http://www.k-wave.org/forum/topic/ring-in-plane-waves-transmissions Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 09:05:04 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/ring-in-plane-waves-transmissions#post-5288 Fri, 23 Oct 2015 09:46:30 +0000 Bradley Treeby 5288@http://www.k-wave.org/forum/ <p>Hi rpfeynman,</p> <p>These are edges waves, and are a fundamental part of the acoustic field produced by a finite aperture (not related in any way to k-Wave). If you look up the field from a plane piston transducer in any good acoustics textbook, you should find an explanation. As you have discovered, this is exactly the reason apodisation is used in some imaging systems. For a CW field, this is equivalent to reducing the side lobes.</p> <p>Hope that helps,</p> <p>Brad. </p> http://www.k-wave.org/forum/topic/ring-in-plane-waves-transmissions#post-5281 Tue, 20 Oct 2015 14:13:50 +0000 rpfeynman 5281@http://www.k-wave.org/forum/ <p>Hello!<br /> I'd like to have some hints about what are the rings that can be seen in the example "Steering A Linear Array Example".</p> <p>What I mean by rings is the fact that the all the circular-propagating waves from each transducer correctly sum up to create a plane-wave, but the ones coming from the extremities of the source line seem to not cancel out.</p> <p>They are indicated by a red "arrow" in this image: <a href="http://i.imgur.com/bvrMLun.png" rel="nofollow">http://i.imgur.com/bvrMLun.png</a></p> <p>I've noted that they are independent of transmission angle or aperture size (i.e. always happen at the extremities).<br /> Using a smooth apodization, like the Hanning window, removes this phenomena; but a non-smooth window, like the Tukey window for example, just shifts the rings position to the location of the window discontinuity.</p> <p>Why is that happening? Is it because kWave is based the Fourier transform and therefore badly handles situations which are non-smooth in space?</p> <p>Thanks a lot :) </p>