| Autor(en) | Behr, Christian | Wierach, Peter | Sinapius, Michael |
|---|---|
| Titel | DIFFUSION-RESISTANT COATING FOR HARSH ENVIRONMENT APPLICATION OF PIEZOELECTRIC ACTUATORS |
| Herausgeber | SMASIS, San Antonio, USA, 2018. |
| Erscheinungsjahr | 2018 |
| Abstract | This paper presents the development process of an electrically insulating and liquid-impermeable coating for piezoelectric actuators. Against the background of flow investigations of an adaptive airfoil in a water tunnel the adaptive lip including PZT-ceramics for the active lip deformation must be insulated and sealed up against the ingress of moisture. Due to high electric field strength of 2 kV/mm between electrodes of multilayer actuators any ingress of moisture would lead to a reduction of the dielectric strength and may cause a short circuit. In order to prevent failure of the adaptive lip the electrical connections of the actuators have to be insulated by a waterproof coating. A service life of at least 107 load cycles at a frequency of 100 Hz is required for the actuators. Therefore the coating should be as ductile as possible otherwise it could crack and water could diffuse into the actuators. That is why the yield strength of the coating has to be higher than of the actuators, which is 0.3 %. For the investigation of the waterproofness several samples are coated with different materials in various processes. First the actuators are moulded in epoxy resin and then a diffusion-resistant PVF-foil is applied. After a screening of different materials, an additional coating with a two-component tar-epoxy resin in combination with a gold coating applied by a PVD process seems to be the most suitable process. Another promising waterproof coating is the atomic layer deposition (ALD). It is a slightly changed chemical vapor deposition (CVD) and referring to the studies of Abdulagatov et al. an ALD of aluminum oxide (Al2O3) and titanium dioxide (TiO2) can slow down the corrosion of static copper specimens in water for ~80 days [1]. Through a redrying procedure during test intermissions an increased underwater service life of the piezoelectric actuators is achieved. |
| Autor(en) | El Sayed M., Yosef | Oswald, Philipp | Sattler, Stephan | Kumar, Pradeep | Radespiel, Rolf | Behr, Christian | Sinapius, Michael | Petersen, Jan | Wierach, Peter | Quade, Markus | Abel, Markus | Noack, Bernd R. | Semaan, Richard | Wierach, Peter | Sinapius, Michael |
|---|---|
| Titel | Experimental investigations of spanwise-segmented unsteady Coanda actuation on a high-lift configuration |
| Herausgeber | 2018 Flow Control Conference, AIAA AVIATION Forum, Atlanta, USA, 2018. |
| Erscheinungsjahr | 2018 |
| Abstract | The present study investigates the lift gains and losses generated by the superposition of a periodic spanwise-synchronous and spanwise-varied actuation component onto a steady component on an airfoil with a highly deflected Coanda flap. The unsteady actuation is provided by 33 specially-designed lip segments that deliver actuation frequencies up to 300 Hz and actuation amplitudes up to 100% of the mean blowing intensity. The results demonstrate the benefits of superimposing a periodic spanwise-synchronous component onto the steady actuation component for a separated or partially-attached flow, where up to ∆C l = 0.2 lift increase is achieved. Square wave motion is shown to be more robust than sinusoidal motion with a broader lift gain region. Spanwise traveling wave yield the highest lift gains with ∆C l = 0.25 with a relatively slow wave frequency and long wavelength. Machine learning control has also been successfully implemented with promising initial results. |
| Autor(en) | Sinapius, Michael |
|---|---|
| Titel | Adaptronik |
| Herausgeber | ISBN: 978-3-662-55884-3, Auflage 1, Springer Vieweg Verlag |
| Erscheinungsjahr | 2018 |
| Abstract | Seit den achtziger Jahren forschen Wissenschaftler an adaptiven Strukturen für Materialien, für multifunktionale Elemente oder sogar für vollständige Systeme. Dabei ist die Adaptronik (englisch: smart materials, smart structures, smart systems) ein Fachgebiet von ausgeprägter Interdisziplinarität. Das Buch bietet daher eine interdisziplinäre Betrachtung von adaptronischen Systemen, Werkstoffen und Funktionselementen und ihren Anwendungen. Der Lehrstoff integriert verschiedene ingenieurwissenschaftliche Disziplinen, von Elektro- und Informationstechnik über Fertigungs- und Regelungstechnik bis zu Werkstofftechnik und Strukturmechanik – um nur einige der relevanten Fachgebiete zu nennen. Ausgehend von den grundlegenden Prinzipien und Varianten adaptronischer Systeme und Funktionswerkstoffe werden in dem Lehrbuch die unterschiedlichen Bauweisen von Funktionselementen erläutert. Darauf aufbauend lernen Leser, wie diese Kenntnisse auf die aktive Formkontrolle, die aktive Vibrationskontrolle und die aktive Vibroakustik anzuwenden sind. Für jedes dieser Themenfelder stellt der Autor aktuelle Beispiele aus der Forschung vor, diskutiert Forschungsergebnisse und zukünftige Forschungsfragen. Jedes der neun Kapitel schließt mit Hinweisen auf weiterführende Literatur. Ein Verzeichnis der verwendeten mathematischen Symbole und ein Stichwortverzeichnis erleichtern Lesern das Lernen.Das Buch wendet sich an Masterstudierende in ingenieurwissenschaftlichen Studiengängen wie Maschinenbau, Luft- und Raumfahrttechnik, Mechatronik, Kraftfahrzeugtechnik sowie verwandte Studiengänge. Praktikern in der Industrie, die sich in das Gebiet der Adaptronik einarbeiten wollen, bietet das Buch einen umfassenden Überblick und es dient zugleich ein zuverlässiges Nachschlagewerk. |
| Autor(en) | Wierach, Peter | Opitz, Steffen | Kalow, Steffen |
