k-Wave User Forum » Topic: medium.alpha

k-Wave User Forum » Topic: medium.alpha_coeff http://www.k-wave.org/forum/topic/mediumalpha_coeff Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 01:42:53 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://www.k-wave.org/forum/search.php Bradley Treeby on "medium.alpha_coeff" http://www.k-wave.org/forum/topic/mediumalpha_coeff#post-5426 Thu, 17 Mar 2016 14:36:11 +0000 Bradley Treeby 5426@http://www.k-wave.org/forum/ Hi maryam, The very high value of absorption inside the layer is making the simulation unstable (you can see this on the display as the screen becoming black). You can counteract this by using a smaller time step (or CFL number if using <code>makeTime</code>). In your case, the stability is made worse by the power law exponent (<code>alpha_power</code>) being less than 1. Unfortunately, I don't have an answer off hand as to why this should be the case. If you change <code>alpha_power</code> to 1.1 (for example), and reduce the size of your time step to use a CFL of 0.1, then the simulation runs stably. Brad. maryam.parto on "medium.alpha_coeff" http://www.k-wave.org/forum/topic/mediumalpha_coeff#post-5408 Mon, 29 Feb 2016 15:08:45 +0000 maryam.parto 5408@http://www.k-wave.org/forum/ HI I changed the “example_us_defining_transducer” Example of the k-wave so that medium.alpha_coeff having different values in different parts of the medium. But actually I didn’t get any data in my sensor-data matrix after running it . can somebody help me what happens? Here are my codes: clear all; DATA_CAST = 'single'; % ========================================================================= % DEFINE THE K-WAVE GRID % ========================================================================= % set the size of the perfectly matched layer (PML) PML_X_SIZE = 20; % [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 = 128 - 2*PML_X_SIZE; % [grid points] Ny = 128 - 2*PML_Y_SIZE; % [grid points] Nz = 64 - 2*PML_Z_SIZE; % [grid points] % set desired grid size in the x-direction not including the PML x = 40e-3; % [m] % calculate the spacing between the grid points dx = x/Nx; % [m] dy = dx; % [m] dz = dx; % [m] % create the k-space grid kgrid = makeGrid(Nx, dx, Ny, dy, Nz, dz); % ========================================================================= % DEFINE THE MEDIUM PARAMETERS % ========================================================================= % define the properties of the propagation medium medium.sound_speed = 1540*ones(Nx, Ny, Nz); % [m/s] medium.density = 1030*ones(Nx, Ny, Nz ); % [kg/m^3] medium.sound_speed((0.01*Nx+5):(0.01*Nx+5)+16,:,:) = 2300; % [m/s] medium.density((0.01*Nx+5):(0.01*Nx+5)+16,:,:) = 1912; medium.alpha_coeff=0.435*ones(Nx, Ny, Nz ); medium.alpha_power=0.9; medium.alpha_coeff(8:24,:, :) = 22; medium.BonA = 6; % create the time array t_end = 40e-6; % [s] kgrid.t_array = makeTime(kgrid, medium.sound_speed, [], t_end); % ========================================================================= % DEFINE THE INPUT SIGNAL % ========================================================================= % define properties of the input signal source_strength = 1e6; % [Pa] tone_burst_freq = 0.5e6; % [Hz] tone_burst_cycles = 1; % create the input signal using toneBurst input_signal = toneBurst(1/kgrid.dt, tone_burst_freq, tone_burst_cycles); % ========================================================================= % DEFINE THE ULTRASOUND TRANSDUCER % ========================================================================= % physical properties of the transducer transducer.number_elements = 72; % total number of transducer elements transducer.element_width = 1; % width of each element [grid points] transducer.element_length = 1; % 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; % 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 = 1540; % sound speed [m/s] transducer.focus_distance = 20e-3; % focus distance [m] transducer.steering_angle = 0; % steering angle [degrees] % apodization transducer.transmit_apodization = 'Rectangular'; % append input signal used to drive the transducer transducer.input_signal = input_signal; % create the transducer using the defined settings transducer = makeTransducer(kgrid, transducer); % print out transducer properties transducer.properties; % ========================================================================= % DEFINE SENSOR MASK % ========================================================================= % create a binary sensor mask with four detection positions sensor.mask = zeros(Nx, Ny, Nz); sensor.mask([Nx/4, Nx/2, 3*Nx/4], Ny/2, Nz/2) = 1; % ========================================================================= % RUN THE SIMULATION % ========================================================================= % set the input settings input_args = {'DisplayMask', transducer.all_elements_mask | sensor.mask, ... 'PMLInside', false, 'PlotPML', false, 'PMLSize', [PML_X_SIZE, PML_Y_SIZE, PML_Z_SIZE], ... 'PMLInside', false, 'DataCast', DATA_CAST, 'PlotScale', [-source_strength/2, source_strength/2]}; % run the simulation [sensor_data] = kspaceFirstOrder3D(kgrid, medium, transducer, sensor, input_args{:});