http://www.k-wave.org/forum/topic/different-focal-distance-compared-to-radius-in-makebowl Support for the k-Wave MATLAB toolbox en-US Tue, 12 May 2026 23:30:32 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/different-focal-distance-compared-to-radius-in-makebowl#post-7714 Tue, 28 Jul 2020 12:51:30 +0000 jackYANG 7714@http://www.k-wave.org/forum/ <p>Hi Bard and Angela,<br /> I would like to ask you a question, why do I not observe any focus shift in a single concave spherical focus transducer or a phased array multi-array concave spherical focus transducer when I excite them with a Gaussian envelope pulse?Even after passing through multiple layers of tissue, is it necessary to use a continuous signal for excitation transmission as Angela said?<br /> The question has bothered me for a long, long time, although I know the focal shift and a lot of factors, I have changed almost about so I can change the amount of control, but I have no success, but through other software or kit can create focus offset, and the phenomenon clearly, I hope I can see in the Kwave focus to produce the phenomenon of migration, after all, it also conforms to the practical and theoretical, hope someone can help me, thank you sincerely.<br /> JACKyang </p> http://www.k-wave.org/forum/topic/different-focal-distance-compared-to-radius-in-makebowl#post-7713 Tue, 28 Jul 2020 09:09:01 +0000 Bradley Treeby 7713@http://www.k-wave.org/forum/ <p>Hi Angela,</p> <p>I haven't run your code, but the position of maximum pressure for a focused bowl transducer doesn't correspond with the radius of curvature (unless your f-number is 0.5). See for example, <a href="https://doi.org/10.1121/1.1906542">O'Neil's classic paper on focusing radiators</a>.</p> <p>Brad </p> http://www.k-wave.org/forum/topic/different-focal-distance-compared-to-radius-in-makebowl#post-7707 Mon, 27 Jul 2020 03:03:06 +0000 Angela 7707@http://www.k-wave.org/forum/ <p>Dear all, </p> <p>I have problem in simulating focused ultrasound transducer. </p> <p>I use a k-wave transducer with a center frequency of 0.5 MHz, a diameter of 30 mm, and a focal length of 30 mm.I set medium properties by free water. However, when I see spatial distribution of peak pressure field, they showed focal distance at 26.8 mm. I don't know what is the problem.Please let me know how to fix it. </p> <p>Below is my code. </p> <p>% set total number of grid points not including the PML<br /> resolution = 0.2; %[mm]<br /> Nx = 80/resolution; % [grid points]<br /> Ny = Nx;<br /> Nz = Nx;</p> <p>% set desired grid size in the -direction not including PML<br /> dx = resolution*1e-03; % grid point spacing in the x direction [m: 1mm = 1e-03m]<br /> dy = dx;<br /> dz = dx;<br /> kgrid = kWaveGrid(Nx, dx, Ny, dy, Nz, dz);</p> <p>% homogeneous<br /> T = 20; %[degC]<br /> f = 0.5; %[mHz]<br /> y = 1.43;<br /> medium.sound_speed = speedSoundWater(T); % [m/s]<br /> medium.density = 999.5; % [kg/m^3]</p> <p>kgrid.makeTime(medium.sound_speed);</p> <p>% define the k-wave transducer<br /> grid_size = [Nx Ny Nz];<br /> bowl_pos = [1 round(Nx/2) round(Nx/2)];<br /> radius = round(30e-03/dx);<br /> diameter = (30e-03/dx)-mod(30e-03/dx,2)+1;<br /> focus_pos = [round(Nx/2) round(Nx/2) round(Nx/2)];<br /> source.p_mask = makeBowl(grid_size, bowl_pos, radius, diameter, focus_pos);</p> <p>% define properties of the input signal<br /> source_freq = f*1e06; % [Hz]<br /> source_mag = 1; % [Pa]<br /> source.p = source_mag * sin(2*pi*source_freq*kgrid.t_array);<br /> source.p = filterTimeSeries(kgrid, medium, source.p);</p> <p>sensor.mask = ones(Nx, Ny, Nz);</p> <p>sensor.record = {'p_max'};<br /> input_args = {'DisplayMask', source.p_mask, ...<br /> 'PMLInside', false, 'PlotPML', false, 'DataCast', 'single'};<br /> sensor_data= kspaceFirstOrder3D(kgrid, medium, source, sensor, input_args{:}); </p>