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
