A feasibility study on using inkjet technology, micropumps, and MEMs as fuel injectors for bipropellant rocket engines

Control over drop size distributions, injection rates, and geometrical distribution of fuel and oxidizer sprays in bi-propellant rocket engines has the potential to produce more efficient, more stable, less polluting rocket engines. This control also offers the potential of an engine that can be throttled, working efficiently over a wide range of output thrusts. Inkjet printing technologies, MEMS fuel atomizers, and piezoelectric injectors similar in concept to those used in diesel engines are considered for their potential to yield a new, more active injection scheme for a rocket engine. Inkjets are found to be unable to pump at sufficient pressures, and have possibly dangerous failure modes. Active injection is found to be feasible if high pressure drop along the injector plate are used. A conceptual design is presented and its basic behavior assessed

Design, modeling, fabrication, and testing of a multistage micro gas compressor with piezoelectric unimorph diaphragm and passive microvalves for microcooling applications

This dissertation investigates the development of a multistage micro gas compressor utilizing multiple pump stages cascaded in series to increase the pressure rise with passive microvalves and piezoelectric unimorph diaphragms. This research was conducted through modeling, simulation, design, and fabrication of the microcompressor and its components. A single-stage and a two-stage microcompressor were developed to demonstrate and compare the performance and effectiveness of using a cascaded multistage design. Steady fluid flow through static microvalves structure was studied to gain insight on its gas flow dynamics and characteristics. Transient analysis combined with the structure\u27s interaction was investigated with an analytical model and FEM model. The static analysis and transient analysis enabled lumped model parameter extraction for modeling and simulations. The transient FEM solution of the microvalve fluid-structure interaction (FSI) allows for extraction of the damping ratio for the lumped model. The microvalves were fabricated with MEMS microfabrication methods and integrated into a machined microcompressor housing. Study from the simulation of the microvalve fluid-structure dynamics in Simulink showed the frequency of the microvalves, at which frequency the mierovalve is more prone to leakage. Simulation indicated that the reverse leakage from the sealing of the microvalve can have a significant impact on the pressure rise performance of the compressor. A model of the single- and the two-stage microcompressor were developed with Simulink to observe the dynamics and performance of the multistage microcompressor. The simulation shows the dead volume between the two chambers to decrease in the overall pressure rise of the multistage microcompressor. Operating scenarios with different frequency and in phase and out of phase actuation between stages were simulated to understand the dynamics and performance of the multistage design. The fabricated single- and two-stage microcompressor produced a maximum pressure rise of 10 kPa and 18 kPa, respectively, and a maximum flow rate of 32 sccm for both. To obtain these maximum pressure rises, the microcompressors were operated at high frequency at the resonance of the piezoelectric diaphragm. This dissertation investigated the feasibility and operation of a multistage gas microcompressor with passive microvalves, allowing the exploration of its miniaturization

Implantable Microsystem Technologies For Nanoliter-Resolution Inner Ear Drug Delivery

Advances in protective and restorative biotherapies have created new opportunities to use site-directed, programmable drug delivery systems to treat auditory and vestibular disorders. Successful therapy development that leverages the transgenic, knock-in, and knock-out variants of mouse models of human disease requires advanced microsystems specifically designed to function with nanoliter precision and with system volumes suitable for implantation. The present work demonstrates a novel biocompatible, implantable, and scalable microsystem consisted of a thermal phase-change peristaltic micropump with wireless control and a refillable reservoir. The micropump is fabricated around a catheter microtubing (250 μm OD, 125 μm ID) that provided a biocompatible leak-free flow path while avoiding complicated microfluidic interconnects. Direct-write micro-scale printing technology was used to build the mechanical components of the pump around the microtubing directly on the back of a printed circuit board assembly. In vitro characterization results indicated nanoliter resolution control over the desired flow rates of 10–100 nL/min by changing the actuation frequency, with negligible deviations in presence of up to 10× greater than physiological backpressures and ±3°C ambient temperature variation. A biocompatibility study was performed to evaluate material suitability for chronic subcutaneous implantation and clinical translational development. A stand-alone, refillable, in-plane, scalable, and fully implantable microreservoir platform was designed and fabricated to be integrated with the micropump. The microreservoir consists two main components: a cavity for storing the drug and a septum for refilling. The cavity membrane is fabricated with thin Parylene-C layers, using a polyethylene glycol (PEG) sacrificial layer. The septum thickness is minimized by pre-compression down to 1 mm. The results of in vitro characterization indicated negligible restoring force for the optimized cavity membrane and thousands of punctures through the septum without leakage. The micropump and microreservoir were integrated into microsystems which were implanted in mice. The microtubing was implanted into the round window membrane niche for infusion of a known ototoxic compound (sodium salicylate) at 50 nL/min for 20 min. Real-time shifts in distortion product otoacoustic emission thresholds and amplitudes were measured during the infusion. The results match with syringe pump gold standard. For the first time a miniature and yet scalable microsystem for inner ear drug delivery was developed, enabling drug discovery opportunities and translation to human

