Introducing phase analysis light scattering for dielectric characterization: measurement of traveling-wave pumping.

Phase analysis light scattering (PALS) was applied to characterize a high-frequency traveling-wave (TW) micropump. Field strength and frequency characteristics were measured for aqueous solutions up to 40 MHz and conductivities of 16 mS/m. The TW field was generated by an ultramicroelectrode array of intercastellated electrodes, which were driven by square-topped signals. Pumping exhibited one major relaxation peak, which strongly increased for conductivities above 4 mS/m. The conductivity dependence of the peak frequency showed an unexpected nonlinear behavior. Around 20 MHz an additional peak caused by electronic resonance was found. Additional coils or capacitors shifted the resonance peak and allowed us to determine the electronic properties of the array. Analysis of distortions in the pump spectra caused by the harmonic content of the driving signals showed that the pump direction is determined by the traveling direction of the field. For measurement of AC-field-induced particle translations, the advantage of PALS over the commonly used microscopic analysis is that it offers an objective method for statistically significant, computerized registration of extremely slow motions. Thus, for dielectric characterization, low field strengths can be used, which is advantageous not only for analyzing liquid pumping, but also for measuring particle translations induced by dielectrophoresis or TW dielectrophoresis.