ECG Saji  Suggested by donshottype 

Available fonts can give you an up and down fluctuation like an ecg or curves like a neon sign.

Your image looks like something an oscilloscope could produce if a sine wave was transformed by a second order sine wave.
I can't recall the equation.

Getting font letters to behave in this way would take a lot of customization.

Letter height would range from very short to very tall [amplitude] but width would be the same [frequency].

Could be done manually by having a collection of perhaps a dozen fonts from short to tall and the user would pick letters from them to follow the amplitude of the sine curve.

Would work best for a connected monoline script.

AFAIK nobody has produced a font collection that could do this.