TY - JOUR A1 - Rus, J. A1 - Gustschin, A. A1 - Mooshofer, H. A1 - Grager, J.-C. A1 - Bente, Klaas A1 - Gaal, Mate A1 - Pfeiffer, F. A1 - Grosse, C. U. T1 - Qualitative comparison of non-destructive methods for inspection of carbon fiber-reinforced polymer laminates N2 - In the rapidly expanding composite industry, novel inspection methods have been developed in recent years. Particularly promising for air-coupled testing are cellular polypropylene transducers which offer better impedance matching to air than piezoelectric transducers. Furthermore, broadband transmitters (laser-induced ultrasound and thermoacoustic emitters) and receivers (optical microphones) have opened a completely new chapter for advanced contact-free ultra-sound inspection. X-ray dark-field radiography offers a different approach to detect porosity and microcracks, employing small angle X-ray scattering. These innovative ultrasonic and radiographic alternatives were evaluated in comparison with well-established inspection techniques. We applied thirteen different non-destructive methods to inspect the same specimen (a carbon fiber-reinforced polymer laminate with induced impact damage): air-coupled ultrasound testing (using piezoelectric transducers, broadband optical microphones, cellular polypropylene transducers, and a thermoa- coustic emitter), laser-induced ultrasound testing, ultrasonic immersion testing, phased array ultrasonic testing, optically excited lock-in thermography, and X-ray radiography (projectional absorption and dark-field, tomosynthesis, and micro-computed tomography). The inspection methods were qualitatively characterized by comparing the scan results. The conclusions are advantageous for a decision on the optimal method for certain testing constraints. KW - Carbon fiber-reinforced polymer KW - Air-coupled ultrasound KW - Optically excited lock-in thermography KW - X-ray micro-computed tomography KW - X-ray dark-field radiography PY - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-509473 SN - 0021-9983 VL - 54 IS - 27 SP - 4325 EP - 4337 PB - SAGE AN - OPUS4-50947 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gaal, Mate A1 - Hufschläger, Daniel A1 - Bente, Klaas T1 - Advances in air-coupled ultrasonic transducers for non-destructive testing N2 - Commercially available air-coupled transducers applied in non-destructive testing consist of a piezocomposite material and matching layers to reduce the impedance mismatch between the transducer and air. This contribution is an overview of innovative approaches using new piezoelectric materials and other physical principles to transmit and receive an ultrasonic pulse in air. Capacitive and piezoelectric micromachined ultrasonic transducers (CMUTs and PMUTs) produce high pressure levels, but they exhibit a very narrow bandwidth. Optical laser-based methods for transmitting and receiving ultrasound promise a higher bandwidth, but do not achieve the same sensitivity as conventional air-coupled transducers. Ferroelectrets are charged cellular polymers exhibiting piezoelectric properties, having a very small acoustic impedance well matched to air. Ferroelectret transducers achieve about the same bandwidth as the most broadband conventional air-coupled transducers, having a higher sensitivity. Thermoacoustic transducers use heat to initiate an acoustic wave, acting as transmitters in ultrasonic range. Thermoacoustic transducers enable excitation of extremely broadband pulses while producing high pressure levels, which opens new possibilities for advanced signal processing. The newest member of the family of air-coupled ultrasonic transmitters is the plasma-based transducer, using both the thermoacoustic effect and the movements of the ions (so called ionic wind) to create acoustic waves. T2 - International Congress on Ultrasonics CY - Bruges, Belgium DA - 03.09.2019 KW - Air-coupled transducers KW - Ferroelectret KW - Thermoacoustics KW - Plasma acoustics KW - Non-destructive testing PY - 2019 U6 - https://doi.org/10.1121/2.0001072 SN - 1939-800X N1 - Geburtsname von Hufschläger, Daniel: Kotschate, D. - Birth name of Hufschläger, Daniel: Kotschate, D. VL - 38 IS - 1 