Abstract
A simple and powerful design of an electromagnetic acoustic transducer (EMAT) without bulky permanent magnets is presented. The EMAT is operated in a pulse echo modality and generates longitudinal ultrasound at about 1 MHz. Unlike shear waves, these longitudinal ultrasound pulses can propagate in liquids.
The generally addressed application scenario is the examination of a liquid volume inside a metallic container or tank, e. g., the detection of inhomogeneities within the liquid. The herein proposed EMAT operates for virtually all metallic containers, i. e., it succeeds for container walls made of aluminum or ferromagnetic steel, and even for non-ferromagnetic (stainless) steel. Moreover, unlike piezo transducers, EMAT techniques allow for a non-contacting ultrasound transduction: the air gap between the EMAT sensor coil and the tank’s metallic surface extends up to 2 mm. Even with this relatively large air gap, the biasing magnetic field approaches a flux density of 3.2 T at the surface, more than what is possible to achieve with the permanent magnets of conventional and bulkier EMATs. Strong fields improve the coupling efficiency of the principally low-efficiency EMAT mechanism, which is important for both ultrasound transmission and reception.
For that superior field intensity, a unipolar current pulse of up to 3.6 kA is applied through the thin windings (0.5 mm) of the EMAT coil. This paper presents a novel solid-state EMAT circuitry for such strong currents and MHz pulsed voltages >1 kV.
As a particularly delicate task, the powerful circuitry must also detect the rather weak echo signals in the μV range. A very short recovery time is required after such a strong emission burst. The discussed circuitry consists of three unipolar high-current modules, which can each be independently launched. This allows for received echo signals that can be timed independently, e. g., objects deep inside the liquid tank can be specifically addressed. In general, this work concentrates on the novel circuitry in parallel connection, the general pulse-echo functionality and the magnetic fields. A detailed analysis and shaping of the ultrasonic fields through different EMAT coil geometries would exceed the scope of this contribution and is to be reported separately.
Zusammenfassung
In diesem Beitrag wird das Design eines einfachen und leistungsfähigen elektromagnetischen Akustikwandlers (EMAT) ohne die Verwendung eines Permanentmagneten vorgestellt. Der EMAT arbeitet nach dem Impuls-Echo-Verfahren und erzeugt longitudinalen Ultraschall bei einer Frequenz von 1 MHz. Longitudinaler Ultraschall läuft im Vergleich zu transversalem Ultraschall durch Flüssigkeiten hindurch. Das Anwendungsszenario dieses EMATs ist die Detektion von Inhomogenitäten in metallischen Flüssigkeitsbehältern. Im Gegensatz zu Piezoelementen erzeugen EMATs Ultraschall kontaktlos im Prüfobjekt. Der vorgestellte EMAT funktioniert praktisch bei allen metallischen Behältern: explizit gezeigt wird die Funktionalität bei Aluminium, ferromagnetischem Stahl und nicht ferromagnetischem Edelstahl. Der Luftspalt zwischen EMAT-Spule und Oberfläche des Metalltanks kann bis zu 2 mm betragen. Selbst für diesen relativ kleinen Luftspalt ist eine magnetische Flussdichte von 3.2 T an der Oberfläche des Metalltanks notwendig, die ein Permanentmagnet nicht erzeugen kann. Ein starkes Magnetfeld erhöht die Kopplungseffizienz und verstärkt somit den gesendeten Ultraschall als auch das Echosignal des reflektierenden Ultraschalls. Zur Erzeugung der hohen magnetischen Flussdichte fließen Ströme von bis zu 3.6 kA durch die dünnen Windungen (0.5 mm) der EMAT Spule. In diesem Beitrag wird eine elektrische Schaltung für starke Strompulse und MHz-Spannungspulse für >1kV vorgestellt. Gleichzeitig ist die Schaltung in der Lage, kleine Echosignale im μV-Bereich zu detektieren. Eine sehr kurze Erholungszeit nach einem Strompuls ist erforderlich. Die vorgestellte Schaltung verfügt über drei unabhängige Module zur Erzeugung eines starken Strompulses, jedes Modul kann zu einem beliebigen Zeitpunkt gestartet werden. Somit ist es möglich, Echosignale zeitunabhängig zu empfangen und auch tiefliegende Objekte im Wasserbecken zu detektieren. Der Fokus der Arbeit liegt auf der Schaltung, dem Impuls-Echo-Verfahren und den magnetischen Feldern. Eine detaillierte Analyse und Gestaltung des Ultraschallfeldes durch unterschiedliche EMAT-Spulengeometrien gehen in diesem Beitrag zu weit und werden daher in einem separaten Beitrag vorgestellt.
Funding source: Deutsche Forschungsgemeinschaft
Award Identifier / Grant number: RU 2120/4-1
Funding statement: Funded by Deutsche Forschungsgemeinschaft (DFG) , Grant Number: RU 2120/4-1.
About the authors
Kai Rieger received a B.Sc. degree in Biomedical Engineering from the Technical University Ilmenau, Ilmenau, Germany in 2015, and a M.Sc. degree in Electrical Engineering and Information Technology from the University of Ilmenau, Ilmenau, Germany in 2017. From 2017 until 2018, he was an employee at the Fraunhofer Institute for Integrated Circuits (IIS). He is currently working towards a Ph.D. degree in electrical engineering at the University of Duisburg-Essen. His general research interests include contactless inductive power transfer, inductive localization and electromagnetic acoustic transducers.
