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This paper investigates the fabrication of magnetic films via electroplating to be applied into electromagnetic actuated micro electro-mechanical systems (MEMS) switches. Cobalt and nickel films (1 µm thicknesses) were deposited on gold coated silicon substrates via electrochemical deposition. Different deposition conditions were investigated, regarding temperature and deposition voltage. The films morphologies were characterized via atomic force microscopy, while the magnetic properties of the films were characterized via vibrating sample magnetometer measurements. In order to evaluate the integration of these magnetic films into MEMS switches with low energy consumption, a mathematical model was developed and the results show that these films can be applied into efficient actuation with reduced power dissipation.

Zeitschriftenartikel

R. White, P. Coman, Stefan Mátéfi-Tempfli, S. Veje

Modeling Vaporization, Gas Generation and Venting in Li-Ion Battery Cells with a Dimethyl Carbonate Electrolyte

Electrochemical Society Journal, vol. 164, no. 9

2017

This paper presents a mathematical model developed for predicting the temperature-pressure behavior and gas generation inside 18650 LCO/Graphite cells with a DMC (Dimethyl Carbonate) electrolyte. The cell was modeled using oven heating conditions, and the analysis was done at time intervals around the venting event. The paper also presents the thermodynamic property table for DMC, as extracted from different resources and calculated using various assumptions. The model was developed by deriving the energy balance for an unsteady-flow control volume and applying the isentropic flow equations corresponding to the venting of gas. The results show that the model fails to predict the pressure measured experimentally when no gas is generated inside. When adding the gas generation due to pre-venting reactions occurring, the model can predict the pressure profile measured experimentally.

Zeitschriftenartikel

D. Cook, M. Mátéfi-Tempfli, P. Richardson, M. Bampton, T. Cookson, D. Smith, J. Branch, Stefan Mátéfi-Tempfli, P. Connell, P. Bartlett, M. Alibouri

Plastic Reactor Suitable for High Pressure and Supercritical Fluid Electrochemistry

Journal of The Electrochemical Society, vol. 164, no. 6

2017

The paper describes a reactor suitable for high pressure, particularly supercritical fluid, electrochemistry and electrodeposition at pressures up to 30 MPa at 115°C. The reactor incorporates two key, new design concepts; a plastic reactor vessel and the use of o-ring sealed brittle electrodes. These two innovations widen what can be achieved with supercritical fluid electrodeposition. The suitability of the reactor for electroanalytical experiments is demonstrated by studies of the voltammetry of decamethylferrocene in supercritical difluromethane and for electrodeposition is demonstrated by the deposition of Bi. The application of the reactor to the production of nanostructures is demonstrated by the electrodeposition of ∼80 nm diameter Te nanowires into an anodic alumina on silicon template. Key advantages of the new reactor design include reduction of the number of wetted materials, particularly glues used for insulating electrodes, compatability with reagents incompatible with steel, compatability with microfabricated planar multiple electrodes, small volume which brings safety advantages and reduced reagent useage, and a significant reduction in experimental time.

R. Brehm, S. Top, Stefan Mátéfi-Tempfli

Beitrag (Sammelband oder Tagungsband)

A distributed multi-agent linear bi-objective algorithm for energy flow optimization in microgrids

Proceedings of 2015 IEEE International Renewable and Sustainable Energy Conference (IRSEC'15)

2016

ISBN: 978-1-4673-7894-9

Stefan Mátéfi-Tempfli, P. Manoonpong, V. Jankovics

Beitrag (Sammelband oder Tagungsband)

Artifcial neural network based complaint control for robot arms

From Animals to Animats 14, vol. 9825

2016

ISBN: 978-3-319-43488-9

Zeitschriftenartikel

G. Denuault, M. Mátéfi-Tempfli, H. Bülter, C. Dosche, Stefan Mátéfi-Tempfli, G. Wittstock

Electrochemical analysis of nanostructured iron oxides using cyclic voltammetry and scanning electrochemical microscopy

Electrochimica Acta, vol. 222, pp. 1326-1334

2016

Iron oxides in general and especially hematite, α-Fe2O3, have become promising materials for the alkaline water electrolysis and photoelectrochemical water splitting, respectively. In the present study electrocatalytic electrodes with a thin film of α-Fe2O3 and with vertically aligned α-Fe2O3 nanowires were prepared. Cyclic voltammograms of the α-Fe2O3 nanowires revealed differences including a series of three unreported cathodic signals when compared to previously published voltammograms for polycrystalline iron oxides. The generation-collection mode of scanning electrochemical microscopy (SECM) using nanostructured Pt microdisc probes was exploited to detect soluble reaction products formed at the voltammetric peaks of the α-Fe2O3 electrode. SECM tip-substrate voltammetry unexpectedly showed that the reduction of FeVI to FeIII on the cathodic sweep is accompanied by significant O2 evolution.

