Dear Cox and Treeby,
I am trying to set properties of my own simulation which is :
1-Eight 100 μm radius spherical absorbers were positioned along the vertical axis every 10 mm with the first two point targets located 1 mm away from the transducer surface. Two absorbers at each depth were laterally 1 mm away from the center of each absorber. Imaging region was 40 mm
laterally and 50 mm axially.
2- Point targets were visualized by modeled 128 element
linear array of transducers operating at 5 MHz center frequency
and having 77% fractional bandwidth.
3- speed of sound was assumed to be 1540.
4- radiofrequency signals were digitized using 40MHz sampling frequency.
for these properties i wrote these codes :
%% create the computational grid
Nx = 501; % number of grid points in the x (row) direction
Ny = 400; % 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 = makeGrid(Nx, dx, Ny, dy);
%% define the properties of the propagation medium
medium.sound_speed = 1540; % [m/s]
medium.alpha_coeff = 0.75; % [dB/(MHz^y cm)]
medium.alpha_power = 1.5;
%% create initial pressure distribution using makeDisc (phantom definition)
%1
disc_magnitude = 1e4; % [Pa]
disc_x_pos = 101; % [grid points]
disc_y_pos = 206; % [grid points]
disc_radius = 1; % [grid points]
disc_1 = disc_magnitude*makeDisc(Nx, Ny, disc_x_pos, disc_y_pos, disc_radius);
%1c
disc_x_pos = 101; % [grid points]
disc_y_pos = 194; % [grid points]
disc_radius = 1; % [grid points]
disc_1c = disc_magnitude*makeDisc(Nx, Ny, disc_x_pos, disc_y_pos, disc_radius);
%2
disc_x_pos = 201; % [grid points]
disc_y_pos = 206; % [grid points]
disc_radius = 1; % [grid points]
disc_2 = disc_magnitude*makeDisc(Nx, Ny, disc_x_pos, disc_y_pos, disc_radius);
%2c
disc_x_pos = 201; % [grid points]
disc_y_pos = 194; % [grid points]
disc_radius = 1; % [grid points]
disc_2c = disc_magnitude*makeDisc(Nx, Ny, disc_x_pos, disc_y_pos, disc_radius);
%3
disc_x_pos = 301; % [grid points]
disc_y_pos = 206; % [grid points]
disc_radius = 1; % [grid points]
disc_3 = disc_magnitude*makeDisc(Nx, Ny, disc_x_pos, disc_y_pos, disc_radius);
%3c
disc_x_pos = 301; % [grid points]
disc_y_pos = 194; % [grid points]
disc_radius = 1; % [grid points]
disc_3c = disc_magnitude*makeDisc(Nx, Ny, disc_x_pos, disc_y_pos, disc_radius);
%4
disc_x_pos = 401; % [grid points]
disc_y_pos = 206; % [grid points]
disc_radius = 1; % [grid points]
disc_4 = disc_magnitude*makeDisc(Nx, Ny, disc_x_pos, disc_y_pos, disc_radius);
%4c
disc_x_pos = 401; % [grid points]
disc_y_pos = 194; % [grid points]
disc_radius = 1; % [grid points]
disc_4c = disc_magnitude*makeDisc(Nx, Ny, disc_x_pos, disc_y_pos, disc_radius);
%sume of point absorber
source.p0 = (disc_4 + disc_3 + disc_2 + disc_1) + (disc_1c + disc_2c + disc_3c + disc_4c);
%% define a linear array sensor
sensor.mask = zeros(Nx, Ny);
nomber_of_transducer=128;
sensor.mask(1,(Ny/2)-(nomber_of_transducer/2)+1:(Ny/2)+(nomber_of_transducer/2)) = 1;
%% create the time array
[kgrid.t_array, dt] = makeTime(kgrid, medium.sound_speed);
%% define the frequency response of the sensor elements
center_freq = 5e6; % [Hz]
bandwidth = 77; % [%]
sensor.frequency_response = [center_freq, bandwidth];
%% run the simulation
sensor_data = kspaceFirstOrder2D(kgrid, medium, source, sensor);
%%
% plot the initial pressure and sensor distribution
figure;
imagesc(kgrid.y_vec*1e3, kgrid.x_vec*1e3, source.p0 + sensor.mask*disc_magnitude, [-disc_magnitude disc_magnitude]);
colormap(getColorMap);
ylabel('x-position [mm]');
xlabel('y-position [mm]');
axis image;
colorbar;
here are my questions :
1- I do not know how to set the 40MHz sampling frequency, because in this code sampling frequency -that is declared by kgrid is 5.1333e+07
2- we set initial pressure to propagate as source of acoustic waves, what is the idea and assumption about excitation laser source? i mean if someone ask me, how did the initial pressure emerged, what should i say ?