[Show abstract][Hide abstract] ABSTRACT: A novel pattern recognition algorithm is developed, which detects concentration of different gases automatically with impedance spectroscopy (IS) using a conducting poly sensor or a WO3 sensor. It consists of adaptive- simulated-annealing-supported-parameter-estimation (ASA-PE) for feature-extraction and committee-machine (CM) for classification. The results of ASA-PE, complex-principle-component-analysis (CPCA) and discriminant- analysis-via-support-vector (SVDA) are compared. All algorithms are satisfied. But ASA-PE ensures minimal loss of information. The classifiers: distance-weighted-k-nearest-neighbor (DW-kNN), multiple-layer-perceptron (MLP), support-vector-machine (SVM) and CM are combined with feature-extraction methods and compared with each other. Recognition result is satisfying. However, if gas or gas condition is unknown, only CM with SVDA showed best performance.
[Show abstract][Hide abstract] ABSTRACT: Passive RFID transponder applications that require integrated sensors can greatly benefit from unconventional sensing strategies especially in situations where there is a need to continuously monitor environmental properties without having access to an integrated source of electric energy or an omnipresent reader station within communication range. Since, in many cases, information about the violation of a threshold value is of interest, alternative sensing strategies exploiting irreversible phenomena not considered or even avoided before, have the potential to find successful use in low-cost (e.g., chip-based sensor RFIDs) or lowest cost (e.g., chipless sensor RFIDs-either with or without transistors) wireless sensor applications. In this paper, a stand-alone, simple, passive, wireless humidity threshold sensor concept, and its realization are presented. This exploits the deliquescence phenomenon of salts. Based on a double planar coil arrangement, for which an electric model is given and a transfer function has been deduced, an oscillating circuit is formed. Its resonance frequency changes irreversibly, if a threshold relative humidity is exceeded for a certain exposition time. The sensor principle is demonstrated by the example of sodium chloride. Various measurements demonstrate the feasibility of the presented sensor approach. Sensor solutions based on a threshold activated irreversible state change might be a promising approach in order to monitor environmental parameters without a permanent supply of electric energy.
[Show abstract][Hide abstract] ABSTRACT: Textile-reinforced composites with thermoplastic matrices are characterised by high specific mechanical properties and enable short processing times. In addition, function-integrative lightweight components can be realised by embedding sensor networks into such composite structures. In the present study, composites with integrated sensor networks consisting of strain gauges, interconnection buses and application-specific integrated circuits (ASIC) are analysed. At first, the mechanical behaviour of glass fibre-reinforced polypropylene (GF/PP) with embedded sensor network components is investigated. Micrograph investigations and computer tomography analyses are used to study fibre orientations and interface qualities between the thermoplastic composite and the embedded components. Mechanical tests under tensile and flexural loading are accomplished with strip specimens in order to study the effects of the embedding on the structural stiffness and strength of the composite. Afterwards, the strains measured by embedded strain gauges are evaluated by means of optical measuring techniques under tensile loading. The results confirm that integrated sensor networks are suited for the structural health monitoring of GF/PP structures.
[Show abstract][Hide abstract] ABSTRACT: The material built-up at sharp corners of a workpiece during electroplating, so-called dog-boning, was utilized for bottom-up creation of nanofences – free standing lines of high aspect ratio nanowires – on silicon oxide substrates. This was realized by electroplating gold into nanoporous aluminum oxide templates with underlying micropatterned gold pads, serving as working electrodes. Using the right parameter set, initial preferred nucleation at the gold pad rim site and the unique nanomatrix geometry led to the formation of lines of nanowires at the rim site separated by an adjacent depletion area from an extended bulk nanorod array region. It was found that the underlying mechanisms of this growth process are the increased electric field densities at the electrode edges and a field screening effect due to already grown neighboring wires, both identified by finite element electric field simulations, as well as the restricted diffusion dynamics of gold ions in the presence of nanopores. The obtained high aspect ratio nanofences might be applicable for enhanced catalysis, dielectric index sensing or in optical filters.