|---|---|
| Titel | Experimental investigation of an active twist model rotor blade with a low voltage actuation system |
| Herausgeber | The Aeronautical Journal, 119, 1499-1512 |
| Erscheinungsjahr | 2018 |
| Abstract | Smart materials that are directly embedded in the rotor blade structure are an attractive concept for active blade control. A promising approach is the use of anisotropic piezoelectric strain actuators embedded in the rotor blade skin. Especially in Europe and the US this concept has been intensively investigated over the past years. A major drawback of all confgurations studied so far is the high operation voltage of up to 2,000V of state of the art piezoelectric actuators. Within the Green Rotorcraft Project of the European Joint Technology Initiative Clean Sky, a new approach with a low voltage piezoelectric actuation system is investigated to demonstrate the feasibility of this technology. A frst major step in this direction was completed by conducting a centrifugal test with a model rotor blade. The objective of the centrifugal test was to demonstrate the performance of the actuation system and the structural concept under centrifugal loads by showing that the expected twist deformation can be achieved at the nominal rotation speed and different actuation frequencies. It was demonstrated that the new actuation system is capable of operating under representative centrifugal loads. In comparison to state-of-the-art actuators (operation voltage 500V to +1500V) the new actuation system (operation voltage −20V to 120V) exhibits higher active twist performance per active area. |
| Autor(en) | Kauth, Felix | Narjes, Gerrit | Müller, Jan | Seume, Jörg | Vasista, Srinivas | Müller, Thomas | Francois, Daniela | El Sayed, Yosef | Semaan, Richard | Behr, Christian | Schwerter, Martin | Leester-Schädel, Monika | Nolte, Felix | Giesecke, Daniel | Atalayer, Caglar | Radespiel, Rolf |
|---|---|
| Titel | Progress in Efficient High-Lift |
| Herausgeber | AIAA AVIATION Forum, 35th AIAA Applied Aerodynamics Conference, Denver, 2017 |
| Erscheinungsjahr | 2017 |
| Abstract | This paper presents some of the progress in research on efficient high-lift systems for future civil aircraft achieved by the Coordinated Research Centre CRC 880 sponsored by the German Research Foundation. Several new approaches to increasing the lift are applied as part of the design of a reference aircraft with short take-off and landing ca- pability: The numerically predicted positive effect of Coanda jet blowing at the trailing edge flap is validated in water tunnel experiments. Robust miniature pressure and hot- film sensors are developed for the closed-loop control of a piezo-actuated blowing lip. A flexible leading-edge device utilizes composite materials, for which new structural designs are developed. Additionally, a potential de-icing system, as well as a lightning-strike pro- tection are presented. A high power-density electrically driven compressor with a broad operating range is designed to provide the blowing airflow. Different propulsion systems for the reference aircraft are evaluated. An ultra-high bypass ratio engine is considered to be most promising, and thus a preliminary fan stage design process is established. The rotor dynamic influences of the engine on the aircraft structure are investigated through a hybrid approach using a multibody model and modal reduction. |
| Autor(en) | Schwerter, Martin | Gäding, Marcel | Leester-Schädel, Monika | Dietzel, Andreas |
|---|---|
| Titel | A flexible sensor system in foil for combined absolute pressure and flow velocity measurements |
| Herausgeber | Transducers 2017 (International Conference on Solid-State Sensors, Actuators and Microsystems), Kaohsiung, Taiwan, 2017 |
| Erscheinungsjahr | 2017 |
| Abstract | This work reports on a foil integrated, flexible pressure- and hot-film sensor system for measuring flows over curved surfaces. The miniaturized rigid silicon piezoresistive pressure transducer with enclosed reference cavity allows absolute pressure sensing. Together with a foil-based hot-film transducer both transducers are embedded in a combination of thin epoxy resin with polyimide. This in-foil sensor system is surface passive and waterproof and can be bent to a radius of 20 mm while maintaining full functionality. |
| Autor(en) | Schwerter, Martin | Leester-Schädel, Monika | Dietzel, Andreas |
| Titel | Waterproof sensor system for simultaneous pressure and hot-film flow measurements |
| Herausgeber | Sensors and Actuators A: Physical, vol. 257, 2017, pp. 208-215 |
| Erscheinungsjahr | 2017 |
| Abstract | For simultaneous measurement of pressure and near surface flow conditions allowing indirect determination of wall shear stress in experimental water tunnel environment an integrated hybrid sensor system has been developed. In contrast to known approaches, which are limited to the use in gas atmosphere due to protruding electrical and fragile parts, our sensor system is waterproof shielded and embedded in epoxy resin. Furthermore an amplification circuit for the pressure signal based on a programmable gain amplifier is integrated in direct vicinity to the pressure sensor in order to minimize noise by electromagnetic disturbances. Also sensor systems with on-board digitalization of the pressure signal for direct digital read-out were realized. We present all aspects of system assembly and embedding to one waterproof module. Furthermore, read-out strategies as well as sensor test results in air and water are shown and watertightness is confirmed. |
| Autor(en) | Behr, Christian | Wierach, Peter | Leester-Schädel, Monika | Sinapius, Michael | Dietzel, Andreas |