P. Farhang, Stefan Mátéfi-Tempfli

Beitrag (Sammelband oder Tagungsband)

A New Approach to Control the Modified LinVerter for High Frequency Applications

Proceedings of the 31st Annual IEEE Applied Power Electronics Conference and Exposition (APEC2016) [March 20-24, 2016; Long Beach, USA]

2016

A. Drimus, Stefan Mátéfi-Tempfli

Beitrag (Sammelband oder Tagungsband)

Tactile shoe inlays for high speed pressure monitoring

Intelligent Robotics and Applications, Berlin, vol. 9245

2015

ISBN: 978-3-319-22876-1

P. Farhang, Stefan Mátéfi-Tempfli, A. Drimus

Beitrag (Sammelband oder Tagungsband)

New technique for voltage tracking control of a boost converter based on the PSO algorithm and LTspice

2015 56th International Scientific Conference on Power and Electrical Engineering of Riga Technical University (RTUCON)

2015

DOI: 10.1109/RTUCON.2015.7343157

L. Duggen, Stefan Mátéfi-Tempfli

Beitrag (Sammelband oder Tagungsband)

Forces in Liquid Metal Contacts

Proceedings of the ASME 12th Biennial Conference on Engineering Systems Design and Analysis--2014, New York, N.Y.

2014

ISBN: 978-0-7918-4585-1

DOI: 10.1115/ESDA2014-20114

Using rather well known theory about capillary bridges between two electrodes we calculate the tensile force that can be applied to liquid metal contacts in the micrometer regime. Assuming circular symmetry, full wetting of the electrodes, and neglecting gravity, we present a brief review of the necessary theory and find numerically the forces to be in the 100μN range for liquid metals as mercury and liquid Gallium suspended between electrodes of 20μm radius.

DOI: 10.1007/978-3-319-09435-9_37

Beitrag (Sammelband oder Tagungsband)

M. Gorsic, A. Drimus, Stefan Mátéfi-Tempfli, V. Jankovics

High Resolution Tactile Sensors for Curved Robotic Fingertips

Biomimetic and Biohybrid Systems, Cham, vol. 8608 : Lecture notes in artificial intelligence

2014

ISBN: 978-3-319-09435-9

Digital Europan Campus Rottal-Inn

Tactile sensing is a key element for various animals that interact with the environment and surrounding objects. Touch provides information about contact forces, torques and pressure distribution and by the means of exploration it provides object properties such as geometry, stiffness and texture[5]. For humans, extracting high level information from touch provides a better understanding of the objects manipulated while for insects it is essential for locomotion[3]. While robot designers have been using vision systems to provide the robot with information about its surroundings, this is not always trivial to obtain, dealing with limited accuracy, occlusions and calibration problems. In terms of sensors for static stimuli, such as pressure, there are a range of technologies that can be used to manufacture transducers with various results[5]. A simple approach is to use fingertips with a 6-DOF force-torque sensor for estimating contact conditions[1], but this only allows a single point of contact and is costly. In terms of fingertip and foot tip prototypes, tactile sensors are used for multi modal sensing, similar to biology, for pressure and dynamic stimuli. In this respect Hosoda et al. [4] propose an anthropomorphic fingertip which has randomly distributed straingauges and PVDF (polyvinylidene fluoride) transducers. In [7] a biomimetic tactile array is proposed that shows a low hysteresis and good sensitivity for skin like deformations.

