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Non-Contact Damage Detection under Operational Conditions with Multipoint Laservibrometry
摘要： Scanning laser–Doppler vibrometry (SLDV) can localize and visualize damages in mechanical structures. In order to enable scanning, it is necessary to repeat the vibration. Therefore, this technique is not suited to detect emerging hazards in working machinery that change the vibration behavior. A common technique for such cases is monitoring the vibration excited by machine operation with accelerometers. This technique requires mechanical coupling between sensors and the measurement object, which in?uences the high-frequency vibration responses. However, in the low-frequency range, local damages do not shift resonances or distort operational de?ection shapes (ODS) signi?cantly. These alterations in the vibration behavior are tiny and hard to detect. This paper shows that multipoint laservibrometry (MPV) with laser excitation can measure these e?ects e?ciently, and it further demonstrates that damages in?uence ODSs at frequencies above 20 kHz much stronger than at frequencies below 20 kHz. In addition, ODS-based damage indices are discussed; these are highly sensitive to minute visible changes of the ODSs. In order to enhance the sensitivity of hazard detection, the response vector assurance criterion value is computed and evaluated during operation. The capabilities and limitations of the methodology on the example of a cantilever with manually emerging damage are demonstrated.
关键词： structural health monitoring,multipoint laser-Doppler vibrometer,operational de?ection shape,operational condition,damage detection,laser–Doppler vibrometry,non-destructive testing,laser ablation
更新于2025-09-19 17:13:59
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The Vibration Behavior of Suba??Micrometer Gas Vesicles in Response to Acoustic Excitation Determined via Laser Doppler Vibrometry
摘要： The ability to monitor sub-micrometer gas vesicles’ (GVs) vibration behavior to nonlinear buckling and collapse using laser Doppler vibrometry is reported, providing a precise noncontact technique for monitoring the motion of sub-micrometer objects. The fundamental and first harmonic resonance frequencies of the vesicles are found to be 1.024 and 1.710 GHz, respectively. An interparticle resonance is furthermore identified at ≈300 MHz, inversely dependent upon the agglomerated GV size of around 615 nm. Most importantly, the vesicles amplify and broaden input acoustic signals at far lower frequencies—for example, 7 MHz—associated with medical and industrial applications, and they are found to transition from a linear to nonlinear response at 150 kPa and to collapse at 350 kPa or greater.
关键词： bubble dynamics,gas vesicles,sub-micrometer object metrology,acoustofluidics,laser Doppler vibrometry
更新于2025-09-19 17:13:59
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[IEEE 2019 IEEE International Ultrasonics Symposium (IUS) - Glasgow, United Kingdom (2019.10.6-2019.10.9)] 2019 IEEE International Ultrasonics Symposium (IUS) - Non-Contact laser ultrasound (N-CLUS) system for medical imaging and elastography
摘要： MIT Lincoln Laboratory, the Medical Device Realization Center (MEDRC) at MIT, and the Massachusetts General Hospital (MGH) are collaboratively developing a novel optical system that acquires ultrasound images within the human body without physical contact to the patient. The system is termed, non-contact laser ultrasound (N-CLUS) and yields anatomical images in tissue and bone and can also measure elastographic properties, in-vivo, all from an operational standoff of a few inches to several meters as desired. N-CLUS employs a pulsed laser that converts optical energy into ultrasonic waves at the skin surface via photoacoustic mechanisms, while, a laser Doppler vibrometer measures reflected-emerging ultrasonic waves from tissue at depth at the skin surface. The key of the N-CLUS approach is driven by shallow optical absorptivity that creates an acoustic source that enables ultrasound propagation deeper into the tissue. We discuss the motivation of the non-contact laser concept, its development path involving signal generation, skin and eye safe laser measurement, and system design perspectives. Elastogrphic measurements are then demonstrated with determination of bone elastic moduli for beef rib within tissue. N-CLUS images from soft tissue specimens are also compared with commercial ultrasound, showing that the noncontact optical approach may have potential as a viable method in medical ultrasound.
