Search

• A multi-feature ultrasonic (MFU) method was proposed to evaluate the bonding condition of dual-layer coatings. • Parametric numerical studies were carried out to study the influence of stiffness at two interfaces on different ultrasonic features. • Stacked sparse autoencoder (SSAE) was applied to automatically extract multiple features from ultrasonic waveforms and spectra sensitive to the bonding quality of coating. • The correlation between feature sets extracted by SSAE and those traditional selected features was explored. • The proposed method is effective to detect both the topcoat debonding and primer debonding in the industrial coatings. Ultrasound has been extensively utilized to evaluate the bonding quality of coatings. However, current ultrasonic methods based on single temporal or spectral feature cannot accurately characterize the bonding quality within industrial coatings, especially for potential debonding at different layers. This paper proposed an ultrasonic method with multiple temporal and spectral features to evaluate the bonding condition of dual-layer coatings. Ultrasonic features were automatically extracted based on stacked sparse autoencoder (SSAE) to compare with the conventional selected features. Firstly, numerical simulations were carried out to analyze the variation of ultrasonic signals with different stiffnesses at topcoat and primer interfaces. Two temporal and three spectral features were manually extracted and show high sensitivity to different bonding conditions of the two interfaces. Meanwhile, a SSAE network was designed to automatically extract ultrasonic features. The high correlation between the manually and automatically extracted features demonstrates its effectiveness of automatic feature extraction via SSAE. Then, a 50 MHz ultrasonic pulse-echo system was applied to collect signals from 115 coating samples of laptop shell. Four sets of ultrasonic features were extracted via manual method and SSAE networks. Principal components analysis was then employed to reduce the feature space and support vector machine was applied to distinguish topcoat debonding and primer debonding from the intact coatings. The results show that the feature set including 64 temporal and spectral features extracted by SSAE exhibit the best classification with an accuracy of 95.652 %. This proposed multi-feature ultrasonic method can accurately assess the bonding quality of different interfaces in the multi-layer coatings. [ABSTRACT FROM AUTHOR]

Ultrasonic guided wave (UGW) has shown great potential in the field of structural health monitoring of rail tracks due to its long-range capability and full cross section coverage. However, the practical application of UGW has been hindered by the complicated signal interpretation because of the natures of multiple modes and dispersion. Therefore, it is desirable that the effective UGW modes with high excitability and least dispersion can be identified and extracted for practical applications. In this paper, a numerical study on the guided wave propagation was carried out on a standard rail with 56E1 profile. Firstly, Floquet-Bloch theory was applied to obtain the dispersion curves of guided wave in a rail. Then, a 3D FE model was built to investigate the UGW propagation along the rail within the frequency range of 0–120 kHz. Wavenumber-frequency analysis method was applied to decompose and identify the propagating UGW modes. With a carefully designed 2D bandpass filter, a specific mode W0 was extracted in the wavenumber-frequency domain. Finally, a frequency band sweep technique was also proposed to get the optimal frequency band to achieve a pure and least-dispersive UGW mode along the rail web. The proposed method provides an effective way to extract efficient UGW modes to assess the integrity of the rail track, as well as other waveguides with complex geometry. [ABSTRACT FROM AUTHOR]

Residual stress and its distribution are the key indicators to ensure structural integrity. However, current ultrasonic methods are not appropriate for complex stress measurement. Considering the proximity of zero-group-velocity (ZGV) mode with the cut-off frequency and its sensitivity to local material property, this paper proposed a local stress measurement method based on S1-ZGV mode. The stress field reconstruction was demonstrated numerically with a nonuniform plate. Then, a FE model was built to investigate the excitation of S1-ZGV mode by oblique incidence approach, proving that S1-ZGV mode can be effectively excited and received with a small distance. Thus, a contact ultrasonic system along with a tailor-made compact wedged transducer was built for experimental validation. Parametric studies were performed to obtain the optimal excitation conditions for S1-ZGV mode. At last, experimental validation was carried out by standard tensile testing. The stress coefficient between the frequency shift and the applied stress was obtained with a uniform plate. The stresses of the nonuniform plate at three different positions were measured, proving that S1-ZGV method is effective for local stress measurement in thin plates. [ABSTRACT FROM AUTHOR]

