Schizophrenic molecules and materials with multiple personalities - how materials science could revolutionise how we do chemical sensing

Molecular photoswitches like spiropyrans derivatives offer exciting possibilities for the development of analytical platforms incorporating photo-responsive materials for functions such as light-activated guest uptake and release and optical reporting on status (passive form, free active form, guest bound to active form). In particular, these switchable materials hold tremendous promise for microflow-systems, in view of the fact that their behaviour can be controlled and interrogated remotely using light from LEDs, without the need for direct physical contact. We demonstrate the immobilisation of these materials on microbeads which can be incorporated into a microflow system to facilitate photoswitchable guest uptake and release. We also introduce novel hybrid materials based on spiropyrans derivatives grafted onto a polymer backbone which, in the presence of an ionic liquid, produces a gel-like material capable of significant photoactuation behaviour. We demonstrate how this material can be incorporated into microfluidic platforms to produce valve-like structures capable of controlling liquid movement using light

Single Substrate Electromagnetic Actuator

A microvalve which utilizes a low temperature ( <300° C.) fabrication process on a single substrate. The valve uses buckling and an electromagnetic actuator to provide a relatively large closing force and lower power consumption. A buckling technique of the membrane is used to provide two stable positions for the membrane, and to reduce the power consumption and the overall size of the microvalve. The use of a permanent magnet is an alternative to the buckled membrane, or it can be used in combination with the buckled membrane, or two sets of micro-coils can be used in order to open and close the valve, providing the capability for the valve to operate under normally opened or normally closed conditions. Magnetic analysis using ANSYS 5.7 shows that the addition of Orthonol between the coils increases the electromagnetic force by more than 1.5 times. At a flow rate of 1 mL/m, the pressure drop is < 100 Pa. The maximum pressure tested was 57 kPa and the time to open or close the valve in air is under 100 ms. This results in an estimated power consumption of 0.1 mW.Georgia Tech Research Corp

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

Development of the technological process for the production of the electrostatic curved beam actuator for pneumatic microvalves

This work focuses on the development of an effective technological process for the production of the electrostatic curved beam actuator capable to be used as a driving element in different devices such as microswitches or microvalves. Main attention was drawn to the investigation of electroplating technique as a critical process in the microactuator fabrication as well as to the design of the actuator. In addition, usability of ceramic substrates for the microactuator and microvalve production was examined. The idea behind it was that ceramic substrates can be preprocessed and delivered already with necessary electrical connections on it. This would make the entire production process simpler and cheaper. Several types of polished alumina (Al2O3) substrates were used for this purpose. Electrostatic actuation principle was chosen for its good scaling properties to small dimensions, low power consumption, smaller size and higher switching speed. Curved shape of the actuator allows to reduce its pull-in voltage and thus to increase the amplitude of motion as compared to the parallel-plate structures. The material of the actuator is nickel. It was chosen for its good mechanical properties and relative simplicity of processing. Double layer nickel electroplating was used to produce the microactuator. The layers have different stress gradients controlled by current density during the electroplating process, making it possible to achieve the desired bending of the structure. Compared to bimetallic bending cantilever actuators, the curvature of the single-metal beam is less dependable on temperature and aging. Thus, more stable performance under changing working conditions was ensured. In order to avoid sticking of the microactuator to the isolation layer in the closed state, an array of stand-off bumps was added on the back-side of the beam. These bumps reduce the contact area and increase the distance between the actuator and the isolation layer. Fifteen design variants of the actuator differing in length and width were fabricated in order find the most effective solution for given system requirements. Based on the actuators technological process developed in this work, a simple electrostatic microvalve was designed and produced. Final variants of microvalve were fabricated on a standard 380 µm thick silicon wafer. Gas inlet channel as well as the electrodes and the actuator itself are all placed on the same substrate in order to reduce the size and cost of the system. During characterization, mechanical stability of the actuators and microvalves were studied by means of drop, temperature and shear tests in order to prove the reliability of the system. System performance tests proved stable pull-in voltages from 8,6 V to 11,6 V. Maximal gas flow through the valve was 110±5 ml/min at applied differential pressure of 2 bar

