title: Reconstruction of the acoustic impedance profile in a plate using an inverse spectral procedure.
abstract: An inverse spectral procedure was applied to reconstruct the acoustic impedance profile along the thickness direction of a plate using its thickness resonance frequencies, density and thickness. For a successful reconstruction, the material-property profile must be symmetric about the mid-plane of the plate. Several cases of numerical simulations, including plates with a few layers and with a high number of layers are described. The calculated resonance frequencies were used to reconstruct the acoustic impedance profile, a process that was successful for all cases. We assume that a plate with a high number of layers, each with a different but constant acoustic impedance, simulates a plate with a smoothly varying acoustic impedance profile. It can be concluded that such a plate, which generates small, virtually undetectable, internally reflected waves, can also be reconstructed. In the special case of a plate of unknown thickness and unknown but constant density, the method is still useful, because a relative variation of the material property can be reconstructed using only the resonance frequencies. An experiment using a resonance-mode electromagnetic acoustic transducer (resonance-mode EMAT) is also described. EMAT is a non-contact ultrasonic method that can measure thickness resonance frequencies, making it appropriate for this method. Some examples of applications are measurement of the temperature profile inside a rolled metal sheet, measurement of a clad metal plate, and monitoring of a metal casting.
authors.affiliation: Professor Emeritus, Tokyo University of Technology, 1404-1 Katakura, Hachioji, Tokyo 192-0982, Japan. kwsmk@jcom.home.ne.jp
authors.forename: Katsuhiro
authors.initials: K
authors.lastname: Kawashima
mesh_terms: D000158:Acoustic Impedance Tests / Q000379:methods*; D000535:Aluminum; D004548:Elasticity; D008670:Metals; D013696:Temperature
chemical_list: D008670:Metals; D000535:Aluminum