Journal of The Electrochemical Society 11/2013; 161(1):D26-D30. DOI:10.1149/2.024401jes · 3.27 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Continuous monitoring of environmental parameters to determine threshold or dosage violations is of strong interest throughout the life cycle of goods. The task is challenging, when there is no continuous supply of electric energy available and lowest cost sensor solutions are required - two common application constraints in passive RFID applications which are also required to fulfill monitoring tasks. Presented is a humidity threshold violation sensor concept, in which the exceedance of a humidity threshold value leads to a permanent sensor resistance change. The principle is based upon the deliquescence of salts as a threshold detection mechanism, as well as chemical sintering of metal nanoparticles, used as irreversible state change mechanism. The introduced sensor arrangement is completely inkjet printed. Several experiments demonstrate the feasibility of the approach. Due to the strong resistance change, the sensor elements can serve as humidity triggered switches in electric circuits as demonstrated by the integration into a freely programmable RFID UHF transponder tag.
[Show abstract][Hide abstract] ABSTRACT: The cross-industry trend towards efficient lightweight solutions continues unabatedly and leads to an increasing use of structural components made of fibre composites. At the same time, there is an increasing demand for the realization and integration of additional functions such as sensory properties. For the widespread application of intelligent lightweight components, manufacturing technologies suitable for series production are required. Fibre-reinforced polyurethane composites offer a great potential for the production of smart lightweight structures. A novel method based on the Long Fibre Injection (LFI) technology enables the integration of piezoceramic components and by their direct connection to suitable electrode structures the process immanent fabrication of sensory elements.
[Show abstract][Hide abstract] ABSTRACT: The determination of wine additives such as sulfur dioxide and ascorbic acid is motivated by limiting these substances because of their potential noxious effects. Cyclic voltammetry with inkjet printed electrodes on a PET foil was used to quantify free sulfur dioxide and ascorbic acid in a model wine solution. Two different kinds of electrodes were manufactured: Silver electrodes and silver electrodes modified with gold nanoparticles. Inkjet printed electrodes showed high sensitivity and selectivity towards ascorbic acid and sulfur dioxide and a linear relationship between concentration and peak current was observed. Modification of the inkjet printed silver electrode with gold nanoparticles increased the sensitivity. Additionally, more defined current peaks were obtained, that proved the excellent suitability of the silver electrodes modified with gold nanoparticles for precise determination of sulfur dioxide and ascorbic acid in wine.
[Show abstract][Hide abstract] ABSTRACT: Vibration analysis is a promising approach in order to detect early hip prosthesis loosening, with the potential to extend the range of diagnostic tools currently available in clinical routine. Ongoing research efforts and developments in the area of multi-functional implants, which integrate sensors, wireless power supply, communication and signal processing, provide means to obtain valuable in vivo information otherwise not available. In the current work a medical wireless measurement system is presented, which is integrated in the femoral head of a hip prosthesis. The passive miniaturized system includes a 3-axis acceleration sensor and signal pre-processing based on a lock-in amplifier circuit. Bidirectional data communication and power supply is reached through inductive coupling with an operating frequency of 125 kHz in accordance with the ISO 18000-2 protocol standard. The system allows the acquisition of the acceleration frequency response of the femur-prosthesis system between 500 to 2500 Hz. Applied laboratory measurements with system prototypes on artificial bones and integrated prostheses demonstrate the feasibility of the measurement system approach, clearly showing differences in the vibration behavior due to an implant loosening. In addition a possibility to evaluate the non-linear mechanic system behavior is presented.
[Show abstract][Hide abstract] ABSTRACT: A wireless, near-field coupled sensor based on two planar spiral coils embedded in a thin fiber-reinforced composite material is presented. The measurement effect exploits the fact that penetrating water changes the effective dielectric permittivity in the volume surrounding the planar coils. This leads to an increase of the sensor self-capacitance and to a decrease of the sensor self-resonant frequency. The sensor targets applications in which non tactile, in-situ monitoring of water uptake, within a confined volume of material, is of interest. In order to describe the general electric behavior a circuit model, considering the sensor and an inductively coupled detection coil, has been developed and verified. An analytic expression for the resonance frequency was deduced. Sensor prototypes were integrated in a glass fiber polypropylene composite. Applied measurements demonstrate the resonance frequency change due to water entering and leaving the material during immersion and drying tests. (C) 2012 Elsevier Ltd....Selection and/or peer-review under responsibility of the Symposium Cracoviense Sp. z.o.o.
