1、xdc center focus
xdc_center_focus就是用来确定聚焦的点，这个点是在计算聚焦延时时间的一个参考点，也是动态聚焦的起始点。
Purpose: Procedure for setting the center point for the focusing. This point is used as a reference for calculating
the focusing delay times and as a starting point for dynamic focusing.
Calling: xdc center focus (Th, point);
Input: Th Pointer to the transducer aperture.
point Focus center point.
Output: none
2、xdc focus
purpose：创建孔径的聚焦时间线
input：传感器孔径指针；相关联的焦点valid的时间；聚焦点坐标
Purpose: Procedure for creating a focus time line for an aperture
Calling: xdc focus (Th, times, points);
Input: Th Pointer to the transducer aperture.
times Time after which the associated focus is valid.
points Focus points. Vector with three columns (x,y,z) and one row for each field point.
Output: none.
3、xdc linear array
Purpose: Procedure for creating a linear array aperture.创建线性阵列孔径
Calling: Th = xdc linear array (no elements, width, height, kerf, no sub x, no sub y, focus);
Input: no elements Number of physical elements.
width Width in x-direction of elements.
height Width in y-direction of elements.
kerf Distance in x-direction between elements.
no sub x Number of sub-divisions in x-direction of elements.
no sub y Number of sub-divisions in y-direction of elements.
focus[] Fixed focus for array (x,y,z). Vector with three elements.固定聚焦点
Output: Th A pointer to this transducer aperture.
Example of transducer definition:
Create a 16 elements linear array, and divide the physical elements into 2 by 3 mathematical elements to increase the
accuracy of the simulation.
% Set initial parameters
height=5/1000; % Height of element [m]
width=1/1000; % Width of element [m]
kerf=width/4; % Distance between transducer elements [m]
N_elements=16; % 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);