Industrial printing today suffers from major drawbacks due to the use of water based inks. Water based inks can bleed and cause warpage of the recording surface. Supercritical carbon dioxide is being investigated as an alternative solvent to water. Supercritical carbon dioxide eliminates many of the drawbacks of water based inks because it undergoes a phase change as it leaves the print head, and the ink particles hit the recording surface dry.
The long range goal of the research presented in this thesis is to design and characterize a MEMS supercritical carbon dioxide valve(SCV)The valve must meet the following performance criteria: 300 bars operating pressure, ink delivery rate of10 milligrams per second, and a resolution of 150 dpi. The SCV actuator has a bi-chevron layout with the arms of the chevron being made from aluminum nitride (AlN). Several new bi-chevron actuator designs have been studied using the finite element simulation software, ANSYS. These designs include bi-chevrons with: S shaped arms, horizontal tethers, tapered tethers, and angled tethers. The straight-armed bi-chevron was shown to consistently outperform the bi-chevron with S shaped arms. The simulation results show that the maximum unrestricted stroke of the straight-armed bi-chevron is 1.32 μm, and the maximum force generated is 1.55 mN. The angled tether was shown to outperform the other tether geometries. The maximum unrestricted stroke of a bi-chevron with angled tethers is .76 μm, and the maximum force generated is .74 mN. Modal and harmonic analyses of the straight-armed bi-chevron actuator were performed. These analyses reveal that if the actuator is driven at its in-plane resonance mode, the stroke of the actuator can be increased by as much as 277% compared to static actuation.Driving the actuator at its in-plane resonance mode is one way to help the SCV meet its performance goals.
A number of experiments have been designed to study the bi-chevron actuator as well as the SCV system. In order to meet the sealing force requirements of the SCV, an experiment that uses a load cell and two high-precision x-y-z tables has been designed to directly measure the force generated by the bi-chevron actuator. In order to meet the flow requirements of the SCV, microchannel experiments have been designed to characterize flow behavior of supercritical CO2. Microchannel geometric parameters that will be studied are: channel length, channel width, number of 90deg turns, flow around a simulated plug, and channel turn radius. Also, a modified clamping fixture has been designed and fabricated in order to make electrical connections to a MEMS die when it is installed in our supercritical carbon dioxide testing apparatus. The results from these experiments will guide the design of the SCV system towards meeting its performance goals.