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Now showing items 1 - 13 of 13

  • Air coupled ultrasonic defect detection in polymer pipes

    Rommeler, Arno   Furrer, Roman   Sennhauser, Urs   Lubke, Bastian   Wermelinger, Jorg   de Agostini, Antonio   Dual, Jurg   Zolliker, Peter   Neuenschwander, Jurg  

    Ultrasonic, non-contact defect detection for polymer pipes can provide an easy and reliable method to establish on site quality control without destructive mechanical testing and finally may help to prevent damage from leaking pipes. The target is to inspect thin walled polymer pipes made of PVDF and PP with small defects in the pipe wall. Air coupled transducers with a nominal frequency of 200 kHz are used to excite Lamb waves in the pipe wall that interact with potential defects. A reference measurement on a flawless part of the pipe helps to mitigate the effects of geometrical and material inhomogeneities. The possibility to excite only the Ao Lamb wave mode in thin plates and pipes using air coupled transducers is shown. Defects attenuate the propagating Lamb waves, resulting in a characteristic pattern in the receiver signal. Simulations on the Lamb wave propagation help to identify the dispersion parameters and allow to understand the effect of defects better. The detection of defects is challenging because of other imperfections in the specimen. With a reference measurement the detection of defects down to a size of 1 mm is possible.
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  • Air coupled ultrasonic defect detection in polymer pipes

    Römmeler, Arno   Furrer, Roman   Sennhauser, Urs   Lübke, Bastian   Wermelinger, Jörg   de Agostini, Antonio   Dual, Jürg   Zolliker, Peter   Neuenschwander, Jürg  

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  • Air-Coupled Ultrasound Time Reversal (ACU-TR) For Subwavelength Nondestructive Imaging

    Marhenke, Torben   Neuenschwander, Jurg   Furrer, Roman   Zolliker, Peter   Twiefel, Jens   Hasener, Joerg   Wallaschek, Joerg   Sanabria, Sergio J.  

    Air-coupled ultrasound (ACU) is increasingly used for nondestructive testing (NDT). With ACU, no contact or coupling agent (e.g., water and ultrasound gel) is needed between transducers and test sample, which provides high measurement reproducibility. However, for testing in production, a minimum separation is often necessary between the sample and the transducers to avoid contamination or transducer damage. Due to wave diffraction, the collimation of the ultrasound beam decreases for larger propagation distances, and ACU images become blurred and show lower defect lateral resolution with increasing sample-transducer separation. This is especially critical to thick composites, where large-size planar sources are used to bridge the large ACU transmission loss with good collimation. In this work, ACU reradiation in unbounded media is extended to NDT of multilayered composites. The extended method is named ACU time reversal (ACU-TR) and significantly improves the defect resolution of ACU imaging. With ACU-TR, the complete pressure distribution radiated by large ACU source is measured with point receivers (RXs) in one plane arbitrarily separated from the sample. By applying acoustic holography physics, it is then possible to quantitatively reconstruct the pressure field directly at arbitrary sample defect planes, which compensates for undesired diffraction phenomena and improves minimum detectable defect size, thereby achieving subwavelength lateral resolution. We tested the method on complex wood-based composite samples based on the ACU far-field measurements at a separation of 160 mm between the sample and the RX transducer. With the proposed method, it is possible to detect surface defects as well as inner defects within composite boards. In the future, by using point RX arrays instead of a scanned microphone, both data acquisition and evaluation can be potentially implemented in real time.
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  • Air-coupled ultrasound inspection of glued laminated timber RID A-1781-2009

    Sanabria, Sergio J.   Furrer, Roman   Neuenschwander, Juerg   Niemz, Peter   Sennhauser, Urs  

    A novel air-coupled ultrasound (ACU) 120 kHz normal transmission system enabled successful imaging of bonding and saw cut defects in multilayered glulam beams up to 280 mm in height with a signal-to-noise ratio (SNR) of 40 dB. The main wave propagation paths were modeled; quasi-longitudinal and quasi-transverse modes were coupled in each lamella and the sound field was found to be shifted from the insonification axis as a function of the ring angle, leading to interference of wave paths in the receiver and to 15 dB amplitude variability in defect-free glulam. The assessment was improved with spatial processing algorithms that profited from the arbitrary scanning resolution and high reproducibility of ACU. Overlapped averaging reduced in-band noise by 15 dB, amplitude tracking captured only the first incoming oscillation, thus minimizing diffraction around defect regions, and image normalization compensated 6 dB of systematic amplitude variability across the fiber direction. The application of ACU to in situ defect monitoring was demonstrated by using multiparameter difference imaging of measurements of the same sample with and without saw cut defects. The segmentation of the defect geometry was improved significantly and the amplitude variability was reduced by 10 dB. Further work is planned to model additional insonification setups and grain and density heterogeneities.
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  • BRUSHLESS DIRECT-CURRENT MOTOR HAVING CURRENTLESS STOPPAGE

