A novel piezo actuated high stroke membrane for micropumps

Abstract

Piezo micropumps traditionally use a piezoelectric bimorph actuation method, which is a piezo material mounted on top of a membrane. By applying a voltage difference on the two electrodes of the piezo material, it bends and therefore the membrane will deflect, leading to a displacement of fluid. While these actuators can produce a rather high force, they are unable to create a very large deflection. The first reason is due to the intrinsic characteristics of the piezo material itself. On one hand it has usually a high Young's modulus and therefore resists the deflection. On the other hand, due to its brittle nature, it will break if it undergoes very large deflections. This paper presents a novel method to achieve very high strokes in membranes using piezo actuators. With a new configuration, the bending piezo is eliminated from the centre of the membrane, where there is the maximum displacement. Instead, a piezo ring is mounted around the membrane to change the mechanical actuation regime from bending to buckling. Hence, the energy that we are putting into the system by our piezo material is focused to deform the membrane, instead of being used in terms of strain energy and damping in the stiff piezo material itself. The whole system is analyzed using finite element simulation and the promising simulation results and achieved experimental results with this new actuation method are compared. When using a 50μm thick steel membrane with 22mm diameter actuated with piezo actuators of 250μm thickness, we have achieved deflections up to an average of 197μm, which fits well to our simulated deflection of 180μm. Using a 100μm Rigid-PVC membrane results in an average of 177μm, which again corresponds very well to our simulated deflection of 170μm. This tremendously high deflection can be compared to the one of a traditional piezo bimorph actuator which can be up to 24μm, with the same parameters.