Eric Starke

Acoustic tomography on the basis of travel-time measurement

Acoustic images of variable parameters of objects can be reconstructed by means of tomographic techniques which utilize the propagation of sound waves in the investigated medium. The technique described here utilizes sound frequencies in the audio range for acoustic imaging. The temperature-dependent sound speed as well as the flow field can be estimated by measuring the travel time of a defined acoustic signal between a sound source and a receiver when the distance between them is known exactly. The properties of the flow field are reconstructed using reciprocal sound rays to separate the direction-independent Laplace sound speed from the effective sound velocity. The temperatures in the flow field are then calculated by a combined inversion of all travel-time information resulting from the Laplace sound speed using an algebraic reconstruction technique. This reconstruction technique provides a cross section of the temperature distribution throughout the investigated area or volume. The tomographic system has been generalized to allow flow phenomena and temperature fields to be investigated with adapted sampling rates. The technique and procedures are exemplified by means of a scalable (from model-sized up to large-scale outdoor tomography) commercially oriented prototype of a tomograph which can utilize the whole audio and near-audio ultrasonic range. The software technology approach forms an inherent part of the realization.

Flexible polymer humidity sensor fabricated by inkjet printing

In this paper a humidity sensor concept is presented which is fully fabricated by inkjet printing. In the first step conductive finger electrodes are inkjet printed on flexible polyimide substrate with a silver neodecanoate based ink. Afterwards a humidity sensitive layer is printed upon using a polymer particle based ink. Two approaches are presented for minimizing the line width of the electrode fingers. The humidity sensitivities of the sensor capacitances are investigated. The results are promising and demonstrate, that inkjet printed sensors are potentially suited for label applications. The achieved sensitivity, repeatability and hysteresis are in acceptable ranges.

Sensor Networks for Integration into Textile-Reinforced Composites

The integration of sensor networks into textile-reinforced composites enables monitoring of different physical values like strain, acceleration and temperature in a component. This paper presents a system concept of a modular sensor network supporting different sensor types and the wireless transmission of stored measurements. Sensor and transponder ASICs have been developed for realizing first demonstration examples. The feasibility of integration of discrete components and silicon chips was successfully verified in experiments with a composite made of glass fibers and polypropylene. Two demonstrators with fully functional integrated modules were fabricated in order to show the possibility of integrated strain monitoring and recording of impact events with wireless data transmission.

Messtechnische Eigenschaften von Dehnungssensoren aus Kohlenstoff-Filamentgarn in einem VerbundwerkstoffMeasuring Performance of Carbon Filament Yarn Strain Sensors Embedded in a Composite

Zusammenfassung Mit in Verbundwerkstoffen eingebettetem Kohlenstoff-Filamentgarn können mittlere Dehnungen großer Messflächen erfasst werden. Zur Abschätzung der messtechnischen Praxistauglichkeit wurden in einen Glasfaser-Polypropylen-Verbundwerkstoff integrierte Kohlenstoff-Filamentgarn-Dehnungssensoren hinsichtlich der erreichbaren Messgenauigkeit bei Kurzzeitmessungen (maximal 15 Minuten Messzeit) untersucht. Anhand vergleichender Dehnungsmessungen mit Metallfolien-Dehnungsmessstreifen wurden der Übertragungsfaktor, der Linearitäts-, Hysterese- und Kriechfehler sowie die Wiederholbarkeit bestimmt. Die Einflüsse des Verbundwerkstoffes und der Temperatur wurden ebenso untersucht wie verschiedene Technologien zur elektrischen Kontaktierung von Kohlenstoff-Filamentgarn.

Design and properties of a sensor network embedded in thin fiber-reinforced composites

So far, embedded sensor networks in composites have mostly been used for structure health monitoring. In contrast to that, in the present work a new stand-alone embedded sensor network for load monitoring of a composite component is presented. Design considerations for the manufacturing of a demonstrator as well as measurement results for cyclic loading are discussed. The presented demonstrator comprises two textile manufactured carbon filament yarn strain sensors for measuring the average bending strain of a large area, embedded capacitive keys for manually controlling the load monitoring process, a sensor ASIC for the processing of the measured data as well as a transponder ASIC with an antenna for the wireless transmission of the measured strains to an external reading station.

Combining network models and FE-models for the simulation of electromechanical systems

The combination of Network Methods and Finite Element Methods on user level is a time-efficient method for the simulation of dynamic behavior of electromechanical systems. Combined simulation can be structured into five areas of application: determination of network structures with FE-simulations, determination of network parameters with FEsimulations, inclusion of network elements in FE-models, inclusion of equivalent network structures in FE-models and simulation of models incorporating different model levels. The capabilities of the combined simulation are demonstrated by sample applications. Combined Simulation is suited for a better system insight and fast simulation-based optimization.

Setup and properties of a fully inkjet printed humidity sensor on PET substrate

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.

Equivalent Circuit of a Piezomagnetic Unimorph Incorporating Single-Crystal Galfenol

In this paper, the reversible transducer properties of a piezomagnetic unimorph are investigated experimentally and aggregated in a linear equivalent circuit. The unimorph consists of a single-crystal Galfenol plate, which is mounted to an aluminum plate. Such two-layer piezomagnetic elements are used in bending actuators or sensors. The completed two-port model of the transducer describes the dynamic behavior in sensing, as well as actuation direction, and includes the magnetomechanical interaction. The coupling of the transducer with a solenoid and demagnetization are considered. A circuit simulator can be used to investigate efficiently the dynamic behavior of the system, and circuit theory can be applied to analyze and simplify the equivalent circuit model.

Electromagnetic Network Models of Planar Coils on a Thin or Thick Magnetic Layer

A method is presented to determine the magnetic reluctance of a thin or a thick magnetic layer of permeability ¿ underneath a planar coil based on inductance measurements. The procedure is substantiated on the basis of the linear electromagnetic network model. The influence of the involved magnetic reluctances on the inductance is analyzed by a transformation into the electrical domain applying linear network theory. From inductance measurements the individual contributing inductances can be calculated and from the back transformation into the magnetic domain the reluctances and further parameters, such as the magnetic field strength for a given electrical current or the permeability. Analytical results are compared with FEM simulations and with measurements obtained from a magnetostrictive bending sensor.

Integrated Sensor Network with Event-Driven Activation for Recording Impact Events in Textile-Reinforced Composites

This paper presents the system concept and first experimental results of the realization of a sensor network for monitoring suddenly occurring temporary events such as impacts. The system consists of modules with sensor and transponder ASIC that can be integrated into a composite component made of glass fibers and polypropylene. The power consumption in standby is very low because the power supply for the ASICs is only activated when a relevant event is detected by a startup sensor. A fast start of the data acquisition process at the beginning of the event is therefore extremely important. The achievable startup time is demonstrated with a test setup.