Other researchers have examined the use of square wave perturbations in frequency response, including Rees and co-workers, who used square wave modulation of the volume of a batch system to measure gas diffusion in various adsorbents. They found that the technique allowed them to extend the frequency range of the measurement, enabling the measurement of particularly fast diffusing systems. However, to our knowledge, such methods have not been applied in flowthrough frequency response techniques, such as CSFR.