• Feedforward comb filtering effect is proposed to extract the phase information of overlapped signals from immersed ultrasonic testing of coatings. • A quantitative relation between the notch frequency and interfacial stiffness is obtained from the numerical simulation. • Decimal part of the ratio of notch frequencies to interval frequencies is proposed as a novel index to evaluate the bonding strength of coatings. • A comparative study on bonding strength assessment is conducted based on ultrasonic nondestructive test and destructive cross-cut test. • A baseline-free ultrasonic nondestructive method is proposed for quantitative evaluation of bonding strength of coatings. Because of the ability to protect and decorate materials, polyurethane coatings (PU) are being applied more and more extensively in the transportation, furniture, automotive, and electronic industries. However, it is difficult to effectively evaluate the bonding quality of coatings by conventional destructive methods for high-volume products in industrial applications. In this work, an ultrasonic nondestructive method based on the feedforward comb filtering effect was proposed to assess the bonding strength of the PU coatings. The coating and substrate interface can be modeled as a distributed spring system. The phase of the reflected ultrasonic wave is highly related to the interfacial stiffness. The superimposed signals can be well analyzed based on the comb filtering effect, and an index called the ratio of notch frequencies to interval frequencies (NIR) was constructed to represent the phase difference. Finite element simulations were conducted to show the index's construction method and variation with different interfacial stiffnesses. Immersed ultrasonic testing experiments with a transducer of 39.43 MHz were then conducted on PU coatings on two kinds of substrates made of aluminum and magnesium alloys. Each specimen was scanned as a grid to mimic the procedure of the well-known cross-cut test. The notch frequencies of the scanned received signals were applied to obtain the NIR index. To avoid the interference of the thickness of coatings, the decimal part of NIR was further proposed to link with the bonding strength obtained by the cross-cut test. This index changes accordingly with aluminum- and magnesium-based coatings' bonding strength. The results prove that the proposed ultrasonic method based on the feedforward comb filter effect is high potential to assess the bonding strength of coatings nondestructively. [ABSTRACT FROM AUTHOR]

Non-linear interaction of waves with contact interfaces has been widely applied in non-destructive evaluation fields such as bonding quality evaluation, and the detection of closed microcracks and composite delamination. This paper proposes an absolute measurement of the ultrasonic non-linearity parameter using a piezoelectric detection method for two aluminum alloy blocks of different lengths. The results of a two-dimensional finite element method model verified by models for hard and soft contact interfaces, depending on the interface property, were compared with the measured non-linearity parameter. The measured values show good agreement with the modelled results, indicating good potential for measuring the non-linearity parameter at interfaces experimentally and numerically. [ABSTRACT FROM PUBLISHER]

The excitation and propagation of an electromagnetic field is a very complex problem in Stratified conductive structures (SCS) because of their complicated physical properties. In single air-cored coil above multilayered conductive structures, the impedance of an eddy-current coil is calculated based on the electromagnetic field. This paper provides insight into eddy current models for stratified conductive structures using three types of analytical approaches, including Cheng's matrix method, Truncated region eigenfunction expansion (TREE) method, and the innovative method based on the reflection and transmission theory of the electromagnetic waves. The analytical expressions of the three models are discussed and compared. Numerical simulation of an FEM model is performed, and the experimental results verify the developed models. [ABSTRACT FROM AUTHOR]

A number of interesting phenomena at fluid-solid interfaces can be observed when the incident angle approaches the Rayleigh angle, including Schoch displacement and leaky Rayleigh waves. Besides the experimental and theoretical research on these problems, numerical tools have been more and more widely used for these complex problems. Based on previous experimental and numerical researches, a 2D finite element model has been built to reproduce the Schoch effects. With the same model, the minimum reflection profile is investigated for the feasibility of material characterization, especially for residual stress evaluation. Residual stress is one of the important properties for structures, and its measurement is a popular research topic in nondestructive evaluation. However, it is not possible to put the residual stress into the numerical model directly. According to the relation of residual stress with mechanical properties, the material damping and wave speed have been alternatively adopted in this work. The influence of minimum reflection profile by residual stress has been shown by the change of wave speed and damping factor. Simulation results show that the minimum reflection profile is a potential method for residual stress evaluation. [ABSTRACT FROM AUTHOR]