Daniel Erni is a full professor for General and Theoretical Electrical Engineering at the University of Duisburg-Essen, Germany. After an apprenticeship as an electrician and mechanic he received his two degrees in electrical engineering from HSR Rapperswil and ETH Zürich in 1986 and 1990, respectively, and a PhD degree in laser physics from ETH Zurich in 1996. He has co-authored and authored over 400 scientific publications. His current research interests include optical interconnects, nanophotonics, plasmonics, optical and electromagnetic metamaterials, RF, mm-wave and THz engineering, biomedical engineering, marine electromagnetics, computational electromagnetics, multiscale and multiphysics modeling, numerical structural optimization, and science and technology studies (STS).
Dirk Rueter received his diploma degree in electrical engineering from the Technical University in Karlsruhe (Germany) in 1990. Since 1991, he has been working at the Institute for Optical and Electronic Materials at the Technical University Hamburg, where he obtained his Ph.D. degree in 1997. From 1997–2007, he has been the founding partner of UVC (www.uvc.de), an engineering company for electronic and measurement techniques in Hamburg. In 2007, he became the Saalfeld site manager for LumaSense Technologies GmbH (www.lumasenseinc.com), an industrial infrared systems company. He managed and guided their production and engineering team and was involved in the development of new products or customized solutions. Since 2010, he has been a professor at the University of Applied Science Ruhr West in Muelheim. At the Institute of Measurement and Sensor Technology, he teaches and conducts research in electrical engineering, materials and optoelectronics. His research interests and activities cover applied electromagnetic and RF systems, ultrasound techniques, optoelectronic systems and phenomena, novel materials or structures and medical applications.
References
1. M. Hirao and H. Ogi: Electromagnetic Acoustic Transducers Noncontacting Ultrasonic Measurements using EMATs. 3rd ed. Springer Series in Measurement Science and Technology. Springer Japan, 2017.10.1007/978-4-431-56036-4Search in Google Scholar
2. F. Le Bourdais, T. Le Pollés, and F. Baqué: “Liquid sodium testing of in-house phased array EMAT transducer for L-wave applications.” In: 4th International Conference on Advancements in Nuclear Instrumentation Measurement Methods and their Applications (ANIMMA), (2015), pp. 1–5.10.1109/ANIMMA.2015.7465510Search in Google Scholar
3. F. Le Bourdais et al. “Design of ultrasonic inspection methods for sodium cooled reactors by CIVA simulation.” In: 3rd International Conference on Advancements in Nuclear Instrumentation, Measurement Methods and Their Applications, ANIMMA, 2013 (2013), pp. 1–8.10.1109/ANIMMA.2013.6727955Search in Google Scholar
4. J. Tkocz, D. Greenshields, and S. Dixon: “High power phased EMAT arrays for nondestructive testing of as-cast steel.” In: NDT and E International 102.July 2018 (2019), pp. 47–55.10.1016/j.ndteint.2018.11.001Search in Google Scholar
5. K. S. Ho, D. R. Billson, and D. A. Hutchins. “Inspection of drinks cans using noncontact electromagnetic acoustic transducers.” In: Journal of Food Engineering 80.2 (2007), pp. 431–444.10.1016/j.jfoodeng.2006.04.025Search in Google Scholar
6. F. Hernandez-Valle and S. Dixon. “Pulsed electromagnet EMAT for ultrasonic measurements at elevated temperatures.” In: Insight - Non-Destructive Testing and Condition Monitoring 53.2 (2011), pp. 96–99.10.1784/insi.2011.53.2.96Search in Google Scholar
7. J. Isla and F. Cegla. “Optimization of the bias magnetic field of shear wave EMATs.” In: IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 63.8 (2016), pp. 1148–1160.10.1109/TUFFC.2016.2558467Search in Google Scholar
8. D. Rueter: “Experimental demonstration and circuitry for a very compact coil-only pulse echo EMAT.” In: Sensors (Switzerland) 17.4 (2017).10.3390/s17040926Search in Google Scholar PubMed PubMed Central
9. W. M. Haynes: Handbook of Chemistry and Physiks. Taylor & Francis Group, 2012.Search in Google Scholar
10. E. Grimsehl: Grimsehl Lehrbuch der Physik Band 1 Mechanik Akustik Wärmelehre. Vieweg+Teubner Verlag, 1977.Search in Google Scholar
11. G. Ulbricht. Netzwerkanalyse, Netzwerksynthese und Leitungstheorie. Vieweg+Teubner Verlag, 1986.10.1007/978-3-322-82960-3Search in Google Scholar
12. V. A. Sutilov: Physik des Ultraschalls-Grundlagen. Springer-Verlag Wien New York, 1984.10.1515/9783112530160Search in Google Scholar
13. R. H. Good: “Elliptic integrals, the forgotten functions.” In: European Journal of Physics (2001).10.1088/0143-0807/22/2/303Search in Google Scholar
14. D. Rueter: “Induction coil as a non-contacting ultrasound transmitter and detector: Modeling of magnetic fields for improving the performance.” In: Ultrasonics 65 (2016), pp. 200–210.10.1016/j.ultras.2015.10.003Search in Google Scholar PubMed
15. J. Krautkraemer and H. Krautkraemer: Ultrasonic testing of materials. Springer-Verlag, Berlin, New York, 1990.10.1007/978-3-662-10680-8Search in Google Scholar
© 2020 Walter de Gruyter GmbH, Berlin/Boston