SP - 030003-1 EP - 030003-7 PB - American Institute of Physics CY - Lancaster, Pa. AN - OPUS4-50103 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Reichel, V. E. A1 - Matuszak, J. A1 - Bente, Klaas A1 - Heil, T. A1 - Kraupner, A. A1 - Dutz, S. A1 - Cicha, I. A1 - Faivre, D. T1 - Magnetite-Arginine Nanoparticles as a Multifunctional Biomedical Tool N2 - Iron oxide nanoparticles are a promising platform for biomedical applications, both in terms of diagnostics and therapeutics. In addition, arginine-rich polypeptides are known to penetrate across cell membranes. Here, we thus introduce a system based on magnetite nanoparticles and the polypeptide poly-l-arginine (polyR-Fe3O4). We show that the hybrid nanoparticles exhibit a low cytotoxicity that is comparable to Resovist®, a commercially available drug. PolyR-Fe3O4 particles perform very well in diagnostic applications, such as magnetic particle imaging (1.7 and 1.35 higher signal respectively for the 3rd and 11th harmonic when compared to Resovist®), or as contrast agents for magnetic resonance imaging (R2/R1 ratio of 17 as compared to 11 at 0.94 T for Resovist®). Moreover, these novel particles can also be used for therapeutic purposes such as hyperthermia, achieving a specific heating power ratio of 208 W/g as compared to 83 W/g for Feridex®, another commercially available product. Therefore, we envision such materials to play a role in the future theranostic applications, where the arginine ability to deliver cargo into the cell can be coupled to the magnetite imaging properties and cancer fighting activity. KW - Iron oxide KW - Nanoparticle KW - Theranostics KW - MRI KW - Hyperthermia PY - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-515993 VL - 10 IS - 10 SP - 2014 PB - MDPI AN - OPUS4-51599 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bente, Klaas A1 - Kotschate, Daniel A1 - Wendland, Saskia A1 - Gaal, Mate T1 - The thermoacoustic effect and its application in air-coupled testing of composite structures N2 - Airborne ultrasonic testing of lightweight, structured composite materials enables fast and contact-free non-destructive testing in aerospace and avoids material degradation due to contact with a coupling liquid. Established resonant air-coupled transducers consist of piezocomposite materials and several matching layers or more advanced materials like charged cellular polypropylene. The relaxation time and the specific frequency of such mechanical ultrasound emitters limit the spectrum of applications for each device. A short pulse length is key for reliable defect detection and each component at test can be best characterized at material- and geometry-specific frequencies. Here we show that focused thermoacoustic transducers are suited for testing lightweight, structured composite plates. Since the ultrasound is generated in air, these transducers show no resonance behavior and emit a broadband acoustic spectrum between 1.2 kHz and 1 MHz. Composite specimens of 3 mm to 9 mm thickness made of polylactide with a honeycomb structure were tested. Flat bottom holes were introduced to quantify the spatial resolution of the imaging method inside the strongly anisotropic specimen. As no broadband receivers are available yet, cellular polypropylene transducers were used as receivers, which limits the bandwidth of the method towards the bandwidth of the receiver. Nevertheless, we demonstrate the competitiveness of the thermoacoustic transducer compared to mechanical emitters at their respective resonance frequencies. Because a thermoacoustic transmitter features a nearly ideal pulse width, a single transmitter can be coupled with receivers with different resonance frequencies. With the development of broadband ultrasound receivers, air-coupled ultrasound spectroscopy will likely be possible in the near future. The analyzed transducer holds the potential to speed up testing during production and maintenance in aerospace and automotives. Its combination with a broadband receiver could also expand the application field of air-coupled ultrasonic testing from a qualitative error detection towards a quantitative, spatially resolved analysis of