k-Wave User Forum » Topic: Ultrasonic three-layer medium propagation simulation

k-Wave User Forum » Topic: Ultrasonic three-layer medium propagation simulation http://www.k-wave.org/forum/topic/ultrasonic-three-layer-medium-propagation-simulation Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 14:55:42 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://www.k-wave.org/forum/search.php Bradley Treeby on "Ultrasonic three-layer medium propagation simulation" http://www.k-wave.org/forum/topic/ultrasonic-three-layer-medium-propagation-simulation#post-6833 Wed, 10 Apr 2019 12:50:53 +0000 Bradley Treeby 6833@http://www.k-wave.org/forum/ Hi zhangwei198202, You set: <code>air(2/3*Nx:end, :) = 2;</code> But later use: <code>medium.sound_speed_compression(air == 1) = cp3;</code> (etc) You should use either both 1 or both 2. Brad zhangwei198202 on "Ultrasonic three-layer medium propagation simulation" http://www.k-wave.org/forum/topic/ultrasonic-three-layer-medium-propagation-simulation#post-6789 Mon, 18 Mar 2019 16:06:31 +0000 zhangwei198202 6789@http://www.k-wave.org/forum/ Hello, Bradley Treeby, thank you for your advice. I carefully refer to the example "Shear Waves And Critical Angle Reflection Example" in the software, because this example is very similar to the model I want to do. But my ability is limited, I can't fully understand the program. I added a layer of air medium to the program, placed it on the bottom as the third layer medium, and set all the parameters of the air to zero. Although the program can run, I know that it is definitely not correct. I sent the program to you. Please help me check it. What I don't understand is that the difference in acoustic impedance between the second medium and the third layer is obvious, why the reflected wave is not visible in the second medium. I hope that you can take the time to give your answer, thank you very much! Here is the program: clearvars; % ========================================================================= % SIMULATION PARAMETERS % ========================================================================= % change scale to 2 to reproduce higher resolution figures in help file scale = 1; % create the computational grid PML_size = 10; % [grid points] Nx = 128*scale - 2*PML_size; % [grid points] Ny = 192*scale - 2*PML_size; % [grid points] dx = 0.5e-3/scale; % [m] dy = 0.5e-3/scale; % [m] kgrid = kWaveGrid(Nx, dx, Ny, dy); % define the medium properties for the top layer cp1 = 1540; % compressional wave speed [m/s] cs1 = 0; % shear wave speed [m/s] rho1 = 1000; % density [kg/m^3] alpha0_p1 = 0.1; % compressional absorption [dB/(MHz^2 cm)] alpha0_s1 = 0.1; % shear absorption [dB/(MHz^2 cm)] % define the medium properties for the bottom layer cp2 = 3000; % compressional wave speed [m/s] cs2 = 1400; % shear wave speed [m/s] rho2 = 1850; % density [kg/m^3] alpha0_p2 = 1; % compressional absorption [dB/(MHz^2 cm)] alpha0_s2 = 1; % shear absorption [dB/(MHz^2 cm)] % define the third layer medium properties for the bottom layer cp3 = 0; % compressional wave speed [m/s] cs3 = 0; % shear wave speed [m/s] rho3 = 0; % density [kg/m^3] alpha0_p3 = 0; % compressional absorption [dB/(MHz^2 cm)] alpha0_s3 = 0; % shear absorption [dB/(MHz^2 cm)] % create the time array cfl = 0.1; t_end = 60e-6; kgrid.makeTime(cp1, cfl, t_end); % define position of heterogeneous slab slab = zeros(Nx, Ny); slab(Nx/3:2/3*Nx, :) = 1; % define position of heterogeneous slab air = zeros(Nx, Ny); air(2/3*Nx:end, :) = 2; % define the source geometry in SI units (where 0, 0 is the grid center) arc_pos = [-15e-3, -25e-3]; % [m] focus_pos = [5e-3, 5e-3]; % [m] radius = 25e-3; % [m] diameter = 20e-3; % [m] % define the driving signal source_freq = 500e3; % [Hz] source_strength = 1e6; % [Pa] source_cycles = 3; % number of tone burst cycles % define the sensor to record the maximum particle velocity everywhere sensor.record = {'u_max_all'}; % set the input arguments input_args = {'PMLSize', PML_size, 'PMLAlpha', 2, 'PlotPML', false, ... 'PMLInside', false, 'PlotScale', [-1, 1]*source_strength, ... 