http://www.k-wave.org/forum/topic/heterogeneous-alpha_power Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 00:09:00 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/heterogeneous-alpha_power#post-5290 Fri, 23 Oct 2015 10:35:22 +0000 Anthony 5290@http://www.k-wave.org/forum/ <p>Hi Brad,</p> <p>Thanks a lot for your answer. It arouse my curiosity so I quickly checked the state of the art on the subject and it seems there is currently no numerical method to solve this in the Fourier domain (I only fond some preliminary work about a finite difference method <a href="http://www.sciencedirect.com/science/article/pii/S0096300309001751)" rel="nofollow">http://www.sciencedirect.com/science/article/pii/S0096300309001751)</a>. </p> <p>Well, it seems I will continue to split my simulation domains for a while ;-)</p> <p>Best regards :-)<br /> Anthony </p> http://www.k-wave.org/forum/topic/heterogeneous-alpha_power#post-5285 Fri, 23 Oct 2015 09:18:53 +0000 Bradley Treeby 5285@http://www.k-wave.org/forum/ <p>Hi Anthony,</p> <p>The power law absorption in k-Wave is implemented using a fractional Laplacian operator. This can be evaluated efficiently in the spatial frequency domain using the FFT (e.g., see <a href="http://www.k-wave.org/papers/2010-Treeby-JASA.pdf">this paper</a>). However, because the operator is applied in the frequency domain, the power law exponent cannot depend on spatial position. </p> <p>If you are using CW sources and linear wave propagation, one way would be to choose a fixed value of <code>alpha_power</code>, and then tweak <code>alpha_coeff</code> to give the correct attenuation in dB/cm at the frequency of interest. Unfortunately, there is no work around in the more general case, which is one of the limitations of the approach.</p> <p>Brad. </p> http://www.k-wave.org/forum/topic/heterogeneous-alpha_power#post-5274 Thu, 15 Oct 2015 07:53:24 +0000 Anthony 5274@http://www.k-wave.org/forum/ <p>Hi Brad, </p> <p>Would it be possible to set a heterogeneous <code>alpha_power</code> coefficient?</p> <p>I guess it is impossible (otherwise, you would have allowed it) but, out of curiosity, could you explain the fundamental reason? </p> <p>By the way, do you have a workaround for this when you deal with several different materials? Currently, I just split my simulation domain and run several simulations, one for each material...</p> <p>Best regards,<br /> Anthony </p>