Reflections and standing waves for particle concentration in microfluidic channels

Standing waves in a microfluidic channel can be applied for the concentration and separation of particles and biological cells. In this paper we examine the formation of surface standing waves from pairs of interdigitated transducers with 100 μm and 200 μm periodicity on a lithium niobate substrate 500 μm thick. A 200 μm open-circuited transducer is a weak reflector while reflections from the 100 μm transducer are much stronger. Finite element simulations have been used to understand the nature of the waves formed when the substrate thickness is of the order of the wavelength. With both transducers driven, concentration of 6 μm particles has been observed and the time required to align has been measured as a function of drive voltage. We also discuss the impact of various channel materials on the electrical terminal characteristics.