A procedure where the variation of a physical property in time can be represented by a triangular wave is considered. This triangular modulation can be used in FTIR instruments operating in the step-and-integrate mode.
P. L. Polavarapu,
"Spectroscopy With Triangular Modulation", Proc. SPIE 1145, 7th Intl Conf on Fourier Transform Spectroscopy, (1 December 1989); doi: 10.1117/12.969412; https://doi.org/10.1117/12.969412