k-Wave User Forum » Topic: Power Law Loss Equation Verification

k-Wave User Forum » Topic: Power Law Loss Equation Verification http://www.k-wave.org/forum/topic/power-law-loss-equation-verification Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 06:53:53 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://www.k-wave.org/forum/search.php Bradley Treeby on "Power Law Loss Equation Verification" http://www.k-wave.org/forum/topic/power-law-loss-equation-verification#post-7711 Tue, 28 Jul 2020 09:02:21 +0000 Bradley Treeby 7711@http://www.k-wave.org/forum/ Hi vibhav, I haven't run your code, but if you don't simulate an infinite plane wave, then the wave will also decay due to geometric spreading as well as absorption (this is expected). Brad. vibhav on "Power Law Loss Equation Verification" http://www.k-wave.org/forum/topic/power-law-loss-equation-verification#post-7703 Wed, 22 Jul 2020 10:40:50 +0000 vibhav 7703@http://www.k-wave.org/forum/ Hi Bradley, Thanks for the suggestion, it was helpful. Although i noticed that this example done in a 1D space. If the same simulation were to be done in using 'kspaceFirstOrder2D', i see the observed and theoretical losses do not match (the lines are parallel, but with an separation of roughly 10dB). Any reason why this may happen? Please find below the code used. %----------------------------------------------------------------- Nx = 1024; % [grid points] x = 12.8e-3; % [m] dx = 1e-5;%x / Nx; % [m] kgrid = kWaveGrid(Nx, dx,Nx,dx); % define the properties of the propagation medium medium.sound_speed = 5702; % [m/s] medium.density=3.772e6; % define time array t_end = 3e-6; kgrid.makeTime(medium.sound_speed, [], t_end); % create a spatial delta pulse source_pos = 20; % [grid points] source.p_mask=zeros(Nx,Nx); source.p_mask(source_pos,Nx/2)=1; source.p = 100 * sin(2 * pi * 10e6 * kgrid.t_array(1:20)); % define the sensor positions source_sensor_dist = 5e-4; % [m] sensor_sensor_dist = 5e-3; % [m] sensor_pos_1 = source_pos + round(source_sensor_dist / dx); sensor_pos_2 = source_pos + round((source_sensor_dist + sensor_sensor_dist) / dx); % calculate discrete distance between the sensor positions d = (sensor_pos_2 - sensor_pos_1) * dx; % [m] d_cm = d * 100; % [cm] % index where the relative dispersion is defined f_index = 30; % create a Binary sensor mask sensor.mask = zeros(Nx,Nx); sensor.mask(sensor_pos_1,Nx/2) = 1; sensor.mask(sensor_pos_2,Nx/2) = 1; % define the absorption properties of the propagation medium medium.alpha_coeff = 1.2; medium.alpha_power = 1; medium.alpha_mode='no_dispersion'; % run the simulation without visualisation sensor_data = kspaceFirstOrder2D(kgrid, medium, source, sensor); % calculate the amplitude and phase spectrum at the two sensor % positions [f1, as1, ps1] = spect(sensor_data(1, :), 1/kgrid.dt,'Plot',[true false]); [f2, as2, ps2] = spect(sensor_data(2, :), 1/kgrid.dt,'Plot',[true false]); % calculate the attenuation from the amplitude spectrums attenuation = -20 * log10(as2 ./ as1); % calculate the corresponding theoretical attenuation in dB/cm attenuation_th = d_cm*medium.alpha_coeff .* (f2 .* 1e-6).^medium.alpha_power; % calculate the dispersion (dependence of the sound speed on frequency) % from the phase spectrums cp = 2 .* pi .* f2 .* d ./ (unwrap(ps1) - unwrap(ps2)); % calculate the corresponding theoretical dispersion using the % Kramers-Kronig relation for power law absorption cp_kk = powerLawKramersKronig(2 * pi * f2, 2 * pi * f2(f_index), cp(f_index), db2neper(medium.alpha_coeff, medium.alpha_power), medium.alpha_power); % ========================================================================= % VISUALISATION % ========================================================================= % set downsampling factor so there is sufficient space between plot markers ds = 8; % plot the attenuation figure; f_max = 50; % [MHz] plot(f2.* 1e-6, attenuation); hold on;plot(f2 .* 1e-6, attenuation_th,'r'); legend('observed loss','calculated loss'); set(gca, 'XLim', [0, f_max]); box on; xlabel('Frequency [MHz]'); ylabel('loss [dB]'); Bradley Treeby on "Power Law Loss Equation Verification" http://www.k-wave.org/forum/topic/power-law-loss-equation-verification#post-7700 Mon, 20 Jul 2020 09:30:29 +0000 Bradley Treeby 7700@http://www.k-wave.org/forum/ Hi vibhav, Have you looked at the <a href="http://www.k-wave.org/documentation/example_na_modelling_absorption.php">Modelling Power Law Absorption Example</a>? You can open this in the MATLAB help browser to access the documentation and the code. vibhav on "Power Law Loss Equation Verification" http://www.k-wave.org/forum/topic/power-law-loss-equation-verification#post-7698 Mon, 20 Jul 2020 07:20:17 +0000 vibhav 7698@http://www.k-wave.org/forum/ Hi, I am trying to verify the power law absorption equation provided in the kwave documentation. From what i read the transmission loss is given by "alpha_coeff*distance*(frequency)^y". I am simulating a case where a transducer source and sensor are separated by 5mm distance, and comparing the input/output values seen. I have added the script used below. Theoretically, on calculating the loss i get a value of 18.97dB. But on observing the data recorded I get a value of 38.63dB. I am calculating the observed loss as 10log10(input_signal/output_signal). Is there a loss that i am not taking into account, like the electromechanical coupling? Or am i calculating the loss incorrectly? Any feedback here would be helpful. Thanks in advance. %---------------------------------- medium.sound_speed(:,:,:)=5702; medium.density(:,:,:)=3.2777e6; %grid setup, step size 10^-4m(0.1mm) kgrid = kWaveGrid(100, 1e-4, 100, 1e-4, 100, 1e-4); kgrid.makeTime(max(medium.sound_speed(:))); medium.alpha_coeff = 1.2; % [dB/(MHz^y cm)] medium.alpha_power = 1.5; grid=zeros(100,100,100); grid(31,50,50)=1; grid(81,50,50)=1; sensor.mask=grid; source_strength = 100; % [MPa] tone_burst_freq = 10e6; % [Hz] tone_burst_cycles = 5; input_signal = toneBurst(40e6, tone_burst_freq, tone_burst_cycles,'Envelope','Rectangular'); input_signal = (source_strength ./ (max(medium.sound_speed(:))*max(medium.density(:)))) .* input_signal; settings.number_elements = 1; settings.active_elements = 1; settings.element_width = 1; % width of each element [grid points] settings.element_length = 1; % length of each element [grid points] settings.element_spacing = 0; % spacing (kerf width) between the elements [grid points] settings.radius = inf; % radius of curvature of the transducer [m] settings.position = [31,50,50]; % position of transducer settings.sound_speed =max(medium.sound_speed(:)); % sound speed [m/s] settings.focus_distance = 20e-3; % focus distance [m] settings.elevation_focus_distance = 19e-3; % focus distance in the elevation plane [m] settings.steering_angle = 0; % steering angle [degrees] settings.input_signal = input_signal; transducer = kWaveTransducer(kgrid, settings); transducer.properties input_args = {'RecordMovie', true, 'MovieName', 'loss_verify'}; [sensor_data] = kspaceFirstOrder3D(kgrid, medium,transducer,sensor,input_args{:});