Development of micropump for microfluidic applications

This dissertation covers the research work on two types of micropumps, one is based on magnetohydrodynamic (MHD) principle that utilizes Lorentz force for actuation, and the other is based on electrochemical actuation. The AC-type MHD micropump was designed and analyzed as a solution to the bubble formation problem encountered in DC-type MHD micropump. A UV-LIGA process using thick layer of SU-8 negative photoresist was successfully developed to microfabricate the AC MHD micropump. Preliminary studies and tests of the AC MHD micropumps demonstrate that bubble formation was significantly reduced to permit the proper function of the micropump. A continuous flow was also successfully demonstrated with no moving mechanical parts needed. To develop the mathematical model for flow of conductive fluids between the electrodes was a challenging issue. To overcome this problem, the impedance of conductive fluids between two electrodes was measured by Electrochemical Impedance Spectroscopy, which then helped to obtain a relatively accurate mathematical model for the system. The design, simulation, fabrication, and test results of the AC MHD micropump are presented in this dissertation. Electrochemical actuator was investigated for micropumping applications. In our research efforts to develop DC-type MHD micropump, bubble formation problem caused by electrolysis proved to be one of the most difficult issues. However, microactuation based on expanding bubbles from electrolysis effect has scale advantages compared with other commonly used microactuation mechanisms. It can therefore be used as a very efficient actuation source for micropumping applications. We have designed, analyzed, and fabricated a microactuator based on the electrochemical principle. Preliminary experiments have proved that the bubbles generated in electrolysis can be manipulated by carefully controlling the direction and amplitude of the input signal. This has demonstrated that efficient pumping at micro volume of fluid can be realized by addition of required valves. The microfluidic system with micropump and integrated active microvalve has been successfully demonstrated. The working principle, design, simulation, and preliminary results of the electrochemical actuator have also been presented in the dissertation

MEMS micropump for a Micro Gas Analyzer

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 164-177).This thesis presents a MEMS micro-vacuum pump designed for use in a portable gas analysis system. It is designed to be pneumatically-driven and as such does not have self-contained actuation (the focus of future work). This research was carried out through a series of modeling, design, fabrication, and experimental testing tasks. Non-linear stress modeling tools characterizing the structural deformations of the micropump pistons and tethers, and fluid-flow modeling tools characterizing the vacuum generation and pumping rates were developed. A systematic design procedure based on these tools enabled the design and prediction of different valve and pump layouts to satisfy the stress limitations, and flow and power consumption requirements set forth by the MIT Micro Gas Analyzer project. The micropumps were fabricated using MEMS fabrication techniques, comprised of silicon and pyrex micromachining and bonding. Fabrication challenges, in particular the deep-reactive ion etching (DRIE) of the drive pistons and membrane structures, were overcome, and a completely computer controlled pneumatic testing platform for the rapid characterization of valve and micropump performance at different actuation pressures and frequencies was developed. Valve leakage data for various valve designs was collected and compared with models, and a micropump capable of generating 258Torr of vacuum below atmosphere was demonstrated at 0.75Hz operation. The maximum frequency of operation for these devices was experimentally measured to be just above 2Hz, which was consistent with fluid flow models.(cont.) This thesis presents vacuum generating micropump performance that comparables well with the best published to date, and explores future micropump designs and modeling/testing approaches that could improve overall performance and bring us closer to meeting the specifications set forth by the MGA project. Finally, general guidelines for micropump design and fabrication for any application are also presented.by Vikas Sharma.Ph.D

Velocity-independent thermal conductivity and volumetric heat capacity measurement of binary gas mixtures

In this paper, we present a single hot wire suspended over a V-groove cavity that is used to measure the thermal conductivity ($k$) and volumetric heat capacity ($\rho c_p$) for both pure gases and binary gas mixtures through DC and AC excitation, respectively. The working principle and measurement results are discussed

Microfabrication Technology for Isolated Silicon Sidewall Electrodes and Heaters

This paper presents a novel microfabricationtechnology for highly doped silicon sidewall electrodesparallel to – and isolated from – the microchannel. Thesidewall electrodes can be utilised for both electricaland thermal actuation of sensor systems. Thetechnology is scalable to a wide range of channelgeometries, simplifies the release etch, and allows forfurther integration with other Surface ChannelTechnology-based systems. Furthermore, thefabrication technology is demonstrated through thefabrication of a relative permittivity sensor. The sensormeasures relative permittivity values ranging from 1 to80, within 3% accuracy of full scale, including waterand water-containing mixtures