Dr. Johannes Riemenschneider Profile

Dr. Johannes Riemenschneider

at Deutsches Zentrum für Luft- und Raumfahrt eV

SPIE Involvement:

Author

Proceedings Article | 28 April 2023 Presentation + Paper

SMA blade twist system: from the requirements to the demonstration in relevant environment

Salvatore Ameduri, Monica Ciminello, Antonio Concilio, Ignazio Dimino, Bernardino Galasso, Mariano Guida, Johannes Riemenschneider, Benjamin Woods

Proceedings Volume 12483, 124831D (2023) https://doi.org/10.1117/12.2674195

KEYWORDS: Shape memory alloys, Safety, Aerodynamics, Prototyping, Design and modelling, Modeling, Temperature control, Solids, Sensors, Actuators

Read Abstract +

Proceedings Article | 18 April 2023 Presentation + Paper

Lamb-wave and impedance based ice accretion sensing on airfoil structures

Martin Pohl, Julia Feder, Johannes Riemenschneider

Proceedings Volume 12486, 124860Y (2023) https://doi.org/10.1117/12.2658311

KEYWORDS: Ice, Sensors, Transducers, Receivers, Pulse signals, Ultrasonics, Transmitters

Read Abstract +

Icing is a well known phenomenon in aviation. It happens, when an aircraft is flying in a freezing air mass containing water droplets which are then accreting to the surface of the aircraft. If the ice accretion gets too severe, it reduces the aerodynamic performance and increases the weight which may lead to a catastrophic failure of the aircraft. Recognizing an ice accretion is essential to initiate countermeasures against icing e.g. switching on ice protection systems or leaving the icing zone. By now, this mostly relies on the pilot looking to the front fuselage to detect ice accretion, which may be too late. To overcome this, ice accretion sensors can be used. Two types of ice accretion sensors have therefore been developed and tested at the German Aerospace Center (DLR). The first type is based on sending ultrasonic lamb waves through an icing prone structure, e.g. the leading edge of an airfoil. If an ice accretion happens, this will alter the waveguide characteristics of the structure. This change in the waveguide parameters hence influences the sensor signal, which can be detected by the sensor electronics. For the lamb wave sensor, piezoelectric transducers are therefore applied on the structure at a certain distance since the lamb wave signal needs a minimum amount of traveling time. The second sensor type also uses piezoelectric transducers and is based on measuring the impedance of the transducer. Due to the electromechanical coupling via the piezoelectric effect, the measured impedance of the transducer also contains the characteristics of the structure where it is applied to. Since an ice accretion will change these structural characteristics, measuring the impedance generates an obtainable sensor signal. Both of these sensor principles have been tested in a icing wind tunnels on a typical airfoil structures. There, the impedance sensor was mounted on three different positions in chord direction. The lamb wave based sensor has been mounted on the leading edge and further downstream positions to detect an ice accretion along the flow. During the icing tests multiple icing runs have been performed. It could be shown, that both sensors are capable of detecting the beginning of the ice accretion and the presence of ice on the structure. The lamb wave sensor reacts nearly instantaneously to the presence of ice. According to preliminary data, the impedance sensor needs a slightly larger ice thickness to produce a signal, but can handle larger ice thicknesses compared to the lamb wave sensor.

Proceedings Article | 15 April 2016 Presentation + Paper

Lessons learned from wind tunnel testing of a droop-nose morphing wingtip

Srinivas Vasista, Johannes Riemenschneider, Bram van de Kamp, Hans Peter Monner, Ronald C. Cheung, Christopher Wales, Jonathan Cooper

Proceedings Volume 9799, 979929 (2016) https://doi.org/10.1117/12.2219163

KEYWORDS: Wind measurement, Design for manufacturability, Manufacturing, Composites, Actuators, Structural design, Aerodynamics, Finite element methods, Optimization (mathematics), 3D acquisition

Read Abstract +

Proceedings Article | 9 April 2013 Paper

Strain measurements on scattered, highly oriented CNTs

Sebastian Geier, Thorsten Mahrholz, Johannes Riemenschneider, Peter Wierach, Michael Sinapius

Proceedings Volume 8691, 869110 (2013) https://doi.org/10.1117/12.2009855

KEYWORDS: Electrodes, Chemical analysis, Actuators, Liquids, Analytical research, Carbon, Silicon, Thermal effects, Smart materials, Ferroelectric materials