3D printing technique can be used to fabricating complex-structure ceramics, but the internal microstructure and properties along vertical and horizontal directions may show certain anisotropy due to the layer-by-layer process. This work aims to evaluate 3D printing anisotropy quantitatively for performance optimization via the stereolithography method. The square-shaped barium titanate (BTO) ceramics with three different solid contents (75 %, 80 % and 85 %) were prepared to characterize the differences between the vertical and horizontal directions of the ceramics, including microstructure, phase structure, electrical properties and mechanical properties. The electrical and mechanical performances of the printed BTO ceramics in vertical direction are superior to that of horizontal direction, and the differences firstly decrease with the solid contents increasing to 80 % and then increase slightly with further solid content increasing. Besides, the printed BTO ceramic with 80 wt% solid content has excellent electrical performance. This study may provide a potential way for achieving high performance and low anisotropy in the vertical and horizontal of printed ceramics. [ABSTRACT FROM AUTHOR]

Ultrasonic is one of the well-known methods for surface roughness measurement, but small roughness will only lead to a subtle variation of transmission or reflection. To explore sensitive techniques for surfaces with small roughness, nonlinear ultrasonic measurement in through-transmission and pulse-echo modes was proposed and studied based on an effective unit-cell finite element (FE) model. Higher harmonic generation in solids was realized by applying the Murnaghan hyperelastic material model. This FE model was verified by comparing the absolute value of the nonlinearity parameter with the analytical solution. Then, random surfaces with different roughness values ranging from 0 μm to 200 μm were repeatedly generated and studied in the two modes. The through-transmission mode is very suitable to measure the surfaces with roughness as small as 3% of the wavelength. The pulse-echo mode is sensitive and effective to measure the surface roughness ranging from 0.78% to 5.47% of the wavelength. This study offers a potential nondestructive testing and monitoring method for the interfaces or inner surfaces of the in-service structures. [ABSTRACT FROM AUTHOR]

The transparent [Li 0.04 (K 0.5 Na 0.5) 0.96 ]NbO 3 +0.5mol% Er 2 O 3 (KNNLN-Er) lead-free piezoelectric ceramics were prepared by stereolithography technique. The influence of different sintering holding time (4h∼8h) on the micromorphology, relative density, shrinkage, electric properties, and photoluminescence properties were systematically investigated. The KNNLN-Er ceramics show the coexistence of orthorhombic and tetragonal structures. The grain size increases obviously and then decreases slightly with the holding time increasing. The KNNLN-Er ceramics exhibit good piezoelectric performance (piezoelectric constant d 33 ∼97 pC/N, electromechanical couple coefficient k t ∼0.36) and the moderate transparency of 34% when the holding time is 6h during sintering at 1120°C. Besides, the intensity of the photoluminescence emission spectra increases with the holding time increasing. Furthermore, in order to estimate the properties of the KNNLN-Er transparent ceramics, an ultrasonic transducer with a center frequency of 10.5 MHz was fabricated, which can be used for photoacoustic and fluorescence imaging. The results indicate that the KNNLN-Er ceramics have potential for multimode imaging applications. [ABSTRACT FROM AUTHOR]

• Boundary-driven acoustic streaming (AS) induced by both flat and curved walls is studied experimentally and numerically. • The Chladni figures formed in a semi-circular channel are similar to those observed in a circular channel. • PIV accurately measures the AS fields generated by the motion of 1 µm particles, which aligns with simulations. • The ratio of AS velocity generated by the curved wall and that by the flat wall depends on the acoustic modes. While boundary-driven acoustic streaming in fluids surrounded by flat walls has been extensively studied in the literature, theoretical studies on boundary-driven acoustic streaming generated by curved walls have recently emerged. This paper aims to present a quantitative analysis of acoustic streaming fields driven by forces induced by both flat and curved walls. A semi-circular channel made of stainless steel was designed to serve as a model channel with both flat and curved boundaries. A multi-layered glass-steel-glass device, actuated by a piezoelectric transducer, was assembled for experimental characterization of boundary-driven acoustic streaming in such scenarios. First, the various standing acoustic modes in the semi-circular channel were measured through the acoustophoretic patterning of 20 µm polystyrene particles. Next, the acoustic radiation force fields and boundary-driven acoustic streaming patterns under various resonant acoustic modes were characterized through micro-particle-image-velocimetry measurements of the motion of 20 µm and 1 µm polystyrene particles, respectively. Finally, the experimental results were explained using efficient finite element simulations of acoustofluidics and acoustophoresis in a semi-circular reduced-fluid model, with a focus on analyzing the streaming velocities driven by the flat and curved walls. Both experimental and numerical results demonstrated that the ratio of streaming velocities induced by the flat wall and the curved wall in this semi-circular channel depends on the resonant acoustic modes. This research highlights the diverse boundary-driven acoustic streaming patterns that arise in irregular channels and provides a theoretical foundation for choosing strategies for shape optimization to suppress acoustic streaming in acoustofluidic devices. [ABSTRACT FROM AUTHOR]