|---|---|
| Titel | Structural integrated sensor and actuator systems for active flow control |
| Herausgeber | SPIE Smart Structures/NDE, Las Vegas, USA, 2016. |
| Erscheinungsjahr | 2016 |
| Abstract | An adaptive flow separation control system is designed and implemented as an essential part of a novel high-lift device for future aircraft. The system consists of MEMS pressure sensors to determine the flow conditions and adaptive lips to regulate the mass flow and the velocity of a wall near stream over the internally blown Coanda flap. By the oscillating lip the mass flow in the blowing slot changes dynamically, consequently the momentum exchange of the boundary layer over a high lift flap required mass flow can be reduced. These new compact and highly integrated systems provide a realtime monitoring and manipulation of the flow conditions. In this context the integration of pressure sensors into flow sensing airfoils of composite material is investigated. Mechanical and electrical properties of the integrated sensors are investigated under mechanical loads during tensile tests. The sensors contain a reference pressure chamber isolated to the ambient by a deformable membrane with integrated piezoresistors connected as a Wheatstone bridge, which outputs voltage signals depending on the ambient pressure. The composite material in which the sensors are embedded consists of 22 individual layers of unidirectional glass fiber reinforced plastic (GFRP) prepreg. The results of the experiments are used for adapting the design of the sensors and the layout of the laminate to ensure an optimized flux of force in highly loaded structures primarily for future aeronautical applications. It can be shown that the pressure sensor withstands the embedding process into fiber composites with full functional capability and predictable behavior under stress. |
| Autor(en) | Schwerter, Martin | Gräbner, Daniel | Hecht, Lars | Vierheller, Anke | Leester-Schädel, Monika | Dietzel, Andreas |
|---|---|
| Titel | Surface-Passive Pressure Sensor by Femtosecond Laser Glass Structuring for Flip-Chip-in-Foil Integration |
| Herausgeber | Journal of Microelectromechanical Systems, ISSN 1057-7157, vol. 25, no. 3, IEEE , pp. 517-523, 2016 |
| Erscheinungsjahr | 2016 |
| Abstract | To allow for smaller sizes, smoothness and robustness of exposed surface, and for integration in flexible sensor arrays, an innovative piezoresistive pressure sensor design has been developed. In contrast to known concepts, the sensing elements and the conducting tracks are positioned within the pressure reference chamber and, thus, protected against environmental influences such as water or particles. Sensing elements are electrically accessible from the backside by vias, thus enabling a fully flat surface totally free of electrical elements as desired for flow experiments. The sensor comprises a thin silicon sensing membrane and a body made from glass holding the reference chamber and the vias. The structuring of the sensor body is performed by femtosecond laser ablation. Steep ablation edges are realized, leading to small sensor dimensions. The sensing membrane is fabricated using potassium hydroxide (KOH) wet etching. The glass body and the silicon membrane can be connected with different techniques, hitherto, adhesive bonding by an epoxy resin layer was successfully tested. A sensitivity of 10 mV/V/bar and stable operation up to 7 bar absolute pressure could already be demonstrated. The new concept simplifies micromanufacture and allows for flip-chip-assembly in foil-based flexible systems that can be used in liquids and harsh environments. |
| Autor(en) | Schwerter, Martin | Leester-Schädel, Monika | Dietzel, Andreas |
|---|---|
| Titel | Flip-Chip montierbarer Mikro-Drucksensor zum Einsatz in harscher Umgebung |
| Herausgeber | Tagungsband des 4SMARTS Symposiums vom 6. - 7. April 2016 in Darmstadt, Seite 353–359 |
| Erscheinungsjahr | 2016 |
| Abstract | Im Folgenden wird ein neuartiger, „umgekrempelter“ piezoresistiver Drucksensor vorgestellt. Der Sensorgrundkörper wird statt aus dem sonst üblichen Silizium aus Borofloat-Glas hergestellt, aus ersterem wird dagegen nur eine dünne, funktionale Membran mit den piezoresistiven Elementen gefertigt. Der Herstellungsvorgang erlaubt eine invertierte Anordnung der Siliziummembran, sodass die piezoresistiven Elemente im Sensorinneren liegen und eine Kontaktierung dieser durch das Glas nach unten ermöglicht wird. Der Sensor kann daher mittels Flip-Chip-Technik montiert und verlötet werden. Die Herstellung der Kontaktierungslöcher und der Referenzdruckkammer im Glas sowie die Strukturierung der Bond-Metallschicht erfolgen mittels Femtosekundenlaser-Ablation bei einer Wellenlänger von 1030 nm. Die elektrische Kontaktierung und die metallische Bondschicht resultieren aus derselben Metallisierung. Dieser Aufbau führt zu einer kleinen Grundfläche von nur 3 x 3 mm² und einer Sensorhöhe von 220 μm. Im Gegensatz zu bestehenden Drucksensorsystemen wird eine absolut flache Sensoroberfläche realisiert, die keine elektrischen Elemente oder Anschlusspads beinhaltet. Somit ist der Sensor sowohl an Luft als auch in Wasser einsetzbar, ohne die Strömung selbst zu beeinflussen. Im Anwendungsfeld stehen daher beispielsweise adaptronische Systeme in der Luftfahrt oder die Integration in dünne, flexible Substrate. |
| Autor(en) | Behr, Christian | Lippmann, Fabian | Wierach, Peter | Sinapius, Michael |
|---|---|
| Titel | Tailored Multilayer Stack Actuators for Harsh Environment |
| Herausgeber | SMART 2015, 7th ECCOMAS Thematic Conference on Smart Structures and Materials, S. Miguel, Azores, Portugal, 2015. |
