Browsing by Subject "Acoustic variables measurement"
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Item Open Access Bi-angular lens for material characterization(IEEE, 1994) Yaralıoğlu, Göksen Göksenin; Atalar, Abdullah; Köymen, HayrettinIn this paper a new lens design is proposed for characterization of layered materials. Lamb wave lens employs Lamb waves for this purpose since these waves propagate along interfaces. However, below cut-off angle, the critical angles of Lamb wave modes are low and the generated V(z) curves have small number of oscillations, which in turn causes measurement difficulties and accuracy degradation. Bi-angular lens described in this paper, generates an extra obliquely incident wave, instead of normally incident beam, in order to provide the reference specular reflection. Simulation results as well as experimental results are presented and it is shown that a high sensitivity can be obtained by using this new lens.Item Open Access Measurement of sensitivity of different wave modes to subsurface defects(IEEE, 1988) Atalar, Abdullah; Köymen, Hayrettin; Yemişçiler, O.Excitation of acoustic wave modes in a layered solid is investigated when the solid is immersed in a liquid. This is done by computing the reflection coefficient of acoustic plane waves at the liquid-layered-solid interface. Then, a method to evaluate the sensitivity of various modes supported in the layered structure to subsurface defects is introduced. The method involves insonification of the layered structure with a conical wave whose axis coincides with the defect. Since all the rays in the conical wavefront hit the planar interface at the same angle, it is possible to excite a single kind of mode in the layer. By adjusting the angle of inclination of the cone, it is possible to excite the modes selectively. Since the conical waves converge to a line focus at the cone axis, the excited mode will focus on the defect. By recording the reflected signal amplitude as the cone angle is varied, a curve is obtained from which it is possible to conclude the sensitivity of various modes to the subsurface flaw. The results of such measurements indicated that the generalized Lamb wave modes are more sensitive to subsurface defects than the Rayleigh waves. An imaging system which makes use of focused Lamb waves was built and the system produced images of very small subsurface defects.Item Open Access Recognition of vessel acoustic signatures using non-linear teager energy based features(IEEE, 2016-10) Can, Gökmen; Akbaş, Cem Emre; Çetin, A. EnisThis paper proposes a vessel recognition and classification system based on vessel acoustic signatures. Teager Energy Operator (TEO) based Mel Frequency Cepstral Coefficients (MFCC) are used for the first time in Underwater Acoustic Signal Recognition (UASR) to identify platforms the acoustic noise they generate. TEO based MFCC (TEO-MFCC), being more robust in noisy conditions than conventional MFCC, provides a better estimation platform energy. Conventionally, acoustic noise is recognized by sonar oper-ators who listen to audio signals received by ship sonars. The aim of this work is to replace this conventional human-based recognition system with a TEO-MFCC features-based classification system. TEO is applied to short-time Fourier transform (STFT) of acoustic signal frames and Mel-scale filter bank is used to obtain Mel Teager-energy spectrum. The feature vector is constructed by discrete cosine transform (DCT) of logarithmic Mel Teager-energy spectrum. Obtained spectrum is transformed into cepstral coefficients that are labeled as TEO-MFCC. This analysis and implementation are carried out with datasets of 24 different noise recordings that belong to 10 separate classes of vessels. These datasets are partially provided by National Park Service (NPS). Artificial Neural Networks (ANN) are used as a classification method. Experimental results demonstrate that TEO-MFCC achieves 99.5% accuracy in classification of vessel noises. © 2016 IEEE.