Zeitschriftenartikel

M. Gorsic, A. Drimus, Stefan Mátéfi-Tempfli, V. Jankovics

Novel high resolution tactile robotic fingertips

IEEE SENSORS, pp. 791-794

2014

DOI: 10.1109/ICSENS.2014.6985118

This paper describes a novel robotic fingertip based on piezoresistive rubber that can sense pressure tactile stimuli with a high spatial resolution over curved surfaces. The working principle is based on a three-layer sandwich structure (conductive electrodes on top and bottom and piezoresistive rubber in the middle). For the conductive layers we use ring patterns of silver epoxy and flex PCB electrode arrays. The proposed sensorised fingertip has 60 sensitive regions (taxels) arranged in 5 rings and 12 columns that have a smooth pressure to resistance characteristic. Using the sensor with specialized data acquisition electronics that acquire 500 frames per second provides rich information regarding contact force, shape and angle for bio-inspired robotic fingertips. Furthermore, a model of estimating the force of contact based on values of the cells is proposed.

DOI: 10.1103/PhysRevB.87.174429

Zeitschriftenartikel

B. Rana, M. Mátéfi-Tempfli, M. Agrawal, A. Barman, R. Hicken, U.A.S. Al-Jarah, O. Dmytriiev, Gangmei P., L. Piraux, V. Kruglyak, Stefan Mátéfi-Tempfli, B. Mahato

Static and dynamic magnetic properties of densely packed magnetic nanowire arrays

Physical Review B, vol. 87, no. 17

2013

The static and dynamic magnetic properties of magnetic nanowire arrays with high packing density (>0.4) and wire diameter much greater than the exchange length have been studied by static and time-resolved magneto-optical Kerr effect measurements and micromagnetic simulations. The nanowires were formed by electrodeposition within a nanoporous template such that their symmetry axes lay normal to the plane of the substrate. A quantitative and systematic investigation has been made of the static and dynamic properties of the array, which lie between the limiting cases of a single wire and a continuous ferromagnetic thin film. In particular, the competition between anisotropies associated with the shape of the individual nanowires and that of the array as a whole has been studied. Measured and simulated hysteresis loops are largely anhysteretic with zero remanence, and the micromagnetic configuration is such that the net magnetization vanishes in directions orthogonal to the applied field. Simulations of the remanent state reveal antiferromagnetic alignment of the magnetization in adjacent nanowires and the formation of vortex flux closure structures at the ends of each nanowire. The excitation spectra obtained from experiment and micromagnetic simulations are in qualitative agreement for magnetic fields applied both parallel and perpendicular to the axes of the nanowires. For the field parallel to the nanowire axes, there is also good quantitative agreement between experiment and simulation. The resonant frequencies are initially found to decrease as the applied field is increased from remanence. This is the result of a change of mode profile within the plane of the array from nonuniform to uniform as the ground state evolves with increasing applied field. Quantitative differences between experimental and simulated spectra are observed when the field is applied perpendicular to the nanowire axes. The dependence of the magnetic excitation spectra upon the array packing density is explored, and dispersion curves for spin waves propagating within the array parallel to the nanowire axis are presented. Finally, a tunneling of end modes through the middle region of the nanowires was observed. The tunneling is more efficient for wires forming densely packed arrays, as a result of the extended penetration of the dynamic demagnetizing fields into the middle of the wires and due to the lowering of the tunneling barrier by the static demagnetizing field of the array.

Zeitschriftenartikel

A. Milosavljević, M. Mátéfi-Tempfli, K. Schiessl, J. Burgdörfer, C. Lemell, B. Marinković, Stefan Mátéfi-Tempfli, K. Tökési

Charging dynamics in electron transmission through Al2O3 capillaries

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, vol. 279, pp. 190-193

2012

We have measured the transmission of low-energy electrons through insulating Al2O3 nanocapillaries. We find that transmission at the incident energy is quickly suppressed with increasing tilt angle of the capillary axis relative to the incoming electron beam while inelastic transmission becomes more important. For small angles of incidence charging dynamics lead to a decrease of total transmission (elastic and inelastic) with time. Our results are interpreted on the basis of a microscopic model for the electron transport within the capillary including also close interactions with the capillary wall.