| Erscheinungsjahr | 2015 |
| Abstract | The development process of an electrically insulating and liquid-impermeable coating for piezoelectric actuators is described in this paper. Against the background of flow investigations of an adaptive trailing edge of an airfoil in a water tunnel the included PZT-ceramics must be insulated and sealed up against the ingress of moisture. Due to high electric field strength of 2 kV/mm between electrodes of multilayer actuators any ingress of moisture would lead to a reduction of the dielectric strength and may cause a short circuit. In order to prevent failure of the adaptive lip the electrical connections of the actuators have to be insulated by a waterproof coating. A service life of at least 10^7 load cycles at a frequency of 100 Hz is required for the actuators. Therefore the coating should be as ductile as possible otherwise it could crack and water could diffuse into the actuators. That is why the yield strength of the coating has to be higher than of the actuators, which is 0.3 %. For the investigation of the waterproofness several samples are coated with different materials in various processes. First the actuators are moulded in epoxy resin and then a diffusion-resistant PVF-foil is applied. After a screening of different materials, an additional coating with a two-component tar-epoxy resin in combination with a gold coating applied by a PVD process seems to be the most suitable process. Through a redrying procedure during test intermissions an increased underwater service life of the piezoelectric actuators is achieved. |
| Autor(en) | Schwerter, Martin | Hecht, Lars | Koch, Eugen V. | Leester-Schädel, Monika | Büttgenbach, Stephanus | Dietzel, Andreas |
|---|---|
| Titel | Liquid polyimide as a substrate for aeronautical sensor systems |
| Herausgeber | SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring, San Diego, 2015 |
| Erscheinungsjahr | 2015 |
| Abstract | Using more and more controlled systems in future aircraft the need of flexible sensors to be applied on curved aircraft structures increases. An appropriate substrate material for such flexible sensors is polyimide, which is available both as ready-made foil and as liquid polyimide to be spun-on. Latest results in producing and processing of polyimide layers with a thickness of down to 1 μm including designs for thin foil sensors are presented respectively. The successful processing of liquid polyimide is outlined first including the spin-on procedure, soft bake and curing for polymerization. Parameters for spin-on volume and rotation speed on glass substrates along with a comparison with ordinary polyimide foil are presented. High-precision structuring of the polyimide layer is performed either by etching (wet-etching as well as dry etching in a barrel etcher) or ablative removal using a femtosecond laser. In combination with a layer of silicon nitride as an inorganic diffusion barrier a reliable protection for water tunnel experiments can be realized. The fabrication of a protection layer and test results in water with protected sensors are presented. The design of a hot-film anemometric sensor array made on spin-on polyimide is demonstrated. With a thickness of down to 7 μm the sensors can be applied on the surface of wind tunnel models and water tunnel models without impacting the flow substantially. Additionally both the concept and recent results of a silicon sensor integrated in a polyimide foil substrate that can measure pressure as a complementary measurand for aeronautics are illustrated. |
| Autor(en) | Beutel, Tobias | Sattler, Stefan | El Sayed, Yosef | Schwerter, Martin | Zander, Martin | Büttgenbach, Stephanus | Leester-Schädel, Monika | Radespiel, Rolf | Sinapius, Michael | Radespiel, Rolf |
|---|---|
| Titel | Design of a high-lift experiment in water including active flow control |
| Herausgeber | Smart Materials and Structures, Vol. 23 , 077004 (10pp) |
| Erscheinungsjahr | 2014 |
| Abstract | This paper describes the structural design of an active flow-control experiment. The aim of the experiment is to investigate the increase in efficiency of an internally blown Coanda flap using unsteady blowing. The system uses tailor-made microelectromechanical (MEMS) pressure sensors to determine the state of the oncoming flow and an actuated lip to regulate the mass flow and velocity of a stream near a wall over the internally blown flap. Sensors and actuators are integrated into a highly loaded system that is extremely compact. The sensors are connected to a bus system that feeds the data into a real-time control system. The piezoelectric actuators using the d33 effect at a comparable low voltage of 120 V are integrated into a lip that controls the blowout slot height. The system is designed for closed-loop control that efficiently avoids flow separation on the Coanda flap. The setup is designed for water-tunnel experiments in order to reduce the free-stream velocity and the system’s control frequency by a factor of 10 compared with that in air. This paper outlines the function and verification of the system’s main components and their development. |
| Autor(en) | Schwerter, Martin | Behr, Christian | Leester-Schädel, Monika | Wierach, Peter | Sinapius, Michael | Büttgenbach, Stephanus | Dietzel, Andreas |
|---|---|
| Titel | Stress-unsusceptible pressure sensors embedded in fiber composite |
| Herausgeber | Proceedings of Eurosensors 2014, Brescia, 2014 |
| Erscheinungsjahr | 2014 |
