http://www.k-wave.org/forum/topic/adding-an-absorptive-material Support for the k-Wave MATLAB toolbox en-US Tue, 12 May 2026 23:28:18 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/adding-an-absorptive-material#post-7037 Sun, 08 Sep 2019 17:18:39 +0000 vich 7037@http://www.k-wave.org/forum/ <p>As far as reflection goes, I would suspect it is only to be expected. For plane waves at normal incidence, the pressure reflection coefficient <code>R</code> is given by:</p> <p><code><br /> R = P_reflect / P_incid = (r_2 - r_1) / (r_2 + r_1)<br /> </code></p> <p>where the <code>P</code> are pressures, the lower-case <code>r</code> are characteristic acoustic impedances of the involved media, the direction of wave transmission is from medium 1 to 2, and:</p> <p><code><br /> r_n = rho_n * c_n<br /> </code></p> <p>with <code>rho,c</code> being the equilibrium density and speed of sound.</p> <p>Thus, if you set <code>rho_2</code> too low in your simulations, <code>R</code> approaches -1; the reflected waves are strong and 180° out of phase with the incident waves.</p> <p>As for the attenuating layer, I guess you would need it to be many voxels thick in order to prevent the same reflection problem that occurs when using a PML with very high attenuations per voxel. And then your attenuation would still not be strictly complete, although probably sufficient.</p> <p>Maybe you could use 2 Np/voxel (the default for the PML) as a starting point (after conversion to dB/MHz^y/cm)? </p> http://www.k-wave.org/forum/topic/adding-an-absorptive-material#post-7030 Wed, 04 Sep 2019 10:27:47 +0000 abode2100 7030@http://www.k-wave.org/forum/ <p>Hi,</p> <p>I have been trying to add a vacuum layer in my simulation to block the direct arrival signals from the receivers. I've successfully blocked them when I set the medium.density parameter to a small values (e.g., one) for this vacuum layer. However, the signals always get reflected, which is not what I want. I want to have an absorptive layer that completely absorbs the signal and reflects nothing (does not matter which material this is). Is this doable in K-wave? Note that I've been tuning medium.alpha_power and medium.alpha_coeff to have high attenuation coefficient in this layer but didn't get what I want. </p> <p>Any suggestion for such a layer with the corresponding parameters will be really helpful. </p> <p>Thanks in advance. </p>