ln vorliegender Arbeit werden Methoden für die kostengünstige und schnelle Herstellung von Funktionsmodellen für die Mikrosystemtechnik entwickelt. Für die Mikrostrukturierung von Substraten werden sowohl für die Laserbearbeitung als auch für das Trennschleifen die notwendigen Fertigungsparameter abgeleitet. Die Montage von Funktionskomponenten wird über einen neu entwickelten Mikromontageplatz mit Klebstoffauftragswerkzeug realisiert. ln weniger als 10 Stunden können mit den vorgestellten Verfahren fünf Funktionsmodelle eines Mikrotropfen­erzeugers hergestellt werden. ...

Piezoelectric actuators are commonly used in Micro-Electro-Mechanical Systems (MEMS). They can deliver high forces, large accelerations, and high power densities. However, one of their weaknesses is the comparatively small actuator travel that can be readily achieved. The elongation attainable by a slab of piezoelectric material is only a few tenth of a percent. Therefore, it is often useful to employ mechanical structures which are capable of amplifying those minute deflections. A particularly often used configuration is a sandwich structure consisting of either two differently poled strips of piezoelectric material or a single strip of piezoelectric and a layer of passive material. Such a structure is called a bimorph. If one of the layers is mounted above a cavity, the structure forms a membrane actuator. Because of their capability to displace fluid volume, those actuators are suitable for a wide range of applications in the area of microfluidics, including, but not limited to, micropumps, microvalves, microdroplet generators, and high frequency acoustic transducers. The directed design of those actuators demands the determination of their mechanical and electrical properties in advance. In the present paper a compact model for the characterization of such a bimorphic membrane actuator is presented. The model is based on an analytical description of the bending line of the membrane by means of Euler-Bernoulli-Beam theory. Relationships for the dependency of the actuator deflection and the volume displaced by the membrane on the geometry and the material properties of the actuator are established. Other model parameters like the moving mass and the effective stiffness are also determined. The identified parameters are used to create a behavioral model of the full dynamic characteristics of the actuator. This allows the prediction of the dynamic response to an arbitrary input excitation signal. The model is validated by comparing the predicted static and dynamic behavior of the membrane actuator with empirically derived results. For this purpose a number of test specimen with different actuator geometries are fabricated. The quasi-static deflection of the actuator is monitored with a laser-vibrometer for different drive voltages. Furthermore the dynamic behavior of the actuator is determined by recording its step response function. Overall, a model for the prediction of the static and dynamic behavior of a piezoelectrically driven bimorph membrane actuator is presented. The model validation shows good agreement between the predicted and measured behavior for the quasi-static deflection of the actuator and reasonable agreement for its dynamic properties.

Dispensing minute amounts of fluid is used in many industries, such as in life science, bioengineering, 3D printing, or in electronics manufacturing. Each application for drop-on-demand (DoD) printheads requires different drop volumes and drop velocities. Furthermore, it is necessary to eject droplets made of fluids with different fluid properties, like viscosity, surface tension, or density. Due to this wide range of different applications and demands on printheads it is important to investigate the influence of relevant factors on the droplet formation process. Therefore, the influence of the fluid properties, the printhead geometry, and the electrical excitation form on the droplet formation process are described in this project. In detail, the influence of the surface tension as well as the viscosity of the fluid, the nozzle length and its width, and the amplitude of the applied voltage at different pulse widths on the droplet characteristics are investigated. The used printhead consists of a silicon chip, which includes the fluidic components, and of a bimorph piezoelectric actuator. The printhead is manufactured with rapid manufacturing techniques, such as laser micromachining. The advantage of this method is that the printhead is adaptable to new boundary conditions in a time- and cost-saving manner. In this project, the nozzles have a square shape with a sidelength between 50 and 100 μm and the nozzle length varies between 50 and 200 μm. A fluid mixture is provided which can be varied in its fluid properties. Therefore, the possibility for the independent adjustment of its viscosity and its surface tension is given. The mixture consists of glycerin, distilled water, and isopropanol. An analytical description for each amount of its substances enables to provide a fluid with defined properties. Three kinds of experiments are carried out in order to determine the influence of the fluid properties, the printhead geometry, and the electrical excitation on the droplet formation process. The determination of the minimum excitation voltage needed for droplet ejection and the determination of the droplet volume and its velocity. The main results are: The higher the surface tension, viscosity, and nozzle length, the higher is the minimum excitation voltage. Furthermore, the droplet velocity decreases for an increased surface tension, viscosity, and nozzle length. On the other hand, the droplet velocity increases with an enlarged amplitude of the voltage and pulse width. The droplet volume increases for an increased surface tension, nozzle width, pulse width, and amplitude of the voltage. In general, the reasons for these correlations are the interaction between the strength of the pressure pulse, friction forces, fluidic resistances, and fluid properties. Overall, the possibility to achieve microdroplets made of different fluids and with a specific velocity and volume is described. Furthermore, a fluid mixture, which can be varied in its fluid properties, is presented.

