Optimization of the Electro-Mechanical Behavior of a Bimorph Piezoelectric Actuator for Drop-on-Demand Techniques Based on Finite Element Method

The optimization of the electro-mechanical behavior of a bimorph piezoelectric actuator for microdrop generation is presented. The objective of this project is to enlarge the travel of this actuator which is mounted above a fluid filled chamber. Its bending inwards this chamber leads to the reduction of its volume. The generated pressure pulse leads to the ejection of a droplet out of the nozzle. The higher the travel, the higher the pressure pulse. Especially for printing high viscous media high pressure pulses are required. This microdrop generator consists of a piezoelectric transducer with surface electrodes, of a borosilicate glass diaphragm, and of a silicon chip including the fluidic components (nozzle, fluid filled chamber, throttle, and fluid inlet port). The transducer is bonded with a two component adhesive onto the glass diaphragm. Hereby, the bimorphic actuator is formed. Up to now, the electrodes have a width of 1.5 mm and they are electrically separated from each other by ablated areas with a depth of 20 μm. Each electrode belongs to one nozzle. Three nozzles are integrated in one microdrop generator. The advantage is that two other nozzles are working even if one nozzle is clogged. Within this optimization process the depth of the ablated area between the electrodes, the width of the electrodes, and the thickness of the diaphragm, of the adhesive layer as well as of the piezoelectric transducer are investigated. The simulation tool “ANSYS® 14” is used. The results show, the deeper the ablated area between the electrodes, the higher the travel. To ablate this area respectively to cut grooves through the piezoelectric material up to the glass diaphragm lead to a higher travel because the electrodes are not clamped laterally. Here, a solid state hinge characteristic enables the bending. Furthermore, widening the electrodes also leads to a higher travel because the capacitance is enlarged. Moreover, reducing the thickness of the glass diaphragm also leads to the enlargement of the travel up to a thickness of 25 μm. But during this optimization process a strong attention is paid to the manufacturability of all components with the available rapid manufacturing (RM) machines, such as laser system, dicing saw, or anodic bonding device. Glass diaphragms thinner than 100 μm are difficult to handle because the material is very brittle and the risk for damaging them during the manufacturing process of the microdrop generator is too high. For thicker diaphragms the resultant travel decreases due to the enlarged bending stiffness. The result is that a 100 μm thick glass diaphragm is chosen. The result for the adhesive layer thickness is, the thinner this layer, the higher the travel of the actuator. The adhesive has a small Young’s modulus. Therefore, the direct transmission of forces is reduced for thick adhesive layers. For production-related reasons a thickness of 20 μm is chosen. All components can be manufactured with the available RM machines.

Experimental and Numerical Studies on the Performance of a Polydimethylsiloxane Valveless Micropump

A low cost, simply structured micropump, which is actuated by piezoelectric discs, was fabricated using polydimethylsiloxane. As a flow-rectifying element, diffusers were used instead of passive check valves. To evaluate the performance of a micropump, the deflection of a diaphragm and the flowrate of a pump were measured experimentally for various applied voltages. The deflection of a glass diaphragm was measured using an atomic force microscope. It increased linearly (up to 0.4 μm) with the voltage (up to 150 V) when square voltage waves were applied across a piezoelectric disc. The flowrate of a micropump increased with the applied voltage and decreased with the backpressure. The maximum flowrate was 32.9 μI/min and the shut off pressure was 173 Pa when 150 V square wave voltages were applied at 300 Hz. The micropump was numerically modelled based on the experimentally measured diaphragm deflection-flowrate relationships, and the flow fields were analysed using a numerical method. The calculated flowrates were compared with the experimental measurements, and the results showed that the performance of a micropump could be predicted accurately using a computational model.

Heat of transport and heat capacity of transport of some aqueous electrolytes

The thermal diffusion of aqueous solutions of NaCl, KCl, MgCl2, BaCl2, MgSO4, and CuSO4 (0.05 m) contained in the pores of a sintered glass diaphragm has been studied. A cell is designed and fabricated for this purpose, and the resulting heat of transport values are compared with those available from the literature and obtained by using independent techniques.

Transient rates of gas sorption. I. Measurement of rapid gas uptake by Oxide Catalysts

The rate of gas uptake by a porous solid in a constant volume system was deter- mined by measuring the decrease in pressure, using a capacitance-type glass diaphragm manometer. Techniques are described for admitting gas to adsorbent quickly, and for measuring rapid changes at low pressures and high temperatures. For water and alcohols the rates of uptake by thoria and alumina at 110-200 �C were found to have a negative temperature coefficient. Rates were first order with respect to initial pressure. Three types of rate dependence on mass of adsorbent were found - first, zero, and second order or exponential.

THE SOLUBILITY OF HYDROGEN SULPHIDE IN WATER FROM THE VAPOR PRESSURES OF THE SOLUTIONS

The vapor pressures of a number of solutions of H2S in water have been measured at temperatures between 5° and 60 °C. A new type of glass diaphragm manometer having several advantages is described, and a bibliography of flexible glass manometers is given. The results show that Henry's law is not strictly obeyed and that previously reported values may require correction. Discussion of the results is reserved for a later paper.