| Abstract | This paper discusses the integration of pressure sensors into flow sensing airfoils made of fiber composite material to be used in future aircraft. An embedding procedure for damage-free integration is described, in which the sensors experience stresses by vacuum and curing during the integration at composite lamination. The mechanical characteristics and the influences of external mechanical stresses on the integrated sensor are further investigated. A sensor design unsusceptible to external mechanical stresses parallel to the air wing surface is proposed and verified by tensile stress tests. |
| Autor(en) | Schwerter, Martin | Behr, Christian | Leester-Schädel, Monika | Wierach, Peter | Sinapius, Michael | Büttgenbach, Stephanus | Dietzel, Andreas |
|---|---|
| Titel | MEMS Pressure Sensors Embedded into Fiber Composite Airfoils |
| Herausgeber | Proceedings of IEEE Sensors, Valencia, 2014 |
| Erscheinungsjahr | 2014 |
| Abstract | The paper describes the integration of pressure sensors into fiber composite in order to obtain flow sensing airfoils to be used in future aircrafts. First, the sensor design and working principle is described, followed by an embedding procedure for damage-free integration. Here the sensors are faced to stresses by vacuum and curing during the embedding process into fiber-reinforced plastic. The mechanical characteristics and the influence of external mechanical stresses on the integrated sensor are further investigated. Finally, a sensor design unsusceptible to external mechanical stresses parallel to the surface of the airfoil is proposed and verified by tensile stress tests. |
| Autor(en) | Schwerter, Martin | Beutel, Tobias | Leester-Schädel, Monika | Büttgenbach, Stephanus | Dietzel, Andreas |
|---|---|
| Titel | Flexible hot-film anemometer arrays on curved structures for active flow control on airplane wings |
| Herausgeber | Microsystem Technologies Special Issue: Smart Sensors, Actuators and MEMS 2013, ISSN: 0946-7076, Springer, 2014 |
| Erscheinungsjahr | 2014 |
| Abstract | A set of flexible MEMS sensor arrays for flow measurements in boundary layers is presented. The sensor principle of these anemometers is based on convective heat transfer from a hot-film into the fluid. Each sensor consists of a nickel sensing element between copper supply tracks. The functional layers are attached either on a ready-made polyimide foil or on a spin-on polyimide layer. These variants are designed to meet the requirements of measurements in different environments. Spin-on technology enables the use of very thin polyimide layers, ideally suited for measurements in transient flows. It is a unique characteristic of the presented arrays that their total thickness can be scaled from 7 to 52 μm. This is essential, because the sensor thickness has to be adapted to the varying thickness of the boundary layers in different aerodynamic tests. With these sensors we meet the special requirements of a wide range of fluid mechanic experiments but in particular those of future active flow control on airplane wings. For less critical flow conditions with much thicker boundary layers, thicker sensors might be sufficient and cheaper, so that sensors fabricated on ready-made foils are perfect for these applications. Since the presented sensors are flexible, they can be attached on curved aerodynamic structures without any geometric mismatches. The entire development, starting from theoretical investigations, is described. Further, the micro-fabrication is discussed, including photolithography, sputtering and wet-etching. In particular the wet-etching of the sensing element is found to be critical for the functional characteristics. |
| Autor(en) | Sinapius, Michael | Monner, Hans Peter | Riemenschneider, Johannes | Kintscher, Markus |
|---|---|
| Titel | DLRs morphing wing activities within the European network |
| Herausgeber | Procedia IUTAM 10, pp. 416 – 426 |
| Erscheinungsjahr | 2014 |
| Abstract | Smart Structures technology called Adaptronics in Germany covers the entire field of making the elastomechanicalbehaviour of structures adaptable. The main objectives are vibration control, noise reduction and shape control. The latter is directly related to morphing of airframes, thus being a focus of DLR’s aeronautical research program. DLR initiated the national morphing wing activities in the mid-nineties with research projects on morphing wing trailing egdes. The lessons learned where exploited continuously in different national and international projects up today. The research covers the most relevant application scenarios of morphing like smart trailing egde, smart winglet, or smart leading egde including the smart slat. Presently the gapless droop nose for laminar wings of future civil transport aircrafts is in the focus of the investigations at DLR in collaboration with European partners. This paper gives a survey of the related national and international activities where DLR has been involved in since the mid-nineties and elaborates the challenge of designing morphing wing structures, i.e. to provide flexibility for the deformation andstiffness for carrying high loads at the same time. |
| Autor(en) | Beutel, Tobias | Leester-Schädel, Monika | Dietzel, Andreas |
|---|---|
| Titel | Manufacturing of flexible micro hot-film probes for aeronautical purposes |
| Herausgeber | Microelectronic Engineering, Volume 111, Elsevier, Pages 238–241 |
| Erscheinungsjahr | 2013 |
