Ultrasound Measurement Technology

Prof. Dr. rer. nat. et Ing. habil Kühnicke leads the ultrasound workgroup, which studies with the following subjects:

Sound field modelling

Ultrasound testing requires an applied adaptation of testing methodology and ultrasound transducers on geometrical shape of the specimen and the location of the expected defect. For these kinds of optimisation tasks, algorithms and simulation programs were developed based on Green's functions to calculate the harmonic and transient sound field. With this sound field modelling, the development of new measurement methods and the improvement of existing methods was achieved:

• non-scanning determination of radius of curvature
• optimisation and adaptation of ultrasound transducers for predefined test set-ups (for example design of lens and distance between transducers and specimen on testing specimens with curved surfaces)
• improvement of the resolution in ultrasound imaging
• simultaneous determination of sound velocity and layer thickness in multilayer structures
• optimisation of array structures of transducers

Publicationen

• E. Kühnicke: „Three-dimensional waves in layered media with non-parallel and curvedinterfaces - A theoretical approach“; J. ACOUST. SOC. AM. 100; 1996; 2; pp. 709-716
• E. Kühnicke: „Elastische Wellen in geschichteten Festkörpersystemen: Modellierungen mit Hilfe von Integraltransformationsmethoden“; Simulationsrechnungen für Ultraschallanwendungen; Schriftenreihe der TIMUG Technologie in Medizin und Gesundheitswesen e.V.; Bonn 2001; ISBN 3-934244-01-7
• E. Kühnicke, M. Lenz, N. Gust: „Nutzung von Schallfeldinformationen zur Entwicklung von neuen Ultraschallmessverfahren“; Neue Entwicklungen in der Elektroakustik und elektromechanischen Messtechnik; Band 40; 59 – 68

Ultrasound Measurement Technology

Scanning acoustic microscopy is an imaging technique used to visualise hidden structures inside of opaque objects. The devices are working in the frequency range from 10 to 230 MHz and show the reflected signals of the pulse-echo method in A, B or C scans. Common commercial devices only work with one single channel and a focused transducer that contains an acoustic lens. The acoustic coupling is realised by immersion technique. To generate an image the transducer scans in parallel across the surface of the probe.

To apply the new measurement methods based on annular arrays, a measuring system built in-house was developed, that contains 16 independent channels to control the array and a 3-axis displacement device to perform the scan.

Objectives for new projects include the improvement of the hardware of the microscopy system and the development of ultrasound transducers that contain structured annular arrays, to have the possibility to control and focus the ultrasound beam. By the usage of new measurement techniques at high frequencies, it is aspired to improve the quality of ultrasound imaging, to extend the amount of test set-ups and to reduce the measurement duration in scanning acoustic microscopy.

The development of new measurement techniques requires the precise characterisation of the ultrasound transducers. In order for annular arrays to function effectively, each single ring segment must have the same area. Under these conditions, they all have the same natural focus position. Furthermore it is necessary that the curvature of pre-focussed arrays is manufactured exactly. The quality of manufactured ultrasound transducers is tested by measurement of the sound field and focal point by using a hydrophone, scattering particles or point-reflectors.

Publicationen

• N. Gust, F. Schellhorn: „High frequency 16 channel ultrasonic microscope for annular arrays“; IEEE International Ultrasonics Symposium; 2012; pp. 2435-2437
• A. Juhrig, S. Kümmritz, M. Wolf, E. Kühnicke: „Development of a Multichannel Pulser for Acoustic Scanning Microscopy“; Physics Procedia Vol. 70; 2015; pp. 892-895
• Lenz, M.; Gust, N.; Wolf, M.; Kühnicke, E.; Rödig, T.: „Transducer characterisation by sound field measurements”; IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control; vol. 60; no. 5; May 2013; pp. 998-1009. ISSN 0885-3010

Development of measurement techniques based on the sound fieldThe usage of transducers containing annular arrays offers the control of the ultrasound beam and focal point. Furthermore, additional information can be obtained from the received echo signals. From these received signals, the time of flight of the ultrasound pulse and its amplitude are typically evaluated. When using annular arrays, additional information in the form of the pressure distribution on the surface of the transducer can be collected. This information can be analysed to develop measurement techniques for the following different disciplines:

• material characterisation: simultaneous determination of layer thickness and sound velocity in multilayer structures
• Zerstörungsfreie Prüfung z.B.: Bestimmung von Größe und Form von Einschlüssen kleiner als die Schallbündelbreite, Bestimmung von Krümmungsradien akustischer Grenzflächen
• non-destructive testing: determination of size and shape of inclusions smaller than the width of the ultrasound beam, determination of the radius of curvature of acoustical interfaces
• medical imaging: temperature monitoring during hyperthermia therapy in biological tissue by ultrasound

Publicationen

• Sebastian Kümmritz, Mario Wolf und Elfgard Kühnicke: „Simultane Bestimmung von Dicken und Schallgeschwindigkeiten geschichteter Strukturen“; tm – Technisches Messen; 2015; 82(3): 127–134
• Mario Wolf, Sebastian Kümmritz, Elfgard Kühnicke: “Advanced signal analysis for the examination of multilayered structures using annular arrays”; 11th European Conference on Non-Destructive Testing (ECNDT 2014); October 6-10, 2014; Prague, Czech Republic
• S. Kümmritz, M. Wolf, E. Kühnicke: “Material Characterization of Layered Structures with Ultrasound”; 2015 International Congress on Ultrasonics; 2015 ICU Metz
• Sebastian Kümmritz, Mario Wolf, Elfgard Kühnicke: “Improvement of the resolution limit caused by the width of the sound beam”; 2012 IEEE International Ultrasonics Symposium Proceedings, Dresden; October 7-10, 2012; pp. 44-47
• M. Wolf, E. Kühnicke: „Non-invasive and Locally Resolved Measurement of Sound Velocity by Ultrasound”; Sensors & Transducers Journal; Vol. 184; Issue 1; January 2015; pp. 53- 59; ISSN: 2306-8515
• Michael Lenz, Martin Bock, Elfgard Kühnicke, Josef Pal, Andreas Cramer: „Measurement of the sound velocity in fluids using the echo signals from scattering particles”; Ultrasonics; Vol. 52; Issue 1; 2012; S. 117-124; ISSN 0041-624X
• Mario Wolf, Katharina Rath, Andrés Eduardo Ramos Ruiz, Elfgard Kühnicke: “Ultrasound thermometry for optimizing heat supply during a hyperthermia therapy of cancer”; 2015 International Congress on Ultrasonics; 2015 ICU Metz