Non-speech acoustic signals are widely used as the input of systems for non-destructive testing. ... more Non-speech acoustic signals are widely used as the input of systems for non-destructive testing. In this rapidly growing field, the signals have an increasing complexity leading to the fact that powerful models are required. Methods like DTW and HMM, which are established in speech recognition, have been successfully used but are not sufficient in all cases. We propose the application of generalized structured Markov graphs (SMG). We describe a task independent structure learning technique which automatically adapts the models to the structure of the test signals. We demonstrate that our solution outperforms hand-tuned HMM structures in terms of class discrimination by two case studies using data from real applications.
Guided elastic waves in the frequency range of a few hundred kHz, generated and detected by appro... more Guided elastic waves in the frequency range of a few hundred kHz, generated and detected by appro- priate transducer arrays, are used to monitor the structural integrity of pipes by comparing their actual state with a predefined reference state. For these purposes, theoretical, numerical, and experimental results are combined to study guided wave propagation and wave interaction with relevant defects in detail. Based on these findings, a guided wave based multi-channel structural health monitoring (SHM) system is designed and applied to identify and monitor structural defects in various piping components. The potential use of synthetic aperture techniques is discussed yielding spatial distributions of damage parameters along the pipe. The results reveal that guided wave based SHM in the kHz frequency regime has great potential for online monitoring of piping systems. It combines imaging techniques with long range detection capabilities and therefore closes the gap between local high...
ABSTRACT Future safety and maintenance strategies for industrial components and vehicles are base... more ABSTRACT Future safety and maintenance strategies for industrial components and vehicles are based on combinations of monitoring systems that are permanently attached to or embedded in the structure, and periodic inspections. The latter belongs to conventional nondestructive evaluation (NDE) and can be enhanced or partially replaced by structural health monitoring systems. However, the main benefit of this technology for the future will consist of systems that can be differently designed based on improved safety philosophies, including continuous monitoring. This approach will increase the efficiency of inspection procedures at reduced inspection times. The Fraunhofer IZFP Dresden Branch has developed network nodes, miniaturized transmitter and receiver systems for active and passive acoustical techniques and sensor systems that can be attached to or embedded into components or structures. These systems have been used to demonstrate intelligent sensor networks for the monitoring of aerospace structures, railway systems, wind energy generators, piping system and other components. Material discontinuities and flaws have been detected and monitored during full scale fatigue testing. This paper will discuss opportunities and future trends in nondestructive evaluation and health monitoring based on new sensor principles and advanced microelectronics. It will outline various application examples of monitoring systems based on acoustic techniques and will indicate further needs for research and development.
Non-speech acoustic signals are widely used as the input of systems for non-destructive testing. ... more Non-speech acoustic signals are widely used as the input of systems for non-destructive testing. In this rapidly growing field, the signals have an increasing complexity leading to the fact that powerful models are required. Methods like DTW and HMM, which are established in speech recognition, have been successfully used but are not sufficient in all cases. We propose the application of generalized structured Markov graphs (SMG). We describe a task independent structure learning technique which automatically adapts the models to the structure of the test signals. We demonstrate that our solution outperforms hand-tuned HMM structures in terms of class discrimination by two case studies using data from real applications.
Guided elastic waves in the frequency range of a few hundred kHz, generated and detected by appro... more Guided elastic waves in the frequency range of a few hundred kHz, generated and detected by appro- priate transducer arrays, are used to monitor the structural integrity of pipes by comparing their actual state with a predefined reference state. For these purposes, theoretical, numerical, and experimental results are combined to study guided wave propagation and wave interaction with relevant defects in detail. Based on these findings, a guided wave based multi-channel structural health monitoring (SHM) system is designed and applied to identify and monitor structural defects in various piping components. The potential use of synthetic aperture techniques is discussed yielding spatial distributions of damage parameters along the pipe. The results reveal that guided wave based SHM in the kHz frequency regime has great potential for online monitoring of piping systems. It combines imaging techniques with long range detection capabilities and therefore closes the gap between local high...
ABSTRACT Future safety and maintenance strategies for industrial components and vehicles are base... more ABSTRACT Future safety and maintenance strategies for industrial components and vehicles are based on combinations of monitoring systems that are permanently attached to or embedded in the structure, and periodic inspections. The latter belongs to conventional nondestructive evaluation (NDE) and can be enhanced or partially replaced by structural health monitoring systems. However, the main benefit of this technology for the future will consist of systems that can be differently designed based on improved safety philosophies, including continuous monitoring. This approach will increase the efficiency of inspection procedures at reduced inspection times. The Fraunhofer IZFP Dresden Branch has developed network nodes, miniaturized transmitter and receiver systems for active and passive acoustical techniques and sensor systems that can be attached to or embedded into components or structures. These systems have been used to demonstrate intelligent sensor networks for the monitoring of aerospace structures, railway systems, wind energy generators, piping system and other components. Material discontinuities and flaws have been detected and monitored during full scale fatigue testing. This paper will discuss opportunities and future trends in nondestructive evaluation and health monitoring based on new sensor principles and advanced microelectronics. It will outline various application examples of monitoring systems based on acoustic techniques and will indicate further needs for research and development.
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Papers by D. Hentschel