In the present paper a compact model for a piezoelectric drop-on-demand (DoD) printhead is derived from basic electrical, mechanical and fluid mechanical relationships. The model covers the whole droplet generation process, spanning over the electrical as well as the mechanical and fluidmechanical domains. It allows predictions about essential droplet characteristics, such as droplet volume and flight velocity, for a given set of droplet generator (DG) dimensions, material and fluid properties and a predetermined electrical excitation. This enables the targeted adaption of the droplet generator's design to varying application requirements, such as different fluid properties, with a minimum number of design iterations. The model is implemented by transferring the resulting differential equations to the Matlab/SIMULINK™ simulation environment. It is verified by comparing its output with an extensive empirical dataset which is obtained by fabricating a selection of droplet generators with different geometrical dimensions and testing them with several different fluids. Despite the fact that the model is based on strongly simplified physical relationships, it is able to accurately predict the minimum excitation voltage needed for droplet generation as well as the droplet velocity. However, the volume of the ejected droplets could not be predicted with satisfactory results, which is attributed to the limited accuracy of the nozzle submodel.

This paper presents a piezoelectrically driven microdrop generator based on a diaphragm design. The complete microdrop generator is manufactured by rapid manufacturing techniques, such as laser micromachining. This leads to a short production time which amounts to less than 2 hours per device.After the fabrication of the microdrop generators they have to be put into operation. This means that they have to be fluidically as well as electrically connected. Therefore, the microdrop generator is bonded onto a carrier board which includes the fluid supply, conducting paths, and soldering pads. Afterwards, the carrier board is mounted on a support plate. Here, a fluid reservoir and heating elements are integrated.Fluidic investigations are carried out with isopropanol and distilled water for validation purposes. The dependency of the minimum excitation voltage needed for droplet ejection on the pulse width and the relation between the droplet velocity and the excitation voltage are determined. The results show that increasing the pulse width reduces the minimum excitation voltage. The reason is the prolonged energy supply. Ejecting distilled water droplets requires a lower minimum excitation voltage in comparison to isopropanol due to the lower viscosity. Furthermore, droplet velocities are determined for various excitation voltages. A linear relationship between the velocity and the excitation voltage is observed. For excitation voltages greater than 65 V droplet velocities greater than 10 m/s are achieved for isopropanol.

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.

A fluidic experimentation platform, consisting of a piezoelectrically driven microdrop generator which is mounted on a quick-action clamping device, is introduced. Microdrop generators are playing an increasingly important role in many industries. Even though their beginnings were in the printing and coating sector, their strengths are more and more used in other sectors. The wide variety of properties of the fluids like molten polymers, dispersions, or monomers usually require a redesign of the microdrop generator for each application to achieve drops of the size, with the speed, and uniformity that are needed. Therefore, the use of rapid prototyping (RP) techniques for the adaption of microdrop generators to new boundary conditions is indispensable. The presented microdrop generator is based on the diaphragm design. A silicon base plate includes the fluidic components. The number of nozzles is three. Even if one nozzle is clogged two other nozzles are working. The diaphragm is made of borosilicate glass. On top of the diaphragm a piezoelectric transducer is glued. The piezoelectric transducer and the diaphragm form a bimorph actuator. Since only the borosilicate glass and the silicon are in contact with the fluid the assembly is highly chemical resistant to aggressive media. Thus, a very broad range of fluids is ejectable. Besides the laser as main tool a dicing saw is involved in the process flow. Investigations for the optimum machining parameters are presented. In this project four equal microdrop generators respectively 12 nozzles and one further silicon base plate for further quality inspection of the whole batch are manufactured simultaneously. They serve as a good basis for fluidic experiments. Only six process steps are necessary to fabricate one microdrop generator within 25 min. Up to 16 microdrop generators can be batch fabricated in a 4″ process chain with rapid prototyping techniques. The realized quick-action clamping device supports a rapid exchange of the microdrop generators and enables future technologies. Here, the electrical and the fluidic connection of the microdrop generator are realized. The microdrop generator is inserted into a groove and is at the same time fluidically and electrically connected via four spring contacts. Special feature is that no gluing or soldering processes are necessary. The device is constructed in a modular way to add further components like a heating cartridge or a fluid reservoir. Overall, the exchange of one microdrop generator can be realized within one minute. The use of the batch fabricated microdrop generator in combination with the presented quick-action clamping device guarantees an efficient execution of fluidic experiments.

