基于超声源在超声光栅盒中来回反射形成的行驻波，利用连续性方程建立了在超声波作用下液体介质密度随时间和空间变化的关系式，然后利用介质密度和折射率的关系推导任意位置的附加相位差，最后利用相位差讨论了声源功率对超声光栅衍射条纹的影响，得到了Raman-Nath衍射中，实验测量时所需的声源功率的最佳参数，以及可能的缺级与声源功率间的关系。%It is a representative experiment which is measured the velocity of sonic wave by the method of ultrasonic grating in college physical experiments . At present , many experiments about measured sonic velocity by ultrasonic grating have been reported ,but the research into the effect on diffraction fringe of ultrasonic grating by power of sound source has not been reported yet .Based on the moving standing wave ,an expression is set up by echo wave in ultrasonic grating box by using the equation of continuity ,in which the liquid density in ultrasonic grating box changes with time and space ,and then the phase difference of anywhere is derived with the expression of medium density and refractive index .At last ,the effect of diffraction fringe which is due to the power of sound source is discussed ,and the relationship between bright fringe or lacking bright fringe and the power of sound source are derived in Raman-Nath diffraction ,and then the best parameters of sound power for bright fringe in the experiment of ultrasonic gating are gotten .
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