[Show abstract][Hide abstract] ABSTRACT: The automated high-volume production of lightweight and intelligent composite parts is one of the key technologies for the automotive industry. Modern concepts introduce “intelligent” parts by integrating sensor networks into the composite. These networks record different physical signals and can even work as active components. A popular application scenario is the permanent structural health monitoring. This paper presents a novel high-volume production technology that addresses the integration of large piezoceramic sensor and actor elements in glass fibre polyurethane composite parts using the Multi-Fibre-Injection (MFI) spraying technology. By directly integrating the piezo fibres, this technology combines sensor production and part production into one single step. First experiments showed that such piezoceramic sensors are functional. Other experiments demonstrated the successful integration of different electronic components and batteries into composite parts.
[Show abstract][Hide abstract] ABSTRACT: Due to their small footprint and high sensitivity to biological molecule binding, planar optical microring resonators gained high interest for use as optical biosensors. Typically, microring resonators are made of semiconductor based materials, and are manufactured by time-consuming lithography and etching steps. Semiconductor based waveguides have high refractive indices, and thus, a high refractive index contrast between core and cladding. In this case, due to strong mode confinement, bending loss is a comparably minor issue and becomes relevant only at small bending radii of less than 5 μm. The main loss is determined by surface scattering, and thus, semiconductor based curved waveguides need to be designed and manufactured to have very smooth sidewalls. If polymer materials are used, microring resonators can be cost-efficiently manufactured by nanoimprint lithography. The resulting larger polymer waveguide dimensions facilitate in- and out-coupling, and polymer surfaces allow using established surface biofunctionalization techniques. For polymer waveguides, due to the small refractive index contrast, surface scattering loss is a minor issue, but bending loss becomes dominant for radii of less than 80 μm due to the low mode confinement to the core. In this work, design guidelines for polymer microring resonator waveguides are given and compared to semiconductor based waveguides. Waveguide losses due to bending and surface roughness are determined analytically or numerically by finite element methods. Coupling coefficients are calculated by finite element methods and coupled-mode theory. Resulting conclusions for designing polymer waveguides and semiconductor waveguides are derived.
Proceedings of SPIE - The International Society for Optical Engineering 11/2012; 8561:85610Q. DOI:10.1117/12.999970 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Defects to due resist pre-exposure as well as the relevance of the initial film thickness during stamp-and-repeat UV-assisted nanoimprint lithography are reported. The demolding force was found to be an indirect measure for the development of the photoinitiator concentration and for the curing behavior of the resist. Multiple imprints into pre-exposed resist are possible due to oxygen cure inhibition. The first curing defects due to significantly reduced photoinitiator concentrations in UVCur21SF resist occurred at accumulated doses of about three times the imprint dose. Molds having only a small fraction of patterned area require very thin initial films with an thickness being optimized for the low mold cavity volume. Helium is essential for the complete mold filling from such thin spin coated films.
