非简谐波对声速测量的影响

Discuss on anharmonic phenomenon in experiment of sound speed measurement

声速测量实验是高校普通物理实验的重要组成部分,通常采用驻波法进行声速测量实验.入射波与反射波叠加后的状态将随反射界面到声源的距离不同而呈现周期性变化,声速测量正是根据该特点进行测量的.然而实际情况比理想情况复杂很多.在驻波法测量空气中的声速实验中,采用数字示波器逐点测量得到超声波的共振曲线,观察到一些非简谐假峰现象.提出对测量到的振幅极大值的大小进行判断,去除这些假峰,使测量的误差降低到最小.

The measure of sound speed is an important part of general physics experiment at the university. The standing wave method is widely used in the velocity measurement experiment. Sound speed is measured according to the character that, the composed wave state between incident wave and reflected wave is changed cyclically as the distance between reflecting interface and sound source changed. However, the practical situation is much more complicated than the ideal situation. In the experiment of measuring sound speed by standing wave method, the resonance curve of ultrasonic wave was obtained through pointwise measurement by using digital oscilloscope, and some anharmonic false peaks were observed. It is suggest that we should judge the size of the maximum value of the amplitude, wipe out the false peak, to minimize the measurement error.