'DisplayMask', 'off', 'DataCast', 'single'}; % ========================================================================= % FLUID SIMULATION % ========================================================================= % assign the medium properties medium.sound_speed = cp1*ones(Nx, Ny); medium.sound_speed(slab == 1) = cp2; medium.density = rho1*ones(Nx, Ny); medium.density(slab == 1) = rho2; medium.alpha_coeff = alpha0_p1*ones(Nx, Ny); medium.alpha_coeff(slab == 1) = alpha0_p2; medium.alpha_power = 2; % convert the source parameters to grid points arc_pos = round(arc_pos / dx) + [Nx/2, Ny/2]; focus_pos = round(focus_pos / dx) + [Nx/2, Ny/2]; radius = round(radius / dx); diameter = round(diameter / dx); % force the diameter to be odd if ~rem(diameter, 2) diameter = diameter + 1; end % generate the source geometry source_mask = makeArc([Nx, Ny], arc_pos, radius, diameter, focus_pos); % assign the source source.p_mask = source_mask; source.p = source_strength*toneBurst(1/kgrid.dt, source_freq, source_cycles); % run the fluid simulation sensor_data_fluid = kspaceFirstOrder2D(kgrid, medium, source, sensor, input_args{:}); % ========================================================================= % ELASTIC SIMULATION % ========================================================================= % define the medium properties clear medium medium.sound_speed_compression = cp1*ones(Nx, Ny); medium.sound_speed_compression(slab == 1) = cp2; medium.sound_speed_compression(air == 1) = cp3; medium.sound_speed_shear = cs1*ones(Nx, Ny); medium.sound_speed_shear(slab == 1) = cs2; medium.sound_speed_shear(air == 1) = cs3; medium.density = rho1*ones(Nx, Ny); medium.density(slab == 1) = rho2; medium.density(air == 1) = rho3; medium.alpha_coeff_compression = alpha0_p1*ones(Nx, Ny); medium.alpha_coeff_compression(slab == 1) = alpha0_p2; medium.alpha_coeff_compression(air == 1) = alpha0_p3; medium.alpha_coeff_shear = alpha0_s1*ones(Nx, Ny); medium.alpha_coeff_shear(slab == 1) = alpha0_s2; medium.alpha_coeff_shear(air == 1) = alpha0_s3; % assign the source clear source source.s_mask = source_mask; source.sxx = -source_strength*toneBurst(1/kgrid.dt, source_freq, source_cycles); source.syy = source.sxx; % run the elastic simulation sensor_data_elastic = pstdElastic2D(kgrid, medium, source, sensor, input_args{:}); % ========================================================================= % VISUALISATION % ========================================================================= % define plot vector x_vec = kgrid.x_vec * 1e3; y_vec = kgrid.y_vec * 1e3; % calculate square of velocity magnitude u_e = sensor_data_elastic.ux_max_all.^2 + sensor_data_elastic.uy_max_all.^2; u_f = sensor_data_fluid.ux_max_all.^2 + sensor_data_fluid.uy_max_all.^2; % plot layout figure; imagesc(y_vec, x_vec, double(source_mask | slab)); xlabel('y [mm]'); ylabel('x [mm]'); axis image; colormap(flipud(gray)); % plot beam patterns for the fluid simulation figure; subplot(2, 1, 1); imagesc(y_vec, x_vec, 20*log10(u_f./max(u_f(:)))); xlabel('y [mm]'); ylabel('x [mm]'); axis image; h = colorbar; caxis([-50, 0]); title('Fluid Model'); ylabel(h, '[dB]'); % plot beam patterns for the elastic simulation subplot(2, 1, 2); imagesc(y_vec, x_vec, 20*log10(u_e./max(u_e(:)))); xlabel('y [mm]'); ylabel('x [mm]'); axis image; h = colorbar; caxis([-50, 0]); title('Elastic Model'); colormap(jet(256)); ylabel(h, '[dB]'); scaleFig(1, 1.5); Bradley Treeby on "Ultrasonic three-layer medium propagation simulation" http://www.k-wave.org/forum/topic/ultrasonic-three-layer-medium-propagation-simulation#post-6786 Sun, 17 Mar 2019 22:45:30 +0000 Bradley Treeby 6786@http://www.k-wave.org/forum/ Hi zhangwei198202, (1) Yes this is possible. Take a look at the examples included in k-Wave, in particular, the "Snell's Law And Critical Angle Reflection Example". (2) It is not currently possible to turn off just one PML. In any case, k-Wave uses a Fourier collocation spectral method, so turning off the PML results in wave wrapping rather than reflections. Brad. zhangwei198202 on "Ultrasonic three-layer medium propagation simulation" http://www.k-wave.org/forum/topic/ultrasonic-three-layer-medium-propagation-simulation#post-6772 Fri, 15 Mar 2019 14:56:55 +0000 zhangwei198202 6772@http://www.k-wave.org/forum/ Hello, ask for a question: 1. I want to simulate the sound wave from the first medium obliquely incident into the second medium, reflect and refract at the interface of the two layers of media, then the sound wave re-enters the third medium from the second medium, and produces reflection at the interface between the two media. And refraction. I tried to program, but it didn't work. I don't know if I can simulate three layers of media using this software, or there are other ways to solve my problem. I am looking forward to the expert's answer, thank you very much. 2.Regarding the PML problem, I have not understood thoroughly whether one of the four boundaries of the square region can be set to be non-PML, so that when the sound wave is incident on the bottom surface of the medium, it is reflected back instead of being absorbed. I look forward to your answer, thank you very much.