This paper describes a squeegee device for a manual microassembly system. The device consists basically of a height axis, of a squeegee clamp, and of a squeegee blade. The squeegee device is connected via a supporting arm to the base frame of a microassembly system. The objective of this work is to obtain a homogenous, thin, and defined adhesive layer for piezoelectric actuators which are used in microdroplet generators. Here, a droplet is ejected due to the bending of the actuator into a fluid filled chamber. The actuators are mostly based on bi-or multimorphic layer structures. Here, two or more layers, of which at least one is a piezoelectric material, are glued together. In this connection homogenous and thin adhesive layers are indispensable. The thinner this layer, the higher the bending of the actuator due to its reduced bending stiffness. As a result, more energy can be supplied to the droplet generation process. In this project two adhesives - one - as well as two-component - are used for the validation of the device. This shows that this device can work with different materials. The result is that homogenous adhesive layers between 10 μm and 80 μm can be spread homogenously onto substrates.

Purpose: Patient-specific models of organs improve the planning of surgical resections and the intraoperative approach. In particular, pancreatic cancer surgery can benefit from a manufactured, patient-specific model. Therewith, the complex anatomical structures of and around the pancreas, especially the vessels, can be visualized. Methods: Several CT data sets showing the pancreas / pancreatic cancer were segmented. A special software system was used which allows segmentation of different tissues and export of three dimensional model data. A patient-specific model containing the pancreas, pancreatic cancer, arteries and veins was created for each case using rapid prototyping technologies. Different prototyping techniques were applied to show details and anatomical structures within the pancreas. Results: The patient-specific models of the pancreas / pancreatic cancer allowed better visualization of the three-dimensional anatomical structure as well as the perception of size and relations of dimensions and volume. Additionally, the vessels and the cancer within the pancreas were highlighted. Conclusions: The described procedure of creating patient-specific models of the pancreas promises advantages for pre-and intraoperative planning of pancreatic cancer surgery.

Dosing liquids in small quantities is present in a lot of different applications as inkjet printing, heating devices, and 3D-printing methods. This paper deals with a drop on demand (DOD) printhead based on a piezo-element bender actuator which can generate drops out of wax. The aim is to provide a testing system where changes of significant design parameters can be done easily in order to proof the working principle in early stages of development. In this work a given drop on demand printhead is modified making the manufacturing process more reliable. Putting single drops on each other can be regarded as both proof of functionality and an outlook on future applications for direct 3D-printing and rapid prototyping.

Laser micro machining belongs to the most important processes in rapid prototyping / rapid manufacturing. Especially Nd:YAG lasers with a galvanometer scanner are extremely common in manufacturing Micro-Electro-Mechanical-Systems (MEMS) in a time and cost saving manner. Moreover, laser micro milling is one of the most significant processes in laser micro machining apart from laser micro cutting and micro welding. In recent years a lot of investigations were done for direct parameters of the laser source such as the laser power, the fluence, the repetition rate, the lamp current, and the pulse duration. These parameters are not applicable to other laser systems because they are depending on the used laser source. The basic parameters (focus position, pulse overlap, track overlap), which are completely independent of the used laser sources, were mostly neglected although they have a huge influence on the result of the process. Therefore, this project investigates laser micro milling square pockets in silicon with a nanosecond Nd:YAG IR laser. For each basic parameter the ablation rate, the surface roughness as well as the machining diameter are determined.

