k-Wave User Forum » Topic: Unreasonable waveforms are received in heterogeneous media under closed conditio

k-Wave User Forum » Topic: Unreasonable waveforms are received in heterogeneous media under closed conditio http://www.k-wave.org/forum/topic/unreasonable-waveforms-are-received-in-heterogeneous-media-under-closed-conditio Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 22:54:25 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://www.k-wave.org/forum/search.php alau on "Unreasonable waveforms are received in heterogeneous media under closed conditio" http://www.k-wave.org/forum/topic/unreasonable-waveforms-are-received-in-heterogeneous-media-under-closed-conditio#post-9192 Wed, 05 Mar 2025 10:10:48 +0000 alau 9192@http://www.k-wave.org/forum/ Hi everyone, recently I have been trying to simulate point source propagation using straight tubes as a fixed acoustic path. The inside of the straight pipe is water and the outside is air. The point source propagates from the outside of the straight tube to the inside, and the sensor is at the other end of the straight tube. It is expected that the sensor can receive the signal only when the sound wave propagation time is: t=L_ tube /c_ water, but the actual simulation result is that there is a strange signal at the beginning, and the envelope of this signal is in the form of sine waves. When I increase the initial pressure amplitude, I can see that at the beginning of the simulation, there are strange waves reaching the sensor directly. I checked the code but can not find the problem. Can anyone helo? Best Regards The code is as follows: If the disc_magnitude is set to 50000, the phenomenon can be clearly seen. %%%%%straight pipe d_length=8e-2; % length d_wide=10e-3; % wide d_x=2.5e-5; %50um 40um d_y=2.5e-5; %50um n_wide=d_wide./d_y; n_length=d_length./d_x; r_Nx=n_length+100; r_Ny=n_wide+100; mask=zeros(r_Nx,r_Ny); mask(50:n_length+50,50:n_wide+50)=1; %%%%%Sensor position [row_sensor,cow_sensor]=find(mask(50,:)==1); n_cow_sensor=length(cow_sensor); sensor_mask=zeros(r_Nx,r_Ny); sensor_mask(50,50:n_cow_sensor)=1; %%%%simulation PML_size =20; % size of the PML in grid points Nx = r_Nx ; % number of grid points in the x direction Ny = r_Ny ; % number of grid points in the y direction dx = d_y; % grid point spacing in the x direction [m] dy = d_x; % grid point spacing in the y direction [m] kgrid = kWaveGrid(Nx, dx, Ny, dy); % define a sensor line sensor.mask = sensor_mask; % define the properties of the propagation medium result = logical(mask); medium.sound_speed = 343 * ones(Nx, Ny); % [m/s] 空气中声速 343 medium.sound_speed(result) = 1500; % [m/s] 水中声速 medium.density = 1.225 * ones(Nx, Ny); % [kg/m^3] 空气密度 1.225 medium.density(result) = 1000; % [kg/m^3] 水密度 % set the simulation time to capture the reflections t_end =6.5e-5; % 2.5 * kgrid.x_size / max(medium.sound_speed(:)); % define the time array cfl=0.25; kgrid.makeTime(medium.sound_speed, cfl,t_end); % create initial pressure distribution using makeDisc n_row_source=3255; n_cow_source=310; disc_magnitude =50000; % [Pa] disc_y_pos = n_cow_source; % [grid points] disc_x_pos =n_row_source; % [grid points] disc_radius=2; disc_1 = disc_magnitude * makeDisc(Nx, Ny, disc_x_pos, disc_y_pos, disc_radius); % smooth the initial pressure distribution and restore the magnitude p0 = smooth(disc_1, true); % assign to the source structure source.p0 = p0; input_args = {'PMLSize', PML_size}; % run the simulation sensor_data = kspaceFirstOrder2D(kgrid, medium, source, sensor,input_args{:}); sensor_t=sum(sensor_data); plot(sensor_data); %% % ========================================================================= % VISUALISATION % ========================================================================= % plot the initial pressure and sensor distribution figure; imagesc(kgrid.y_vec * 1e3, kgrid.x_vec * 1e3, p0 + sensor.mask * disc_magnitude, [-disc_magnitude, disc_magnitude]); colormap(getColorMap); ylabel('x-position [mm]'); xlabel('y-position [mm]'); axis image; colorbar; scaleFig(1, 0.65); %% %% 单探测器 sensordata=mean(sensor_data); %之前用的是mean plot(kgrid.dt:kgrid.dt:kgrid.dt*kgrid.Nt,sensordata); xlabel('t/s'); ylabel('PA'); title(disc_y_pos); %% plot(kgrid.dt:kgrid.dt:kgrid.dt*kgrid.Nt,sensor_data(25,:)); xlabel('t/s'); ylabel('PA'); title('原信号');