http://www.k-wave.org/forum/topic/incorrect-time-domain-propagation-in-heterogeneous-medium Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 17:24:46 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/incorrect-time-domain-propagation-in-heterogeneous-medium#post-6487 Thu, 14 Jun 2018 22:47:26 +0000 Bradley Treeby 6487@http://www.k-wave.org/forum/ <p>Hi Maryam,</p> <p>The doubling of the time sounds suspicious. Could you post your whole code?</p> <p>Note, when using a heterogeneous medium, it's sometimes useful to specify the reference sound speed (this is used in the k-space correction) to the sound speed in the background medium by defining <code>medium.sound_speed_ref</code>. This reduces the accumulation of numerical dispersion in the background medium. </p> <p>Brad. </p> http://www.k-wave.org/forum/topic/incorrect-time-domain-propagation-in-heterogeneous-medium#post-6480 Sat, 09 Jun 2018 03:47:12 +0000 siamak 6480@http://www.k-wave.org/forum/ <p>My setup includes a set of source points consisting 16 planes, each of 10x10 voxels placed on top of an imaginary sphere. I have also a set of sensors from Z = 0 to Z = top of the Sphere passing through its center. The sensor recordings are used to compute the propagation delay and from there the speed.<br /> When there is only Water as the medium, the propagation is matching to 1500 m/s which I set for water.<br /> In the next experiment I add another layer of medium using below lines:</p> <p>medium.sound_speed = 1500*ones(kgrid.Nx, kgrid.Ny, kgrid.Nz);<br /> medium.sound_speed(Volume==1) = 2900;</p> <p>medium.density = 1000*ones(kgrid.Nx, kgrid.Ny, kgrid.Nz);<br /> medium.density(Volume==1) = 2150;</p> <p>medium.alpha_power = 1.5;<br /> medium.alpha_coeff = 0.75*ones(kgrid.Nx, kgrid.Ny, kgrid.Nz);<br /> medium.alpha_coeff(Volume==1) = 20.4307; </p> <p>medium.BonA = 6*ones(kgrid.Nx, kgrid.Ny, kgrid.Nz);<br /> medium.BonA(Volume==1) = 10;</p> <p>in which Volume is a logical variable of size (Nx,Ny,Nz) and indicates an object which is designated using 1s and all other entries are 0.</p> <p>The problem is after adding this layer of new material, the propagation speed slows down even before wave reach the new layer. The time signal peaks reach to the sensors, even for those in the first medium is exactly doubled and even though the sound speed for the second medium is set much higher than the first medium.</p> <p>I have investigated this issue and if I comment this line:<br /> medium.sound_speed(Volume==1) = 2900;</p> <p>and leave all other lines there, the issue does not appear. Though this means I have neglected the second layer.</p> <p>I appreciate if K-wave team can have a look at this issue, and I wonder if anybody else has measured propagation delays in heterogeneous mediums to see if it matches to what it should be.</p> <p>Thanks for your times,<br /> Maryam </p>