| Abstract | In this work we present the design, fabrication and characterization of flexible AeroMEMS hot-film probes. The hot-films are fabricated on polyimide foil (PI). The foil is bonded onto a glass or silicon substrate in order to get a rigid structure for using standard silicon bulk-micromachining processes. After micro fabrication is finished the PI foil can be easily removed from the substrate. The foil itself is flexible enough to be placed on complex curved contours typically used in aerodynamic tests. This study discusses the failures introduced by geometry effects which occur due to isotropic wet etching of the metal layers. After these investigations, one hot-film design was chosen to create a sensor array for special measurements of wall shear stress in fluid mechanics. The array consists of 32 hot-film sensors custom made for an aerodynamic test. The properties of the sensing elements are optimized for the measurement set-up, providing a simple implementation. The sensing elements were finally made of Nickel, while the wiring was electroplated with 2 μm of Copper. Using the advantages of both materials is unique. It is assumed that due to the extremely flat design, the sensor including its Cu wiring has no influence on the flow. The foil, including the thin wiring is bendable enough to lead the contacts into the wing, making the electrical connection very convenient. |
| Autor(en) | Beutel, Tobias | Schwerter, Martin | Leester-Schädel, Monika | Dietzel, Andreas | Büttgenbach, Stephanus |
|---|---|
| Titel | Flexible Hot-film Anemometer Arrays for Flow Measurements on Curved Structures |
| Herausgeber | Proceedings of SPIE 8763 Smart Sensors, Actuators, and MEMS VI, SPIE Microtechnologies, Grenoble, France, 2013 |
| Erscheinungsjahr | 2013 |
| Abstract | In this paper, a set of flexible aeroMEMS sensor arrays for flow measurements in boundary layers is presented. The sensor principle of these anemometers is based on convective heat transfer from a hot-film into the fluid. All sensors consist of a nickel sensing element and copper tracks. The functional layers are attached either on a ready-made polyimide foil or on a spin-on polyimide layer. These variants are necessary to meet the varying requirements of measurements in different environments. Spin-on technology enables the use of very thin PI layers, being ideal for measurements in transient flows. It is a unique characteristic of the presented arrays that their total thickness can be scaled from 5 to 52 μm. This is essential, because the maximum sensor thickness has to be adapted to the various thicknesses of the boundary layers in different flow experiments. With these sensors we meet the special requirements of a wide range of fluid mechanics. For less critical flow conditions with much thicker boundary layers, thicker sensors might be sufficient and cheaper, so that ready-made foils are perfect for these applications. Since the presented sensors are flexible, they can be attached on curved aerodynamic structures without any geometric mismatches. The entire development, starting from theoretical investigations is described. Further, the micro-fabrication is explained, including all typical processes e.g. photolithography, sputtering and wet-etching. The wet-etching of the sensing element is described precisely, because the resulting final dimensions are critical for the functional characteristics. |
| Autor(en) | Schwerter, Martin | Beutel, Tobias | Leester-Schädel, Monika | Dietzel, Andreas | Büttgenbach, Stephanus |
|---|---|
| Titel | Flexible Heißfilm-Anemometrie-Arrays zur Strömungsmessung an gekrümmten Strukturen |
| Herausgeber | MikroSystemTechnik Kongress 2013 Proceedings, ISBN 978-3-8007-3555-6, S. 749-752, Aachen |
| Erscheinungsjahr | 2013 |
| Abstract | In dieser Arbeit werden der Entwurf, die Herstellung und die Charakterisierung von neuartigen flexiblen AeroMEMS-Heißfilmsensorarrays beschrieben. Als Substrat wird ein Polyimid verwendet, das entweder als fertige Folie vorliegt oder flüssig aufgeschleudert werden kann. Mit letzterem lassen sich Sensorhöhen bis hinab zu 7 μm realisieren. Für die Herstellung der sensitiven Schicht werden zunächst mit verschiedenen Materialien Versuche zur Leitfähigkeit und zum Temperaturkoeffizienten durchgeführt und bewertet, sodass dann ein Sensor mit den gewünschten Eigen-schaften hergestellt werden kann. In der Arbeit wird die vollständige Entwicklung, beginnend bei den theoretischen Überlegungen, bis hin zur mikrotech-nischen Produktion, beschrieben. Dabei wird das nasschemische Ätzen vertieft diskutiert, da es einen besonders kriti-schen Einfluss auf die Eigenschaften des Sensors hat. |
| Autor(en) | Seume, Jörg | Burnazzi, Marco | Schwerter, Martin | Behr, Christian | Rudenko, Anton | Schmitz, Andre | Dörbaum, Michael | Atalayer, Caglar |
|---|---|
| Titel | SFB 880 – Efficient High Lift |
| Herausgeber | 62nd DLRK, Stuttgart, Germany, 2013 |
| Erscheinungsjahr | 2013 |
| Abstract | The collaborative research center (Sonderforschungsbereich, abbreviated SFB) 880 investigates the fundamentals of high-lift generation for future civil aircraft, focusing on the fields of aeroacoustics, lift generation and flight dynamics. The present paper addresses the research on efficient lift generation which is denoted as Research Area B. The underlying research hypothesis of the present work is that further significant increases in lift generation of civil aircraft compared to the current state technology are possible using active lift systems. The investigated high-lift concept utilizes a combination of internally blown flaps and circulation control to achieve high flow turning over the wing. A flexible leading edge device for the wing without gap or step is designed to reduce noise generation and to increase the efficiency of the active blowing system. Further, closed-loop control of blowing is envisaged. The overall objective of the project is to design an active lift system that requires a minimum of additional engine power to generate the required lift. A multidisciplinary, collaborative approach is taken, combining the fields of aerodynamics, material science, microtechnology, turbomachinery and electrical engineering to obtain optimum performance of the overall lift generation system. The research progress during the first two years of this ongoing work is presented in this paper. |
