Sinus Displacement

The Sinus Displacement modifier adds a sinusoidal displacement to the stroke.

Wavelength

How wide the undulations are along the stroke.

Amplitude

How high the undulations are across the stroke.

Phase

Allows "offsetting" ("moving") the undulations along the stroke.

ちなみに

The undulations this modifier produces look exactly the same at a Phase of 0 and any positive or negative multiple of the Wavelength set on the modifier. This can be used for rendering short video sequences with wavy lines that can then be seamlessly looped without any visual jumps in the undulations along the line.

Sinus Displacement modifier demo by T.K. (blend-file).