参考Field II的使用说明，进行了四个例子的练习。仿真程序和结果如下：
PURPOSE1：Calculate the received response from all elements of a linear array and plot the responses and the summed response 【计算来自所有线性阵元的接收响应，并绘制该响应以及叠加响应。】
>> path(path,'D:\MATLAB\R2016a\Field_II_PC7');field_init
%set initial parameters
>> f0=3e6;%Transducer center frequency
>> fs=100e6;%sampling frequency>> c=1540;%speed of sound
>> lambda=c/f0;%wave length
>> height=5/1000;%height of element
>> width=1/1000;%width of element
>> kerf=width/4;%distance between transducer elements
>> N_elements=32;%number of elements
>> focus=[0 0 40]/1000;%initial electronic focus
%define the transducer
>> Th=xdc_linear_array(N_elements, width, height ,kerf ,2, 3, focus);%set the impulse response and excitation of the emit aperture>> impulse_response=sin(2*pi*f0*(0:1/fs:2/f0));
>> impulse_response=impulse_response.*hanning(max(size(impulse_response)))';
>> xdc_impulse(Th,impulse_response);
>> excitation=sin(2*pi*f0*(0:1/fs:2/f0));
>> xdc_excitation(Th,excitation);
%Do the calculation
>> [v,t]=calc_scat_multi(Th,Th,[0 0 20]/1000,1);
%plot the individual response
>> subplot(211)>> [N,M]=size(v);
>> v=v/max(max(v));
>> for i=1:N_elements
plot((0:N-1)/fs+t,v(:,i)+i),hold on
end
>> hold off
>> title('Individual traces')
>> xlabel('Time [s]')
>> ylabel('Normalized response')
>> subplot(212)
>> plot((0:N-1)/fs+t,sum(v'))
>> title('Summed response')
>> xlabel('Time[s]')
>> ylabel('Normalized response')
>>
绘制结果：
PURPOSE2：calculate the received response from all elements of a linear array with 3 transmitting and 16receiving elements and plot the responses and the summed response [计算来自一个带有3个发送和16个接收元的线性阵的所有阵元的接收响应，并绘制该响应和叠加相应。
f0=3e6;
fs=100e6;
c=1540;
lambda=c/f0;
height=5/1000;
width=1/1000;
kerf=width/5;
N_elements=3;
N_elements2=16;
focus=[0 0 40]/1000;
%define the transducers
Th=xdc_linear_array(N_elements,width,height,kerf,2,3,focus);
Th2=xdc_linear_array(N_elements2,width,height,kerf,2,3,focus);
%Set the impulse response and excitation of the emit aperture
impulse_response =sin(2*pi*f0*(0:1/fs:2/f0));
impulse_response=impulse_response.*hanning(max(size(impulse_response)))';
xdc_impulse(Th,impulse_response);
xdc_impulse(Th2,impulse_response);
excitation=sin(2*pi*f0*(0:1/fs:2/f0));
xdc_excitation(Th,excitation);
%define a small phantom with scatterers
N=200;
x_size = 20/1000;%width of phantom
y_size=10/1000;%transverse width of phantom
z_size=20/1000;%hight of phantom
z_start=5/1000;%start of phantom surface
%creat the general scatters
x=(rand (N,1)-0.5)*x_size;
y=(rand (N,1)-0.5)*y_size;
z=rand (N,1)*z_size + z_start;
positions=[x y z];
%Generate the amplitudes with a Gaussian distribution
>> amp=randn(N,1);
>> %dO the calculations
>> [v,t]=calc_scat_all(Th,Th2,positions,amp,1);
>> %plot the indicidual response
>> [N,M]=size(v);
>> scale=max(max(v));
>> v=v/scale;
>> for i=1:M
plot ((0:N-1)/fs+t,v(:,1)+i,'b'),hold on
end
>> hold off
>> title ('Individual traces')
>> xlabel('Time[s]')
>> ylabel('Normalized response')
>> axis([t t+N/fs 0 M+1])
得到图：当用三个不同的元发送，得到的16个线性阵列换能器的单个元件的接收电压的痕迹（？）
PURPOSE3:to show how the procedures can be used for making a phased array scan of a point target【用于说明程序如何可以用于一个点目标的相控阵扫描】
%generate the transducer aperture for send and receive
f0=3e6;
fs=100e6;
c=1540;
lambda=c/f0;
element_hight=5/1000;
kerf=0.1/1000;
focus=[0 0 70]/1000;
%generate aperture for emission
emit_aperture = xdc_linear_array (128,lambda/2,element_hight,kerf,1,1,focus);
%set the impulse response and excitation of the emit aperture
impulse_response =sin(2*pi*f0*(0:1/fs:2/f0));
impulse_response=impulse_response.*hanning(max(size(impulse_response)))';
>> xdc_impulse (emit_aperture,impulse_response);
