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

This paper investigates the mechanism of self-stabilizing, three-dimensional Mie particle manipulation in water via an acoustic tweezer with a single transducer. A carefully designed acoustic lens is attached to the transducer to form an acoustic vortex, which provides angular momentum on the trapped polymer sphere and leads to a fast-spinning motion. The sphere can find equilibrium positions spontaneously during the manipulation by slightly adjusting its relative position, angular velocity, and spinning axis. The spinning motion greatly enhances the low-pressure recirculation region around the sphere, resulting in a larger pressure induced drag. Simultaneously, the Magnus effect is induced to generate an additional lateral force. The spinning motion of the trapped sphere links the acoustic radiation force and hydrodynamic forces together, so that the sphere can spontaneously achieve new force balance and follow the translational motion of the acoustic tweezer. Non-spherical objects can also be manipulated by this acoustic tweezer.

Self-stabilizing three-dimensional particle manipulation via a single-transducer acoustic tweezer

A sound attenuating subwavelength metamaterial efficient in the low audible frequency range is proposed. The metasurface unit cell has a hexagonal shape with an axial ventilation channel inside. The side walls of the hexagonal cell are sub-divided into six hollow chambers connected to the central air path via the six thinner channels of different diameters. The hollow chambers act as Helmholtz resonators providing six different resonant frequencies for each cell. The negative effective bulk modulus property of the metasurface allows near-full sound block at the resonant frequencies and partial sound adsorption inside the intermediate frequency bands. By carefully designing the size of the connecting side holes we can adjust the desired sound attenuation frequency range. The thickness of the metasurface is in the range of 0.05–0.15 wavelengths for the sound frequency range between 300 and 1000 Hz. The hexagonal shape of the unit cell allows full honeycomb tessellation of the metasurface volume. By designing a hybrid metasurface containing individual cells with different resonators, the absorption peaks can be multiplied or merged together thus further broadening the frequency range with the transmission coefficient lower than the desired threshold value.

/pdf/a-modular-sound-attenuating-metasurface-with-subwavelength-420ro60289.pdf

A modular sound-attenuating metasurface with subwavelength thickness and hexagonal unit cells

Noise attenuating performance of metasurfaces with regular Euclidean tiling and uniformly embedded Helmholtz resonators

Ventilated acoustic meta-barrier based on layered Helmholtz resonators

This paper investigates the inspection and monitoring structural bends using a special ultrasonic bend-guided wave, which concentrates the energy in and around the bend. Modal studies are carried out using the Semi-Analytical Finite Element (SAFE) method, while 3D finite element (FE) simulations are used to gain visualization of results and also obtain cross-validation. Our studies reveal, perhaps for the first time, the possibility of bend-guided modes of the shear-horizontal (SH) family, in addition those of the Rayleigh-Lamb family reported earlier in the literature. This mode has attractive properties including low attenuation and limited dispersion. We investigate effects of plate thickness and bend radius on the physics of FGW in bends, arguing the strong role of geometry and curvature effects in causing mode confinement. Experiments have also been carried out to validate the existence of such bend-guided mode. doi: 10.12783/SHM2015/83

Zheng Fan

Papers

Self-stabilizing three-dimensional particle manipulation via a single-transducer acoustic tweezer

A modular sound-attenuating metasurface with subwavelength thickness and hexagonal unit cells

Noise attenuating performance of metasurfaces with regular Euclidean tiling and uniformly embedded Helmholtz resonators

Ventilated acoustic meta-barrier based on layered Helmholtz resonators

Investigation of Ultrasonic Feature Guided Waves for the Monitoring of Structural Bends