Contents

close all;

field_init(0);

      *------------------------------------------------------------*
      *                                                            *
      *                      F I E L D   I I                       *
      *                                                            *
      *              Simulator for ultrasound systems              *
      *                                                            *
      *             Copyright by Joergen Arendt Jensen             *
      *    Version 3.30, April 5, 2021 (Matlab 2021a version)      *
      *                  Web-site: field-ii.dk                     *
      *                                                            *
      *     This is citationware. Note the terms and conditions    *
      *     for use on the web-site at:                            *
      *               field-ii.dk/?copyright.html                  *
      *  It is illegal to use this program, if the rules in the    *
      *  copyright statement is not followed.                      *
      *------------------------------------------------------------*

basic constants

c0=1540;      % Speed of sound [m/s]
rho0=1020;    % Density [kg/m3]
fs=100e6;     % Sampling frequency [Hz]
dt=1/fs;      % Sampling step [s]
f0=5e6;       % Transducer center frequency [Hz]
lambda=c0/f0; % Wavelength [m]

probe geometry

height=4.0e-3;                  % Height of element [m]
width=270e-6;                   % Width of element [m]
kerf=30e-6;                     % Distance between transducer elements [m]
N_elements=64;                  % Number of elements
no_sub_x=8;                     % Number of sub-divisions in x-direction of elements.
no_sub_y=8;                     % Number of sub-divisions in y-direction of elements.
elevation_focus=20e-3;          % Elevation focus (lens)
focus=[0 0 elevation_focus];    % Initial electronic focus
fractional_bandwidth = 0.65;    % probe fractional bandwidth [1]

excitation pulse

pulse_duration          = 2.5; % pulse duration [cycles]

% Define the transducer
%Th = xdc_linear_array (N_elements, width, height, kerf, no_sub_x, no_sub_y, focus);
Th = xdc_focused_array (N_elements, width, height, kerf, elevation_focus, no_sub_x, no_sub_y, focus);

element electromechanical impulse response

t0 = (-1/fractional_bandwidth/f0): dt : (1/fractional_bandwidth/f0);
impulse_response = gauspuls(t0, f0, fractional_bandwidth);
xdc_impulse (Th, impulse_response);

excitation pulse

te = (-pulse_duration/2/f0): dt : (pulse_duration/2/f0);
excitation = square(2*pi*f0*te+pi/2);
xdc_excitation (Th, excitation);

scan area

scan_x = uff.linear_scan('x_axis',linspace(-20e-3,20e-3,128).','z_axis',linspace(0e-3,40e-3,256).');
scan_y = uff.linear_3D_scan('radial_axis',linspace(-20e-3,20e-3,128).','axial_axis',linspace(0e-3,40e-3,256).','roll',pi/2);

calculate the field

[px, t] = calc_hp (Th,scan_x.xyz);
[py, t] = calc_hp (Th,scan_y.xyz);

  25.0 % performed (roughly 18 seconds remaining)                               56.4 % performed (roughly  9 seconds remaining)                               86.0 % performed (roughly  3 seconds remaining)                             21 seconds used for the calculation                           
  17.5 % performed (roughly 28 seconds remaining)                               40.1 % performed (roughly 18 seconds remaining)                               68.1 % performed (roughly  8 seconds remaining)                               88.8 % performed (roughly  3 seconds remaining)                             27 seconds used for the calculation                           

pulse intensity integral [J/m^2]

pii_x=reshape(sum(px.^2,1)*dt/rho0/c0,[scan_x.N_z_axis scan_x.N_x_axis]);
pii_y=reshape(sum(py.^2,1)*dt/rho0/c0,[scan_y.N_axial_axis scan_y.N_radial_axis]);

depth normalized, dB, PII map

pii_x_dB=10*log10(bsxfun(@rdivide,pii_x, max(pii_x,[],2)));
pii_y_dB=10*log10(bsxfun(@rdivide,pii_y, max(pii_y,[],2)));

figure;
subplot(1,2,1);
imagesc(scan_x.x_axis*1e3,scan_x.z_axis*1e3,pii_x_dB); axis equal tight; colorbar
ylabel('z [mm]')
xlabel('x [mm]')
title('Lateral plane');
caxis([-60 0]);

subplot(1,2,2);
imagesc(scan_y.radial_axis*1e3,scan_y.axial_axis*1e3,pii_y_dB); axis equal tight; colorbar
ylabel('z [mm]')
xlabel('x [mm]')
title('Elevation plane')
caxis([-60 0]);

compute elevation FWHM

mask=find(scan_y.radial_axis>=0);
for n=1:scan_y.N_axial_axis
    el_6dB(n)=interp1(pii_y_dB(n,mask).',scan_y.radial_axis(mask),-6);
end

figure;
plot(scan_y.axial_axis*1e3,2*el_6dB*1e3,'k','linewidth',2); grid on; hold on;
xlabel('Depth [mm]');
ylabel('Scanplane thickness [mm]');
set(gca,'fontsize', 14);

Published with MATLAB® R2020b