This paper proposes an analytical approach that can describe the Pulsed Eddy Current Testing (PECT) of stratified conductive structures by a single air-coil used for detecting and sizing of metal loss due to interlayer corrosion. Specifically for a single air-cored coil above a multilayered conductive structure, the coil impendance response of the cylindrical eddy-current probe is calculated based on the truncated region eigenfunction expansion (TREE) method using the generalized matrix coefficients in series form. Analytical modeling of pulsed eddy current is developed using the Fourier series for multilayered conductive structures. A simulation study is carried out for demonstrating the capability of the proposed approach for sizing the metal loss in a two-layer specimen. Furthermore, the experiment is set up to confirm the simulating results of the analytical model for multilayered steels. Good agreement between the theoretical results and measured signals is observed. [ABSTRACT FROM AUTHOR]

Abstract: Computed laminography (CL) is different from conventional computed tomography(CT) for its specialization in testing plate-type structures, such as integrated circuit boards (ICB), multilayer printing circuit boards (MPCB), and ball grid arrays (BGA). It adopts a different scanning way to successfully produce cross-sectional images of the plate-type objects, while the conventional CT cannot be used. According to the CL reconstruction algorithm, precise determination of the origin of the projection coordinate system is the first step during cone-beam CL scanning system calibration. But unfortunately, for the practical CL scanning system, it is impossible to measure the position of the X-ray focus projection by direct means. A new method to determine the X-ray focus projection coordinates with high accuracy is proposed. Firstly the angle between the central X-ray and the axis of rotation is set to zero by rotating the X-ray source and detector synchronously. Acquiring digital radiography (DR) images of several spherical objects at two geometrical magnification ratio positions in the cone X-ray beam, the two DR images are combined to one image, on the base of which image processing methods are employed to get the center points of each projection of the spherical object. And every two-positioned center points of the same spherical object determine a line, so all couples of projection centers of all the spherical objects construct a group of lines, mathematically an over-determined equation set. After solving the over-determined equation, the X-ray focus projection coordinates are finally obtained. The experimental results prove that the accuracy of this method can satisfy the requirements of the practical scanning system, meanwhile it is feasible to realize. [Copyright &y& Elsevier]

Transcranial focused ultrasound (tFUS) is increasingly used in experimental neuroscience due to its neuromodulatory effectiveness in animal studies. However, achieving multitarget tFUS in small animals is typically limited by transducer size, energy transfer efficiency, and brain volume. The objective of this work was to construct an ultrasound system for multitarget neuromodulation in small animals. First, a miniaturized high-powered 2-D array transducer was developed. The phase delay of each array element was calculated based on the multifocal time-reversal method, generating multiple foci simultaneously in a 3-D field. The effects of the axial focal length, interfocus spacing (lateral distance between the two focal centers), and the number of foci on the focal properties of the pressure field were examined through numerical simulations. In-vitro ultrasonic measurements and transcranial simulations on a rat skull were conducted. The minimum interfocus spacing separating two −6-dB foci and the peak full-width at half-maximum were positively correlated with axial focal length; the relative relationship between the interfocus spacing and pressure field properties was similar for each axial focal length. The maximum acoustic pressure and spatial average intensity at focus in deionized water were 2.21 MPa and 133 W/cm2, respectively. The simulated and experimental results were compared, demonstrating agreement in both peak position and focus shape. The ultrasound system can provide a neuroscientific platform for evaluating the feasibility of multitarget ultrasound stimulation treatment protocols, thus improving the understanding of functional neuroanatomy. [ABSTRACT FROM AUTHOR]

Transcranial ultrasound therapy has become a noninvasive method for treating neurological and psychiatric disorders, and studies have further demonstrated that multitarget transcranial ultrasound therapy is a better solution. At present, multitarget transcranial ultrasound therapy in small animals can only be achieved by the multitransducer or phased array. However, multiple transducers may cause spatial interference, and the phased array system is complicated, expensive, and especially unsuitable for small animals. This study is the first to design and fabricate a miniature acoustic holography lens for multitarget transcranial ultrasound therapy in rats. The acoustic holographic lens, working at a frequency of 1.0 MHz, with a size of 10.08 mm $\times10.08$ mm and a pixel resolution of 0.72 mm, was designed, optimized, and fabricated. The dual-focus transcranial ultrasound generated based on the lens was measured; the full-width at half-maximum (FWHM) of the focal spots in the ${y}$ -direction was 2.15 and 2.27 mm and in the ${z}$ -direction was 2.3 and 2.36 mm. The focal length was 5.4 mm, and the distance between the two focuses was 5.6 mm, close to the desired values of 5.4 and 6.0 mm. Finally, the multiple-target blood–brain barrier opening in rats’ bilateral secondary visual cortex (mediolateral area, V2ML) was demonstrated using the transcranial ultrasound therapy system based on the lens. These results demonstrate the good performance of the multitarget transcranial ultrasound therapy system for small animals, including high spatial resolution, small size, and low cost. [ABSTRACT FROM AUTHOR]

