% Focussed Detector in 3D Example
%
% This example shows how k-Wave can be used to model the output of a
% focussed bowl detector in 3D where the directionality arises from
% spatially averaging across the detector surface. It builds on the
% Focussed Detector in 2D example. 
%
% author: Ben Cox
% date: 29th October 2010
% last update: 18th September 2012
%  
% This function is part of the k-Wave Toolbox (http://www.k-wave.org)
% Copyright (C) 2009-2012 Bradley Treeby and Ben Cox

% This file is part of k-Wave. k-Wave is free software: you can
% redistribute it and/or modify it under the terms of the GNU Lesser
% General Public License as published by the Free Software Foundation,
% either version 3 of the License, or (at your option) any later version.
% 
% k-Wave is distributed in the hope that it will be useful, but WITHOUT ANY
% WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
% FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for
% more details. 
% 
% You should have received a copy of the GNU Lesser General Public License
% along with k-Wave. If not, see <http://www.gnu.org/licenses/>. 

clear all;

% =========================================================================
% SIMULATION
% =========================================================================

% create the computational grid
Nx = 64;            % number of grid points in the x direction
Ny = 64;            % number of grid points in the y direction
Nz = 64;            % number of grid points in the z direction
dx = 100e-3/Nx;     % grid point spacing in the x direction [m]
dy = dx;            % grid point spacing in the y direction [m]
dz = dx;            % grid point spacing in the z direction [m]
kgrid = makeGrid(Nx, dx, Ny, dy, Nz, dz);

% define the properties of the propagation medium
medium.sound_speed = 1500;	% [m/s]

% create the time array
[kgrid.t_array, dt] = makeTime(kgrid, medium.sound_speed);
Nt = length(kgrid.t_array);

% create a concave sensor
radius = Nx/4-1;
height = 10;
ss = makeSphericalSection(radius, height);

% add it to a mask of the correct size
sensor.mask = zeros(Nx, Ny, Nz);
[a,b,c] = size(ss);
sphere_offset = 10;
sensor.mask(sphere_offset+(1:a),(Ny-b+1)/2+(1:b),(Nz-c+1)/2+(1:c)) = ss;

% define a time varying sinusoidal source
source_freq = 0.25e6;
source_mag = 1;
source.p = source_mag*sin(2*pi*source_freq*kgrid.t_array);
source.p = filterTimeSeries(kgrid, medium, source.p);

% place the first point source near the focus of the detector
source1 = zeros(Nx, Ny, Nz);
source1(sphere_offset+radius, Ny/2+1, Nz/2+1) = 1;

% place the second point source off axis
source2 = zeros(Nx, Ny, Nz);
source2(sphere_offset+radius, Ny/2+6, Nz/2+6) = 1;

% run the first simulation
source.p_mask = source1;
input_args = {'PMLSize', 10, 'DataCast', 'single', 'PlotSim', false};
sensor_data1 = kspaceFirstOrder3D(kgrid, medium, source, sensor, input_args{:});

% average the data recorded at each grid point to simulate the measured
% signal from a single element focussed detector
sensor_data1 = sum(sensor_data1, 1);

% run the second simulation
source.p_mask = source2;
sensor_data2 = kspaceFirstOrder3D(kgrid, medium, source, sensor, input_args{:});

% average the data recorded at each grid point to simulate the measured
% signal from a single element focussed detector
sensor_data2 = sum(sensor_data2, 1);

% =========================================================================
% VISUALISATION
% =========================================================================

% plot the detector and on-axis and off-axis point sources
voxelPlot(sensor.mask + source1 + source2);
view([99, 18]);

% plot the time series corresponding to the on-axis and off-axis sources
figure
[t_sc, t_scale, t_prefix] = scaleSI(kgrid.t_array(end));
plot(kgrid.t_array.*t_scale, sensor_data1, '-');
hold on
plot(kgrid.t_array.*t_scale, sensor_data2, 'r-');
xlabel(['Time [' t_prefix 's]']);
ylabel('Average Pressure Measured By Focussed Detector [Pa]');
legend('Source on axis', 'Source off axis');
