http://ieeexplore.ieee.org/iel5/5/31047/01444179.pdf

Fundamentals of acoustics

The paper provides a state of the art review of guided wave based structural health monitoring (SHM). First, the fundamental concepts of guided wave propagation and its implementation for SHM is explained. Following sections present the different modeling schemes adopted, developments in the area of transducers for generation, and sensing of wave, signal processing and imaging technique, statistical and machine learning schemes for feature extraction. Next, a section is presented on the recent advancements in nonlinear guided wave for SHM. This is followed by section on Rayleigh and SH waves. Next is a section on real-life implementation of guided wave for industrial problems. The paper, though briefly talks about the early development for completeness,. is primarily focussed on the recent progress made in the last decade. The paper ends by discussing and highlighting the future directions and open areas of research in guided wave based SHM.

https://iopscience.iop.org/article/10.1088/0964-1726/25/5/053001/pdf

Guided wave based structural health monitoring: A review

The detection of acoustic signals is of relevance for a range of practical applications, for example in medical diagnostics. However, whereas rectification of electric current and other energy forms such as thermal flux has been demonstrated, acoustic rectification has not yet been achieved. Here, on the basis of the earlier theoretical proposal of an 'acoustic diode', we present the first experimental demonstration of a rectified energy flux of acoustic waves. A one-dimensional acoustic rectifier is fabricated by coupling a superlattice with a layer of ultrasound contrast agent microbubble suspension. A significant rectifying effect is observed within two frequency bands at locations that agree well with theoretical predictions. Following optimization of the concentration of the microbubble suspension, rectifying ratios can be as high as ~10(4). This realization of an acoustic rectifier should have substantial practical significance, for example in the focusing of ultrasound in medical applications.

An acoustic rectifier

Ultrasonic testing of materials: Josef and Herbert Krautkramer Springer-Verlag Publishing Company, Berlin, Heidelberg, New York (1975) 669 pp, $63.00

X-ray microcomputed tomography (microCT) has become an established method of testing and analyzing additively manufactured parts in recent years, being especially useful and accurate for d...

X-Ray microcomputed tomography in additive manufacturing : a review of the current technology and applications

Guided torsional waves in a bar with a noncircular cross section have been exploited by previous researchers to measure the density of fluids. However, due to the complexity of the wave behavior in the noncircular cross-sectional shape, the previous theory can only provide an approximate prediction; thus the accuracy of the measurement has been compromised. In this paper, a semianalytical finite element method is developed to model accurately the propagation velocity and leakage of guided waves along an immersed waveguide with arbitrary noncircular cross section. An accurate inverse model is then provided to measure the density of the fluid by measuring the change of the torsional wave speed. Experimental results obtained with a rectangular bar in a range of fluids show very good agreement with the theoretical predictions. Finally, the potentials to use the model for sensor optimization are discussed.

Torsional waves propagation along a waveguide of arbitrary cross section immersed in a perfect fluid.

https://dr.ntu.edu.sg/bitstream/10356/83470/1/Damage%20detection%20in%20quasi-isotropic%20composite%20bends%20using%20ultrasonic.pdf

Damage detection in quasi-isotropic composite bends using ultrasonic feature guided waves

Adhesively bonded stiffeners are employed in aerospace applications to increase structural stiffness The potential of feature-guided wave modes for the verification of adhesion and curing state in difficult-to-access regions has been investigated The properties of guided wave modes propagating along a T-shaped stiffener bonded to an aluminium plate were calculated using the Semi-Analytical Finite Element (SAFE) method Feature-guided modes dominated by shearing motion were identified to be well suited, with energy concentrated at the stiffener and bond line, limiting energy radiation into the plate and thus maximising inspection length The influences of the bond line stiffness and thickness on the guided wave behaviour were investigated using SAFE and 3D Finite Element calculations, and found to be significant Experiments were conducted to measure the properties of the guided waves during the curing of an epoxy joint attaching a stiffener to a plate The feature-guided mode was excited using a piezo-electric shear transducer and measured using a laser interferometer The measured phase speed changed significantly during curing The frequency dependency was found to match well with the SAFE calculations for a variation of the shear (Coulomb) modulus of the adhesive The potential of the feature-guided shear wave mode for bond line inspection and monitoring has been shown and the choice of guided wave mode and frequency range for good sensitivity to the bond line state discussed

https://www.ndt.net/article/aero2013/content/papers/52_Fan.pdf

Feature-guided waves for monitoring adhesive shear modulus in bonded stiffeners

Analytical insight into "breathing" crack-induced acoustic nonlinearity with an application to quantitative evaluation of contact cracks.

Nonlinear ultrasonic Lamb waves are popular to characterize the nonlinearity of materials. However, the widely used nonlinear Lamb mode suffers from two associated complications: inherent dispersive and multimode natures. To overcome these, the symmetric Lamb mode (S0) at low frequency region is explored. At the low frequency region, the S0 mode is little dispersive and easy to generate. However, the secondary mode still exists, and increases linearly for significant distance. Numerical simulations and experiments are used to validate the nonlinear features and therefore demonstrate an easy alternative for nonlinear Lamb wave applications.

/pdf/numerical-and-experimental-investigation-of-nonlinear-3hkae0aca2.pdf

Zheng Fan

Papers

Torsional waves propagation along a waveguide of arbitrary cross section immersed in a perfect fluid.

Damage detection in quasi-isotropic composite bends using ultrasonic feature guided waves

Feature-guided waves for monitoring adhesive shear modulus in bonded stiffeners

Analytical insight into "breathing" crack-induced acoustic nonlinearity with an application to quantitative evaluation of contact cracks.

Numerical and experimental investigation of nonlinear ultrasonic Lamb waves at low frequency