mechanical material properties. T2 - 10th International Symposium on NDT in Aerospace CY - Dresden, Germany DA - 24.10.2018 KW - Thermoacoustics KW - Ultrasonic Testing KW - Broadband KW - Ultrasound Emission PY - 2018 AN - OPUS4-46466 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bente, Klaas T1 - The thermoacoustic effect and its application in air-coupled testing of composite structures N2 - Airborne ultrasonic testing of lightweight, structured composite materials enables fast and contact-free non-destructive testing in aerospace and avoids material degradation due to contact with a coupling liquid. Established resonant air-coupled transducers consist of piezocomposite materials and several matching layers or more advanced materials like charged cellular polypropylene. The relaxation time and the specific frequency of such mechanical ultrasound emitters limit the spectrum of applications for each device. A short pulse length is key for reliable defect detection and each component at test can be best characterized at material- and geometry-specific frequencies. Here we show that focused thermoacoustic transducers are suited for testing lightweight, structured composite plates. Since the ultrasound is generated in air, these transducers show no resonance behavior and emit a broadband acoustic spectrum between 1.2 kHz and 1 MHz. Composite specimens of 3 mm to 9 mm thickness made of polylactide with a honeycomb structure were tested. Flat bottom holes were introduced to quantify the spatial resolution of the imaging method inside the strongly anisotropic specimen. As no broadband receivers are available yet, cellular polypropylene transducers were used as receivers, which limits the bandwidth of the method towards the bandwidth of the receiver. Nevertheless, we demonstrate the competitiveness of the thermoacoustic transducer compared to mechanical emitters at their respective resonance frequencies. Because a thermoacoustic transmitter features a nearly ideal pulse width, a single transmitter can be coupled with receivers with different resonance frequencies. With the development of broadband ultrasound receivers, air-coupled ultrasound spectroscopy will likely be possible in the near future. The analysed transducer holds the potential to speed up testing during production and maintenance in aerospace and automotives. Its combination with a broadband receiver could also expand the application field of air-coupled ultrasonic testing from a qualitative error detection towards a quantitative, spatially resolved analysis of mechanical material properties. T2 - 10th International Symposium on NDT in Aerospace CY - Dresden, Germany DA - 24.10.2018 KW - Thermoacoustics KW - Ultrasonic Testing KW - Broadband KW - Ultrasound Emission PY - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-464677 SN - 978-3-940283-96-2 SP - 1 EP - 8 PB - Deutsche Gesellschaft für Zerstörungsfreie Prüfung (DGZfP) CY - Berlin AN - OPUS4-46467 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bente, Klaas A1 - Oeff, Julius A1 - Gaal, Mate T1 - Quantitative, zeiteffiziente, winkel- und frequenzaufgelöste Analyse von Elektretwandlern im Hör- und Ultraschallbereich N2 - Die Bildgebung oder Analyse von Materialien mittels luftgekoppelten Ultraschalls profitiert von einer hohen Geschwindigkeit, Flexibilität und Materialschonung des assoziierten Verfahrens. Die Luftankopplung hat jedoch den wesentlichen Nachteil, dass die auftretenden Impedanzsprünge an Grenzflächen zu enormen Verlusten in den Signalamplituden führen. Ultraschallwandler, die laut genug senden und sensitiv genug empfangen, um die geringen Signalamplituden noch auswerten zu können, sind somit zentraler Gegenstand der aktuellen Forschung und Entwicklung. Vielversprechende Wandlertypen sind piezokeramische Wandler, Elektretwandler, aber auch passive, breitbandige Ultraschallempfänger, wie optische Mikrophone. Die quantitative Charakterisierung der Sensitivitäten solcher Wandler wird oft vernachlässigt, da kein simples, universelles Verfahren zur Verfügung steht. In diesem Beitrag geht es um die Methodik der Charakterisierung von Luftultraschallwandlern mittels thermoakustischer