[Show abstract][Hide abstract] ABSTRACT: Cyclic voltammetry was used to investigate the electrochemistry of sulfur dioxide, polyphenols and ascorbic acid in a pH 3.3 model wine solution (0.033 M tartaric acid and 12 vol% ethanol) at conducting polymer electrodes. The oxidation of sulfur dioxide, an important wine preservative, was successfully achieved using poly(3,4-ethylenedioxythiophene) (PEDOT) as a redox mediator grown electrochemically on a gold electrode. The deposition conditions and the film thickness were investigated for their effects on the oxidation current due to free sulfur dioxide.The simultaneous detection of sulfur dioxide and wine polyphenols using voltammetry is challenging, as the oxidation potentials lie close to each other. Four representative white wine polyphenols were investigated in combination with sulfur dioxide. It was found that the oxidation current at a PEDOT covered gold electrode increased linearly at 760 mV (Ag/AgCl) with increasing sulfur dioxide concentrations, and largely independent of the earlier polyphenol oxidation peak at around 400 mV. Through the addition of acetaldehyde, a subtractive measure of free sulfur dioxide concentration was obtained. At the PEDOT electrodes, ascorbic acid oxidation with a 240 mV peak was well separated from the main polyphenol oxidation peak, and unlike the merging of peaks seen at glassy carbon electrodes.
[Show abstract][Hide abstract] ABSTRACT: A main task in RFID chip design is the determination of its input impedance. Standard methods involving the use of a state-of-the-art network analyzer require expensive equipment. Here a new approach is proposed to determine the chip impedance by measuring the activation power or distance with a standard RFID reader. The RFID chip is connected to several antennas with different impedances and for each the activation power or distance is determined. From these measurements the chip impedance can be calculated.
Antennas and Propagation (EUCAP), 2012 6th European Conference on; 01/2012
[Show abstract][Hide abstract] ABSTRACT: A fully ink jet printed humidity sensor on a thin PET foil is presented in this paper. Conductive silver electrodes were ink jet printed in the first step. Afterwards film forming polymer particles were printed on top as the humidity sensitive layer. Capacitance measurements were performed to investigate the sensor behavior at different humidity levels. By optimization of the electrode printing parameters the required sensor area was significantly reduced. Systematic investigations for the improvement of the humidity dependent layer led to a suitable polymer film, which combines good processability by inkjet printing with adequate humidity sensitivity and small hysteresis. The proposed sensor shows a high potential for low cost applications, which requires thin and flexible humidity sensors. For the correction of the nonlinear sensor transfer function a correction function with three calibration points is proposed.
[Show abstract][Hide abstract] ABSTRACT: A method and a simplified analytical expression are presented for the calculation of the effective reluctance of a magnetic substrate underneath a planar coil as parameter in a simplified electromechanical network model. The investigated magnetic substrates have a toroid geometry with rectangular cross section, different thicknesses and permeabilities. The method is based on a combined simulation of the magnetic quantities where network parameters are determined by a Finite Element simulation. A network transformation allows the computation of partial inductances which are related to the reluctances. Depending on thickness and permeability the effective substrate reluctance differs from a geometrically based reluctance calculation, where an axisymmetric field distribution without axial component is assumed. From the almost linear relation between the reluctances a correction factor can be given. This factor allows the simplified calculation of the effective reluctance of a magnetic substrate underneath a planar coil.
[Show abstract][Hide abstract] ABSTRACT: Sensor applications for RFID systems received a lot of attention in the last years. Here a compact planar patch antenna that provides space for sensor elements and their connection network is presented. The proposed antenna is built up from a standard patch antenna, shortened by through-holes at two edges and has an opening in the patch metallization for placing sensor components. Placed on a metal surface the antenna behaves as a patch antenna, and in free space it has the radiation pattern of a dipole antenna.
[Show abstract][Hide abstract] ABSTRACT: Passive RFID transponder applications, requiring integrated sensors, can greatly benefit from unconventional sensing strategies. Especially in situations where there is the need to continuously monitor environmental properties, but without having access to an energy source or an omnipresent reader station in communication range. Since in many cases the violation of a threshold value is of interest, alternative sensing strategies, exploiting irreversible phenomena not considered or even avoided before, have the potential of finding a successful use in low cost (e.g. chip-based sensor RFIDs) or lowest cost (e.g. chipless sensor RFIDs) wireless sensor applications. In this work, a stand-alone, simple, passive, wireless humidity threshold sensor is presented, which exploits the deliquescence behavior of salts. Based on a double planar coil arrangement, an oscillating circuit is formed. Its resonance frequency irreversibly changes, if a threshold relative humidity is exceeded for a certain exposition time.