• A head-mounted transcranial ultrasound stimulation system for mice was built. • Ultrasound stimulation of DRN safely increased c-fos gene expression in the DRN. • Ultrasound stimulation of DRN increased 5-hydroxytryptamine levels in DRN. • Ultrasound stimulation of DRN promoted recovery from anesthesia and improved cognition in mice. • Antagonizing the 5-HT 2A receptor inhibited anesthesia recovery and cognition in mice after ultrasound stimulation of DRN. Delayed arousal and cognitive dysfunction are common, especially in older patients after general anesthesia (GA). Elevating central nervous system serotonin (5-HT) levels can promote recovery from GA and increase synaptic plasticity to improve cognition. Ultrasound neuromodulation has become a noninvasive physical intervention therapy with high spatial resolution and penetration depth, which can modulate neuronal excitability to treat psychiatric and neurodegenerative diseases. This study aims to use ultrasound to noninvasively modulate the brain 5-HT levels of mice to promote recovery from GA and improve cognition in mice. The dorsal raphe nucleus (DRN) of mice during GA was stimulated by the 1.1 MHz ultrasound with a negative pressure of 356 kPa, and the liquid chromatography coupled tandem mass spectrometry (LC-MS/MS) method was used to measure the DRN 5-HT concentrations. The mice's recovery time from GA was assessed, and the cognition was evaluated through spontaneous alternation Y-maze and novel object recognition (NOR) tests. After ultrasound stimulation, the mice's DRN 5-HT levels were significantly increased (control: 554.0 ± 103.2 ng/g, anesthesia + US: 664.2 ± 84.1 ng/g, *p = 0.0389); the GA recovery time (return of the righting reflex (RORR) emergence latency time) of mice was significantly reduced (anesthesia: 331.6 ± 70 s, anesthesia + US: 223.2 ± 67.7 s, *p = 0.0215); the spontaneous rotation behavior score of mice was significantly increased (anesthesia: 59.46 ± 5.26 %, anesthesia + US: 68.55 ± 5.24 %; *p = 0.0126); the recognition index was significantly increased (anesthesia: 55.02 ± 6.23 %, anesthesia + US: 78.52 ± 12.21 %; ***p = 0.0009). This study indicates that ultrasound stimulation of DRN increases serotonin levels, accelerates recovery from anesthesia, and improves cognition, which could be an important strategy for treating delayed arousal, postoperative delirium, or even lasting cognitive dysfunction after GA. [ABSTRACT FROM AUTHOR]

[Display omitted] • The influencing mechanism of ultrasound on the size of Cu nanoparticles is studied. • The mean size and size dispersion are significantly reduced ultrasound treatment. • A competition model between surface energy and ultrasonic force is proposed. • An exponential relation of between particle size and ultrasonic power is revealed. • Ultrasonic power and surface energy are keys to control the final particle size. Ultrasonic treatment is an effective method for size refinement and dispersion of nanomaterials during their synthesis process. However, the quantitative relationship between ultrasonic conditions and particle size in the synthesis of metal nanoparticles has not been fully revealed. In this study, Cu nanoparticles were synthesized via the wet-chemical redox method under ultrasonic treatment, and statistical analysis on the evolution of particle size distribution was carried out. It was found that the particle size decreased exponentially with increasing ultrasonic power. A quantitative model was then proposed to describe the influence of ultrasonic power on the size distribution of metal nanoparticles from the perspective of the competition between the surface energy and the ultrasonic force. A relational expression of R c ∝ γ 4 7 P - 3 7 was revealed, and it was proved to fit well with the experimental results. Our study provides new experimental basis and theoretical method for understanding the mechanism of ultrasonic-induced size refinement of metal nanoparticles. [ABSTRACT FROM AUTHOR]