer); % print out transducer properties transducer.properties; %% DEFINE THE MEDIUM PROPERTIES % define properties sound_speed_map = c0 * ones(Nz, Nx, Ny) ; density_map = rho0 * ones(Nz, Nx, Ny) ; scatterRadius = 1; scatterCoef = 1.06; % define a sphere for a highly scattering region scattering_region1 = makeBall(Nz, Nx, Ny, 4*Nz/5, ... Nx/2, Ny/2, scatterRadius(1)); % assign region sound_speed_map(scattering_region1 == 1) = c0*scatterCoef(1); density_map(scattering_region1 == 1) = rho0*scatterCoef(1); medium.sound_speed = sound_speed_map; medium.density = density_map; voxelPlot(single(transducer.mask | scattering_region1)); view(142,25); %% simulation input_args = {... 'PMLInside', false, 'PMLSize', [pml_x_size, pml_y_size, pml_z_size], ... 'DataCast', 'gpuArray-single', 'DataRecast', true}; % run the simulation tic sensor_data = kspaceFirstOrder3DG(kgrid, medium, transducer, transducer, input_args{:}); toc %% sensor_data sensor_data_com = transducer.combine_sensor_data(sensor_data); data_win = getWin(kgrid.Nt * 2, 'Tukey', 'Param', 0.05).'; data_win = [zeros(1, ceil(length(transducer.input_signal) * 2)), data_win(1:end/2 - ceil(length(transducer.input_signal) * 2))]; figure; subplot(211); plot(sensor_data_com(40,:));title('before windowing'); subplot(212); sensor_data_com = bsxfun(@times, data_win, sensor_data_com); plot(sensor_data_com(40,:));title('after windowing');' If you have tried the code above, you may have already seen the sensor_data after the windowing operation, some strong signals appeared in the near field and around the half of the time series, but there were no scatter points, can you please tell me is there anything wrong with my code or is it hard to simulate such a small scatter in k-Wave? If it is the latter, why is it? And I noticed that if the scan_line() method is used, I will get one smooth sensor_data plot, does anyone know what operation was done beneath scan_line() function? Thank you for your responses in advance. Kind regards, Bing