k-Wave User Forum » Topic: only change alpha coef but still have reflection and question about steer angle

k-Wave User Forum » Topic: only change alpha coef but still have reflection and question about steer angle http://www.k-wave.org/forum/topic/only-change-alpha-coef-but-still-have-reflection-and-question-about-steer-angle Support for the k-Wave MATLAB toolbox en-US Tue, 12 May 2026 23:40:11 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://www.k-wave.org/forum/search.php Bradley Treeby on "only change alpha coef but still have reflection and question about steer angle" http://www.k-wave.org/forum/topic/only-change-alpha-coef-but-still-have-reflection-and-question-about-steer-angle#post-8769 Sun, 21 May 2023 14:05:16 +0000 Bradley Treeby 8769@http://www.k-wave.org/forum/ I haven't run your code, but regarding the reflection coefficient, there are two things to consider: 1. For <code>alpha_power</code> not equal to 2, the medium will be dispersive. This means the sound speed will vary as a function of frequency, and as a function of <code>alpha_coeff</code>. In this case, having a heterogeneous <code>alpha_coeff</code> also means you have a heterogeneous sound speed (even if you didn't set one using <code>medium.sound_speed</code>). 2. Even in a non-dispersive medium (e.g., with <code>alpha_power</code> set to 2), you will still get a (very small) reflection when the absorption is non-constant (even if the sound speed and density are matched). This is because changing the absorption will modify the specific acoustic impedance. daibingze on "only change alpha coef but still have reflection and question about steer angle" http://www.k-wave.org/forum/topic/only-change-alpha-coef-but-still-have-reflection-and-question-about-steer-angle#post-8683 Thu, 01 Dec 2022 23:53:24 +0000 daibingze 8683@http://www.k-wave.org/forum/ Hi, i met a problem while simulating with k-wave. The case i test is keeping the 3-D medium's properties all the same but alpha coef which is the attenuation coeff at the middle of the area with a cylinder shape. I set c0 = 1540m/s rho0 = 1000, alpha_power = 1.5 or 1.01, and a map of alpha coef, within the cylinder, it's 1 and the other area is 0.5. i'm imaging the area with single angle planewave. Theoretically, i should get an only black backscattered bmode image becausethere's no impedence mismatch which related to rho and c,so there should not be a reflector in the backscattered image.But what i actually got is it seems like there are two reflectors at the top and bottom edge of the circle area. Can anyone help explain this? And during the testing, i met another problem about steering angle of the transducer,i wanted to tranmit steered planewaves and compound them into one image, but it seems like the steer is not electronic steering, it's mechanically steer the transducer, so when i do delay and sum, i should not add the steered angle there. Am i understanding it correct? Thank you! and the following is the code. clearvars;close all; addpath(genpath([pwd,'/k-wave-toolbox-version-1.3'])) % simulation settings DATA_CAST = 'gpuArray-single'; % set to 'single' or 'gpuArray-single' to speed up computations RUN_SIMULATION = true; % set to false to reload previous results instead of running simulation % ========================================================================= % DEFINE THE K-WAVE GRID % ========================================================================= % set the size of the perfectly matched layer (PML) pml_x_size = 20; % [grid points] pml_y_size = 20; % [grid points] pml_z_size = 10; % [grid points] % set total number of grid points not including the PML %Nx = 1024+44 - 2 * pml_x_size; % [grid points] Nx = 512+44 - 2 * pml_x_size; % [grid points] %Ny = 1024+44 - 2 * pml_y_size; % [grid points] Ny = 512+44 - 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 = 50e-3; % [m] % calculate the spacing between the grid points dx = x / Nx; % [m] dy = dx;%1.923076923076923e-04; % [m] %dz = 2*dx; % [m] dz = 2e-4; % create the k-space grid kgrid = kWaveGrid(Nx, dx, Ny, dy, Nz, dz); % ========================================================================= % DEFINE THE MEDIUM PARAMETERS % ========================================================================= % define the properties of the propagation medium c0 = 1500; %for water % [m/s] rho0 = 1000; % [kg/m^3] % medium.alpha_coeff = 0.75; % [dB/(MHz^y cm)] % need to change this paramenters to map also medium.alpha_power = 1.01; %medium.BonA = 20; %BonA non linear % create the time array t_end = (Nx * dx) * 2.2 / c0; % [s] %t_end = (Nx * dx) * 2 / c0; % [s] kgrid.makeTime(c0, [], t_end); %% % ========================================================================= % DEFINE THE INPUT SIGNAL % ========================================================================= % define properties of the input signal source_strength = 10e5; % [Pa] tone_burst_freq = 2e6; % [Hz] tone_burst_cycles = 4; % create the input signal using toneBurst input_signal = toneBurst(1/kgrid.dt, tone_burst_freq, tone_burst_cycles); input_signal = (source_strength ./ (c0 * rho0)) .