To increase the rate of CSFR data collection, a new method was developed in which the concentration of the feed was perturbed in a square wave pattern rather than sinusoidally. Then, by utilizing the Fourier transform, the square wave signal can be decomposed into its constituent sine waves according to the Fourier series of the square wave, given by where  is the angular frequency in radians, and  = 2f where f is the linear frequency in Hz. Figure provides a visualization of the concept where a series of periodic functions can capture square wave behavior. In the case of CSFR, the square wave input is supplied to the bed and then decomposed into various sine wave harmonics, and this modified CSFR technique is referred to as FT-CSFR since it utilizes a Fourier Transform of the square wave CSFR data.