C.-H. Solterbeck, M. Mátéfi-Tempfli, M. Es-Souni, Stefan Mátéfi-Tempfli, S. Habouti

Zeitschriftenartikel

On-substrate, self-standing Au-nanorods arrays showing morphology controlled properties

Nano Today, vol. 6, no. 1, pp. 12-19

2011

DOI: 10.1016/j.nantod.2010.11.001

We use supported alumina templates and electrodeposition to fabricate self-standing Au-nanorods (Au-NR) arrays. Depending on electrolyte and deposition conditions two different NR morphologies with either corrugated or smooth topologies are fabricated. We show that the properties of the NR arrays, including amphiphilic and optical, very much depend on their morphology. Smooth NR arrays are hydrophobic while the corrugated ones are hydrophilic. Also the optical reflectance, though it shows plasmon resonances at very similar wave lengths, is much lower for the corrugated NR arrays. The activity of the NR arrays as substrates for molecular detection using Raman scattering, and Rhodamine 6G (R6G) as model dye, also strongly depends on their morphology. R6G concentrations down to 1 pM are detected on the corrugated arrays yielding an effective enhancement factor (EF) of approximately 1 × 109. In contrast an over-estimated (because of their hydrophobic character) EF of 6 × 106 is obtained for the smooth NR arrays.

Zeitschriftenartikel

A. Radu, L. Piraux, Stefan Mátéfi-Tempfli, V. Antohe

Circuit Modeling on Polyaniline Functionalized Nanowire-Templated Micro-Interdigital Capacitors for pH Sensing

IEEE Transactions on Nanotechnology, vol. 10, no. 6, pp. 1314-1320

2011

This study presents an improved alternative current (ac) circuit modeling of a highly sensitive capacitive pH-sensing element based on polyaniline (PANI) functionalized nanowire-templated micro-interdigited electrodes (NWs μIDEs). While electrical resonance measurements deal with a total equivalent capacity, comparative investigations show a good agreement with the fitting parameters of the corresponding model. A physical interpretation of the model is discussed to help in understanding the detection mechanism and a possible methodology to be used for further integration of the subsequent device is suggested.

C.-H. Solterbeck, M. Mátéfi-Tempfli, M. Es-Souni, Stefan Mátéfi-Tempfli, S. Habouti

Zeitschriftenartikel

Self-standing corrugated Ag and Au-Nanorods as plasmonic substrates

Journal of Materials Chemistry, vol. 21, pp. 6269-6273

2011

We use home-made Si-supported anodized alumina thin film templates for the electrodeposition of large area self-standing Ag- and Au-nanorod (Au-NR) arrays. The deposition conditions chosen, i.e. electrolyte composition and deposition voltage, lead to a corrugated rod morphology, particularly for Au-NRs. Instantaneous nucleation followed by diffusion-controlled growth are thought to be the dominating mechanism for the morphology observed. Diffuse reflectance spectra show specific behaviours of Ag- and Au-NRs with longitudinal and transverse plasmon resonance modes and additional modes for Ag-NRs. The activity of the NR arrays as substrates for molecular detection using Raman scattering and Rhodamine 6G (R6G) as a model dye strongly depends on noble metal. R6G concentrations down to 1 pM are detected on the corrugated arrays yielding an effective enhancement factor (EF) of approximately 2 × 1010 for Ag-NRs and 1 × 109 for Au-NRs. The latter is the highest ever obtained for Au-nanostructures. Both nanostructures provide an enhancement that is high enough to detect single molecules using Raman scattering. The results are rationalized in terms of morphology effects on electromagnetic field intensity.

DOI: 10.1002/smll.201000723

Zeitschriftenartikel

M. Mátéfi-Tempfli, L. Piraux, A. Vlad, S. Melinte, Stefan Mátéfi-Tempfli

Vertical nanowire architectures: Statistical processing of porous templates towards discrete nanochannel integration

Small, vol. 6, no. 18, pp. 1974-1980

2010

Europan Campus Rottal-Inn

Nanowires and statistics: A statistical process for reading ultradense arrays of nanostructured materials is presented (see image). The experimental realization is achieved through selective nanowire growth using porous alumina templates. The statistical patterning approach is found to provide rigorous selection rules for measuring well‐defined numbers of nanowires located into nanoporous templates, and provides a conceptual framework for the fabrication of nanowire‐based crossbar latches.

Zeitschriftenartikel

S. Biri, M. Mátéfi-Tempfli, Z. Juhász, G.A.B. Gál, I. Rajta, S. Szilasi, Stefan Mátéfi-Tempfli

Nanochannel alignment analysis by scanning transmission ion microscopy

Nanotechnology, vol. 21, no. 29

2010

DOI: 10.1088/0957-4484/21/29/295704