A novel experimentation platform, which is based on a piezoelectrically driven inkjet printhead and on a support plate, is presented. A huge number of fluids has to be ejected due to the large variety of possible applications for inkjet printheads. Each fluid with its special characteristics usually requires a redesign of the printhead to be able to be ejected. This inkjet printhead is manufactured in a batch process with rapid prototyping techniques in order to be able to be adapted to new boundary conditions in a time saving manner. The manufacturing time only amounts less than 30 minutes. The inkjet printhead is inserted into a support plate. Here, it is electrically as well as fluidically connected without any soldering or gluing processes. Heating elements, temperature as well as pressure sensors, and a fluid reservoir are integrated. The reproducibility of experiments is thereby given. Furthermore, printing fluids with solid-liquid phase transition is possible. The inkjet printhead can be changed within only one minute.

This paper introduces a chemical resistant piezoelectrically driven microdrop generator which can be fabricated in a cost and time saving manner by using rapid prototyping techniques. Thus it is especially suitable as an experimentation platform.For the adaption of microdrop generators to various fluids, an experimentation platform is needed which allows the rapid change of geometry, dimensions, and material parameters of the microdrop generator. The size of the nozzle, the geometry of the pumping chamber, and the thickness of the used piezo-transducer have to be adaptable to various fluids to achieve drops of the size, speed, and uniformity that are needed.This microdrop generator uses a sandwich structure which consists of a silicon wafer, a Pyrex diaphragm, and a PZT transducer. A pumping chamber is milled into the silicon by laser micromachining; and the Pyrex is anodically bonded on top of the silicon plate to seal off the pumping chamber. The piezo-transducer is then glued to the diaphragm with an epoxy adhesive to obtain a bimorph actuator.When electrically driven, the actuator bends inwards into the pumping chamber which in turn creates a pressure wave inside the chamber that finally leads to the ejection of a drop out of the lateral nozzle. Since only the Pyrex and the silicon are in contact with the fluid the assembly is very resistant to aggressive media like solvents, adhesives, or acids. The thickness of the piezo-actuator can be varied according to the intended application. Depending on the piezoceramic used, the operating temperature is up to 250 degrees C.Single- and multi-nozzle arrays as well as the integration of a heated fluid reservoir can be realized. The drop volume is set by proper dimensioning of the microdrop generator. Manufacturing, assembly, and interconnection technology of the droplet generator will be described later in this paper.The electro-mechanical behaviour of the droplet generator is analyzed by determining the step response function and by measuring the frequency-dependant impedance. For the first fluidic validation of the experimentation platform, isopropanol is used because of its well known properties. The relationship between drop velocity and drive voltage on the PZT transducer is established.Special attention is paid to the calculation of the microdrop generator material cost which only amounts to $ 25 for a multi-nozzle array. By using rapid prototyping techniques the microdrop generator is manufactured within 180 min. This shows the potential for a low-cost and rapidly producible experimentation platform.

This paper describes the development and the application of a low-cost manual micro assembly system with an integrated heater. The presented system consists basically of a massive frame to dampen vibrations, of an observation unit, of a heating element with a 2-point temperature controller, and of an exchangeable vacuum gripper for the deposition of a work piece on a target substrate which is mounted and correctly aligned on a vacuum plate. During the development we place considerable value on a modular system which is easy to use, highly accurate, and cost-efficient. In this connection, we will point out the labor and machine maintenance as well as the material costs. Present micro assembly system only weighs 21 kg and has an engine room of 28 × 35 × 56 cm (length × width × height). This makes it suitable for easy transportation. So it can be installed and used in almost every location. Although the labor and machine maintenance as well as the material costs only amount to less than 9.900 € a positioning accuracy of ±15 μm is achievable. The maximum tooling-up time depends on the required operating temperature.

During the last four decades laser beam machining has been used as a powerful tool in rapid prototyping. Nd:YAG lasers are most widely used in machining of engineering materials, especially silicon for Micro-Electro-Mechanical-Systems (MEMS). Apart from laser micro-welding or laser micro-drilling, laser micro-cutting is one of the most important processes in rapid prototyping. In recent years the researchers have focused on the parameters of the laser beam, such as the pulse duration, the wavelength, the laser power, and the repetition rate. All these parameters depend on the laser system and can be varied in a wide range. The basic parameters - the focus position, the pulse overlap, the track overlap, the number of tracks, and the influence of wobbling - were mostly neglected, although their effect on laser micro-cutting is essential and independent of the above mentioned parameters of the laser system. This research work investigated laser micro-cutting holes in silicon wafers with a nanosecond Nd:YAG UV laser and determines for each parameter the number of scans, the required manufacturing time, the diameter on the laser beam output side as well as on the input side, and the corresponding flank angle.