Read Abstract +

Since carbon nanotubes (CNTs) have been discovered in 1991, worldwide scientific research reveals excellent properties. Most of the found properties refer to almost defect-free, single-walled carbon nanotubes (SWCNTs) with nano-scale dimensions. However, scientists try to incorporate CNTs into applications to transfer their features in order to push the specific performance. Typically the results are comparably lower than expected because of the varying quality of used CNTs. This paper presents results of research using CNTs as actuators. In contrast to published paper which analyzed architectures of entangled CNTs as active components, like papers or yarns, to measure their bulk-strain this paper focuses on scattered, highly aligned CNTs. This approach promises to clarify the effect of actuation, whether it is a quantum-mechanically, or rather an combined electrostatic volume-transfer effect. Two experimental set-ups are presented. The first experiment is carried out using highly aligned multi-walled CNTs (MWCNT-arrays). Their orientation is investigated intensively in comparison to other analyzed CNT-arrays. Furthermore their substrate consists of electrical conductive carbon. The CNT-array is optically analyzed along the longitudinal geometry of the vertically aligned MWCNTs. The interfaces of the set-up, which may influence the measurement, have been analyzed in order to avoid second-order effects like thermal swelling or chemical degradation. The results reveal comparable high deflections starting at an activation-voltage of ±1.75V. The ionic liquid is tested within a voltage-range of ±2V due to time-staple performance. The second presented results are found by using Raman-spectroscopy to analyze single SWCNTs. This paper presents the first results of the challenging test campaign to analyze single-walled nanotubes within an electrolyte during charging. A shifting of Raman-peaks according to the wavenumber can be directly attributed to a geometry-change. Thus, the two presented experiments uses aligned CNTs a driving actuation mechanism of single CNTs may be identified.

Proceedings Article | 28 March 2012 Paper

Investigation of aligned carbon nanotube architectures to understand the actuation mechanism

Sebastian Geier, Johannes Riemenschneider, Thorsten Mahrholz, Peter Wierach, Michael Sinapius

Proceedings Volume 8342, 83421G (2012) https://doi.org/10.1117/12.915269

KEYWORDS: Liquids, Ultrasonics, Carbon, Particles, Manufacturing, Carbon nanotubes, Actuators, Ions, Silicon, Composites

Read Abstract +

Proceedings Article | 28 April 2011 Paper

Fundamental investigations of carbon nanotubes working as actuators

Sebastian Geier, Thea Schnoor, Johannes Riemenschneider, Thorsten Mahrholz, Peter Wierach, Karl Schulte, Michael Sinapius

Proceedings Volume 7978, 79780O (2011) https://doi.org/10.1117/12.879838

KEYWORDS: Actuators, Liquids, Manufacturing, Carbon nanotubes, Ions, Composites, Solids, Analytical research, Scanning electron microscopy, Chemical analysis

Read Abstract +

Excellent properties like low density, high mechanical stiffness as well as an outstanding thermal and electrical conductivity make researchers focusing on carbon nanotubes (CNTs) since years. Beside that it is found that structures made of CNTs can be actuated when they are set up like a capacitor. Usually two dimensional (2D) CNT-papers with randomly oriented CNTs, called Bucky-papers, are used. They are charged and divided by an electrically insulating but ionic conductible electrolyte. Experiments demonstrate low voltages for actuation (±1V). Although the mechanism of CNT-actuation is still an open issue theoretical studies suggest a charge and ion induced lengthening of the C-bonds, which predict theoretical strains up to 1%. These characteristics make CNTs a potential candidate for lightweight and powerful actuators of future adaptive aerospace applications. The presented work gives an overview of possible CNT-actuator configurations. Comprehensive analysis tools for 2D mats of randomly oriented CNTs have been developed to guarantee a consistent data base for the comparison of different CNT-configurations. It is focused on the electro-mechanical properties with respect to the processing and configuration of CNT-actuators. For a more efficient use of the mechanical advantages of the CNT-geometry a new aligning manufacturing approach is presented, to get highly oriented 2D CNT-papers. Their properties are compared with randomly oriented CNT-papers. Finally a new test set-up will be introduced, which enables deflection measurements directly on the top of vertically aligned CNTs (CNT-arrays). The buildup and necessary prework are shown, as well as results of the first experiments. The method of measuring along the axis of aligned CNTs qualifies this set-up to get a deeper understanding about the actuation mechanism of CNTs. Vertically aligned CNTs promise to be a more efficient actuator configuration because of their high stiffness in direction of actuation.

Proceedings Article | 31 March 2010 Paper

Investigations of the key mechanism of carbon-nanotube actuators and their dependencies

Sebastian Geier, Johannes Riemenschneider, Thorsten Mahrholz, Peter Wierach, Michael Sinapius

Proceedings Volume 7644, 76441G (2010) https://doi.org/10.1117/12.847252

KEYWORDS: Actuators, Solids, Manufacturing, Carbon nanotubes, Ions, Thermal effects, Scanning electron microscopy, Capacitors, Single walled carbon nanotubes, Chemical analysis

