激光衍射法测量表面波的衰减系数与频率的关系

Measurement of the spatial damping of low-frequency liquid surface waves by means of optical diffraction

对于频率为几百赫兹的液体表面波,实验上观察到稳定、清晰、反衬度非常高的衍射图样。理论上得到了衍射条纹间距、表面波波矢量与衰减系数之间的解析关系,并建立了表面波衰减特性的检测方法和实验装置。观察到表面波的衰减效应及衰减系数的色散效应,结果表明衰减系数随频率几乎成线性关系,与理论值吻合。

An optical method of measuring spatial damping coefficient, based on the light diffraction for low- frequency liquid surface waves, is developed. The theory of measurement was systematically analyzed and the expression was derived. Highly visible diffraction patterns have been experimentally obtained. It is described how the measurement of the spatial damping coefficient is practically carried fi, om the diffraction patterns. The result of the measurement was achieved. It is found that the damping coefficient, which varied almost lineally with frequeney, has dispersion characteristics. The experimental result is consistent with hydrodynamics theory. This technique is real time and non - contact.