k-Wave User Forum » Topic: Problem with attenuation is homogenous media

k-Wave User Forum » Topic: Problem with attenuation is homogenous media http://www.k-wave.org/forum/topic/problem-with-attenuation-is-homogenous-media Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 00:21:01 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://www.k-wave.org/forum/search.php marioj on "Problem with attenuation is homogenous media" http://www.k-wave.org/forum/topic/problem-with-attenuation-is-homogenous-media#post-6329 Thu, 08 Mar 2018 10:12:28 +0000 marioj 6329@http://www.k-wave.org/forum/ Hi Brad. Thank you for your tip concerning the variation of the attenuation due to the broadband of the excitation pulse. In fact I found an error in my code in the definition of the central frequency of the pulse that give rise to a wrong calculation of the attenuation. After correction everything is ok. Again, thanks for your time. Mário Bradley Treeby on "Problem with attenuation is homogenous media" http://www.k-wave.org/forum/topic/problem-with-attenuation-is-homogenous-media#post-6318 Wed, 07 Mar 2018 01:46:18 +0000 Bradley Treeby 6318@http://www.k-wave.org/forum/ Hi marioj, The absorption in k-Wave follows a frequency power law, meaning that different frequencies are absorbed different amounts. The units of <code>medium.alpha_coeff</code> are actually dB/(MHz^y cm). In your example, the short tone-burst has a relatively broad frequency range. Thus, while the 1 MHz component will be absorbed by 3 dB/cm, the higher frequencies will be absorbed more, and the lower frequencies will be absorbed less. The wave will also change shape as it propagates due to dispersion linked with absorption (in this case physical, not numerical). This means just taking the maximum or peak-to-peak will not yield the desired absorption values. Hope that helps, Brad. marioj on "Problem with attenuation is homogenous media" http://www.k-wave.org/forum/topic/problem-with-attenuation-is-homogenous-media#post-6298 Tue, 20 Feb 2018 18:06:28 +0000 marioj 6298@http://www.k-wave.org/forum/ Hello, I am trying to evaluate attenuation in homogeneous media. Using 3D simulation with a round transducer and a square sensor the pressure is computed at the same point in media without attenuation (a0) and in the same media by introducing attenuation (a1). Using "medium.alpha_coeff =3 dB/cm" and "medium.alpha_power = 1.01", at a distance of 20mm from the emitter the difference between a0 an a1 should be 6dB (50% of decreasing). The pressure values obtained in simulation (using peak to peak or maximum values) indicate only a decreasing of around 10% after introduction of attenuation. I appreciate some help in this matter. Best regards. Here is the simulation code: %%%%%%%%%%%%%%%%%%%%%%%%%%%% % grid dimensions XX=3.2e-3; YY=3.2e-3; ZZ=20e-3; % grid point spacing scat=200e-6; dx=scat; dy=scat; dz=scat; % create the computational grid Nx=round(XX/dx); Ny=round(YY/dy); Nz=round(ZZ/dz); kgrid = makeGrid(Nx, dx, Ny, dy, Nz, dz); % create the time array explicitly kgrid.t_array = 0:20e-9:30e-6; % circular transducer R=round(1.5e-3/scat); %raio da sonda disc = makeDisc(Nx, Ny, Nx/2, Ny/2, R); % size of grid (Nx, Ny), centre (Nx/2,Ny/2) and radius R source.p_mask = zeros(Nx, Ny, Nz); aa=zeros(Nx, Ny, Nz-1);% matriz de zeros com menos uma slice source.p_mask=cat(3,disc,aa); % concatena o disco com a matriz aa % define properties of the input signal source_strength = 10e6; % [Pa] tone_burst_freq = 1e6; % [Hz] tone_burst_cycles = 2; % create the input signal using toneBurst input_signal = toneBurst(1e8, tone_burst_freq, tone_burst_cycles); source.p = input_signal; % define the properties of the propagation medium medium.sound_speed = 1500*ones(Nx, Ny, Nz); % [m/s] medium.density = 1000*ones(Nx, Ny, Nz); % [kg/m^3] % receiver sensor.mask = zeros(Nx, Ny, Nz); sensor.mask(6:10,6:10,100:100)=1 % attenuation medium.alpha_coeff =3; medium.alpha_power = 1.01; % input arguments input_args = {'DisplayMask', source.p_mask, 'DataCast', 'single','PMLInside', false,'PMLAlpha',2};%,'PMLSize', 20 % run the simulation sensor_data = kspaceFirstOrder3D(kgrid, medium, source, sensor, input_args{:}); sensor.record ={'p'} %recorded time signal pp=sum(sensor_data);