Read Abstract +

Future adaptable applications require electro-mechanical actuators with a high weight-related energy. Among modern multi-functional materials carbon nanotubes (CNTs) have some special characteristics which give them the potential to solve this demand. On the one hand raw CNTs have excellent mechanical properties like their low density (1330kg/m³) and very high estimated stiffness of about 1TPa. On the other hand CNTs have the ability under presence of ions, wired like a capacitor and activated by a charge injection to perform a dimensionchange (length of C-C bondings). Calculations and experiments present achievable active strains of 1% at low voltage of ±1V what qualifies CNT-based materials for leightweight powerful actuators. In this paper the former work done with actuators using CNT-containing mats and Nafion as solid electrolyte is evaluated by analyzing the two main-components in more detail. On the one hand the CNT-based modelmaterial SWCNT-mats called Bucky-paper (BP) and on the other hand ion donating electrolytes in liquid-phase like a NaCl-solution and its solid equivalent Nafion as thin-foils are tested. Additional methods of fabrication, preparation and characterization of the CNT-powder and the manufactured BPs containing randomly oriented single-walled carbon nanotubes (SWCNTs) are presented which provide a deeper system-understanding. Both materials (BPs and Nafion-foils) are intensively investigated in different deflection-test-rigs due to their structural assembly. This paper presents a method for electro-mechanical measurements of BPs in an in-plain test set-up which avoids sensing secondary effects like thermal expansion or mass-transport and confirm that BP-deflection should only be a capacity-driven effect. Nafion as solid electrolyte will be tested in an out-of-plane facility to measure its possible actuation within the lamellar-direction. With this approach the dependencies of each component and their individual characters on the deflection can be estimated. The active response can be referred to the internal structure of both components as well as of the whole structural assembly. The results give a certain direction to a BP-optimization referring to active strain, density, structural integrity and conductibility. In addition to these facts the active character of BPs using CNTs of different suppliers and Nafion is analyzed. These investigations are of particular importance for detection of global dependencies and using both materials in a hybrid-assembly like solid actuators which are needed for structural applications.

Proceedings Article | 6 April 2009 Paper

Solid electroytes for CNT-based actuators

Johannes Riemenschneider, Sebastian Geier, Thorsten Mahrholz, Jürgen Mosch, Hans Peter Monner, Michael Sinapius

Proceedings Volume 7287, 728713 (2009) https://doi.org/10.1117/12.815451

KEYWORDS: Actuators, Solids, Electrodes, Liquids, Resistance, Carbon nanotubes, Manufacturing, Raw materials, Capacitors, Ions

Read Abstract +

Actuators based on carbon nanotubes (CNT) have the potential to generate high forces at very low voltages. The density of the raw material is just 1330 kg/m3, which makes them well applicable for lightweight applications. Moreover, active strains of up to 1% can be achieved - due to the CNTs dimensional changes on charge injection. Therefore the nanotubes have to be arranged and electrically wired like electrodes of a capacitor. In previous works the system's response of the Nanotubes comprising a liquid electrolyte was studied in detail. The major challenge is to repeat such experiments with solid electrolytes, which is a prerequisite for structural integration. In this paper a method is proposed which makes sure the expansion is not based on thermal expansion. This is done by analysing the electrical system response. As thermal expansion is dominated by ohmic resistance the CNT based actuators show a strong capacitive behavior. This behavior is referable to the constitution of the electrochemical double layer around the nanotubes, which causes the tubes to expand. Also a novel test setup is described, which guarantees that the displacement which is measured will not be caused by bending of a bimorph but due to expansion of a single layer of nanotubes. This paper also presents experimental results demonstrating both, the method of electrical characterization of CNT based actuators with implemented solid electrolytes and the novel test setup which is used to measure the needed data. The actuators which were characterized are hybrids of CNT and the solid electrolyte NAFION which is supplying the ions needed to constitute the electrochemical double layer. The manufacturing, processing of these actuators and also some first experimental results are shown. Unfortunately, the results are not as clear as those for liquid electrolytes, which depend on the hybrid character of the analyzed devices. In the liquid electrolyte based case the CNTs are the only source of stiffness, whereas in the solid electrolyte case electrodes and electrolyte contribute to the overall stiffness and damping as well. Since the introduction of solid electrolytes is a major stumbling block in the development of such actuators, this work is of particular importance.

Proceedings Article | 17 May 2005 Paper

Development of an active twist rotor blade with distributed actuation and orthotropic material

Peter Wierach, Johannes Riemenschneider, Stefan Keye

Proceedings Volume 5764, (2005) https://doi.org/10.1117/12.599930

KEYWORDS: Skin, Actuators, Manufacturing, Composites, Microsoft Foundation Class Library, Data modeling, Performance modeling, Carbon, Aerodynamics, Glasses

Read Abstract +

Showing 5 of 9 publications

Conference Committee Involvement (1)

Nano-Opto-Mechanical Systems (NOMS)

21 August 2011 | San Diego, California, United States

Keywords/Phrases

Search In:

Publication Years