k-Wave User Forum » Topic: Doubt about Pressure Amplitude recovered

k-Wave User Forum » Topic: Doubt about Pressure Amplitude recovered http://www.k-wave.org/forum/topic/doubt-about-pressure-amplitude-recovered Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 01:48:11 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://www.k-wave.org/forum/search.php bencox on "Doubt about Pressure Amplitude recovered" http://www.k-wave.org/forum/topic/doubt-about-pressure-amplitude-recovered#post-5763 Tue, 22 Nov 2016 16:54:37 +0000 bencox 5763@http://www.k-wave.org/forum/ Hi Manuelbcabo, The reason may be that you are using a time-varying, additive source. Have a look at this post for the reason why that affects the source amplitude, and get back to us if it doesn't answer your question: <a href="http://www.k-wave.org/forum/topic/pressure-depending-on-number-of-gridpoints">http://www.k-wave.org/forum/topic/pressure-depending-on-number-of-gridpoints</a> Hope that helps, Ben manuelbcabo on "Doubt about Pressure Amplitude recovered" http://www.k-wave.org/forum/topic/doubt-about-pressure-amplitude-recovered#post-5753 Sat, 19 Nov 2016 11:23:28 +0000 manuelbcabo 5753@http://www.k-wave.org/forum/ Thanks for the reply, I've checked 1/sqrt(x) decay and fit perfectly the results of the simulation. One thing that I noticed, is that when I feed the simulation with pressure P0 ~ 1e6 Pa assuming sinusoidal signal (tipically I'm working with 120kHz) I obtain pressure signal near to the source greater than P0 (I'm interested to study the threshold for parametric difference beam in function of directivity of planar transducer ). This depends on CFL value? I'm assuming a CFL = ((c_max*dt)/(dx))and spatial step of lambda/6 over x and y axis. Thanks again for the help Cheers. bencox on "Doubt about Pressure Amplitude recovered" http://www.k-wave.org/forum/topic/doubt-about-pressure-amplitude-recovered#post-5751 Fri, 18 Nov 2016 21:25:55 +0000 bencox 5751@http://www.k-wave.org/forum/ Hi Manuelbcabo, You've done a 2D simulation - you used kspaceFirstOrder2D - so you would expect a 1/sqrt(r) type of decay with distance r (cylindrical spreading), which is what you are seeing. In 3D, using kspaceFirstOrder3D, you would see a 1/r decay (spherical spreading). Kind regards, Ben manuelbcabo on "Doubt about Pressure Amplitude recovered" http://www.k-wave.org/forum/topic/doubt-about-pressure-amplitude-recovered#post-5747 Wed, 16 Nov 2016 14:40:47 +0000 manuelbcabo 5747@http://www.k-wave.org/forum/ Hello all, I'm trying to understand how works K-wave toolbox. I'm trying to simulate the propagation of acoustic signal in water and I would like understand well the attenuation of acoustic signal in k-Wave simulations, because next step is simulate non linear parametric armonics in water. With this aim I simulate a easy simulation avoiding the alfa coeff and alfa power and observing how its applied the radial divergence of the acoustic field (that I expect something related to P0/distance). I found a little surprise when I recover the data at sensor points and if I plot pressure over distance for sensor_data.p_max and theoretic P0/distance seems that are not in good agreement (probably because I miss something at simulation code...). Any help would be very appreciated. Here you can find a link for plots <a href="https://drive.google.com/open?id=0B2P-tB_iDXRidDN3SEJoV3IwOEU" rel="nofollow">https://drive.google.com/open?id=0B2P-tB_iDXRidDN3SEJoV3IwOEU</a> <a href="https://drive.google.com/open?id=0B2P-tB_iDXRiNGNDV1BwcEQ3d2c" rel="nofollow">https://drive.google.com/open?id=0B2P-tB_iDXRiNGNDV1BwcEQ3d2c</a> And here is the code used: ________________________________________________________________________________________ close all clear all clc %Mallado del medio. f_max = 50000; % Frecuencia de emision del plano radiante. [Hz] c_max = 1500; % Velocidad maxima del medio [m/s] long_onda = c_max/f_max; %Longitud de onda de la señal emitida step_min = long_onda/6; % Precision minima requerida para simulacion lineal en el mallado dx = 2e-03; % Paso espacial para realizar el mallado debe ser menos a step_min dy = 2e-03; % if dx > step_min % disp('El mallado espacial debe poseer un paso menor.') % break % end % if dx <= step_min % disp('El mallado espacial es menor a long onda/6') % end x = 0.5; % Dimensiones de la malla en la direccion x [m] y = 2.2; % Dimensiones de la malla en la direccion y [m] Nx = round(x/dx); % Elementos de la malla direccion X Ny = round(y/dy); % Elementos de la malla direccion X kgrid = makeGrid(Nx, dx, Ny, dy);% Se define la mallado donde se realizara la simulacion. [t_array, dt1] = makeTime(kgrid, c_max); CFL = (c_max*dt1)/(dx); CFL = 0.6; t_end = y/c_max; [kgrid.t_array, dt] = makeTime(kgrid, c_max, CFL, (t_end)); %Propiedades de los medios. medium.sound_speed = 1500*ones(Nx, Ny); % [m/s] Velocidad del sonido en agua. medium.density = 1000*ones(Nx, Ny); % [kg/m^3] Densidad del agua %Parametrizacion de la atenuacion del medio (El valor del aire no esta bien definido) % att1 = 2.17e-3; %Attenuation dB/cm·MHz2 % medium.alpha_coeff=att1*ones(Nx, Ny); % medium.alpha_power=2; %Propiedades del sistema emisor 2D radio_dist = 0.0375;%Radio del disco emisor. r = radio_dist/dx; em_pos_y = round(0.1/dx); %El emisor se coloca en la posicion 0.5m source.p_mask = zeros(Nx, Ny);% Se genera el espacio 2D donde colocar la linea 2D source.p_mask(round((Nx/2)-r):round((Nx/2)+r),em_pos_y) = 1; f_signal = 50000; Mag_Pa = 15; signal = Mag_Pa.*sin(2*pi*f_signal.*t_array); %signal = signal(1:1000); source.p = signal; %Se genera el array de sensores. rec_pos_y = round(0.2/dx):round(0.1/dx):round(2/dx); rec_pos_x = round(Nx/2); sensor.mask = zeros(Nx, Ny); sensor.mask(rec_pos_x,rec_pos_y) = 1; % imagesc(sensor.mask); colorbar %Comprobar la sensor.record = {'p', 'p_max'}; input_args = { 'DisplayMask', source.p_mask|sensor.mask, 'RecordMovie', true, 'MovieType', 'image', 'MovieName', 'Atenuacion_50kHz_Prueba_0.2m_2m_01m_NOCOEFF', 'PMLInside', false}; sensor_data = kspaceFirstOrder2D(kgrid, medium, source, sensor,input_args{:}); D_P = [dx.*rec_pos_y' sensor_data.p_max]; % Atenuacion comprobacion save('Atenuacion_50kHz_Prueba_0.2m_2m_01m_NOCOEFF.txt','D_P','-ascii')