>> excitation=sin(2*pi*f0*(0:1/fs:2/f0));
>> xdc_excitation (emit_aperture,excitation);
>> %generate aperture for reception
>> receive_aperture =xdc_linear_array (128,lambda/2,element_hight,kerf,1,1,focus);
>> %set the impulse response for the receive aperture
>> xdc_impulse (receive_aperture ,impulse_response);
>> %Do phased array imaging
>> point_position =[0 0 70 ]/1000;
>> no_lines=50;
>> sector=20*pi/180;
>> d_theta=sector/no_lines;
>> %pre_allocate some storage
>> image_data=zeros (800,no_lines);
>> theta=-sector/2;
>> for i=1:no_lines
%set the focus for this direction
xdc_focus (emit_aperture,0,[70*sin(theta) 0 70*cos(theta)]/1000);
xdc_focus (receive_aperture,0,[70*sin(theta) 0 70*cos(theta)]/1000);
%calculate the received response
[v,t1]=calc_scat(emit_aperture, receive_aperture,point_position,1);
%store the result
image_data(1:max(size(v)),i)=v';
times(i)=t1;
%steer in another angle
theta = theta + d_theta;
end
>> %here the display of the data is inserted
>> plot (image_data)
PURPOSE4:generating an artificial phantom with point scatters and a cyst【产生具有点散射和囊肿的人造体模？】
f0=3e6;
fs=100e6;
c=1540;
lambda=c/f0;
width=lambda;
element_height=5/1000;
kerf=width/20;
focus=[0 0 50]/1000;
N_elements=192;
N_active=64;
set_sampling(fs);
emit_aperture =xdc_linear_array (N_elements,width,element_height,kerf,1,5,focus);
%set the impulse response and excitation of the emit aperture
impulse_response = sin(2*pi*f0*(0:1/fs:2/f0));
impulse_response = impulse_response.*hanning(max(size(impulse_response)))';
xdc_impulse (emit_aperture,impulse_response);
excitation=sin(2*pi*f0*(0:1/fs:2/f0));
xdc_excitation(emit_aperture,excitation);
%Generate aperture for reception
receive_aperture =xdc_linear_array (N_elements,width,element_height,kerf,1,5,focus);
%set the impulse response for the receive aperture
xdc_impulse (receive_aperture,impulse_response);
%load the computer phantom
[phantom_positions,phantom_amplitudes]=cyst_phantom(10000);
%Do linear array imaging
no_lines=N_elements-N_active+1;
dx=width;
z_focus=50/1000;
%pre-allocate some storage
image_data=zeros(1,no_lines);
for i=1:no_lines
i
%Find position for imaging
x=(i-1-no_lines/2)*dx;
%set the focus for this direction
xdc_center_focus(emit_aperture,[x 0 0]);
xdc_focus (emit_aperture,0,[x 0 z_focus]);
xdc_focus (receive_aperture,0,[x 0 z_focus]);
%set the active elements using the apodization
apo=[zeros(1,i-1) hamming(N_active)' zeros(1,N_elements - N_active - i + 1)];
xdc_apodization (emit_aperture,0,apo);
xdc_apodization(receive_aperture,0,apo);
%calculate the received response
[v,t1]=calc_scat(emit_aperture,receive_aperture,phantom_positions,phantom_amplitudes);
%store the result
image_data(1:max(size(v)),i)=v;
times(i)=t1;
Warning: Remember to set all pulses in apertures for the new sampling frequency
end
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>> %free space for aperture
>> xdc_free (emit_aperture)
>> xdc_free (receive_aperture)
>> %Adjust the data in time and display it ai a gray scale image
>> min_sample = min(times)*fs;
>> for i=1:no_lines
rf_env=abs(hilbert([zeros(round(times(i)*fs - min_sample),1);image_data(:,i)]));
>> env(1:size(rf_env,1),i)=rf_env;
end
%make logarthmic compression to a 60 db dynamic range
>> %with proper units on the axis
>> env_dB=20*log10(env);
>> env_dB=env_dB-max(max(env_dB));
>> env_gray=127*(env_dB +60)/60;
>> depth=((0:size(env,1)-1)+min_sample)/fs*c/2;
>> x=((1:no_lines)-no_lines/2)*dx;
>> image(x*1000,depth*1000,env_gray)
>> xlabel('Lateral distance [mm]')
>> ylabel('Depth [mm]')
>> axis('image')
>> colormap(gray(128))
>> title('image of cyst phantom(60dB dynamic range)')
得到的结果如下：
