A short review on AC electro-thermal micropumps based on smeared structural polarizations in the presence of a temperature gradient

Abstract

An AC-field will influence smeared spatial charges in the bulk of a polarizable medium in the presence of conductivity and permittivity gradients. Such gradients can be generated by a temperature gradient induced by Joule heating by the AC-field itself or a separate heating element. Finally, the interaction of the AC-field with the spatial charges may drive an effective medium flow in asymmetric systems. The induced pumping force depends on the temperature and field gradients, as well as on the frequency of the driving AC-field. We present various designs for new AC electro-thermal micropumps (ETμPs) that exploit the spatially smeared bulk polarization principle. In some designs, an integrated heating element allows the temperature gradient to be adjusted. Advantages of the ETμP principle are the absence of any moving parts, force plateaus in broad frequency ranges, and a reversal of the pump direction in dependence on the driving frequency. The operating frequencies ranging from kHz to GHz avoid electrolytic electrode processes and electrode deterioration. Designs with evenly shaped cross-sections of the pump channel are possible. Maximum pumping velocities above 1 mm s −1 were observed in channels with a 120 × 60 μm 2 cross-section at an induced temperature increase below 10 °C. For pump volumes of approximately 100 nl the usable conductivity range for aqueous media spans from the extremely low to above physiological values. A further miniaturization of the pumps is viewed as quite feasible.