关键词： laser Doppler vibrometry,photoacoustics,non-contact laser ultrasound,medical ultrasound imaging,elastography
更新于2025-09-16 10:30:52
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Heterodynes Laser-Doppler-Vibrometer mit gekoppelten Diodenlasern zur Schwingungsanalyse von SAW-Filtern / Heterodyne laser-Doppler vibrometer with frequency-offset-locked diode lasers for vibration analysis of SAW filters
摘要： Heterodyne interferometers measure vibration amplitudes at frequencies > 100 MHz with defined measurement uncertainty in contrast to homodyne methods. The low efficieny of Bragg cells for frequency shifting > 409 MHz impedes the application of heterodyne interferometers for the Gigahertz range. In this paper, we present an automated measurement system for the aquisition of operting deflection shapes of microsystems with a laser-Doppler-vibrometer microscope, in which an optical phase-lock loop controls the frequency offset of two diode lasers and, therefore, determines the carrier frequency. Our measurement system provides a vibration-amplitude resolution in the picometer range for vibration frequencies from 10 MHz to 700 MHz. The measurement capability for the absolute amplitude and phase of the vibration is exemplary shown with a vibration analysis of a surface-acoustic-wave filter.
关键词： MEMS testing,heterodyne laser-Doppler vibrometry,Heterodyne interferometry,phase-locked loop
更新于2025-09-16 10:30:52
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Laser-Doppler-Vibrometrie an dynamischen Strukturen von Windenergieanlagen
摘要： Numerous issues in the design, construction and operation of wind turbines require vibration measurements, especially on rotor blades under operating conditions. Built-in sensors can only perform this task selectively, externally mounted sensors only with great effort and possible influence on the object to be measured. A system-independent, distant measuring method will be presented here: the combination of a laser Doppler vibrometer with a method for tracking the rotation of the rotor. It requires a separation of the effects caused by the macroscopic movement of the rotor from the real vibration movements. One is the Doppler effect of the fast rotor movement, additionally, the signal noise of the backscattered coherent laser radiation and motion artifacts due to the oblique viewing angle are discussed. First test measurements demonstrated the applicability of the method despite these challenges.
关键词： tracking method,wind turbine,Laser Doppler vibrometry,heterodyne detection,rotor blade
更新于2025-09-16 10:30:52
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Characterizing the Complex Modulus of Asphalt Concrete Using a Scanning Laser Doppler Vibrometer
摘要： Asphalt mixtures are the most common types of pavement material used in the world. Characterizing the mechanical behavior of these complex materials is essential in durable, cost-effective, and sustainable pavement design. One of the important properties of asphalt mixtures is the complex modulus of elasticity. This parameter can be determined using different standardized methods, which are often expensive, complex to perform, and sensitive to the experimental setup. Therefore, recently, there has been considerable interest in developing new, easier, and more comprehensive techniques to investigate the mechanical properties of asphalt. The main objective of this research is to develop an alternative method based on an optical measurement technique (laser Doppler vibrometry). To do this, a frequency domain system identification technique based on analytical formulas (Timoshenko’s beam theory) is used to determine the complex modulus of asphalt concrete at its natural frequencies and to form their master curve. The master curve plotted by this method is compared with the master curve obtained from the standard four-point bending test, and it is concluded that the proposed method is able to produce a master curve similar to the master curve of the standard method. Therefore, the proposed method has the potential to replace the standard stiffness tests. Furthermore, the standard stiffness methods usually conduct experiments up to the maximum frequency of 30 Hz. However, the proposed method can provide accurate complex modulus at high frequencies. This makes an accurate comparison between the properties of the asphalt mixtures in high frequencies and the development of more accurate theoretical models for simulation of specimens possible.
关键词： laser Doppler vibrometry,asphalt mixtures,modal analysis,complex modulus,master curve,non-destructive testing
更新于2025-09-11 14:15:04
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On the Application of Laser Vibrometry to Perform Structural Health Monitoring in Non-Stationary Conditions of a Hydropower Dam
摘要： This paper presents the ?rst application of the Laser Doppler Vibrometer (LDV) in non-stationary conditions within a hydropower plant powerhouse. The aim of this research is to develop a methodology to include non-contact vibration monitoring as part of structural health monitoring of concrete dams. We have performed in-situ structural vibration measurements on the run-of-the-river Bre?ice dam in Slovenia during the start-up tests and regular operation. In recent decades, the rapid development of laser measurement technology has provided powerful methods for a variety of measuring tasks. Despite these recent developments, the use of lasers for measuring has been limited to sites provided with stationary conditions. This paper explains the elimination of pseudo-vibration and measurement noise inherent in the non-stationary conditions of the site. Upon removal of the noise, fatigue of the different structural elements of the powerhouse could be identi?ed if signi?cant changes over time are observed in the eigenfrequencies. The use of laser technology is to complement the regular monitoring activities on large dams, since observation and analysis of integrity parameters provide indispensable information for decision making and maintaining good structural health of ageing dams.
关键词： concrete dam,dam monitoring,laser doppler vibrometry,vibration,accelerometers
更新于2025-09-11 14:15:04