One difficulty with direct methods is that the designer spends a great deal of time focusing on the velocity distribution; the geometry is secondary.
一个直接的方法就是难度设计者花费大量的时间专注于速度分布；几何为辅。
2
Objective: Study the influence of parameters such as attenuation coefficient, velocity of sound, and temperature of medium on focusing sound field.
前言：目的：研究声衰减系数、声速、温度等媒质参数对声聚焦的影响。
3
Such as how to select focus functions and focus Windows, how to perform feedback control, and how to improve the auto-focusingvelocity etc., are far from completely solved.