http://www.k-wave.org/forum/topic/absorption-cannot-be-too-strong Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 00:26:44 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/absorption-cannot-be-too-strong#post-1129 Thu, 20 Dec 2012 23:43:22 +0000 Bradley Treeby 1129@http://www.k-wave.org/forum/ <p>Hi Chao,</p> <p>The value for y must be defined as 0 &lt; y &lt; 3 with y ~= 1. If you change y to 2.99 in your example, it should run without problems. We will update the error checking to give an error for the next release.</p> <p>In the case of extremely high absorption values, it's likely due to numerical rounding errors. There are no set guidelines I'm afraid, but it shouldn't be a problem for physically relevant absorption values. Incidentally, the implementation of the absorption term in <code>kspaceSecondOrder</code> is more accurate than in the first order codes, so this will be more stable for very high absorption values.</p> <p>Hope that helps,</p> <p>Brad. </p> http://www.k-wave.org/forum/topic/absorption-cannot-be-too-strong#post-1128 Thu, 20 Dec 2012 22:44:22 +0000 huangchao 1128@http://www.k-wave.org/forum/ <p>Hi Dr. Cox and Dr. Treeby,</p> <p>I did some PAT simulations with strong absorption media, and the results blew up. Here are my codes:</p> <p>Nx=256;<br /> dx=1e-3;<br /> kgrid=makeGrid(Nx,dx,Nx,dx);</p> <p>medium.sound_speed=1500;<br /> medium.density=1000;<br /> medium.alpha_coeff=1;<br /> medium.alpha_power=3;</p> <p>source.p0=makeDisc(Nx,Nx,Nx/2,Nx/2,10);</p> <p>sensor.mask=makeCartCircle(50e-3,100);</p> <p>input_args = {'CartInterp','linear', 'PMLInside', true, 'PMLSize', 20, 'DataCast', 'gsingle', 'PlotPML', false, 'PlotSim', false};</p> <p>p=kspaceFirstOrder2D(kgrid,medium,source,sensor,input_args{:});</p> <p>However, if I set medium.alpha_power=2 and medium.alpha_coeff=1, the results were reasonable. But if I increased the medium.alpha_coeff to 1000 (which is not impractical though), the results would blow up again.</p> <p>So I wonder if the parameters alpha_power and alpha_coeff are restricted to some ranges for stable simulations.</p> <p>Thanks,<br /> Chao </p>