Phased array ultrasonic testing (PAUT) techniques are widely used for the non-destructive testing (NDT) of austenitic welds to find defects like cracks. However, the propagation of ultrasound waves through the austenitic material is intricate due to its inhomogeneous and anisotropic nature. Such a characteristic leads beam path distorted which causes the signal to be misinterpreted. By employing a reference block which is cutout from the mockup of which the structure is a dissimilar metal weld (DMW), a new method of PAUT named as Referencing Delay Law Technique (RDLT) is introduced. With the RDLT, full matrix capture (FMC) was used for data acquisition. To reconstruct the images, total focusing method (TFM) was used. After the focal laws were calculated, PAUT was then performed. As a result, the flaws are more precisely positioned with significantly increased signal-to-noise ratio (SNR).
The age-related changes in the visco-elastic properties of the human lens are discussed with respect to presbyopia for a
long time. All known measurement techniques are based on extracted lenses or are damaging the tissue. Hence, in vivo
studies of lens hardness are not possible at the moment. To close this gap in lens diagnostics this project deals with an
approach for a non-contact laser-acoustic characterization technique. Laser-generated wave fronts are reflected by the
tissue interfaces and are also affected by the visco-elastic properties of the lens tissue. After propagating through the eye,
these waves are recorded as corneal vibrations by laser vibrometry. A systematic analysis of amplitude and phase of
these signals and the wave generation process shall give information about the interface locations and the tissues viscoelastic
properties. Our recent studies on extracted porcine eyes proved that laser-acoustic sources can be systematically
used for non-contacting generation and recording of ultrasound inside the human eye. Furthermore, a specific numerical
model provides important contributions to the understanding of the complex wave propagation process. Measurements of the acoustic sources support this approach. Future investigations are scheduled to answer the question, whether this novel technique can be directly used during a laser surgery for monitoring purposes and if a purely diagnostic approach, e.g. by excitation in the aqueous humor, is also possible. In both cases, this technique offers a promising approach for non-contact ultrasound based eye diagnostics.
The constant growth of air traffic leads to increasing demands for the aircraft industry to manufacture airplanes
more economically and to ensure a higher level of efficiency, ecology and safety. During the last years important
improvements for fuselage structures have been achieved by application of new construction principles,
employment of sophisticated and/or alternative materials, and by improved manufacturing processes. In
particular the intensified application of fibre-reinforced plastics components is in the focus of current discussions
and research.
The main goal of an ongoing national project is to improve the existing ultrasonic test technology in such a way
that it is optimally suited for the examination of CFRP multilayer structures. The B-Scan and C-Scan results are
then used for the visualization of individual layers and the complete layer set-up.
First results of the project revealed that with carefully selected transducers and frequencies it is possible to detect defects and irregularities in the layer structure like delaminations, fibre cracking, ondulations, missing layers etc. and even to visualize the fibre orientations in the individual layers.
In the European project SAFE PIPES guided elastic waves in the frequency range between 100 and 250 kHz, generated
and detected by appropriate transducer arrays, are used to monitor the structural integrity of industrial piping systems by
comparing the actual state of the pipe with a predefined reference state. In the present paper, theoretical, numerical, and
experimental investigations 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 SHM system is designed and applied for
monitoring of crack-like defects in steel pipes. The first results reveal that guided wave based SHM in the kHz
frequency regime has great potential for online monitoring of piping systems. It is able to combine imaging techniques
with long range detection capabilities and therefore closes the gap between high-frequency NDE on the one hand and
low-frequency vibration analysis on the other hand.
KEYWORDS: Sensors, Signal processing, Structural health monitoring, Digital signal processing, Transducers, Structured optical fibers, Acoustics, Data communications, Composites, Ferroelectric materials
The presented paper describes a condition monitoring for Aircraft structures based on the evaluation of acoustical Lamb waves. Methods for effective sensor near signal processing are required to detect wave modes and to reduce noise as much as possible. Frequently, a further necessity exists to integrate the measuring technique into the monitored structure. To meet these requirements, sensor near units for signal processing have to be developed, which can be connected as nodes within a network.
A compact, sensor near signal processing structure has been realized containing components for analog preprocessing of acoustic signals, their digitization, algorithms for data reduction and network communication. The core component is a digital signal processor (DSP), which performs the basic algorithms necessary for filtering, down sampling, mode selection and correlation of spectral components particularly effective.
