Microfluidics is a research fields of increasing interest due the intense effort in miniaturize devices to occupy less space and low costs. Components like microactuators and microchannels have been studied to improve the fabrication sequence and to understand the fluid behavior flowing through them.
This work describes a fabrication and test sequence of microvalves installed on micronozzles. The technique used to fabricate the micronozzles was powder blasting. The microvalves are actuators made from PVDF (polivinylidene fluoride), that is a piezoelectric polymer. The micronozzles have convergent-divergent shape with external diameter of 1mm and throat around 230µm. The polymer have low piezoelectric coefficient, for this reason a bimorph structure with dimensions of 2mm width and 4mm of length was build (two piezoelectric sheets were glued together with opposite polarization). Both sheets are recovered with a conductor thin film with 200 nm of thickness used as electrodes. Applying a voltage between the electrodes one sheet expands while the other contracts and this generate a vertical movement to the entire actuator. If the voltage is change this movement can be higher or lower.
Three different flux measurements were performed in a gas line with low pressures. In all cases the inlet pressure was kept constant as 2Torr. In the first case we used a single micronozzle without actuator and found that for a pressure ratio of 0.5 between the inlet and the outlet the volume flux rate was 0.5 sccm. In the second test the micronozzle was covered with the piezoelectric actuator and, applying +200V DC voltage between the electrodes, it moved 20µm vertically in the opposite direction of the micronozzle (it opened). In this case the volume flux rate, for a pressure ratio of 0.5, was 0.44 sccm. Applying -200V DC between the electrodes (that means it closed) the volume flux rate was 0.42 sccm, defining a possible range of flow between 0.42 and 0.5 sccm. The third measurement was performed using AC voltage (200V AC with frequency of 1Hz), where the actuator oscillated. For pressure ratio of 0.5, the flow rate was 0.7sccm. so we concluded that the actuator, in AC mode, was working as a micropump.
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