Hi Mr.Treeby,
Thank you for your help. You can find below the example I worked with.
clearvars;
% =========================================================================
% SIMULATION
% =========================================================================
% create the computational grid
Nx = 128; % number of grid points in the x (row) direction
Ny = 128; % 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 = 1500 * ones(Nx, Ny); % [m/s]
medium.sound_speed(1:Nx/2, :) = 1800; % [m/s]
medium.density = 1000 * ones(Nx, Ny); % [kg/m^3]
medium.density(:, Ny/4:Ny) = 1200; % [kg/m^3]
% create initial pressure distribution using makeDisc
disc_magnitude = 5; % [Pa]
disc_x_pos = 50; % [grid points]
disc_y_pos = 50; % [grid points]
disc_radius = 8; % [grid points]
disc_1 = disc_magnitude * makeDisc(Nx, Ny, disc_x_pos, disc_y_pos, disc_radius);
disc_magnitude = 3; % [Pa]
disc_x_pos = 80; % [grid points]
disc_y_pos = 60; % [grid points]
disc_radius = 5; % [grid points]
disc_2 = disc_magnitude * makeDisc(Nx, Ny, disc_x_pos, disc_y_pos, disc_radius);
% source.p0 = disc_1 + disc_2;
% define a centered circular sensor
sensor_radius = 4e-3; % [m]
num_sensor_points = 50;
sensor.mask = makeCartCircle(sensor_radius, num_sensor_points);
kgrid.Nt=725;
kgrid.dt=1.667e-8;
sampling_freq = 1/(1*kgrid.dt); % [Hz]
tone_burst_freq = 750e3; % [Hz]
tone_burst_cycles = 3;
source.p = toneBurst(sampling_freq, tone_burst_freq, tone_burst_cycles);
source.p=source.p/max(abs(source.p));
source.p_mask=cart2grid(kgrid,sensor.mask(:,1));
% run the simulation with optional inputs for plotting the simulation
% layout in addition to removing the PML from the display
sensor_data = kspaceFirstOrder2D(kgrid, medium, source, sensor, ...
'PlotLayout', false, 'PlotPML', false);
figure; plot(sensor_data(1,:));