k-Wave User Forum » Topic: About piston pressure field

k-Wave User Forum » Topic: About piston pressure field http://www.k-wave.org/forum/topic/about-piston-pressure-field Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 08:58:35 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://www.k-wave.org/forum/search.php Bradley Treeby on "About piston pressure field" http://www.k-wave.org/forum/topic/about-piston-pressure-field#post-5237 Mon, 14 Sep 2015 21:58:12 +0000 Bradley Treeby 5237@http://www.k-wave.org/forum/ Hi Jan, A simulation on a 2D Cartesian grid inherently assumes that everything is infinitely extended in the third dimension. For example, a point source modelled in 2D will give the same response as an infinite line source in 3D. Consequently, if you try to model a piston source as a line in 2D, the response you observe will actually be that of an infinitely long rectangular aperture. This is the difference in the response compared to a piston source in 3D. Note, it is also possible (although not currently in k-Wave) to perform 2D simulations assuming the field is axisymmetric. In this case, you would see the correct response. Brad. hettljan on "About piston pressure field" http://www.k-wave.org/forum/topic/about-piston-pressure-field#post-5234 Thu, 10 Sep 2015 13:02:25 +0000 hettljan 5234@http://www.k-wave.org/forum/ I used the following code" <code> clear all; %% CREATE COMPUTATIONAL GRID Nx= 128; % number of grid points in the x direction Ny= 256; % number of grid points in the y direction dx = 20.6e-3/Nx; % grid point spacing in the y direction [m] dy = 40e-3/Ny; % grid point spacing in the x direction [m] kgrid = makeGrid(Nx, dx, Ny, dy); %% SET MEDIUM medium.sound_speed = 1500; % [m/s] %% DEFINE THE TRANSDUCER dia=2*floor(inch2m(0.5)/(2*dx)); % diameter of the transducer in grid pts source.p_mask = makeLine(Nx, Ny, [Nx/2-dia/2 1], [Nx/2+dia/2 1]); %% DEFINE INPUT SIGNAL excitation='CW'; switch excitation case 'toneBurst' source_mag = 1e5; % [Pa] f = 1e6; % [Hz] tone_burst_cycles = 5; [kgrid.t_array, dt] = makeTime(kgrid, medium.sound_speed); source.p = source_mag.*toneBurst(1/kgrid.dt, f, tone_burst_cycles); case 'CW' f = 1e6; % excitation frequency [Hz] source_mag = 0.5e6; % excitation amplitude [Pa] nTimeSteps=2500; dt=2e-8; kgrid.t_array=(0:1:nTimeSteps)*dt; source.p = source_mag*sin(2*pi*f*kgrid.t_array); % generate cw sine ramp_length = round((2*pi/f)/dt); ramp = (-cos( (0:(ramp_length-1))*pi/ramp_length ) + 1)/2; % prepare ramp wfm for moothing source.p(1:ramp_length) = ramp .* source.p(1:ramp_length); % "windowed" cw sine end %% SENSOR sensor.mask = [1, 1, Nx, Ny].'; sensor.record = {'p'}; sensor.record_start_index = kgrid.Nt - 10*1/(f*dt) + 1; %% ASSIGN INPUT PARAMETERS AND RUN SIMULATION display_mask = source.p_mask; % create a display mask to display the transducer input_args = {'DisplayMask', display_mask, 'PMLInside', false,... 'DataCast', 'gpuArray-single', 'DataRecast', true,... 'PlotScale', [-1, 1]*source_mag, 'DisplayMask', source.p_mask,}; sensor_data = kspaceFirstOrder2D(kgrid, medium, source, sensor, input_args{:}); %% POST-PROCESSING NormPressField=rms(sensor_data.p,3); NormPressField=NormPressField./maxND(NormPressField); %% VISUALISATION figure % beam pattern pcolor((0:1:Ny-1)*dy*1e3, kgrid.x_vec*1e3,NormPressField); shading flat caxis([0 1]) colormap(jet); xlabel('x [mm]','FontSize',14); ylabel('y [mm]','FontSize',14); title('Beam Pattern','FontSize',16) axis image; colorbar figure % on axis pressure Pressure=NormPressField(end/2,2:end); plot((2:1:Ny)*dy*1e3,Pressure,'b*') xlabel('x-position [mm]'); ylabel('RMS pressure'); axis tight; title('On axis RMS pressure'); </code> hettljan on "About piston pressure field" http://www.k-wave.org/forum/topic/about-piston-pressure-field#post-5233 Thu, 10 Sep 2015 13:00:38 +0000 hettljan 5233@http://www.k-wave.org/forum/ Hi, I tried to do the same simulation in 2D instead of a full 3D solution, but I've got very different results. Instead of having the near field/far field interface for 0.5" circular element at approx. 25 cm, it has shifted further to approx. 35 cm. The beam pattern looks reasonable though. Is there any explanation for that? Can I simulate the beam pattern for circular single element transducer accurately in 2D? Thanks for the answer, Jan Bradley Treeby on "About piston pressure field" http://www.k-wave.org/forum/topic/about-piston-pressure-field#post-4844 Thu, 20 Nov 2014 11:19:49 +0000 Bradley Treeby 4844@http://www.k-wave.org/forum/ Most analytical solutions give the variation of the pressure amplitude as a function of distance, given a continuous wave source at a particular frequency. To compare with k-Wave (which is a time domain solver), you will need to wait until the simulation reaches steady state, and then extract the amplitude of the pressure at each position. It also helps if you define the spatial and time grid spacings to be an integer number of points per wavelength and period. I've written a simple example to compare k-Wave with the analytical solution for the on-axis pressure from a circular piston source, which you can download <a href="http://www.k-wave.org/downloads/example_circular_piston.m">here</a>. Let me know if something isn't clear. Brad. nj_fanxudong on "About piston pressure field" http://www.k-wave.org/forum/topic/about-piston-pressure-field#post-4838 Fri, 14 Nov 2014 03:35:22 +0000 nj_fanxudong 4838@http://www.k-wave.org/forum/ Hello, I am also a little bit new to kWave, so my apologies for this low-level question. I am trying to define a source which moves like a piston.And I want to get the pressure distribution along the propagation direction.But the simulation results are not the same as the ones calculated by acoustic theory.Can someone please explain what is the right approach? Thank you in advance.