Ultraschallsender. Thermoakustische Wandler erzeugen Ultraschall durch das schnelle heizen eines finiten Volumens an Luft vor dem Wandler. Die erhöhte interne Energie führt zu einer Druckänderung, welche sich als akustische Welle fortpflanzen kann. Da keine mechanische Volumenarbeit vom Wandler erbracht wird, funktioniert das Verfahren resonanzfrei. Die Charakterisierung wird am Beispiel von Elektretwandlern durchgeführt. Elektretwandler sind sensitive und immer verschleißresistentere Schallwandler, wodurch sie verbreitet Einsatz im Hör- und Ultraschallbereich finden. Geladene, zelluläre Polypropylen-Folien eignen sich besonders gut als Wandlermaterial aufgrund ihrer, verglichen mit Piezokompositen, hundertfach niedrigeren akustischen Impedanz bei gleichem piezoelektrischem Koeffizienten. Doch das winkel- und frequenzabhängige Verhalten der Wandler ist kaum untersucht und wenig quantifiziert. Es wird gezeigt, dass diese Folien eine schichtdickenabhängige Sensitivität in Größenordnungen zwischen 0.1 mV/Pa und 10 mV/Pa aufwiesen. Ein Maximum in der Sensitivität fand sich nahe ihrer mechanischen Resonanzfrequenz im Ultraschallbereich, aber auch im niederfrequenten Hörschallbereich. Darüber hinaus konnte die Winkelabhängigkeit der Sensitivität charakterisiert werden. Die Analyse konnte dabei zeiteffizient gestaltet werden, da pro Winkel eine Messung für die Berechnung der Übertragungsfunktion des Wandlers genügte. Quantifiziert wurden die Ergebnisse durch das einmalige Vermessen des Emitters mittels Laser-Doppler-Vibrometrie (LDV). Mit den erzielten Ergebnissen wurde zum einen das komplexe Sensitivitätsverhalten der Wandler untersucht, aber auch eine grundlegende Methodik aufgezeigt, wie Wandler quantitativ, multivariat charakterisiert werden können. Winkel- und frequenzaufgelöste Sensitivitäten erlauben zum einen die Analyse der Anwendbarkeit der Wandler für sämtliche Einsatzgebiete, zum anderen stehen so Rückschlüsse über die mechanische Dynamik von Elektretfolien in Aussicht, da deren Sensitivität direkt mit ihrem Elastizitätsmodul skaliert. T2 - DAGA 2019 CY - Rostock, Germany DA - 18.03.2019 KW - Luftultraschall KW - Ultraschall KW - Elektretwandler KW - Thermoakustik KW - Wandlercharakterisierung PY - 2019 SP - 748 AN - OPUS4-47712 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bente, Klaas A1 - Oeff, J. A1 - Gaal, Mate T1 - Quantitative, zeiteffiziente, winkel- und frequenzaufgelöste Analyse von Elektretwandlern im Hör- und Ultraschallbereich N2 - Elektretwandler sind sensitive und immer verschleißresistentere Schallwandler, wodurch sie verbreitet Einsatz im Hör- und Ultraschallbereich finden. Geladene, zelluläre Polypropylen-Folien eignen sich besonders gut als Wandlermaterial aufgrund ihrer, verglichen mit Piezokompositen, hundertfach niedrigeren akustischen Impedanz bei gleichem piezoelektrischem Koeffizienten. Doch das winkel- und frequenzabhängige Verhalten der Wandler ist kaum untersucht und wenig quantifiziert. In dieser Arbeit wird gezeigt, dass diese Folien eine schichtdickenabhängige Sensitivität zwischen 0.1 mV/Pa und 10 mV/Pa aufwiesen. Ein Maximum in der Sensitivität fand sich nahe ihrer mechanischen Resonanzfrequenz im Ultraschallbereich, aber auch im niederfrequenten Hörschallbereich. Darüber hinaus konnte die Winkelabhängigkeit der Sensitivität charakterisiert werden. Die Analyse konnte dabei zeiteffizient mit einem breitbandig emittierenden, thermoakustischen Wandler umgesetzt werden, sodass pro Winkel eine Messung für die Berechnung der Übertragungsfunktion des Wandlers genügte. Quantifiziert wurden die Ergebnisse durch das einmalige Vermessen des Schallfeldes des Emitters mittels Laser-Doppler-Vibrometrie. Mit den erzielten Ergebnissen wurde zum einen das komplexe Sensitivitätsverhalten der Wandler untersucht, aber auch eine grundlegende Methodik aufgezeigt, wie Wandler quantitativ, multivariat charakterisiert werden können. Winkel- und frequenzaufgelöste Sensitivitäten erlauben zum einen die Analyse der Anwendbarkeit der Wandler für sämtliche Einsatzgebiete, zum anderen stehen so Rückschlüsse über die mechanische Dynamik von Elektretfolien in Aussicht, da deren Sensitivität