    The invention relates to a brushless direct-current motor (1), comprising a stator (2), a rotor cup (30) that revolves around the stator (2) and has a plurality of permanent-magnet poles (N, S), and a detent torque plate (4) that is connected to the stator (2) and has several pole shoes (41) for generating a detent torque that brings the revolving rotor cup (30) into a detent position. The pole shoes (41) are each arranged in the detent position between two adjacent poles (N, S) of the revolving rotor cup (30) to form a magnetic short circuit. The detent torque plate (4) is arranged substantially outside of the magnetic rotating field produced by the stator (2) during operation, whereby the production of the detent torque is decoupled from the electrical behavior of the brushless direct-current motor (1) and the power of the brushless direct-current motor (1) is not substantially influenced by the presence of the detent torque plate (4).
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  • SAFETY DRIVE FOR A FLAP OR A VALVE

    A safety drive unit (10) with a safety circuit (12) resets a flap or a valve into a specified safety position for controlling a gas or liquid volumetric flow, in particular in the field of heating, ventilation, and air conditioning (HVAC) fire protection and monitoring systems. The safety drive unit (10) essentially comprises an actuator (14) with a controllable electric motor (28), a capacitive energy storage unit (20), an energy converter (22) with a power module, and a power supply (18). During normal operation, the electric current in the power module of the energy converter (22) is converted to a lower voltage and stored in the capacitive energy storage unit (20) with at least one double-layer capacitor. If the voltage drops below a predetermined value or if there is a power failure, the stored electrical charge is converted back to a higher voltage by the same power module, and the electric motor (28) is activated until the specified safety position is reached.
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  • Variable decline of Alpine Rock Ptarmigan (Lagopus muta helvetica) in Switzerland between regions and sites

    Furrer, Roman   Schaub, Michael   Bossert, Andreas   Isler, Res   Jenny, Hannes   Jonas, Tobias   Marti, Christian   Jenni, Lukas  

    Alpine species adapted to mountain climate are particularly vulnerable to environmental changes and have recently come under multiple environmental pressures, such as climate change associated with habitat loss (e.g. upward shift of the treeline) and unfavourable weather, as well as increasing human recreation activities. A prime example is the Alpine Rock Ptarmigan (Lagopus muta helvetica), a subspecies restricted to the Alps. We analysed counts of territorial males from 40 sites in the Swiss Alps since 1995 with state-space models including various environmental variables. Over the 18 study years, population growth rate (as deduced from territorial males) was negative overall (-13 %), but varied greatly between different regions of the Swiss Alps (from -50 to +6 %) and between sites, with some declining drastically and others doing well. Overall and within regions, growth rates showed little evidence for synchrony between local study sites. We did not find an overall factor which explained variation in population growth rates, except for a curvilinear effect of July temperature. It thus seems that various factors act locally to different degrees, such as upward shift of the treeline, unfavourable weather, and perhaps local increase in winter and/or summer tourism and unsustainable hunting. Together with a predicted shrinkage of the distribution area in the future due to global warming, the observed decrease of this isolated subspecies is of conservation concern. A better understanding of the different causes of decline and possibly different management strategies will be essential for the conservation of Alpine Rock Ptarmigan in Switzerland.
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  • Variable decline of Alpine Rock Ptarmigan (Lagopus muta helvetica) in Switzerland between regions and sites

    Furrer, Roman   Schaub, Michael   Bossert, Andreas   Isler, Res   Jenny, Hannes   Jonas, Tobias   Marti, Christian   Jenni, Lukas  

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  • Acoustic Field Characterization of Medical Array Transducers Based on Unfocused Transmits and Single-Plane Hydrophone Measurements

    Marhenke, Torben   Sanabria, Sergio J.   Chintada, Bhaskara Rao   Furrer, Roman   Neuenschwander, Juerg   Goksel, Orcun  

