Application of Fourier and Laplace transform techniques for modeling an electric circuit having time-varying components

Electric field flow fractionation is a technique in which an electric field is applied perpendicular to the direction of the flow of fluid This technique was first introduced in 1972. However, not much progress was made due to an inherent problem associated with polarization near the electrodes. Polarization induces a double layer which causes most of the potential drop to occur near the channel walls (electrodes) leaving a very weak field inside the channel. It is essential to understand the physics behind the formation of the double layer in order to model the channel behavior appropriately. Such would help in the identification of ways-and-means to manipulate the double layer so that higher effective potential in the channel, and hence improved analyte retention, could be achieved. This paper mainly focuses on modeling aspects of the equivalent circuit of a fluid channel. Comparison of simulated current response and experimental data indicate that time varying circuit parameters are necessary to provide a good fit over the entire time domain. Time varying components in an electrical circuit presented a unique set of problems. A discussion of these problems and results of preliminary simulations have been presented in this paper.