振幅下凹
指在某一指定位置处的振幅小于参考位置处振幅的一种状态，两处振幅均在同一表面上、沿同一方向测量。如果整个表面上各处的振幅都小于参考位置处的振幅，则称该整个表面（例如端面）存在振幅下凹。
除非采取矫正措施（例如增加法兰），否则无槽条形变幅杆和圆柱形谐振器在其端面上都会存在振幅下凹（对于轴向振幅而言，以端面中心处的振幅为参考测量）。
Amplitude droop
A condition in which the amplitude at a specified location is less than the amplitude at a reference location, both amplitudes being measured on the same surface and in the same direction. An entire surface (e.g., the face) is said to have amplitude droop if the amplitude everywhere is less than the amplitude at the reference location.
Unslotted bar horns and cylindrical resonators will have amplitude droop on their faces (for the axial amplitude, measured with respect to the amplitude at the center of the face) unless corrective measures are taken (e.g., adding flanges.)
Also see —
Amplitude rise
Uniformity.