direkt mit ihrem Elastizitätsmodul skaliert. T2 - DAGA 2019 CY - Rostock, Germany DA - 18.03.2019 KW - Luftultraschall KW - Ultraschall KW - Elektretwandler KW - Thermoakustik KW - Wandlercharakterisierung PY - 2019 AN - OPUS4-47597 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bachmann, F. A1 - Bente, Klaas A1 - Codutti, A. A1 - Faivre, D. T1 - Using Shape Diversity on the Way to Structure-Function Designs for Magnetic Micropropellers N2 - Synthetic microswimmers mimicking biological movements at the microscale have been developed in recent years. Actuating helical magnetic materials with a homogeneous rotating magnetic field is one of the most widespread techniques for propulsion at the microscale, partly because the actuation strategy revolves around a simple linear relationship between the actuating field frequency and the propeller velocity. However, full control of the swimmers’ motion has remained a challenge. Increasing the controllability of micropropellers is crucial to achieve complex actuation schemes that, in turn, are directly relevant for numerous applications. However, the simplicity of the linear relationship limits the possibilities and flexibilities of swarm control. Using a pool of randomly shaped magnetic microswimmers, we show that the complexity of shape can advantageously be translated into enhanced control. In particular, directional reversal of sorted micropropellers is controlled by the frequency of the actuating field. This directionality change is linked to the balance between magnetic and hydrodynamic forces. We further show an example of how this behavior can experimentally lead to simple and effective sorting of individual swimmers from a group. The ability of these propellers to reverse swimming direction solely by frequency increases the control possibilities and is an example for propeller designs, where the complexity needed for many applications is embedded directly in the propeller geometry rather than external factors such as actuation sequences. KW - Active Matter KW - Low Reynolds number swimmers KW - Actuating materials KW - Microstructure KW - Swarming PY - 2019 U6 - https://doi.org/10.1103/PhysRevApplied.11.034039 VL - 11 IS - 3 SP - 034039 PB - American Physical Society AN - OPUS4-47731 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bente, Klaas A1 - Rus, J. A1 - Mooshofer, H. A1 - Gaal, Mate A1 - Grosse, C.U. T1 - Broadband air-coupled ultrasound emitter and receiver enable simultaneous measurement of thickness and speed of sound in solids N2 - Air-coupled ultrasound sensors have advantages over contact ultrasound sensors when a sample should not become contaminated or influenced by the couplant or the measurement has to be a fast and automated inline process. Thereby, air-coupled transducers must emit high-energy pulses due to the low air-to-solid power transmission ratios (10−3 to 10−8). Currently used resonant transducers trade bandwidth—a prerequisite for material parameter analysis—against pulse energy. Here we show that a combination of a non-resonant ultrasound emitter and a non-resonant detector enables the generation and detection of pulses that are both high in amplitude (130 dB) and bandwidth (2 µs pulse width). We further show an initial application: the detection of reflections inside of a carbon fiber reinforced plastic plate with thicknesses between 1.7 mm and 10 mm. As the sensors work contact-free, the time of flight and the period of the in-plate reflections are independent parameters. Hence, a variation of ultrasound velocity is distinguishable from a variation of plate thickness and both properties are determined simultaneously. The sensor combination is likely to find numerous industrial applications necessitating high automation capacity and opens possibilities for air-coupled, single-side ultrasonic inspection. KW - Thermoacoustic emitter KW - Optical microphone KW - Air-coupled ultrasound KW - Local resonance KW - Thickness measurement KW - Thickness resonance PY - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-569533 VL - 23 IS - 3 SP - 1379 PB - MDPI AN - OPUS4-56953 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -