The Dynamic Behavior of an Adaptive Liquid Microlens Driven by a Ferrofluidic Transducer

Ferrofluids are superparamagnetic suspensions of nanoparticles that can be used as transducers in microfluidic systems, among others. In corresponding setups a microscopic enclosure such as a microchannel is filled with a ferrofluid that is acted on by an external magnetic field. The induced motion of the ferrofluid is utilized to pump or manipulate minute amounts of liquids. Here the dynamic behavior of an adaptive liquid microlens driven by a ferrofluidic transducer is studied. Adaptive microlenses based on that principle promise a number of advantages over existing concepts, such as an increased tuning range of the focal length. It is shown that the delay time of the deformation of the lens surface to the displacement of the magnet producing the external field increases with increasing magnet speed. Dynamic leakage of the lens liquid around the ferrofluid plug, on the other hand, only occurs when the magnet speed exceeds a threshold value and further increases from that point onwards. When the viscosity of the lens liquid increases, both the delay time and the dynamic leakage increase.