http://www.k-wave.org/forum/topic/heterogenous-medium-setting-mediumalpha_coeff-and-mediumalpha_power-values Support for the k-Wave MATLAB toolbox en-US Tue, 12 May 2026 23:28:35 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/heterogenous-medium-setting-mediumalpha_coeff-and-mediumalpha_power-values#post-5372 Mon, 01 Feb 2016 13:31:04 +0000 Anthony 5372@http://www.k-wave.org/forum/ <p>Hi benji,</p> <p>I found the discussion I had with Brad on this particular topic:<br /> <a href="http://www.k-wave.org/forum/topic/heterogeneous-alpha_power" rel="nofollow">http://www.k-wave.org/forum/topic/heterogeneous-alpha_power</a></p> <p>Best regards,<br /> Anthony </p> http://www.k-wave.org/forum/topic/heterogenous-medium-setting-mediumalpha_coeff-and-mediumalpha_power-values#post-5371 Mon, 01 Feb 2016 11:31:38 +0000 Anthony 5371@http://www.k-wave.org/forum/ <p>Hi benji,</p> <p>Unfortunately, alpha_power cannot be heterogeneous because it is involved in the definition of the fractional differential operators used for the absorption... (see the paper "Modeling power law absorption and dispersion for acoustic propagation using the fractional Laplacian." for the formula).</p> <p>I don't know if there would be ways to circumvent this limitation but, with the code as it is, I don't think it is possible.</p> <p>About your second question, could you post a code? </p> <p>Best regards,<br /> Anthony </p> http://www.k-wave.org/forum/topic/heterogenous-medium-setting-mediumalpha_coeff-and-mediumalpha_power-values#post-5367 Fri, 29 Jan 2016 17:29:21 +0000 benji 5367@http://www.k-wave.org/forum/ <p>hi,<br /> first - I have exactly the same question of MO above - can medium.alpha_power be defined as a heterogeneous matrix? </p> <p>secondly - I have tried defining different homogeneous medium.alpha_power and medium.alpha_coeff and run a simple simulation - I keep getting exactly the same pressure profile in the sensor, independent of the loss defined (in other words - seams like the loss parameters do nothing...)</p> <p>How Is that possible?</p> <p>Thank u,<br /> benji </p> http://www.k-wave.org/forum/topic/heterogenous-medium-setting-mediumalpha_coeff-and-mediumalpha_power-values#post-5362 Mon, 18 Jan 2016 17:52:26 +0000 MO_2015 5362@http://www.k-wave.org/forum/ <p>Hello,</p> <p>I got a question regarding medium.alpha_power which is not really answered above. Is it possible to define this parameter as a heterogeneous matrice just like medium.alpha_coeff?</p> <p>Thanks in advance!</p> <p>Kind regards<br /> MO </p> http://www.k-wave.org/forum/topic/heterogenous-medium-setting-mediumalpha_coeff-and-mediumalpha_power-values#post-4551 Tue, 27 May 2014 10:29:50 +0000 Bradley Treeby 4551@http://www.k-wave.org/forum/ <p>Hi Margot,</p> <p>Both <code>medium.alpha_coeff</code> and <code>medium.BonA</code> can be defined as heterogeneous matrices. One thing to keep in mind is that if you set B/A to zero, this will turn off the material nonlinearity, but there will still be a convective nonlinearity. In other words, setting the nonlinear parameter B/A to zero is not the same as setting the coefficient of nonlinearity beta = 1 + B/2A to zero. If you want to do the latter and you are using the MATLAB code, you can modify the simulation functions to do this. For example, using V1.0 in 2D, open <code>kspaceFirstOrder2D</code> and replace lines 808 and 809 with:</p> <pre><code>% force the convective nonlinearity term to be zero in regions of the domain where BonA is zero rhox = bsxfun(@times, pml_x, ( bsxfun(@times, pml_x, rhox) - dt.*rho0 .* duxdx ) ./ (1 + (medium.BonA ~= 0) .* 2*dt.*duxdx)); rhoy = bsxfun(@times, pml_y, ( bsxfun(@times, pml_y, rhoy) - dt.*rho0 .* duydy ) ./ (1 + (medium.BonA ~= 0) .* 2*dt.*duydy));</code></pre> <p>Hope that helps,</p> <p>Brad. </p> http://www.k-wave.org/forum/topic/heterogenous-medium-setting-mediumalpha_coeff-and-mediumalpha_power-values#post-4549 Mon, 26 May 2014 10:31:18 +0000 mgt_p 4549@http://www.k-wave.org/forum/ <p>Hello,</p> <p>Just to check, having BonA and alpha* as matrices as not been implemented yet, right?</p> <p>Thanks</p> <p>Margot </p> http://www.k-wave.org/forum/topic/heterogenous-medium-setting-mediumalpha_coeff-and-mediumalpha_power-values#post-259 Mon, 21 Nov 2011 04:17:42 +0000 Bradley Treeby 259@http://www.k-wave.org/forum/ <p>Thanks for your feedback. There has also been some other discussion of this issue on the forum. In the B.03 release the absorption values must be homogeneous, however, this has been modified in B.04 to allow a heterogeneous <code>medium.alpha_coeff</code> term. </p> http://www.k-wave.org/forum/topic/heterogenous-medium-setting-mediumalpha_coeff-and-mediumalpha_power-values#post-257 Fri, 18 Nov 2011 08:38:50 +0000 rmurthy 257@http://www.k-wave.org/forum/ <p>Hello,</p> <p>I am able to set medium.density and medium.sound_speed as matrices, but I encounter errors when trying to set medium.alpha_coeff and medium.alpha_power to matrices... is there a way to circumvent this? I'm trying to simulate ultrasound propagation through two adjacent tissues with very different attenuation coefficient values, so I'd like to be able to define all of those parameters to reflect that.</p> <p>Thanks! </p>