DESIGN OF A PIEZOELECTRICALLY ACTUATED MICROVALVE FOR FLOW CONTROL IN FUEL CELLS

This thesis presents a novel piezoelectrically actuated microvalve for flow control in fuel cells. A fuel cell is an electrochemical device, which directly converts chemical energy stored in a fuel (e.g. hydrogen) and an oxidizer (e.g. oxygen) directly into electrical energy. Poor flow distributions within the cell have been attributed to degraded performance and even damage. In this study, it is proposed to embed microvalves directly into the fuel cells to manage the gas flows and improve efficiency, performance, and reliability. The microvalve has four parts. The actuator is a piezoelectric trimorph which has two piezoelectric layers and one brass layer sandwiched between them and has dimensions of 20000 x 4000 x 290 microns. It also has a valve gate placed on the tip. For a 5-volt input, a deflection of 32 microns can be achieved in the trimorph tip, which is what modulates the flow through the valve.The valve design and analysis are complete. Maximum stress on the bender reaches up to 60 Mpa when the the fluidic and thermal forces are at their maximum. This maximum stress is below the tensile dynamic strength values of piezoelectric and brass layers used. A minimum factor of safety of 1.5 is obtained at 20 degrees C. At the operating temperature, which is about 100 degrees C the factor of safety is higher since the stresses are much lower. The drag and pressure forces are found to reduce the free deflection by only 0.2 microns whereas the thermal expansion forces increases the deflection almost by the same amount. Finally detailed fabrication plan and drawings were completed

Bucky gel actuator for morphing applications

Since the demonstration of Bucky Gel Actuator (BGA) in 2005, a great deal of effort has been exerted to develop novel applications for electro-active morphing materials. Three-layered bimorph nanocomposite has become an excellent candidate for morphing applications since it can be easily fabricated, operated in air, and driven with few volts. There has been limited published study on the mechanical properties of BGA. In this study, the effect of three parameters: layer thickness, carbon nanotube type, and weight fraction of components, on the mechanical properties was investigated. Samples were characterized via nano-indentation and DMA. It was found that BGA composed of 22 wt% single-walled carbon nanotubes and 45 wt% ionic liquid exhibited the highest hardness, adhesion, elastic and storage moduli. Most of BGA potential applications would require control over one BGA output: displacement. In this study, various sets of experiments were designed to investigate the effect of several parameters on the maximum lateral displacement of BGA. Two input parameters: voltage and frequency, and three material/design parameters: carbon nanotube type, thickness, and weight fraction of constituents, were selected. A new thickness ratio term was also introduced to study the role of individual layers on BGA displacement. In addition, an important factor in the design of BGA-based devices, lifetime, was investigated. Finally, possible degradation of BGA was studied by repeating displacement measurements after several weeks of being stored. Based on displacement studies, a new model was established utilizing nonlinear regression to predict BGA maximum displacement based on the effect of these parameters. This model was verified by comparing its predictions with other reported results in the literature. The model displayed a very good fit with various reported cases of BGA samples made with different types of CNT and ionic liquid. Microfluidics is a promising field of application for BGA. A brief literature review on the electroactive mechanisms used in microfluidics is presented. Preliminary force studies proved that BGA has the capability to be employed as a microvalve. A flow regulator utilizing a BGA microvalve was designed and fabricated. Flow rate measurements showed the capability of BGA-valve in manipulating the flow rate in different ranges

Modular integration and on-chip sensing approaches for tunable fluid control polymer microdevices

228 p.Doktore tesi honetan mikroemariak kontrolatzeko elementuak diseinatu eta garatuko dira, mikrobalbula eta mikrosentsore bat zehazki. Ondoren, gailu horiek batera integratuko dira likido emari kontrolatzaile bat sortzeko asmotan. Helburu nagusia gailuen fabrikazio arkitektura modular bat frogatzea da, non Lab-on-a-Chip prototipoak garatzeko beharrezko fase guztiak harmonizatuz, Cyclic-Olefin-Polymer termoplastikozko mikrogailu merkeak pausu gutxi batzuetan garatuko diren, hauen kalitate industriala bermatuz. Ildo horretan, mikrogailuak prototipotik produkturako trantsizio azkar, erraz, errentagarri eta arriskurik gabeen bidez lortu daitezkeenetz frogatuko da

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, fabrication, and testing of micromachined silicone rubbermembrane valves

Technologies for fabricating silicone rubber membranes and integrating them with other processes on silicon wafers have been developed. Silicone rubber has been found to have exceptional mechanical properties including low modulus, high elongation, and good sealing. Thermopneumatically actuated, normally open, silicone rubber membrane valves with optimized components have been designed, fabricated, and tested. Suspended silicon nitride membrane heaters have been developed for low-power thermopneumatic actuation. Composite silicone rubber on Parylene valve membranes have been shown to have low permeability and modulus. Also, novel valve seats were designed to improve sealing in the presence of particles. The valves have been extensively characterized with respect to power consumption versus flow rate and transient response. Low power consumption, high flow rate, and high pressure have been demonstrated. For example, less than 40 mW is required to switch a 1-slpm nitrogen flow at 33 psi. Water requires dose to 100 mW due to the cooling effect of the liquid