Amplitude

Motion that is described by three parameters:

1. Location. If not otherwise explicitly stated, the location is assumed to be at the center of the resonator's face.
2. Value. Traditionally ultrasonic amplitudes have been specified as peak-to-peak values. However, acceleration forces, stresses, and strains are determined from peak amplitudes, rather than peak-to-peak. Thus, peak amplitudes will be used on this site (with a few legacy exceptions). For text where there may be any confusion the amplitude will be written as "microns_peak". In equations the amplitude will generally be written simply as $$U$$ where peak amplitude is implied.
3. Direction. Often, only a single component of motion is specified or measured, even though motions in other directions exist. If not otherwise explicitly stated, "amplitude" is assumed to refer only to the component parallel to the principal vibration direction (e.g., axial amplitude for axial vibration, radial amplitude for radial vibration, etc.).

Also see —
Asymmetric amplitude
Uniformity