【摘要】 相位比较法测量声速实验中,由于声波在传输过程中存在衰减、反射以及在收、发换能器之间多次反射叠加,当收、发换能器间距较小时,发射信号和接收信号合成的李萨如图形变化规律与理论不一致,即,接收器移动1个波长的距离,示波器中观察到合成直线段在同相和反相区域分别连续出现多次,该现象影响了学生对实验现象的判断和实验测量.本文通过理论计算分析,声波在收、发换能器之间的多次往复反射叠加次数增加,声波传输衰减小和换能器表面反射系数大会增大该现象产生的强度和持续的空间范围,理论计算直观地说明了接收器接收的声压信号与空气振动信号之间的关系和利用相位比较法测量声速的合理性.更多还原

【Abstract】 When measuring sound velocity by phase comparison method,due to the attenuation,reflection and the multipath propagation,the change of Lissajous figure would become irregular and complex.This phenomenon might lead to misjudgment of in-phase and antiphase states and reduce the accuracy of sound velocity.In this paper,the experimental phenomena were confirmed with computer simulation.It is showed from this study that smaller attenuation of sound wave transmission,greater reflection coefficient of transducers and more times of reflection between emitter and receiver made Lissajous figures change more irregularly and make straight lines appear at various positions in single quadrant.The simulation results also confirmed the rationality of measuring sound velocity by comparing the phases between the signal from the receiver and the input signal of the emitter.更多还原