超声为液位检测提供了多种方案。对大孔径密闭容器，一种可能的方案就是通过单探头从容器侧壁采集容器内壁面与液体形成的界面反射回波进行液位评价，这时固-液、固-气反射回波的差异决定了液位评价方法的灵敏度。首先利用斯涅耳定理和边界条件，理论分析了超声纵波由固体一侧倾斜入射到固体-真空和固体-液体界面时纵波的声压反射系数与入射角之间的函数关系；结合密闭绝缘瓷套内部硅油油位的检测实例，在已知容器壁材料及内部液体介质特性的情况下，给出了纵波在陶瓷-硅油界面和陶瓷-空气界面反射系数与入射角之间的函数曲线，获得两者取得最大差异时的最佳角度。为进一步优化超声侧壁油位检测方案及提高检测灵敏度提供依据。

Ultrasonic techniques offer several possible strategies for performing liquid level measurements. One possible solution is to use a pulse-echo measurement of reflection from the liquid-container interface by sigle probe for large container. The improvement of the difference of reflection coefficient between container-liquid and container-air interface is the key technology to enhance the detection sensitivity. Theoretical analysis on the reflection of longitudinal wave incidence obliquely in two types interface was performed based on Snell theorem and the boundary condition when the ultrasonic impedance of container material and liquid medium were fixed in some application.The functional relationship graphics between reflection coefficient and incidence angle in ceramic-silicone oil and ceramic-air interface were given. This is an example used in porcelain-bushing oil level measurement. In addition, there is an optimal incident angle for the incidence longitudinal wave with the maximum difference in the two type interface above mentioned, which is equal to 24.36°. The method would be a useful strategy for performing liquid level measurements, especially to the situation of low impedance liquid inside sealed containment vessels.