As a first application, impact detection and characterization of delaminations were realized for a fiber composite plate. Starting from the simulation of wave propagation, characteristic signal parameters were determined. In some experiments, it could be proven that impact locations and delaminations can be derived from the detected Lamb waves. This work is continued to develop special structural health monitoring systems (SHM) for selected aircraft components (e. g. stringer elements, panels).
A numerical model of an acoustic microscope based on the elastodynamic finite integration technique (EFIT) is presented. It allows time-domain simulations of elastic wave propagation in both, fluids and solids, and includes focusing of the incident wave field as well as scattering at defects and the fluid-solid interface taking mode converted echoes and leaky Rayleigh waves into account. The simulations can be performed for different frequencies and materials and can be used for the continuous and time-resolved mode as well as for transmission and reflection microscopy. The simulation results can be represented by time-domain signals and wave front snapshots. The formation of V(r,z) curves is also possible. In the present paper the simulations are applied to the problem of vertical cracks and spherical inclusions in a solid substrate as well as for subsurface characterization of thin coatings.
Several work performed at the Fraunhofer Institute IZFP Dresden on photo and particle acoustic methods is presented. It includes both, modeling activities by an explicit numerical method (CEFIT) and experimental work. The given examples of applied excitations are photons (Laser acoustics) and electrons (Scanning Electron Acoustic Microscopy, SEAM). Both, time resolved measurements by pulse excitation as well as monofrequent measurements by periodic excitation together with signal recovery (lock-in technique) are discussed.
KEYWORDS: Signal processing, Digital signal processing, Sensors, Acoustics, Diagnostics, System integration, Filtering (signal processing), Electronics, Optical filters, Safety
The economic efficiency and competitiveness of environment-friendly rail transportation depends on safety, availability and maintenance of single highly loaded structure components. Until now these components have been changed in fixed maintenance intervals irrespective of any usage related conditions. With the knowledge and evaluation of the component conditions, life cycle costs can be reduced by means of optimized maintenance and/or “fit for purpose” design. For example, rail-bound vehicle wheel sets are among the most highly stressed travelling gear components of the bogie. if such a component fails, a serious accident may occur. For this reason, a health monitoring system based on the interpretation of ultrasonic sound signatures has been developed. First, the ultrasonic waves generated by an artificial defect on the outer wheel tread of a railroad wheel towards an acoustic sensor, placed inside the hollow shaft of the railroad axis were simulated with a EFIT (Elastodynamic Finite Integration Technique). The results achieved proved that relevant signals can be found in a frequency range up to 300 kHz.
Based on this a diagnostic unit was designed and built for application under rotation conditions, which consists of a piezo-electric sensor, primary electronics, an analog-to-digital converter, a digital signal processor, a trigger unit, and a telemetric transmitter. This diagnostic unit was integrated in the hollow shaft of a railroad wheel axis, a component of a special laboratory test rig. Algorithms which allow for the rotation-synchronized processing of acoustic signals were implemented into the rotating diagnostic unit. After successfully completing a campaign for this test rig, a second test was performed inside the wheel/railroad simulation test rig of the Deutsche Bahn AG under railroad-like conditions. The data generated inside the hollow shaft of the railroad wheel axis by the diagnostic unit were telemetrically transmitted to an industrial computer. The detection of artificial defects of different sizes is shown in correlation with theoretical assumptions.
KEYWORDS: Scattering, Tissue optics, Sensors, Ultrasonography, Signal detection, Modulation transfer functions, Light scattering, Tissues, Modulation, Signal to noise ratio
Acousto-photonic imaging (API) is a new approach in biomedical imaging that combines diffuse imaging by photon density waves (PDW) and light "tagging" inside the tissue by focussed ultrasound. This light "tagging" enables 3D optical imaging with mm resolution in tissue limited only by the geometrical extent of the ultrasound focus and the signal to noise ratio.
We discuss some possible mechanisms of light "tagging" and its dependance of different parameters. We present several phantom measurements which investigate advantages and disadvantages of API against PDW. The main advantage of API is the possibility of real 3D imaging while its biggest disadvantage is the poor light intensity from deeper regions.
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