* input_signal; % ========================================================================= % DEFINE THE ULTRASOUND TRANSDUCER % ========================================================================= % physical properties of the transducer transducer.number_elements = 128; % total number of transducer elements transducer.element_width = 3; % width of each element [grid points] transducer.element_length = 24; % length of each element [grid points] transducer.element_spacing = 0; % 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; pitch = transducer.element_width*dx; %transducer.transmit_apodization = 'Hanning'; %% % use this to position the transducer in the middle of the computational grid transducer.position = round([1, Ny/2 - transducer_width/2, Nz/2 - transducer.element_length/2]); % 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 = 25e-3; % focus distance in the elevation plane [m] %transducer.steering_angle = 0; % steering angle [degrees] % apodization transducer.transmit_apodization = 'Hanning'; transducer.receive_apodization = 'Rectangular'; % define the transducer elements that are currently active 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 = kWaveTransducer(kgrid, transducer); transducer.properties; % ========================================================================= % DEFINE THE MEDIUM PROPERTIES % ========================================================================= % define a large image size to move across Nx_tot = Nx; Ny_tot = Ny; Nz_tot = Nz; alpha_coeff = 0.5; alpha_coeff2 = 1; scattering_map = randn([Nx_tot, Ny_tot, Nz_tot]); % define a random distribution of scatterers for the medium background_map_mean = 1; background_map_std = 0; background_map = background_map_mean + background_map_std * scattering_map; phanton_map_std = 0; % define properties %background_speed = c0 * ones(Nx_tot, Ny_tot, Nz_tot) .* background_map; sound_speed_map = c0 .* background_map; density_map = rho0 .* background_map; alpha_coeff_map = alpha_coeff.* background_map; radius = 4e-3; % [m] x_pos = 25e-3; % [m] y_pos = 25e-3; % [m] for zi = 1:Nz_tot alpha_coeff_slice = alpha_coeff_map(:,:,zi); scattering_regionb = zeros(Nx_tot, Ny_tot); scattering_regionb = makeDisc(Nx_tot, Ny_tot, round(x_pos/dx), round(y_pos/dy), round(radius/dx)); scattering_slice = scattering_map(:,:,zi); scattering_c02 = alpha_coeff2.*(1 + phanton_map_std * scattering_slice); alpha_coeff_slice(scattering_regionb == 1) = scattering_c02(scattering_regionb == 1); alpha_coeff_map(:,:,zi) = alpha_coeff_slice; end alpha_coeff_slice_ori = alpha_coeff_slice; % ========================================================================= % RUN THE SIMULATION % ========================================================================= % set the input settings input_args = {... 'PMLInside', false, 'PMLSize', [pml_x_size, pml_y_size, pml_z_size], ... 'DataCast', DATA_CAST, 'DataRecast', true, 'PlotSim', false}; i = 0; medium.sound_speed = c0;%sound_speed_map;%(:, medium_position:medium_position + Ny - 1, :); medium.density = rho0;%density_map;%(:, medium_position:medium_position + Ny - 1, :); for degree= 0:0 % rotate disp(['Computing scan angle ' num2str(degree)]); rot_alpha_coeff_slice = rotate_kgrid_dbz(alpha_coeff_slice_ori, degree, alpha_coeff); for steer_ang = -1:1:1 i = i+1; transducer.steering_angle = steer_ang; %transducer.input_signal = input_signal; % create the transducer using the defined settings disp(['Computing steer angle ' num2str(steer_ang)]); for zi = 1:Nz_tot alpha_coeff_map(:,:,zi) = rot_alpha_coeff_slice; end medium.alpha_coeff = alpha_coeff_map;%(:, medium_position:medium_position + Ny - 1, :); sensor_data = kspaceFirstOrder3DG(kgrid, medium, transducer, transducer, input_args{:}); back_rf(:,:,i) = sensor_data; %ps_data(:,:,i) = bf_planewave(sensor_data,1/kgrid.dt); end end figure();imagesc(20*log10(abs(hilbert(back_rf(:,:,1)'))));title('raw rf data')