k-Wave User Forum » Topic: Frequency attenuation in Heterogeneous Media

k-Wave User Forum » Topic: Frequency attenuation in Heterogeneous Media http://www.k-wave.org/forum/topic/frequency-attenuation-in-heterogeneous-media Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 14:18:45 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://www.k-wave.org/forum/search.php Bradley Treeby on "Frequency attenuation in Heterogeneous Media" http://www.k-wave.org/forum/topic/frequency-attenuation-in-heterogeneous-media#post-6837 Wed, 10 Apr 2019 13:04:14 +0000 Bradley Treeby 6837@http://www.k-wave.org/forum/ Hi Sumo, The second frequency (5 MHz) is above the maximum supported frequency of the grid (1.67 MHz). Brad. Sumo on "Frequency attenuation in Heterogeneous Media" http://www.k-wave.org/forum/topic/frequency-attenuation-in-heterogeneous-media#post-6804 Thu, 28 Mar 2019 10:32:32 +0000 Sumo 6804@http://www.k-wave.org/forum/ Hi, For simplicity I tried to measure the frequency response in free field and the same type of output is coming i.e low frequency are getting attenuated more compared to high frequency. Below is the code for that. Could you please let me know if there is something wrong with code or is there any reasoning behind this? % create the computational grid Nx = 256; % number of grid points in the x (row) direction Ny = 256; % number of grid points in the y (column) direction dx = 0.1e-3; % grid point spacing in the x direction [m] dy = 0.1e-3; % grid point spacing in the y direction [m] kgrid = kWaveGrid(Nx, dx, Ny, dy); % define the properties of the propagation medium medium.sound_speed_compression = 334 * ones(Nx, Ny); % [m/s] medium.sound_speed_shear = zeros(Nx, Ny); % [m/s] medium.density = 1.225 * ones(Nx, Ny); % [kg/m^3] % create the time array cfl = 0.1; % Courant-Friedrichs-Lewy number t_end = 1e-4; % [s] kgrid.makeTime(max(medium.sound_speed_compression(:)), cfl, t_end); %Define source source.s_mask=zeros(Nx,Ny); source.s_mask(Nx/2,Ny/2)=1; f1=1e5; %Hz f2=5e5; source.sxx=sin(2*pi*f1*kgrid.t_array)+sin(2*pi*f2*kgrid.t_array); source.syy=sin(2*pi*f1*kgrid.t_array)+sin(2*pi*f2*kgrid.t_array); % define sensor sensor.mask = zeros(Nx,Ny); sensor.mask(Nx/4,Ny/2)=1; sensor.record={'p','p_rms','I_avg'}; % define a custom display mask showing the position of the interface from % the fluid side display_mask = false(Nx, Ny); % display_mask(Nx/2 - 1, :) = 1; % define input arguments input_args = {'PlotScale',[-1.5 1.5], 'PlotPML', false,... 'DisplayMask', display_mask, 'DataCast', 'single','Shear',false}; % run the simulation sensor_data = pstdElastic2D(kgrid, medium, source, sensor, input_args{:}); sensor_data_reordered = reorderSensorData(kgrid, sensor, sensor_data); % ========================================================================= % VISUALISATION % ========================================================================= % plot source and sensor data: Time and Frequency figure; [t_sc, scale, prefix] = scaleSI(max(kgrid.t_array(:))); subplot(2, 2, 1); plot(kgrid.t_array * scale, source.sxx, 'k-'); xlabel(['Time [' prefix 's]']); ylabel('Signal Amplitude'); axis tight; title('Input Pressure Signal'); L=length(source.sxx); fs=1/kgrid.dt; t=kgrid.t_array; dt=kgrid.dt; sc=fs/L; source_freq=fft(source.sxx,L)*dt; f=(fs/2)*linspace(0,1,L/2+1); %Frequency Range amp=2*sc*abs(source_freq(1:L/2+1)); %Single sided spectrum subplot(2,2,3); plot(f,amp); subplot(2, 2, 2); plot(kgrid.t_array * scale, sensor_data_reordered.p, 'r-'); xlabel(['Time [' prefix 's]']); ylabel('Signal Amplitude'); axis tight; title('Sensor Pressure Signal'); L=length(sensor_data.p); sc=fs/L; sensor_freq=fft(sensor_data.p,L)*dt; %% fourier transform of data f=(fs/2)*linspace(0,1,L/2+1); % frequency range amp=2*sc*abs(sensor_freq(1:L/2+1)); % Single sided spectrum subplot(2,2,4); plot(f,amp); xlabel('Frequecny [Hz]'); ylabel('Signal Amplitude'); axis tight; title('Sensor frequency'); Thanks Sumo on "Frequency attenuation in Heterogeneous Media" http://www.k-wave.org/forum/topic/frequency-attenuation-in-heterogeneous-media#post-6798 Fri, 22 Mar 2019 15:53:21 +0000 Sumo 6798@http://www.k-wave.org/forum/ Hi Brad, Thanks for your response. It helped me. Thanks Sumo Bradley Treeby on "Frequency attenuation in Heterogeneous Media" http://www.k-wave.org/forum/topic/frequency-attenuation-in-heterogeneous-media#post-6796 Thu, 21 Mar 2019 00:08:46 +0000 Bradley Treeby 6796@http://www.k-wave.org/forum/ Hi Sumo, The transmission through a layered medium depends on the frequency in a cyclical manner. The maximum transmission is when the layer thickness is a quarter of the acoustic wavelength (or higher round-trip multiple). See <a href="http://cleveland.focused-ultrasound.org/PMB%202006%20V51%20P2293.pdf">this paper</a> for example. Thus, it's not as simple as high frequencies are more attenuated than low frequencies. Hope that helps, Brad. Sumo on "Frequency attenuation in Heterogeneous Media" http://www.k-wave.org/forum/topic/frequency-attenuation-in-heterogeneous-media#post-6795 Wed, 20 Mar 2019 20:43:01 +0000 Sumo 6795@http://www.k-wave.org/forum/ Hi, I have a heterogeneous medium consisting of two different densities and sound velocity. For simplicity I am neglecting the compression waves. The schematic of my domain is something like this: 000000000000000000000 00000000SEN0000000000 000000000000000000000 111111111111111111111 111111111111111111111 000000000000000000000 000000000SRC000000000 000000000000000000000 0 and 1 represents two different mediums, SRC and SEN are point source and sensor respectively. My source consists of multiple frequencies and I am trying to see which frequencies are getting attenuated due to barrier. When I am plotting the sensor data, the results are completely opposite. Low frequencies are getting attenuated more as compared to high frequencies which is not true in the real case. Could you please let me know if I am doing something wrong or is there any thing which can explain this result?