    Medical ultrasonic arrays are typically characterized in controlled water baths using measurements by a hydrophone, which can be translated with a positioning stage. Characterization of 3D acoustic fields conventionally requires measurements at each spatial location, which is tedious and time-consuming, and may be prohibitive given limitations of experimental setup (e.g., the bath and stage) and measurement equipment (i.e., the hydrophone). Moreover, with the development of new ultrasound sequences and modalities, multiple measurements are often required to characterize each imaging mode to ensure performance and clinical safety. Acoustic holography allows efficient characterization of source transducer fields based on single plane measurements. In this work, we explore the applicability of a re-radiation method based on the Rayleigh-Sommerfeld integral to medical imaging array characterization. We show that source fields can be reconstructed at single crystal level at wavelength resolution, based on far-field measurements. This is herein presented for three practical application scenarios: for identifying faulty transducer elements; for characterizing acoustic safety parameters in focused ultrasound sequences from 2D planar measurements; and for estimating arbitrary focused fields based on calibration from an unfocused sound field and software beamforming. The results experimentally show that the acquired pressure fields closely match those estimated using our technique.
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  • Acoustic Field Characterization of Medical Array Transducers Based on Unfocused Transmits and Single-Plane Hydrophone Measurements

    Marhenke, Torben   Sanabria, Sergio   Chintada, Bhaskara   Furrer, Roman   Neuenschwander, Jürg   Goksel, Orcun  

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  • Joining with Reactive Nano-Multilayers:Influence of Thermal Properties of Components on Joint Microstructure and Mechanical Performance

    Rheingans, Bastian   Spies, Irina   Schumacher, Axel   Knappmann, Stephan   Furrer, Roman   Jeurgens, Lars P. H.   Janczak-Rusch, Jolanta  

    Reactive nano-multilayers (RNMLs), which are able to undergo a self-heating exothermal reaction, can, e.g., be utilised as a local heat source for soldering or brazing. Upon joining with RNMLs, the heat produced by the exothermal reaction must be carefully adjusted to the joining system in order to provide sufficient heat for bond formation while avoiding damaging of the joining components by excessive heat. This heat balance strongly depends on the thermal properties of the joining components: a low thermal conductivity leads to heat concentration within the joining zone adjacent to the RNML, while a high thermal conductivity leads to fast heat dissipation into the components. The quality of the joint is thus co-determined by the thermal properties of the joining components. This work provides a systematic study on the influence of the thermal properties upon reactive joining for a set of substrate materials with thermal conductivities ranging from very low to very high. In particular, the evolution of the microstructure within the joining zone as a function of the specific time-temperature-profile for the given component material is investigated, focusing on the interaction between solder, RNML foil and surface metallisations, and the associated formation of intermetallic phases. Finally, the specific microstructure of the joints is related to their mechanical performance upon shear testing, and suggestions for optimum joint design are provided.
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  • Joining with Reactive Nano-Multilayers: Influence of Thermal Properties of Components on Joint Microstructure and Mechanical Performance

    Rheingans, Bastian   Spies, Irina   Schumacher, Axel   Knappmann, Stephan   Furrer, Roman   Jeurgens, Lars   Janczak-Rusch, Jolanta  

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  • Experimental investigation of the heat transfer characteristics of spray/wall interaction in diesel selective catalytic reduction systems

    Liao, Yujun   Furrer, Roman   Eggenschwiler, Panayotis Dimopoulos   Boulouchos, Konstantinos  

    This study presents an experimental investigation of the heat transfer characteristics of the spray/wall interaction in diesel selective catalytic reduction (SCR) systems. The work was performed with a commercial 3-Hole pressure-driven injector dosing into a flow channel under typical diesel exhaust flow conditions. Infrared thermography captured the surface temperature of the wall around the impingement area with high temporal and spatial resolution. The resulting temperatures have been used for assessing the heat extracted from the wall. Phase Doppler Anemometry (PDA) was applied to measure the droplet sizes and velocities prior to the wall impingement, providing information on the kinetic properties of the impinging droplets. Based on these, the influence of the gas flow conditions on the heat transfer characteristics is deduced. The spray impingement leads to a substantial and rapid temperature drop on the wall, resulting in a maximum heat flux of several MW/m(2) during the injection duration. The spray cooling effect decreases with increasing exhaust gas flow rate due to the increased entrainment of spray droplets in the flow prior to impingement. Increase in gas flow temperature affects the heat transfer by increasing the wall temperature. At lower wall temperatures, the principal spray/wall interaction regime is deposition. With increasing wall temperature, there is a shift to rebound and thermal breakup. The shorter contact times in the rebound and thermal breakup regimes result in decreased spray/wall heat transfer. (C) 2016 Elsevier Ltd. All rights reserved.
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