Measurement Reciprocity in Laser Ultrasound: Exploring the Equivalence Between Scanning Laser Excitation and Detection

Temel Kavramlar

The common assumption of strict measurement reciprocity between scanning laser detection and scanning laser excitation is disproved by a simple experiment. However, the study reveals correct reciprocal measurement setups for both the probe-excitation/laser-detection and the laser-excitation/probe-detection cases. Similarly, the all-laser measurement, with thermoelastic laser excitation and laser vibrometer detection, is not generally reciprocal with respect to the exchange of excitation and detection positions. Appropriate substitutes for the laser doppler vibrometer out-of-plane displacement measurement are found to ensure measurement reciprocity together with laser excitation.

Özet

The paper investigates the reciprocity in laser ultrasound measurements, where elastic waves are generated and detected using various combinations of laser excitation and piezoelectric/laser detection.
The key highlights are:

The common belief about strict measurement reciprocity between scanning laser detection and scanning laser excitation is disproved by a simple experiment. The wavefield snapshots obtained from the two measurement setups differ significantly.

Analytical derivations based on the electromechanical reciprocity theorem reveal correct reciprocal measurement setups for both the probe-excitation/laser-detection and the laser-excitation/probe-detection cases. The key is to use appropriate surface values, such as the averaged in-plane strain, instead of the out-of-plane displacement.

For the all-laser measurement, with thermoelastic laser excitation and laser vibrometer detection, the reciprocity does not hold when simply exchanging the excitation and detection positions. However, using the divergence of the surface displacement as the detection value ensures measurement reciprocity.

The apparent confusion in the literature about the strict validity/non-validity of measurement reciprocity is mitigated by systematically classifying the different measurement situations and deriving the appropriate reciprocal setups from the electromechanical theory.

The study provides a comprehensive understanding of the reciprocity principles in laser ultrasound measurements, which is crucial for the effective application of these techniques in non-destructive testing and structural health monitoring.

İstatistikler

The sample material parameters used in the numerical simulations are:

Longitudinal sound velocity: 6.4 mm/μs
Transverse sound velocity: 3.15 mm/μs
Specific heat: 905 J/(kg K)
Linear expansion coefficient: 2.31 × 10^-5 /K
Thermal conductivity: 237 W/(m K)

Alıntılar

"The common believe about strict measurement reciprocity between scanning laser detection and scanning laser excitation is disproved by a simple experiment."
"Nevertheless, a deeper study based on the reciprocity relation reveals correct reciprocal measurement set-ups for both the probe-excitation / laser-detection and the laser-excitation / probe-detection case."
"Similarly, the all-laser measurement, that is thermoelastic laser excitation with laser vibrometer detection, is not in general reciprocal with respect to the exchange of excitation and detection positions."

Önemli Bilgiler Şuradan Elde Edildi

Reciprocity in laser ultrasound revisited: Is wavefield characterisation by scanning laser excitation strictly reciprocal to that by scanning laser detection?

by Bern... : arxiv.org 04-26-2024

https://arxiv.org/pdf/2404.16424.pdf

Daha Derin Sorular

How can the insights from this study be extended to more complex measurement scenarios, such as those involving curved surfaces or heterogeneous materials?

The insights gained from the study on reciprocity in laser ultrasound can be extended to more complex measurement scenarios by considering the specific characteristics of the materials and surfaces involved. For curved surfaces, the reciprocity principles derived can be applied by adapting the measurement set-up to account for the curvature. This may involve adjusting the laser excitation and detection positions to ensure accurate wavefield characterization on curved surfaces. Additionally, the reciprocity relations established in the study can guide the selection of appropriate measurement parameters and techniques for curved surfaces, taking into consideration the effects of curvature on wave propagation.
In the case of heterogeneous materials, the reciprocity principles can be utilized to optimize the measurement set-up for accurate wavefield characterization. By understanding the reciprocity between different measurement configurations, researchers can design experiments that account for the heterogeneous nature of the material. This may involve adjusting the excitation and detection positions to capture the variations in wave propagation caused by the heterogeneity. Additionally, the reciprocity principles can guide the selection of suitable transducers and detection methods to ensure reliable measurements in heterogeneous materials.
Overall, the insights from this study can be extended to more complex measurement scenarios by applying the reciprocity principles to tailor the experimental set-up and measurement techniques to the specific characteristics of curved surfaces and heterogeneous materials.

What are the potential implications of the non-reciprocity in all-laser ultrasound measurements for practical applications like non-destructive testing?

The non-reciprocity observed in all-laser ultrasound measurements has significant implications for practical applications like non-destructive testing (NDT). Reciprocity is a fundamental principle in wave-based measurements, and the lack of reciprocity in all-laser ultrasound measurements challenges the traditional assumptions in NDT practices.
One potential implication is the need for careful consideration of the excitation and detection positions in all-laser ultrasound measurements. The non-reciprocity suggests that the positions of the laser excitation and detection cannot be simply interchanged without affecting the measurement results. This implies that NDT practitioners must carefully design their experimental set-ups to account for the non-reciprocal nature of all-laser ultrasound measurements, especially when conducting inspections on complex structures or materials.
Furthermore, the non-reciprocity may impact the interpretation of measurement data in NDT applications. Researchers and practitioners must be aware of the limitations imposed by the non-reciprocal nature of all-laser ultrasound measurements and adjust their data analysis techniques accordingly. This may involve developing new algorithms or methodologies to account for the non-reciprocity and ensure accurate and reliable results in NDT practices.
Overall, the non-reciprocity in all-laser ultrasound measurements poses challenges for practical applications like non-destructive testing, requiring a reevaluation of experimental design, data interpretation, and analysis techniques to address the implications of the non-reciprocal nature of these measurements.

Could the reciprocity principles derived in this work be applied to other types of wave-based measurement techniques beyond ultrasound, such as electromagnetic or acoustic waves?

The reciprocity principles derived in this work for laser ultrasound measurements can be potentially applied to other types of wave-based measurement techniques beyond ultrasound, such as electromagnetic or acoustic waves. Reciprocity is a fundamental concept in wave physics that governs the relationship between excitation and detection in wave propagation phenomena. While the specific details may vary depending on the wave type and medium, the underlying principles of reciprocity can be adapted and extended to different wave-based measurement techniques.
For electromagnetic waves, the reciprocity principles derived in this study can be utilized to establish relationships between excitation sources and detection methods. By considering the reciprocity between different measurement configurations, researchers can optimize the design of electromagnetic wave experiments for various applications, such as remote sensing, communication systems, and antenna design. The reciprocity principles can guide the selection of appropriate excitation sources and detection methods to ensure accurate and reliable measurements in electromagnetic wave systems.
Similarly, for acoustic waves, the reciprocity principles derived in this work can be applied to acoustic wave-based measurement techniques. By understanding the reciprocity between excitation and detection in acoustic wave propagation, researchers can design experiments for applications in areas such as structural health monitoring, underwater acoustics, and seismic imaging. The reciprocity principles can inform the selection of transducers, excitation sources, and detection methods to optimize acoustic wave measurements for specific applications.
In conclusion, the reciprocity principles derived in this work for laser ultrasound measurements can serve as a foundation for extending reciprocity concepts to other types of wave-based measurement techniques, including electromagnetic and acoustic waves. By applying these principles, researchers can enhance the design and implementation of wave-based experiments across different domains and applications.