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 real-time
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.
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.
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.
The implementation of innovative methods and concepts for microsurgery – especially in the context of endovascular
and interventional treatment – require properly fitted and resized instruments. These surgical tools, such as micro-guiding
systems, must be of the highest quality regarding reliability and accuracy while additional medical requirements
for the application in the human body have to be fulfilled.
In this paper an innovative hydrostatic microactuator system for controlling the rotational degree of freedom of
microsurgery instruments is presented. From the possible hydrostatic motor designs, an annular gear motor in orbit setup
has been chosen based on its suitability for micro manufacturing. The innovative actuator design includes a rotor-integrated
control for connecting the actuator’s individual positive-displacement chambers.
Firstly, a macro-model of the new actuator was fabricated and tested. The obtained test results have already confirmed
the functionality and show the actuator’s exciting potential. Currently the macro-model is further resized and the micro
fabrication process is being developed.
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.
Silicon gratings are fabricated using micromachining techniques.
The gratings are used with fiber optic probes to measure highresolution
and long-range linear displacements. Different parameters of
the fabrication process such as the etching solution, the concentration of
the etchant, and the temperature are optimized to achieve a mirror-like
surface quality of the grating steps. For each parameter set, the resulting
roughness and flatness are analyzed and discussed. Finally, linear displacement
measurements are performed with the optimized grating as a
component of a long-range fiber optic sensor. A resolution better than
34 nm and a measurement range up to 8.7 mm are obtained.
The shape memory effect is about to become more and more important as an innovative actuation principle in micro
system technologies. Shape memory alloys (SMA) are able to return into a pre-memorized shape when heated. Due to
this regeneration force and actuation is produced. This publication reports on the design and the functionality of SMA
micro actuators and their applications for active shape control, handling technologies and medical engineering.
Thin NiTi foils have been chosen because of their well defined properties and high strength. In order to integrate them
into micro systems, different manufacturing methods have been applied and improved at the Institute for
Microtechnology (IMT). Laser cutting and wet chemical etching for example are used to fabricate actuator elements for
several applications. Different methods for electrical and mechanical connections of the actuators are employed, for
example soldering by the use of an additional gold layer. A batch fabrication process of SMA actuators is realized by
embedding NiTi-elements into SU-8 structures.
Three different micro actuator concepts are presented: A multi-actuator system for deformation of elastic surfaces,
which is driven by numerous identical single actuators connected in parallel and in series, a micro gripper for handling
and assembling of complex hybrid micro systems and a micro actuator system in medical tools for percutaneous
resection of aortic valves.
The mechanical properties of shape memory alloys (SMAs) are finding more and more attention in micro-system technology. However, only a few processes are available for machining of miniaturized SMA-components. During the machining process, changes of the shape memory properties due to the extension of the heat effected zone or mechanical tensions have to be avoided. Especially for complex geometries with dimensions in the submillimeter-range, these requirements are difficult to fulfill.
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