| Autor(en) | Beutel, Tobias | Leester-Schädel, Monika | Dietzel, Andreas |
|---|---|
| Titel | Design and Manufacturing of Flexible Micro Hot Film Probes for Aeronautical Purposes |
| Herausgeber | Mikro- and Nanoengineering, Toulouse, Frankreich |
| Erscheinungsjahr | 2012 |
| Abstract | In this work the design, fabrication and characterization of flexible AeroMEMS hot-film probes is presented. The sensor principle is based on heat transfer from an electrically heated hot-film into the flow. The power consumed is in relation to the flow [1]. In this new approach the hot films are fabricated on Polyimid foil (PI). The foil is bonded onto a glass or silicon substrate in order to get a rigid structure for using standard silicon bulk-micromachining processes. After micro fabrication is finished the PI foil can be easily removed from the substrate. The foil itself is flexible enough to be placed on complex curved contours typically used in aerodynamic tests. |
| Autor(en) | Beutel, Tobias | Boese, Christoph | Büttgenbach, Stephanus |
|---|---|
| Titel | Analysis of a closed Wheatstone bridge consisting of doped piezo resistors |
| Herausgeber | ISMTII 2011, Daejeon, South Korea |
| Erscheinungsjahr | 2011 |
| Abstract | In this paper, we present a method to calculate all four resistor values in order to balance a closed Wheatstone bridge. The Wheatstone bridge is an often used circuit for pressure or force measurements, where the applied bridge voltage is constant and the output voltage between the two midpoints is proportional to the measured load. For precise measurements, it is important to have an exactly balanced bridge. Balancing the bridge after the manufacturing process is only possible when the resistors’ exact values are known. Unfortunately it is not possible to measure each single resistor because the other resistors are connected in parallel. An analytic system is presented, which provides the possibility to calculate each resistor by measuring equivalent resistances between the corner points. Our method is unique because it provides a solution where all four resistance values are unknown. All other systems of equations found in literature need at least one known value. Another advantage is the simple realization of an automated measuring system. In this article the method for analyzing a micro pressure sensor that has been developed in recent years at the IMT will be presented. Using this example, we will also describe the measurement principle and the entire micro fabrication process. Subsequently, we will discuss the challenge of the resistance measurement and the corresponding analysis of the Wheatstone bridge. Our system of equations for the exact calculation of each resistor will be derived from the original Wheatstone bridge equations. Finally we will make suggestions to manipulate the conducting paths of every single bridge on a wafer. |
| Autor(en) | Beutel, Tobias | Boese, Christoph | Luzemann, Christoph | Holle, Ansgar | Leester-Schädel, Monika | Büttgenbach, Stephanus |
|---|---|
| Titel | Characteristics of micro hot-film probes for aeronautical purposes |
| Herausgeber | ISMTII 2011, Daejeon, South Korea |
| Erscheinungsjahr | 2011 |
| Abstract | In this work we present the design, fabrication and characterization of AeroMEMS hot-film probes. The hot-films are structured on glass or silicon substrates using silicon bulk-micromachining processes. For the initial tests, different metal layers e.g. gold, aluminum, titanium and nickel are magnetron sputtered onto wafer substrates. These hot-films have a variety of geometries and are developed for special measurements of wall-shear stress in fluid mechanics. This study discusses the failures introduced by geometry effects which occur due to isotropic wet etching of the metal layers. Also presented are the non-dynamic and dynamic test procedures used to characterize the hot-film probes. It was discovered that by varying the length and the material, varying electrical properties can be obtained. The determined material constants vary from those known from the bulk material. Dynamic tests in the desktop wind tunnel are also described and the measurement of the heat conduction from the hot-film through the substrate and its influence on the maximum operating frequency is discussed. In the long-term view, hot-films in combination with a pressure sensor on the same chip should be able to detect the state of the flow (laminar or turbulent). |
| Autor(en) | Beutel, Tobias | Ferreira, Nelson | Leester-Schädel, Monika | Büttgenbach, Stephanus |
|---|---|
| Titel | Robust pressure sensor for measurements in boundary layers of liquid fluids with medium total pressures |
| Herausgeber | SPIE Microtechnologies, Proc. of SPIE Vol. 8066, Prague, Czech Republic, 80661U1-11 |
| Erscheinungsjahr | 2011 |
