Vom 22. bis 26. März 2026 fand die 52. Jahrestagung (DAGA) der deutschen Gesellschaft für Akustik in Dresden statt. Das Fachgebiet Elektrische Messtechnik (EMT) war dort mit zwei Beiträgen vertreten.
In seinem Beitrag zeigte Leander Claes erstmalig eine Dispersionsbeziehung für einen akustischen Wellenleiter unter Berücksichtigung scher- und volumenviskoser Effekte. Hieraus ergibt sich potentiell eine Möglichkeit für die Realisierung eines akustischen Messverfahrens für die simultane und selektive Bestimmung der Scher- und Volumenviskosität.
Die quantitative, zerstörungsfreie Materialcharakterisierung wird häufig mittels inverser Messverfahren realisiert. Die in diesem Zusammenhang erforderlichen Simulationen, vor allem im Frequenzbereich, erfordern in der Regel das rechenaufwendige Lösen von Eigenwertproblemen. In seinem Beitrag präsentierte Henning Zeipert einen Ansatz zum Aufstellen alternativer Zielfunktionen, welche das Lösen von Eigenwertproblemen vermeiden und damit eine signifikante Effizienzsteigerung dieser Verfahren ermöglichen.
Im Folgenden finden Sie die Kurzfassungen der beiden Tagungsbeiträge. Sobald der Tagungsband der DAGA 2026 publiziert ist, finden Sie die vollständigen Beiträge im Publikationsverzeichnis des Fachgebietes.
Title: Simultaneous measurement of bulk and shear viscosity using guided acoustic waves
Author: Leander Claes
Both bulk and shear viscosity cause acoustic absorption in fluids, superimposing additively and thus impeding an estimation of both parameters from measured acoustic absorption. Acoustic waves guided in rigid ducts similarly experience absorption caused by both viscosities. However, if viscous effects at the boundaries are also considered, the extent of which only depends on shear viscosity, the dispersive properties of guided waves depend qualitatively different on both viscosities.
In particular the fundamental mode of the waveguide is shown to have frequency-dependent absorption that is distinctly influenced by bulk and shear viscosity. If the frequency-dependent absorption of this mode can be made accessible via measurements, a simultaneous determination of bulk and shear viscosity is possible. The proposed experimental setup consists of a fluid layer enclosed by two acoustically well-known metallic plates, in which broadband, guided waves are analysed.Acoustic absorption of modes in thinner fluid layers will exhibit a higher sensitivity with respect to shear viscosity due to the larger relative extend of the viscous boundary layer. The thickness of the fluid layer, e.g. 2 mm for a water-like fluid, can thus be used to tune the relative sensitivities with respect to both parameters.
Title: An approach for the efficient solution of eigenvalue-based inverse problems for the material characterisation using guided acoustic waves
Authors: Henning Zeipert, Leander Claes, Bernd Henning
Quantitative, non-destructive material parameter estimation methods generally require the solution of an inverse problem. Starting from a set of initial values, the simulation results of a parametrised model are compared with measurement data. The simulation results are aligned with the measurement data through an optimisation-driven, computationally expensive, iterative adaptation of the parameters.
Simulations often require solving an eigenvalue problem, particularly in the context of simulations in the frequency domain. In such cases, the solution of the inverse problem involves identifying a matrix whose eigenvalues are known from the measurement data. The presented approach provides an efficient solution to the inverse problem without having to solve the eigenvalue problem. This is achieved by evaluating the characteristic polynomial of the matrix as objective function for the optimisation procedure.
The material characterisation using guided acoustic waves represents such a case.
Measurements of broadband ultrasonic waves provide the propagating wave modes with values for the wavenumber at a given frequency. The Scaled Boundary Finite Element Method (SBFEM) provides a matrix for each frequency, with the eigenvalues representing the wavenumbers of propagable modes.
The proposed formulation demonstrates that material parameters can be determined without explicit eigenvalue computation, thereby improving computational efficiency.
