domeg Support for the k-Wave MATLAB toolbox en-US Tue, 12 May 2026 22:34:18 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/absorbtion-coefficents#post-1045 Wed, 21 Nov 2012 12:25:51 +0000 shacklepants 1045@http://www.k-wave.org/forum/ <p>Ben,<br /> Thank you for that post I will look the paper up. I was hoping to use K-wave to model the Ultra sound sensors used in vehicles (which means ultrasound in air) I wanted to be able to match what we see now with simulation in order then then move forward and postulate what else could be done with the technology. However I'm relatively new to simulating ultra sound. </p> <p>Chris </p> http://www.k-wave.org/forum/topic/absorbtion-coefficents#post-1042 Tue, 20 Nov 2012 18:23:55 +0000 bencox 1042@http://www.k-wave.org/forum/ <p>Hi Chris,</p> <p>Is the problem that you don't know the absorption coefficient in air at 40 kHz, or that you don't know how to put that into the model?</p> <p>If you don't know the absorption coefficient in air at 40 kHz, can you get hold of this paper: H. E. Bass and F. Douglas Shields, "Absorption of sound in air: High‐frequency measurements" J. Acoust. Soc. Am., Volume 62, Issue 3, pp. 571-576 (1977) ? Note that it depends significantly on the humidity.</p> <p>Once you know what absorption coefficient you want, and if you are really working at a single frequency (so using a source which is a continuous tone), then you can choose <code>alpha_power</code> and <code>alpha_coeff</code> to be whatever you like so long as the combination <code>alpha_coeff * frequency^alpha_power</code> equals your known absorption coefficient. </p> <p>If you are using a tone burst or even more broadband signal then you will want to ensure that the variation with frequency of the absorption coefficient over the bandwidth of your source matches the known values. For that you will need to choose <code>alpha_coeff</code> and <code>alpha_power</code> so that <code>alpha_coeff * frequency^alpha_power</code> is a good fit to the known values over the frequency range.</p> <p>If you don't have absorption that varies with frequency to some power, even approximately, then k-Wave can't help at the moment, I'm afraid.</p> <p>Hope that helps,</p> <p>Ben </p> http://www.k-wave.org/forum/topic/absorbtion-coefficents#post-1041 Tue, 20 Nov 2012 13:16:05 +0000 shacklepants 1041@http://www.k-wave.org/forum/ <p>I'm having much the same issue i need to know the alpha power and coefficients for air, Im using a 40 KHz signal source trying to replicate 40khz ultrasonic emitters. Perhaps its my understanding of the equation which is flawed? </p> <p>Many thanks </p> <p>Chris </p> http://www.k-wave.org/forum/topic/absorbtion-coefficents#post-525 Mon, 28 May 2012 23:47:21 +0000 Bradley Treeby 525@http://www.k-wave.org/forum/ <p>Hi winebra,</p> <p>What frequency range are you trying to model?</p> <p>Brad. </p> http://www.k-wave.org/forum/topic/absorbtion-coefficents#post-522 Tue, 22 May 2012 22:15:43 +0000 winebra 522@http://www.k-wave.org/forum/ <p>Hi,<br /> I wish to know what are absorption factors of air.<br /> alpha_power and alpha_coeff</p> <p>Thanks. </p>