| Abstract | In this work, the latest results of the design, fabrication and characterization of a new MEMS piezoresistive pressure sensor are presented. It is made of silicon using a boron diffusion process to create piezoresistors. Significant changes in the layout as well as in the micro-fabrication process have been made, e.g. anodic bonding of a Pyrex cover on the backside. These lead to a very precise pressure sensor, which is tailor made for high dynamic measurements in fluids with a total pressure up to 4 bar. This new piezoresistive pressure sensor has been developed in order to meet the special requirements of measurements in fluid mechanics, particularly with regard to the non-intrusive nature of the sensor. The sensor development, starting with the simulation of mechanical stresses within the diaphragm is described. These calculations have lead to an optimized placement of the piezoresistors in order to achieve a maximum sensitivity. The result of this work is a sensor which has well known properties. Important parameters including sensitivity, resonance frequency and maximum load are described precisely. These are necessary to enable new measurements in the boundary layer of fluids. The experiments and the initial results, e.g. its linearity and its dynamic capability are demonstrated in several figures. |
| Autor(en) | Beutel, Tobias | Holle, Ansgar | Leester-Schädel, Monika | Büttgenbach, Stephanus |
|---|---|
| Titel | Analysis of a combination of a hot-film and piezo-resistive pressure sensor on a single chip |
| Herausgeber | Mikrosystemtechnik-Kongress, Darmstadt, Germany |
| Erscheinungsjahr | 2011 |
| Abstract | An integrated wall shear stress sensor was developed at the Institute for Microtechnology (IMT) for novel measurement of flow profiles. The sensor consists of a hot film component, which is fabricated on a single chip together with a sili-con-based pressure sensor. Pressure measurement is realized by the use of piezoresistors, which are structured on a sili-con membrane. They are analyzed to detect a possible temperature drift. The wall shear stress is detected with a hot film, whose heat distribution on the silicon chip was investigated. Several varieties of thermal insulation between the hot film and the piezoresistors were tested, including negative tone epoxy-based photo resist (SU-8) filled cavities. |
| Autor(en) | Beutel, Tobias | Leester-Schädel, Monika | Büttgenbach, Stephanus |
|---|---|
| Titel | Design and evaluation process of a robust pressure sensor for measurements in boundary layers of liquid fluids |
| Herausgeber | Microsystem Technologies (ISSN 0946-7076), Volume 18, Issue 7 (2012), Springer Verlag, pp. 893-903 |
| Erscheinungsjahr | 2011 |
| Abstract | In this work, the latest results of the design, fabrication and characterization of a new MEMS piezoresistive pressure sensor are presented. Significant changes in the layout as well as in the micro-fabrication process have been made, e.g. anodic bonding of a glass cover on the backside. The sensor has been developed in order to meet the special requirements of measurements in fluid mechanics, particularly with regard to the non-intrusive nature of the sensor. The sensor development, starting with the simulation of mechanical stresses within the diaphragm resulting from a pressure of up to 4 bar is described. These calculations have lead to an optimized placement of the piezoresistors in order to achieve a maximum sensitivity. Important parameters including sensitivity, resonance frequency and maximum load are described precisely. The experiments and the initial results, e.g. its linearity and its dynamic capability are demonstrated. |
| Autor(en) | Beutel, Tobias | Leester-Schädel, Monika | Wierach, Peter | Sinapius, Michael | Büttgenbach, Stephanus |
|---|---|
| Titel | Novel Pressure Sensor for Aerospace Purposes |
| Herausgeber | Sensors & Transducers Journal (ISSN 1726-5479), Vol.115, Issue 4, pp. 11-19 |
| Erscheinungsjahr | 2011 |
| Abstract | In this work, a novel silicon-based sensor for pressure and flow measurements is presented. To meet the special requirements of the aerospace industry a new piezoresistive pressure sensor with a flat surface has been developed, so that the flow is not affected by the sensor. To avoid bonding-wires on top of the sensor a special through-wafer connection is presented. By making other significant changes in the layout as well as in the micro fabrication process, a novel sensor has been created. It is robust enough to be laminated in fibre material, which opens new possibilities for measurements. With this sensor it is possible to characterize the condition of the flow near the separation point. This article describes the complete process from the development to the laminated sensor. Copyright © 2009 IFSA. |
| Autor(en) | Beutel, Tobias | Niesel, Thalke | Leester-Schädel, Monika | Paces, Pavel | Büttgenbach, Stephanus |
|---|---|
| Titel | 5-hole Probe with Integrated Sensing Devices for Measurement of High Frequency Pressure Fluctuations |
| Herausgeber | Mikrosystemtechnik-Kongress, Darmstadt, Germany |
| Erscheinungsjahr | 2011 |
| Abstract | In the presented application, multiple differential pressure sensors based on bulk micromachining of silicon are used to enable fluid measurements with a five-hole probe. The sensor’s design has been derived from a 3D micro force sensor enabling the measurement of differential pressures in a range of 100 Pa to 120 kPa. The sensors use the piezoresistive effect of doped silicon. The major challenge is the reversibility of the sensors and the linearity of the measurement sig-nals. During the development of the mechanical, electrical and pneumatic subsystems the focus was on reducing the tube’s length. The sensors were therefore placed close to the probe’s head within the mounting pipe, enabling a tube length of only several centimetres. Damping is reduced significantly so that high frequency pressure fluctuations can be detected. With this information the angle of attack (AOA) and the sideslip angle (SSA) can be obtained. The system can be used as a sensing element in an Air Data Computer (ADC) to predict stalling of an airplane, thereby increasing air traffic safety. |