超声侧向贴壁式液位测量一般是基于声脉冲对液体在有和无的状态下，界面反射回波信号的差异来判断液面位置的，常采用的实施方法是纵波垂直入射技术。但当容器内为低阻抗液体时，固/液、固/气两种界面反射回波信号值的差异很小，界面识别判定困难。基于界面声波理论，提出一种小角度斜入射技术以增强声波在两种界面反射系数间的差异，提高液位检测灵敏度。使用该技术，对多种容器与多种液体组合界面进行了计算与试验，结果表明，最佳入射角与界面性质相关；在最佳入射角条件下，有、无液体状态下界面反射系数差异为垂直入射时的数倍，大大提高了声波对界面的识别能力；此时，采用面积正方形法进行液位测量，精度在零点几个厘米。

Measurement of liquid level in sealed container from side wall is generally based on the difference of echo signal in solid-gas and solid-liquid interface. The technique of longitudinal wave vertical incidence was always used this method. However, it is unsuitable for the low impedance liquid because of small differences in the echoes amplitude. A new technique for measuring liquid-level utilizing angle wave is presented and demonstrated through simulation. Using this technique, the calculation and experiment of the composite interface of various containers and liquids are carried out. Results have shown that the optimum angle is related to the character of interface-material of container and the character of inner liquid. The difference of reflection coefficient at the best angle is higher than vertical incidence. The oblique incident wave is easier to detect and identify targets. The level measurement accuracy can reach a few tenths of centimeters while using the squared area method.